COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX64103145 QP355 .Z61 Introduction to phys RECAP cienee lexl OLOGICAl YCHOLOGY Q ?3 !TS ZhL Columbia 5J CC 5) It 3) ?> JJ 3"' } }) JJ "" J> 5) 3J >> )> 4 "*• 1 The importance of conceiving of the elements, by means of which we per- ceive space, as a series, and the possibility of inverting its order, were first emphasized by Herbart (" Psychologie als Wissenschaft "). Sensations of Taste, Smell, and Touch. 8 1 Thus this scale of intensities representing the concomitant ideas of motion, determines the order in which the sensations are localized in space. The sensations are not arranged according to the order of their position in the cerebral cortex, but according to the scale of the accompanying ideas of motion. What we have thus demonstrated in the imaginary case of linear contact, may also be applied somewhat more minutely to superficial contact, and to the taction of solid bodies. In this case also we first project the sensations of touch into space without regard to order ; only the accompanying ideas of motion that we acquire, cause us to project the sensations received from the surfaces bounding an object in just the same spatial order in which the points are really arranged on the surfaces of the external object. It is furthermore obvious that ideas of motion may also be acquired indirectly, not when the hand is moved along the object x, but when the object x is moved over the hand under our eyes. Hence a perception of the world as it exists in space may be developed within us entirely without the help of the visual sense, although, of course, it remains more or less incomplete. The well-known Chesseldens/ who was born blind, and later in life received the power of sight by an operation, only discovered after the operation that all things are solids \ before he had only known of coloured surfaces. On the other hand, Franz 2 related that a certain individual, who had been born blind, was unable to form any idea of a square, even upon seeing it after his sight had been acquired by an operation, until he began to perceive a sensation in the tips of his fingers as though he was really engaged in touching the object at which he was only looking. The patient had constant recourse to his sense of touch, just as the normal man resorts to his sense of sight in the recognition of objects. When we come to consider the theory of visual sensa- tions, we shall have to return to these cases, which are of extra- ordinary importance for physiological psychology, and to the 1 Philosoph. Transact., 1728. 2 Philosoph. Transact. R.S., 1841. 82 Introduction to Physiological Psychology. entire subject of space-intuition in general. At present only one more conclusion is to be mentioned as a direct result of the preceding. The ability to distinguish two sensations that arise in neighbouring nerve-ends, can be considerably cultivated by practice, since it is also chiefly dependent on accompanying ideas of motion. If we place the two points of a compass upon the thigh at a distance of 6 cm. from each other, we generally per- ceive but one touch ; we are able to perceive two touches only when the distance between the points of the compass amounts to 7 cm. This smallest distance within which two sensations may still be distinguished from each other is designated as the " minimum of space ,n that can be perceived or the "just per- ceivable amount of space," and the region of the skin within which we still feel two sensations as one is designated as the " sensation-circle " in accordance with the precedent established by E. H. Weber. Within the area of a single " sensation-circle," therefore, the local signs and the associated ideas of motion are not sufficient to render two sensations distinguishable when they are caused by like stimuli. Thus we can also easily understand why the " sensation-circles " are very large in those regions of the skin which have very few nerves and are little used in active touch, as the trunk, thigh, etc. It is a fact of great importance that two points of contact may be also felt as one when both are at pressure-spots separated by one or more other pressure-spots. It appears therefore that the distribution of pressure- spots is by no means the only factor determining the ability for localization, but that the local signs and particularly the accompanying ideas of motion exert the chief influence. The partition of the sensi- bility of the skin into pressure-spots only renders possible the separate appearance of two like cortical excitations in different cortical elements ; but the distinction of two sensations does not depend on this simple fact of anatomical separation. We may here make the paradoxical statement that if all the nerves of the skin and their cortical terminations were anatomically quite 1 Germ. Raumschwelle = space-threshold. — 'Fs. Sensations of Taste ; Smell, and Touch. 83 identical, and if all were irritated by the same stimulus at the same time, only a single sensation would appear. The distinc- tion of neighbouring sensations from one another is only possible by means of local signs and ideas of motion. That the sensation- circle becomes smaller when just two J>?rssure-spots are touched may be partly explained by the fact that the intensity of the sensations is greater on the pressure-spots than elsewhere ; and within certain limits at least, the distinction of sensation becomes easier, the greater the intensity of the sensation. A further explanation may be sought in the fact that a single, isolated " local stamp " or " coloring " and a single, isolated complex of motor ideas appear only on irritation of a pressure- spot ; if a point between two pressure-spots be irritated, the stimulus acts upon several such spots ; the sensation is therefore associated with several local signs and complexes of motor ideas, and the differences between sensations are thus directly obliter- ated. In regions that possess an abundance of nerves the sensation-circles are smaller. A greater abundance of nerves renders possible a greater variety and speedier change of the local signs and a more extensive association with separate com- plexes of motor ideas. In conclusion one fact must seem remarkable to us. We have succeeded in explaining how the separate sensations of pressure are discretely projected into space in a definite order; in so doing, however, we have simply obtained a regular contiguity of numberless discrete sensations. But whence arises the con- tinuity of the impression produced by an object touching the skin ? We do not feel numberless points, but a continuous sur- face. This fact may be explained as follows : It is true that the pressure-spots are discrete ; but we have already demonstrated at some length that, strictly considered, the same stimulus acting upon different neighbouring pressure-spots, can impart but a single diffused sensation, the localization of which is quite in- definite, somewhat as in the case of sound. Our sensations of touch are only separated spatially and arranged so as to produce a surface by their association with local signs and ideas of 84 Introduction to Physiological Psychology. motion. But the local signs and ideas of motion are regularly graded and therefore form a continuous series. Hence we can easily understand also that the separation of the tactual sensa- tions and their arrangement in a surface has this continuous character. When the continuous gradation of the local signs and ideas of motion is wanting, the sensations do not blend into an image of surface. If we place three needle-points, for example, at a distance of 2 cm. from each other upon the hand, the three sensations will never blend into an image of surface. We have now finished the discussion of that mode of sensi- bility from which all the other senses have probably developed, the sensibility in the narrower sense of the term. We shall next turn to the highest senses, hearing and sight. CHAPTER V. SENSATIONS OF HEARING. We have now come to the discussion of acoustic sensations. The external stimulus producing these sensations is, in fact, very exactly known. It consists exclusively of longitudinal periodic vibrations of the molecules of air. Thus if A (fig. 8) designate a source of sound which sends out waves of sound in all direc- tions, a particle of air at M will first move to the point N, then A return to M and pass on to Z, finally returning to M again. The motion along the entire path M N M L M is called a vibration, and is executed in a single straight line. The latter is somewhat altered in the figure in order to illustrate visibly the reversal of the path, hence the particle of air does not appear to have returned to the exact starting point. In illustrating a series of vibrations it is best to depart still further from a straight line and represent the path of the particle as a wave. This may be accomplished most advantageously by letting the abscissas (fig. 9) indicate the time that has elapsed since the beginning of the motion, while the ordinates indicate the vibra- tion that has taken place. These vibrations are periodic in that they are continuously repeated. A definite number of vibra- 85 S6 Introduction to Physiological Psychology. tions takes place in a second of time. These periodic vibrations may be regular, i.e. the form and number of the vibrations re- main constant. Such vibrations impart sensations of musical sound; the accompanying external stimulus is designated as a musical sound. On the other hand, the periodic vibrations may be irregular ; l form and duration of the vibration change. In this case sensations of noise are produced and the accompanying external stimulus is designated as a noise. Fig. 9 I, represents the wave-line of a tone; 2 fig. 9 II, the wave- line of a noise. a 6 / d f E Fig. 9. A single wave reaches from a to b (fig. 9 I). This distance corresponds to the length of time required for the vibration of one particle. The curves, ab, be, cd, etc. (fig. 9 I), all represent a single vibration of the particle of air ; likewise a'b', b'c 1 , c'd', in the second curve (fig. 9 II). The greatest breadth of displace- ment of a vibrating particle is called the amplitude of vibration. The lengths of the straight lines ab, a'b', be, b'c 1 , etc., represent the duration of each vibration. We see at once that in the first curved line both the form and duration of the single vibrations is always 1 Throughout the entire chapter the reader should bear in mind that the author here makes a peculiar, but important, distinction between regularly periodic and irregularly periodic vibrations. — T's. a In this chapter the term " tone," when used without modification, is to be understood in its restricted sense as designating only a " simple tone," not a " composite tone " or " musical sound." — T's. Sensations of Hearing. 87 the same. This is characteristic of the tone. On the contrary the form and duration of the vibrations in the second curved line are constantly changing, as is characteristic of a noise. The rustling of the leaves is a noise ; if we strike the key of a piano, we produce a musical sound ; both are complex products, as we shall soon see. Both musical sounds and noises may be reduced to simple acoustic elements, or tones, by mathematical computation (construction) or by the use of special instruments, the so-called "resonators." Both noise and musical sound consist of a series of simple tones. The wave-line of both the noise and musical sound may be graphically represented as the product of several wave-lines of especial simplicity, viz. the so-called ei sinusoids" or j. \ \ / Fig. 10. *' curves of sines." Expressed in the language of physics, all the regular, periodic motions of musical sound and all the irregular periodic motions of noise may be reduced to a certain number of regular periodic motions of exceeding simplicity. These com- ponent vibrations, to which both a musical sound and a noise may be reduced, all have the same general form of vibration, the sinusoid, as represented in fig. 10. The vibrations are to be distinguished from one another merely by their duration, or, in other words, by the number of vibrations per second. We may therefore express this general proposition as follows : Each sound, whether musical sound or noise, may be reduced to a series of simple component tones, which, irrespective of their intensity, are to be distinguished from one another merely by the number of vibrations. Musical sound and noise are dif- ferent in that the numbers of vibrations producing the component 88 Introduction to Physiological Psychology. tones of the latter conform to no definite law of proportion, while the numbers of vibrations producing the various component tones of a musical sound stand in a very simple numerical relation to each other. For example, if that component tone (or partial tone) of a musical sound which has the smallest number of vibrations, possesses n vibrations per second, then all the other component tones of the same musical sound have a number of vibrations which is just sufficient to produce an exact multiple of n ; the numbers of their vibrations therefore amounts to 2n, 3^, or 472, etc. Also when the lowest tone has a number of vibrations equal to 4/z, and the following tones have numbers equal to $n, 6«, etc., the form of vibration still remains regularly periodic. It is only essential that the relations between the numbers of vibrations for each component tone are expressed by whole numbers that are not too large. Only tones whose numbers of vibrations stand in such a simple numerical relation as the one above cited, together compose a musical sound. Therefore, to recapitulate briefly, the specific physical stimulus for the organ of hearing consists of simple sound-waves that unite sometimes as musical sound-waves sometimes as sound-waves of noise. It is difficult to determine exactly where organs of hearing first appear in the animal series. Without doubt, however, such organs are already present in the Arthropoda, It is often particularly difficult to determine whether the so-called otoliths of the Cteno- phora and other similar animals are organs of hearing or organs that serve to keep the body in balance. The organ of hearing has been developed into a very complicated structure. A peri- pheral apparatus, which includes the external meatus, the mem- brana tympani and the auditory bones, serves especially to keep back all stimuli from the nerve-terminations, except the adequate stimuli of sound. These latter they transmit to the nerve-ends in the most suitable form possible. The final terminations of the auditory nerve lie partly in the organ of Corti in the cochlea,, partly in the ampullae of the semicircular canals ; in both they come in connection with the so-called "hair-cells." The part of the Sensations of Hearing. 89 auditory nerve that ends in the cochlea is designated as the nervus cochlearis ; the part which ends in the ampullae, as the nervus vestibularis. In their course through the brain they separate again ; the nervus vestibularis reaches the cerebellum, while the nervus cochlearis, which probably performs the chief part of the function of hearing, reaches the cortex of the temporo-sphenoidal lobe in the cerebrum. Now the left auditory nerve, in fact, terminates chiefly in the cortex of the right temporo-sphenoidal lobe, the right auditory nerve in the cortex of the left temporo-sphenoidal lobe. The auditory centre is therefore to be sought in the temporo- sphenoidal lobe. It has not yet been decided whether the am- pullae and the nervus vestibularis take any part in the functions of hearing whatever or whether they simply transmit those sensa- tions which assist us in retaining our balance ; the sensations of noise have also been ascribed to them. In the organ of Corti the nerve-terminations lie in an expanded membrane, the breadth of which is very different in different parts. Sounds that have a large number of vibrations will cause particularly the narrower parts of the membrane to vibrate sympathetically ; sounds having a small number of vibrations, the broader parts. One can con- ceive of the entire membrane as composed of numerous transverse chords, gradually decreasing in length from one end to the other, each of which is tuned to a definite tone. If a musical sound or a noise reach -the ear, it is analyzed into its component tones ; i.e. the membrane is set in vibration at different points, each of which corresponds to a definite component tone. Sound-waves act as stimuli upon the peripheral terminations of the auditory nerve. They constitute the specific adequate stimu- lus. Sensations of musical sound can also be produced by electric stimulation of the auditory nerve ; in this case it is probable that the trunk of the nerve is chiefly irritated. Mechanical stimuli, such as the pressure of tumors on the auditory nerve, for example, also produce sensations of hearing. Those sensations of hearing that are not produced by adequate stimuli are always exceedingly simple and monotonous. Thus far we have dealt with those certain or probable facts 90 Introduction to Physiological Psychology. offered by physiology and anatomy. Let us now analyse the sensations of sound psychologically. We shall first seek their different qualities. From the beginning we may be allowed to exclude that large class of sensations known as noises ; they com- pose an especial group of sensations that are hardly accessible to investigation. We shall occupy ourselves only with the simple sensations of tones and the sensations of musical sounds. We have already heard that the so-called tones of the piano are not simple, but complex; they may be more correctly designated as musical sounds. Simple tones are produced most easily by strik- ing a tuning-fork ; the flute also gives comparatively simple tones. The only difference in the quality of all simple tones lies in the pitch, to which the number of vibrations per second in the stimu- lating medium corresponds. We perceive a tone to be higher the greater the number of its vibrations. The lowest audible tone has sixteen vibrations, 1 the highest about 40,000 vibrations per second. But the various sensation of pitch are not irregularly distributed between sub-contra c and the eight-times-marked e (e 8 ), as is the case, for example, with the different qualities of the sense of smell; on the contrary, the sensations of pitch constitute a continuous series which corresponds to the constant increase in the number of vibrations, of the acoustic stimuli. Without the omission of one interval, we can ascend from sub-contra c to e 8 by a regular scale of simple tones. Strictly speaking, however, there are numberless tones between the lowest and highest tones. For reasons which we shall learn to understand more fully later, we distinguish only a very limited number of tone-pitches. For example, in the interval between the tone of 256 vibrations (c 1 ), and the tone of 1,024 vibra- tions (c z ), there are only 14 whole tones, including the lower tone c\ The chief factors that determined the historical development of this scale were aesthetic. All those tones that directly or in- directly harmonized with c 1 were sought and the above-mentioned 1 4 tones were the result. A more thorough analysis of this develop- ment does not fall within the province of this discussion. Especi- 1 Wundt claims to have heard even eight vibrations per second. Sensations of Hearing. 9 1 ally the tone having twice as many vibrations as c\ or a tone of 5 1 2 vibrations per second, produces a very harmonious accord with c l . Likewise tones that have three and four times as many vibrations, e' d , e A , etc., harmonize with c 1 remarkably well. Between c 1 and e 2 , c 2 and c 3 , etc., are six intermediate tones of harmonious char- acter. C l with the six following tones were embraced in one so- called octave, — likewise c 2 and the six following tones, etc. We have thus obtained a division of the long series of tone-sensations which was determined by aesthetic factors. The series of tones is divided into octaves, and each octave into seven notes. We are acquainted with the seven notes in their various octaves as d, e,f, g, a, b. Next the octave was completed by a series of intervening tones (c sharp, d sharp, f sharp, etc.), which were also determined by aesthetic reasons. Thus the scale of simple musical tones has been developed from the natural series of numberless simple tones. This classification of the sensations of pitch was first developed historically. For this reason the demarcation of the octaves and the number of tones within the octave long varied. In calling to mind the musical scale, the thought readily occurs to us to test or establish our sensibility to differences of pitch. How does the sensation of the pitch of tones increase or, more properly, vary when the number of vibrations changes ? This question has frequently been conceived of as a special case for the application of the Law of Weber. It is obvious that there are no grounds whatever to warrant such an application ; the Law of Weber compares the intensity of stimulus with the intensity of sensation. We shall presently apply the Law of Weber to sen- sations of sound in answer to the question as to how the intensity of acoustic sensations increases in proportion to the increase ot the acoustic stimulus, i.e. in proportion to the increase in the in- tensity of the sound. The question occupying us at present, how- ever, is quite different : — How does the sensation of the pitch of a tone change when the number of its vibrations changes ? Neither has the sensation of pitch anything to do with the in- tensity of the sensation, nor the number of vibrations anything 92 Introduction to Physiological Psychology. to do with the intensity of the acoustic stimulus. On the con- trary, a sensation of pitch depends merely upon the quality of sensation and the intensity of the acoustic stimulus upon the amplitude of vibration. Hence the Law of Weber has no direct connection with the question. In a former chapter we sought the true nature of Weber's Law in an act of association and the incitation of the idea " larger " or " smaller." The comparison of tones of different pitch with the incitation of the idea "higher' 7 or "lower" is, of course, somewhat analogous to the above case. For this reason it is conceivable that if the Law of Weber is valid in the one case within certain limits, similar mathematical relations may also be valid in the other case. A large number of experimental investigations have been employed in this line, the most reliable of which were made by E. Luft. 1 The result of these investigations shows that the relative discriminative sen- sibility is not quite constant, as required by the Law of Weber. If we sound a tone of 120 vibrations and then one of 120^ vibra- tions per second, we can distinguish the pitch of both tones clearly. Hence, at a pitch of 120 vibrations, a difference of \ of vibration is required to render two tones distinguishable, or the barely perceptible difference amounts to \ of a vibration per second. If we now choose as the beginning tone one with four times the number of vibrations, i.e. with 480 vibrations per second, the barely noticeable difference, according to Weber's Law, should also be four times as great. Thus the two tones should only be distinguishable when we increase the number of vibrations by the addition of 4 x \ or § of a vibration per second. This is not the fact however. On the contrary, experiment proves that the addition of only \ of a vibration is sufficient for the distinction of both tones. If we select another pitch twice as high as the last and begin with a tone produced by 960 vibra- tions, it appears that a tone of 960^- vibrations can be clearly distinguished from the first tone of 960 vibrations, while accord- ing to the Law of Weber an increase of pitch should only be 1 Philosoph. Stud., Bd. IV, S. 4. Sensations of Hearing. 93 distinguished when the difference is 8 x } or more than one vibra- tion per second. Therefore the relative discriminative sensibility 1 is not constant, while, on the contrary, the absolute sensibility for medium pitches seems to deviate but little from a constant average magnitude. The threshold of distinction only varies from \ to \ vibration per second, but may be materially affected by practice and musical talent. Persons who are not naturally musical err in the judgment of pitch, even more than we should suppose. For example, Stumpf found that persons not at all musical were mistaken once out of four times when they attempted to tell which of two tones, separated by the interval of a third, was the higher. The ability to distinguish is very limited, especi- ally when the tones are very low or very high, 2 for the individual is not assisted by the experiences of daily life. Still it is astound- ing to reflect how exceedingly sensitive the organ of hearing is in general. We even notice a change from 1,000 to i,oooi vibrations per second ; at the latter limit the quality of sensation has already changed. Some persons have been pleased to speak of this facility as an " unconscious counting " of the vibrations, and have been astonished at the certainty and rapidity with which the soul accomplishes this enumeration. It is unnecessary for us to be shown that no such enumeration takes place. It is only necessary to conceive of the chemical combinations in the termi- nations of the fibres from the auditory nerve as extraordinarily complicated, in order that so slight a difference in the mechanical stimulus may produce a difference in the central chemical process sufficient to render the tone distinguishable as higher or lower. Here for the first time we meet with time as an essential factor in the analysis of sensations. The quality of the sensation of tone corresponds to the number of vibrations of the sound-wave per second ; it is therefore dependent on the duration of the ■p 1 Expressed by the ratio, , while the absolute descriminative sensibility a £ is expressed by the ratio, — — . 2 above c b . 94 Introduction to Physiological Psychology. single vibrations, every change of which is followed by a corre- sponding change in the sensation with remarkable precision. But the qualities of the sense of hearing, however, are not ex- hausted with the simple tones, even though we exclude noises, as we have already done. Apart from the scale of comparatively simple tones, such as the flute produces, we further distinguish a large number of qualities that belong to sensations of sound. The c 1 of the piano sounds very different from the pure c 1 of the tuning fork or flute, despite the sameness of pitch ; and the c 1 of the violin is distinguished from both of the others. Or, if the human voice sing a vowel at the pitch of c\ we can distin- guish this also from the c 1 of the tuning fork, piano, and violin. Furthermore, the human voice can sing the vowels a, o, e, i, u, etc., to the same note. . All these differences in the quality of acoustic sensations that are distinguishable even when the pitch remains the same, are included under one conception, — timbre or colour-tone. The same tone upon each instrument and each vowel of the human voice has its special timbre. Helmholtz l first showed what physical differences in the stimulus condition this difference in the quality of the sensations of sound when the pitch remains the same. As already briefly mentioned, the so- called tones of the violin, piano, horn, and human voice are in fact not simple tones at all. At most, only the tones of the tuning fork and flute may be considered simple. The tones of all other instruments and of the human larynx are composed of several, often of numerous, simple tones. Since the numbers of vibra- tions producing the component tones stand in very simple rela- tions to one another (they are in general multiples of the same number), their combined effect should therefore be designated more properly as a musical sound. Thus, for example, if we strike c 1 upon the piano, six more tones sound with it, c 2 , g 2 , etc. The musical sound c 1 on the piano is therefore composed of seven simple, component tones, or, as it is also expressed, of one fundamental tone and six overtones. The fundamental tone Lehre von den Tonempfindungen." Sensations of Hearing. 95 is loudest, the intensity of the over-tones diminishes as the pitch increases. Let us now compare this with e l of the violin. In this case also over-tones sound in harmony with the fundamental tone; in fact, we find not only the over-tones c 2 , g 2 , e 3 , e z , etc., again, but also from four to five more than before. Hence the intensity of the higher over-tones on the violin is essentially greater than upon the piano ; by this means the violin receives the peculiar timbre characteristic of all stringed instruments. The component tones of the human voice have likewise been recently determined by Helmholtz, Hermann, and others. The physical basis for the differences in timbre, therefore, depends upon the difference in the number and intensity of the overtones blending with the fundamental tone of the musical sound. This analysis of the musical sounds of instruments into their composite tones can be accomplished by means of special resonators. But the musician, and after some practice even one who is not musical, is able to distinguish by the sense of hearing without resonators, at least the lower overtones of c\ struck on the piano, from the fundamental tone. The theory of partial tones or overtones is of the greatest importance in musical aesthetics. Among the various qualities of the sensations of noise, the most important are those that are produced by the consonants of the human voice. A physical analysis demonstrates that the consonants are essentially noises, i.e. they are composed of simple tones, the numbers of whose vibrations do not stand in simple numerical relations to one another. This finishes the consideration of the various qualities belonging to sound. It is obvious that the i?ztensity of acoustic sensations increases with the strength of the sound. The latter may be sub- jected to a still more exact physical analysis. The intensity of a sound is in fact directly dependent on the amplitude of the vibrations produced in the sounding body. The proper formula is more exactly stated as follows : i is proportional to a 2 n 2 . Therefore the intensity (/) of the sound grows in proportion as the square of the amplitude (a), it being understood of course g6 Introduction to Physiological Psychology. that the number of vibrations (n), or, in other words, the pitch, remains the same. Now is the Law of Weber valid in the case of sensations of sound? Is the absolute "threshold of distinction " in constant, direct proportion to the primary or beginning stimulus ? In the investigations that were undertaken for the purpose of solving this question, great difficulty arose in produc- ing any desirable gradation of the intensities of sound. Recently metal or ivory balls, that are allowed to fall upon an ebony or iron plate, have been applied with great advantage. In these experiments the timbre changes but very slightly 1 with the change in the height of falling and in the weight. On the other hand, the intensity of the sound is, within certain limits, pro- portional to the height of falling, the weight being constant, or to the weight, the height of falling being constant. Hence, by selecting balls of different weights or by altering the height of falling, one can vary the objective intensity of the sound at pleasure. The results have shown that Weber's Law is* valid and comparatively exact for the intensity of acoustic sensations. A so-called " lower deviation " is met with in this case also, although it may possibly be caused by concomitant noises which are never wholly avoidable. The average relative threshold of distinction is about one-third. The minimum of stimulus, or the least amount of acoustic stimulus that imparts any sensation at all, has not yet been determined with sufficient precision. 2 The following series of experiments by Merkel is interesting. He permitted the per- son on whom he was experimenting to hear two stimuli of sound, alike in quality but different in intensity, and then requested him to determine an acoustic stimulus that should impart a sensation lying directly midway between the first two sensations. This " method of mean gradations" showed that the stimulus of sound which produced the mean sensation resulted in the approximate arithmetical, but not geometrical, mean between the two beginning 1 Starke, Philosoph. Stud., Bd. V, H. i. Merkel, Philosoph. Stud., Bd. V, H. 4. 2 Norr's values appear to be too high (Zeitschr. f. Biologie, 1879). Sensations of Hearing. 97 stimuli. If Fechner's construction of Weber's Law is correct, i.e. J TO if not only - - , but also dE, is constant, and if therefore 6" is E also proportional to log. E, the geometric mean should be the result. In the case of sensations of sound, therefore, Fechner's formula is shown to be wholly invalid ; the assumption of Plateau 7 c is more correct ; — is constant. Let us here call to mind once more, however, that neither the geometrical nor the arithmetical mean results for other sensations ; the actual outcome is a value between these two. We have already referred to the essential scruple that can be brought against the "method of mean gradations.'' We shall now turn to the question also in reference to sensa- tions of hearing, that has previously been asked concerning other sensations : How is the sensation modified if the same stimulus of sound act on several nerve-terminations ? In the case of the sensibility of the skin it appeared that, aside from the three qualities manifest in sensations of pressure, cold and heat, all nerve-terminations are practically identical in function, and that when the stimulus spreads over a larger number of nerve-ends the numerous like sensations are so arranged with reference to each other as to produce an image of space. In the case of the sense of hearing the result is different. The number of qualities here is much larger • each pitch represents a special quality of sensation. We have already mentioned that the physiological structure of the organ of hearing renders it very probable that each nerve-end of the nervus cochlearis can only be irritated by one pitch, or at most only a very small number of pitches. One and the same stimulus of sound, therefore, cannot act at the same time upon many nerve-ends, as our question would imply, but simply upon one or at most a few neighbouring terminations. The qualitative adaptation or differentiation of the auditory fibres is so far developed that in general no two fibres 1 can partake of the same 1 The membrane of Corti is set in vibration only at a definite place by a H 98 Introduction to Physiological Psychology. kind of excitation. Accordingly a distinct spatial contiguity in the arrangement of several tones heard at the same time is never developed. All sensations of sound are different in quality ; but the favourable condition for the development of the spatial char- acter of our sensations is the simultaneous existence of several sensations alike in quality. Like all sensations, the sensations of hearing are projected out into space; but this projection is extraordinarily inexact. It is of especial importance that the sensations produced by the excitation of different nerve-ends may be projected to about one and the same place. For example, some one strikes a chord on the piano, in which perhaps eighteen simple tones are contained. At least eighteen different nerve-ends are irritated in each auditory nerve, and still we do not project the sensations produced by these excitations into space either separated or side by side, but altogether to about the place from which the tone seems to proceed. This fact cannot be suffi- ciently explained by the highly developed differentiation of the auditory fibres and their adaptation to the numerous qualities of sound ; for the separate projection of the sensations into space is conceivable, even though they are wholly different in quality. In this connection we must consider that association with sensations and ideas of motion, which is so essential for the development of space-perception in the case of touch, is very incomplete in the case of the sense of hearing. We cannot let the ends of the auditory nerve glide over a sounding body, as our hands did over an object, nor construct x an image of space from the successive impressions received by sensations of increasing motion. We can, it is true, turn the head from or toward the sounding body ; we can approach it or recede from it ; but in so doing no other nerve-ends are brought in contact with the stimulus. On the contrary, the same nerve-ends are irritated, and only the intensity definite pitch ; each nerve-fibre thus becomes to a certain extent accustomed and especially sensitive to a certain pitch. 1 Otherwise the formation of an image of space from sensations of hearing is not quite inconceivable. Sensations of Hearing. 99 of the stimulus increases in the one case and decreases in the other. A person with one ear, and without the ability of moving from place to place or of turning the head, would project all tones into space quite indefinitely and without regard to the direction from which they came. Of course the localization of sensations of sound by the normal human being is somewhat more definite, since he is able to observe how the intensity of a sound varies on turning the head or moving from one place to another, and can therefore form some conclusion as to the direc- tion of the sound. When the head is held at rest, we are often mistaken in judging of the direction of a sound, exchanging before for behind, above for below, etc. 1 Slight concomitant sensations of touch on the skin, appearing in different localities according to the direction of the sound, are produced by delicate sympathetic vibrations of the hairs in the concha, and possibly also by vibrations of the bones (cranio-tympanal conduction). These sensations often render at least an approximate judgment possible. Sounds coming from the right and left are also difficult to distinguish when the head is motionless. In this case we are aided in distinguish- ing the direction from which a sound proceeds by our knowledge of the fact that a sound coming from the right is physically com- pelled to produce a stronger excitation in the right ear than in the left. In this case, therefore, in view of the fact that most of the auditory fibres proceeding from one ear cross to the opposite side of the brain, the cortical excitation is also greater in the left temporo-sphenoidal lobe than in the right. Conversely, in response to a sound coming from the left, the cortical excitation is greater in the right temporo-sphenoidal lobe. This fact renders the distinction of direction possible, to a certain extent, for it is very probable that the acoustic fields of the two hemispheres have, for purposes of association, very different connections. But a slight turning of the head still remains the most important and 1 Preyer (Arch. f. d. ges. Physiol, Bd. XL) has recently ascribed the function of localizing the acoustic impressions to the semi- circular canals, but apparently without sufficient grounds. IOO Introduction to Physiological Psychology. natural means for determining the direction of sound. Finally, the localization of our impressions of sound is quite uncertain as regards the distance to which we project sensations. The sensa- tions of touch on the skin are referred directly to the surface of the skin because experience teaches that only mechanical stimuli produce sensations of touch by direct contact. As regards the sensations of sound, we likewise permit ourselves to be guided in general by experience ; weaker sensations of sound are projected to a point remote from us, stronger sensations to one nearer us. In such cases we are assisted by an experiential knowledge of the strength which the sounds of certain things have at a certain distance previously estimated by the eye ; hence after having acquired this experience we are also able to determine with closed eyes whether a distance is greater or less by the greater or less intensity of a sound. We see that the localization of the sensations of hearing is determined in part at least by processes that are essentially associative and to some extent comparatively complicated. The acoustic sensations have no direct spatial relations such as we found for the sensations of touch or such as we shall find most highly developed for the sensations of sight which are presently to be considered. The sense of hearing is not, in fact, a sense that brings us in close relations with space. We may designate it briefly as a purely qualitative sense ; but by virtue of the extremely delicate gradation and the exceedingly rapid perception 1 of the qualities of stimulation, the sense of hearing is fitted to receive the best means of communication employed by mankind, the spoken language. 1 Even eighteen vibrations are sufficient for the recognition of the pitch or quality of a tone. CHAPTER VI. THE SENSATIONS OF SIGHT. The adequate physical stimulus of the eye is furnished by the vibrations of the ether. We conceive that imponderable particles of so-called ether are distributed in infinite numbers between the atoms or molecules of matter. The physics of to-day teaches that light is diffused through space in all directions by the vibra- tion of these particles of ether. These vibrations are not executed longitudinally, as are the vibrations of the molecules of a body conducting sound, but transversely ; in other words, the direction of vibration is perpendicular to the direction in which the rays of light are transmitted. The vibrations of light may also be repre- sented best as wave-lines, governed by laws very similar to those for waves of sound. The vibrations of light without exception are to be regarded as regular periodic vibrations. Not all velo- cities of ethereal vibration impart a sensation of light to the eye ; the number of vibrations per second may be too large or too small to produce such a sensation. In general only more than 400 billion and less than 900 billion vibrations per second are capable of exciting visual sensations. Let us now consider the organ that receives this stimulus — the eye. Even in the lowest animals, the Protozoans, we find spots in the protoplasm that are sensitive to light, and marked by the deposition of special pigments. They may therefore be designated as pigment-spots. Also in the eye of the most highly developed vertebrates the rays of light are conducted through many refract- ing media and finally reach a layer of the so-called retina con- taining pigment. This layer of the retina, which covers the inner 102 Introduction to Physiological Psychology. surface of the posterior wall of the eye-ball, is designated as the " layer of rods and cones." Here numerous structures, part in the form of rods, part in the form of cones, are arranged mosaically, their bases turned toward the inner part of the eye. These rods and cones are connected with the terminations of the optical nerve, but it is not probable that a fibre of this nerve is allotted to each one of the rods and each one of the cones. The most familiar pigment of the retina is the " visual purple " discovered by Boll, which speedily bleaches when exposed to light. This visual purple, however, is only present in the rods. The cones, which are far more numerous in that part of the retina which is of service in sharp, steady sight, contain no visual purple. It is also entirely wanting, for example, in the eye of the snake. Besides the visual purple, the so-called pigment-epithelium of the retina should be taken into consideration, although we cannot undertake the expla- nation of its anatomical arrangement here. The process of an act of sight is as follows : — The vibrations of ether, having reached the retina, decompose its so-called photo-chemical or visual sub- stances, which are sensitive to light. (There are numerous analogies to this decomposing action of light.) By means of this decomposition, the nerve-ends laden with visual substances are set in commotion. The fibres of the optic nerve then conduct this excitation to the occipital lobe of the cerebrum. On their way to the brain, part of the optical fibres of the two nerves cross, part remain on the same side. Hence all the impressions from the right half of the space viewed also reach the left hemi- sphere, all the impressions from the left half of the field of vision also reach the right hemisphere, so that all impressions are re- ceived by both hemispheres. We may here at once observe that, besides the adequate stimulus furnished by the vibrations of ether, the universal nerve-stimuli (mechanical and electrical) can also impart sensations of light. If we press against the eyeball anywhere along the edge of the orbit, an impression of light is produced which is known as a "phosphene." The cause of this phenomenon is obviously mechanical stimulation. When, on account of being generally The Sensations of Sight. 103 diseased, the eyeball is extirpated and the optic nerve severed, the patient on whom the operation is performed sees great masses of light during the moment in which the nerre is being cut. Volta was the first one to establish the electric excitability of the organ of sight. It has been observed that a flash of light appears both on opening and shutting the galvanic current ; it is sufficient to place an electrode upon each temple. After these preliminary observations we can now undertake the psychological analysis of the sensations of sight. We at once meet with numerous qualities of visual sensation, which we desig- nate as colour in the broadest sense. There are no other qualities except those of colour ; these we shall now consider more thoroughly in their relation to the physical stimulus. A long series of colour-sensations is directly produced by the so-called " colours of the spectrum," which include violet, blue, green, yellow, orange, and red. These sensations of colour corre- sponding to the spectral colours compose a series similar to that produced by the different sensations of pitch. Red, which has the least number of vibrations, would correspond to the lowest tones ; violet, having the greatest number, would correspond to the highest tones. Below the following line the series of spectral colours is arranged in order. Red — orange— yellow — green — blue — violet. The red rays both have the greatest wave-length and are least refrangible. Of course we at once observe a difference between the series of sensations of spectral colour and the series of tone-sensations. In considering the latter we discovered certain harmonious relations, the nature of which we shall investigate later. Guided by these relations and proceeding from any given tone, we found it pos- sible to discover all those other tones which stand in certain harmonious relations to the first tone. In this manner we obtained a limited scale whose tones are separated by definite intervals, 104 Introduction to Physiological Psychology. instead of an unlimited, uninterrupted series of tones. It is different with the series of sensations produced by the colours of the spectrum. In this case there are no such harmonious rela- tions and hence there is no colour-scale. We can only select special colours that seem to us to be particularly striking, or that we find occurring very frequently, the intervals between them being thus determined quite arbitrarily. For this reason the designation of colours among the ancients was very indefinite. According to Helmholtz, 1 for example, the Greeks appear to have designated the entire series of colours from golden yellow to bluish green by the term "xanthos" (iav06 with the different points of the circle drawn above it. These connecting lines then represent the different transitions of the single colours of the spectrum to black, on reducing the intensity of light. It is well worthy of notice, in connection with the colour-sense, that a decrease of the intensity of the physical stimulus produces not only a decrease of the intensity of the sensation, but also a modification of its quality. This agrees with the fact just mentioned, that the intensity of light, o, does not produce a sensation of the intensity o ; that is, no sensation at all, but a positive sensation, the sensation of black, which, moreover, is just as positive psychologically as the sensation of white. If we observe a red surface at a constantly increasing distance, or, in other words, in a light that is constantly diminishing in intensity, the intensity of the sensation also changes in fact, but the change of quality is particularly noticeable. There is no true scale of intensities for the sensations of light, corre- sponding to the scale of intensities for sensations of sound. This transition to black, however, is not characteristic of spectral colours alone, but also of all mixed colours, including especially white. We have already become acquainted with the transitions of the latter to black, as the sensation of grey in its various gradations. But after having added to the sensations of the spectral colours the sensations of black, white, purple, grey, brown, grey-blue, etc., we have not yet exhausted all the qualities of the sensations of colour. It is vain to seek simple spectral colours for the colour- sensations of sky-blue, sea-blue, pale green, flesh-colour, and rose. This last group of colour-sensations is essentially characterized by the partial absence of that which we designate as " colour- satura- tion.'''' The physical stimulus that produces these sensations of less saturated colour consists of a mixture of any given spectral colour with white, or a mixture of two suitably chosen spectral colours that are not complementary. In the same way, without the ad- The Sensations of Sight. ii I mixture of white, each spectral colour becomes lighter, or, in other words, less saturated when the intensity of light is increased. If one gradually adds more white to the mixture, or increases the intensity of light, each one of the spectral colours finally becomes Black FIG. 13. apparently white. We may now add, therefore, that a sensation of white is produced not only by mixing two complementary colours, but also by the excessive increase of the intensity of light in which any given spectral colour appears. Thus red gradually passes through flesh-colour, blue through sky-blue, purple through 112 Introduction to Physiological Psychology. rose into white. If we wish to represent these colours also to- gether with white in the illustration, we must place white in the centre of the plane of the circle representing the colours of the spectrum (fig. 13). The radii of the circle then represent the gradations between complete saturation and white. With these colour-sensations produced by the admixture of white, the quali- ties of sensations of light are exhausted. By mixing the qualities thus obtained, no other new colours are produced ; only the old colours are reproduced according to fixed laws. We are indebted to Newton for the most important of these laws of mixture. As a brief summary, we may state that the qualities of the sen- sations of light do not present a simple series as do those of the sensations of tone, but can only be represented by a structure of three dimensions (fig. 13). We are now confronted by the question : In the case of the sense of sight, is each nerve-end trained to a certain pitch, i.e. to vibrations having a certain definite wave-length, as is -the case in the sense of hearing ? We answer this question decidedly in the negative. In the case of the membrane of Corti it is indeed true that each one of its numerous fibres transmits essentially but one shade of sensation. On the other hand, the simplest observation shows that in general every spot upon the retina is sensitive to all shades of colour. Only those parts of the retina that lie near the periphery are characterized by insensibility to green, the outer?nost parts by insensibility to red and green. It appears beyond doubt that all terminations of the nerve-fibres in the central parts of the retina must be very sensitive to many if not all colour-stimuli. To-day physiologists in general assume that only three different photo-chemical substances are to be found at the terminations of the optic nerve. All rays of light act only upon these three sub- stances. The red rays decompose perhaps only one substance, the yellow rays perhaps only half of one and half of another — the orange-coloured rays half of the first, one-third of the second, and one-sixth of the third visual substance, etc. In short, the action of each ray of coloured light is undoubtedly limited, and dis- tinguished from all others in that it decomposes a definite relative The Sensations of Sight. 113 fractional part of each of the three visual substances. This frac- tional part is constant for a given wave-length. One can carry this supposition still farther, supported by the so-called " Young- Helmholtz hypothesis." This theory makes a strict application of the theory of specific energy, and assumes accordingly that a special kind of fibre in the optic nerve, a special central connec- tion and a special fundamental sensation correspond to each visual substance, and that therefore every particle of the retina contains three specific nerve-ends. However, it is just this hypo- thesis which is psychologically difficult to maintain. It is not for us to discuss here in how far the theory of Hering, as opposed to that of Helmholtz, corresponds to the requirements of physiologi- cal psychology. It is sufficient here to simply emphasize the fact as undoubtedly established, that a photo-chemical process im- parts the action of the rays of light to the ends of the optic nerve. Both the number of visual substances and the arrangement of the single substances with reference to definite colours, or even to special kinds of fibres, are still quite uncertain. They are also psychologically of less importance than the above-mentioned re- presentation in which the qualities are arranged in three dimen- sions. A presentation of the most important physiological theories is to be found in the writings of Helmholtz, Hering, Wundt and Kries. 1 It is interesting to note that in the development of both in- dividuals and nations, as also in certain pathological cases, the number of qualities of visual sensation varies. At the age of two years the child gradually learns to name the colours cor- rectly, first yellow, then red, and somewhat later, green and blue. Especially blue is for a long time recognised only with difficulty, being often designated as "grey," or "gar nix" (nothing at all) (Preyer). All the colours are not named correctly before the be- 1 Helmholtz, " Handbuch der physiolog. Optik," 1st and 2nd editions ; Hering, Sitzungsber. d. Wiener Acad. Math.-naturwiss. Klasse, Bd. 66, 68, 69 ; Pfluger's Archiv., Bd. 40-42 ; Wundt, Philos. Studien, Bd. 4 ; Kries, Arch. f. Augenheilk. , Bd. 17, and Du Bois-Reymond's Arch., 1882. 1 1 4 Introduction to Physiological Psychology. ginning of the fourth year. This may be explained by the fact that the action of blue and green rays of light on the child's eye is weakened by purely physiological circumstances. We should furthermore consider that there may be possible differences in the ability to discriminate between the various single sensations of colour as regards quality. Pathological defectiveness in the qualities of visual sensation is generally designated as colour-blindness. Total colour-blindness has been observed in rare cases ; the individuals perceived some difference in brightness, but no difference in quality or colour. All nature, therefore, with its great variety of colours, appears to these individuals as a sort of silhouette, having only different shades. So-called violet-blindness is somewhat more frequent. It may be artificially and temporarily produced in a human being by the use of santonin. Violet and yellow appear to be alike to persons that are either colour-blind to violet, or under the influence of santonin. Still more frequent are " red-blindness " and " green- blindness," or cases of colour-blindness, in which red and green cannot be distinguished. Those who are colour-blind to red see but two chief colours in the spectrum, which they generally de- signate as blue and yellow ; red, orange and green appear to them like their yellow, violet like their blue. In the same way those who are colour-blind to green, distinguish two qualities of colour which they designate as blue and red. It has been claimed that colour-blindness existed at certain stages in the cultural develop- ment of nations, and that it still exists among certain peoples that have fallen behind in culture. On the other hand, we find un- doubted cases of the distinction of colour even in insects. In X858 the then youthful English statesman, Gladstone, claimed that the Greeks were colour-blind to blue. He based his claims chiefly upon the fact that Homer had no proper terms for blue. The fact that, in describing the colours of the rainbow, some of the colours were entirely omitted and others exchanged has been cited in favour of the existence of partial colour-blindness among ancient peoples. It has, however, been shown that a deduction cannot be made with certainty from the different designations of The Sensations of Sight. 115 colour that appear in the literature of a language. A reference to the pages of some of our most modern poets will bring to light some of the most nonsensical designations for colours (as one authority has shown by actual count), which might likewise sug- gest the diagnosis of colour-blindness. It appears to be a fact, however, that sensibility to colours produced by short wave- lengths of vibration (for example, green and blue), is noticeably slight in ancient peoples, in modern peoples living in a state of nature and, we may also add, in the new-born child. Therefore just these colours are often insufficiently designated in a language and the ability to distinguish them is deficient. The Bongo negroes in Central Africa seem to have only the word " red " for all colours produced by long waves of vibration ; and the word " black " for all those produced by short waves. There can be no doubt that our colour-sense has developed gradually. We are also all colour-blind in the peripheral parts of the retiua, and are placed in a condition similar to that of colour- blindness when the coloured objects are very far distant from us. All objects then appear to us to be more and more like black in proportion as the intensity of light decreases. In a similar manner the greatest increase in the intensity of light causes the apparent ultimate transition of each sensation of colour to a sen- sation of white ; in other words, the ability to distinguish quality is entirely removed. 1 In a manner similar to that employed in the last chapter for sensations of tone, we shall now determine the sensibility to differences in colour-qualities in the case of sensations of colour perceived by the normal eye so fixed that objects are imaged upon the centre of the retina. We shall limit ourselves to the series of spectral colours. Here we find 2 that we perceive slight differences in " colour-tone " best in the yellow and blue of the 1 See further on, however. 2 Konig and Dieterici, Ann. d. Phys. u. Chem., 1884. Brodhun, Verh. d. physiol. Ges. zu Berlin, 1885-86. Uhthoff, Du Bois-Reymond's Arch., 1889. Ii6 Introduction to Physiological Psychology. spectrum. A change in the wave-length amounting to f millionth millimeter is sufficient to cause a difference in the sensation of blue (or greenish-blue). The sensibility to differences in quality is considerably less in the case of the other spectral colours. For some distance at the ends of the spectrum we recognise no change of colour-tone at all, but only changes of brightness. We have now finished the consideration of the qualities of visual sensation, i.e. the sensations of colour ; we turn next to the theory of the intensity of colour-sensations. Intensity or bright- ness obviously depend on the amplitude of vibration ; the same as the intensity of sensations of tone. We have already men- tioned above, however, that sensations of light cannot be re- garded as having a proper intensity. A distinct positive sensa- tion, black, corresponds to the intensity of light o. Here, of course, it is impossible that all stimulus is wanting; we must assume chemical processes, characteristic of the retina at rest, which continually irritate the ends of the optic nerve, thus impart- ing a sensation of black. If we now permit the light of a spectral colour, red, for example, to act with gradually increasing intensity upon the retina previously at rest, both the intensity and the quality of sensation change at the same time. We perceive at first a very dark reddish-brown, then a lighter reddish-brown, and finally a complete red. This change is due to the fact that the sensation of black produced by a condition of rest in the retina, is mingled with the sensation of red produced by the irri- tation of the retina, in constantly decreasing proportions. If very weak red rays reach the retina, the sensation of black, when mingled with the weak sensation of red, still retains nearly its complete normal intensity ; the sensation of dark reddish-brown is thus produced. Black becomes less and less a factor in the production of the sensation in proportion as the red rays are intensified, and the retina more severely irritated, until finally a sensation of saturated red is produced. On account of this con- stant commingling of the sensations of black with those of red, we are wholly unable to arrange a scale of the sensations of red, beginning with the intensity o, and ascending without change of The Sensations of Sight. 117 quality to constantly greater intensities of brightness. The scale of intensities for sensations of light does not correspond to the scale of tone-intensities characteristic of sensations of sound. This scale, for example, begins with the softest C\ and ascends to the loudest C 1 without a change of quality. The scale of intensities for sensations of light is mingled with a scale of changes in quality. Therefore observations of pure intensity cannot be employed in the case of sensations of light. If the latter remain the same in quality, it is impossible to obtain any scale of intensities whatever. Even the sensation of white not only loses intensity when the strength of light is decreased, but is also modified in quality by passing through grey into black. The quality may, however, at least be regarded as approximately constant on a very small tract, situated in that part of the mixed scale of intensities where the sensations of red, white, etc., are most saturated. This tract could be applied in the measurement of the intensity of sensa- tion. (Fig. 14.) Before we pass on to these measurements, however, let us carry the above experiments still further. By constantly increasing the intensity of light up to a certain degree we have obtained the sensation of saturated red. Now what takes place when we in- crease the intensity of light still further ? As has already been mentioned above, each simple sensation of spectral colour then passes into a sensation of white. It is inexpedient, however, to consider the transition of sensations of spectral colour to the sensation of white, caused by the constant increase in the in- tensity of light, as parallel to the transition of these same sensa- tions to the sensation of black, caused by the constant decrease in the intensity of light. In the former process it is possible that other complicated phenomena, due to over-irritation and con- trast, are concerned. 1 It is obvious, however, that a pure scale 1 For example, a very intense green light, despite the continuity of its action, might directly produce the contrasting sensation of red. In conse- quence of the blending of the two sensations of colour, a sensation of white would be produced. 1 1 8 Introduction to PJiysiological Psychology. of intensities rising from saturation to white, is also an impossi- bility, for the quality changes in proportion as the shades of colour gradually approach white. For the reasons just given, the testing of Weber's Law will always be more or less uncertain when the law is applied to the intensity of visual sensations. The approximate validity of this law is, of course, at once apparent. As we have already learned, the Law of Weber states that we distinguish between intensities of light by virtue of their relative, but not their absolute, differ- ence. A simple demonstration of this may be obtained by the use of Masson's disks (fig. 14). A broken black line of a Fig. 14. definite breadth is drawn in the path of a radius upon a white circular surface. If the disk is rapidly revolved, each component line blends with the white belonging to the same ring of the circle, into a grey ring. The innermost grey ring is darkest and the other grey rings are lighter in proportion to their nearness to the periphery, because each one of the successive components of the broken line occupies a so much smaller part of the ring in which it lies, and is consequently blended with so much more white the nearer it is to the circumference of the disk. Let us next assume that the disk is illuminated by the light of one candle, and that the grey ring already produced by the black component line 4 is so light that we cannot distinguish it from the white back-ground. We now light six candles instead of one, and find to our astonishment that despite the great change in the absolute The Sensations of Sight. 119 intensity of light, the grey ring No. 4, is still the one that cannot be " just distinguished " from the white back -ground. It is obvious that in this experiment the absolute difference in bright- ness was completely changed, while the relative difference re- mained the same. Hence, in accordance with the Law of Weber, the discriminative sensibility also remained unchanged. Fechner, the founder of psycho-physics, has called attention to a very striking example of the approximate validity of Weber's Law when applied to sensations of light. It has already been stated that this law may also be formulated as follows : The intensity of sensation increases in an arithmetical ratio while the intensity of stimulus increases in geometrical ratio. For ages the astronomers have classified the stars according to the in- tensity of the. sensations of light which the stars produce in the eye of the observer. On this basis they distinguish stars of the first magnitude, stars of the second magnitude, etc. Since this classification was first made on the basis of subjective impressions, we have succeeded in determining the objective brightness of these stars by the help of photo-chemistry. As a result it has been shown that the apparent (subjective) brightness increases in arithmetical ratio, while the real (objective) brightness increases in geometrical ratio. The most recent, thorough experiments upon the intensity of sensations of light have been made by Merkel, 1 Konig and Brodhun. 2 The result of their experi- ments demonstrates that the relative discriminative sensibility, in the case of light stimuli having a medium intensity, is approxi- mately constant and corresponds to the Law of Weber. Devia- tions occur when the stimuli are very weak or very strong, as in the case of the other senses. The so-called " lower deviation ,: is due in part to the fact that the retina has a " light of its own " (Eigenlicht). The weak sensations of light are disturbed by slight irritated conditions of the retina that can never be wholly Temoved. They appear, for example, as a spotted glimmer in the 1 Philosoph. Studien., IV, H. 4. 2 Sitzungsber. d. konigl. preuss. Akad. d. Wiss., i< 120 Introduction to Physiological Psychology. field of vision when the eyes are closed. This light which is in the retina itself, also renders it almost impossible to determine accurately the minimum of stimulus for sensations of light. 1 The threshold of distinction appears to average about y^-y for stimuli of white light. It is larger for very weak and very strong stimuli, especially for weak rays of spectral red. Let us remember that we should not rely too implicitly upon these measurements of intensity, especially in the case of great or slight intensities of light. As regards the medium intensities of light and their variations, with which we are daily familiar, it can easily be conceived that in the course of development by natural selection the sense of sight was trained to perceive chiefly the relative differences of brightness and to ignore the absolute. If the law of Weber did not have at least an approximate validity, and the absolute differences of brightness were per- ceived very vividly, at every flash of sunlight and every time the sun was concealed behind a cloud, all the shades of our environ- ment would be so distorted as to render an accurate and clear perception of the projections and depressions of objects exceed- ingly difficult. The accuracy with which we form our conceptions of the objects of the world as solid bodies, is essentially depen- dent upon the constancy of the relative threshold of distinction for a medium intensity of light. Finally we again raise the important question. How is the sensation affected when not one but several fibres of the optic nerve are simultaneously irritated by the same stimulus of light ? We have already seen that the fibres of the optic nerve are, in general, of equal value, i.e. each termination of the optic nerve receives a stimulus of any wave-length whatever. Even if we accept the assumption of Helmholtz, that there are three different terminations for each nerve-fibre in each element of the retina, we must still remember that this triad is repeated in all parts of 1 The more recent experiments of Ebert's are very worthy of notice. Wiedemann's Annalen, 1888, and Langley, " Energy and Vision," Am. Journ. of Sc, XXXVI. The Sensations of Sight. 12 1 the retina. The obtusion of the sensitiveness of the peripheral parts in the retina to red, and especially to green, may be dis- regarded here. Hence, in the case of the sense under discussion, we find relations bearing a close resemblance to those already considered with reference to the sense of touch. These rela- tions depend on a series of terminations of nerve-fibres that are all essentially identical in function. In fact, the sensations of light produced simultaneously by the excitation of different parts of the retina stand in a relation to one another very similar to that of the sensations of active touch when excited simultaneously on different regions of the skin. They neither blend to a unit in quality nor increase their reciprocal energy, but are arranged together spatially so as to form an image of surface. In the sphere of visual sensations also we must abandon the attempt to explain the fundamental fact that the sensations of sight are projected into space, as are all other sensations, thus producing the so-called field of vision. We have simply to accept the general fact that our sensations are combined so as to present a contiguous arrangement ; we can only attempt to explain the order of this adjacent arrangement. We must therefore restrict ourselves to answering the question : How does it happen that two sensations arising in neighbouring ends of the optical fibres are also combined contiguously in the field of vision? In an- swering this question we shall make use of means (Fig. 15) similar to those employed in the fourth chapter. RR' is a cross-section of the retina ; CC is the corresponding cross- section of the cerebral cortex ; ML represents the so-called Macula lutea, the part of the retina most sensitive to light, which is therefore generally fixed directly upon the object for the pur- pose of distinct vision. The ends of the visual fibres aa', bb', cc\ dd', are arranged in the retina in the definite order just given. In the cortex of the cerebrum this succession has been materially changed. In the most favourable case we might suppose that a certain region of the occipital lobe corresponds to the upper parts of the retina, and another to the lower. But it is wholly improb- able that the succession of the single fibres in the cerebral cortex 122 Introduction to Physiological Psychology. remains the same as in the retina. We know, in fact, that the fibres of the optic nerve from the retina of the left eye, for example, terminate partly in the cortex of the left hemisphere and partly in the cortex of the right hemisphere of the cerebrum. Now how does it happen that in spite of this change in the order of the fibres, the sensations which they conduct to the cortex are arranged so as to correspond to the order of the fibres in the retina, and hence also to the order of the visual stimuli, and of the objects that are seen ? A very accommodating, but untenable, theory is the so-called nativistic theory, which assumes that a definite point in space is allotted to each one of the retinal points from birth ; but the theory is not at all in harmony with the X empirical data of physiological optics. We shall therefore pro- ceed from the genetic standpoint, and attempt to show what data furnished by the physiology of the brain throw any light upon the arrangement of the spatial points, or upon the characteristic features by which they are distinguished. Suppose O to be an approximately point-like object, situated in the upper part of the field of vision, from which rays of light are sent to the retina RR'. These rays are united at one point in the retina by means of the peculiar structure of the eye. This point may be found by drawing a straight line from O to X, the point in the vitreous humour at which the rays intersect, and by producing this line until it reaches the retina. The object O (fig. 15) therefore The Sensations of Sight. 123 « sends all its rays to d, and irritates the ends of the nerve-fibres situated at that point. Let us now move the eye for the purpose of fixing the especially sensitive central point of the retina at a, the Macula lutea, upon the object O so as to obtain a more distinct image of the latter. In so doing the retinal image passes from d over the points c and b to a. On moving the eye a certain distance, it reaches c, a somewhat greater distance b, and a still greater distance a. As the eye is turned, and the retinal image of the object passes from d to a, we have a continuous series of motor sensations. 1 A motor sensation, having a definite magnitude, is associated with each termination of the nerve-fibres, and the intensities of these sensations of motion form a constant series. One retinal point, situated between two others, is con- stantly associated with a sensation of motion whose magnitude lies between the magnitudes of the sensations of motion with which the two adjacent points are associated. In this associated sensation of motion, each termination of the nerve-fibres possesses to a certain extent an acquired local sign. By repeatedly passing over all lines of the retina numberless times both from a and toward a, each retinal point is associated with a definite magni- tude in the system of motor ideas. Thus a foundation is obtained for the localization of sensations. If a larger object 00' irritate the four retinal points, a, b, c, d, simultaneously, four excitations, d', a', b\ c\ will appear in the cerebral cortex followed by the corresponding sensations. The localization of these sensations in space takes place neither in complete confusion, i.e. according to an arbitrary arrangement, nor according to the succession of the ganglion-cells, d', a', b', c'. On the contrary, we localize the sensations of light according to the scale of sensations or ideas of motion associated with them. In this way each sensation is referred to its definite place. The order of sensations accord- ingly corresponds to the order of the points on the retina, and hence also to the order of the points on the object. It is clear that an infinite advantage was gained in the struggle for existence 1 The chief features of the theory here presented originated with Lotze. 124 Introduction to Physiological Psychology. by the first animal that localized its sensations in this way. If the protist, with its pigment-spots sensitive to light, has any sensations of space whatever, it must localize them almost wholly without regard to order. At least those protists in which the direction of the rays of light determines the direction of locomo- tion (Phototaxis, Strassburger) by the association of the sensation of light in one case with the motions of flight, in another case with the motions of approach, have obtained some basis for the distinction of two directions and for the localization of impres- sions in two directions. In the course of the phylogenetic development of the animal series that capacity to localize visual sensations was first developed which made the eye a proper organ for the perception of space. We find the wonderful rapidity, with which this arrangement of the sensations is accomplished, inconceivable; at once and without a moment's thought the image is before us, well arranged and unmarred by the slightest error. To be sure, a process of evolution extending through almost endless ages was necessary to produce and train a cortical apparatus of vision that can react with such fitness. The new- born animal or child inherits this apparatus. 1 Each single in- dividual does not need to acquire it again laboriously, but only to learn to use it. A person who is born blind and receives his eyesight by an operation later in life, at first sees only coloured spots floating before his eyes. He recognises a circle or a square only with difficulty. It is only by degrees that he learns to use his cortical apparatus, and to associate the sensations of sight with ideas of motion and touch. In concluding these investigations we can again render the development of spatial localization clear by comparison. Let us call to mind the position of a musical conductor who leads an orchestra for the first time. Numerous sounds from a large number of instruments are poured into his ears at the same 1 Munk's more recent investigations, perhaps, throw some light on the physiological and anatomical structure of this cortical apparatus. Sitzungs- ber. d. kbnigl. preuss. Akad. d. Wiss., 1890. The Sensations of Sight. 125 instant, and at first he is only able to project the masses of sound outward in confusion. But he gradually learns that the tone of this violin always comes from below to the left, the tone of that flute from the right, etc. In short, he learns to localize the tones of the different instruments by means of distinctions that are almost unnoticeable. Certain subtle distinctions in musical sound and in the sensations on the skin that accompany the tones according to the direction from which they proceed, assist him in localizing at once the tone of one violin in this place, and the tone of another violin in that place. In fact, the musical director is finally able to project the tones outward in the exact order in which the sources of sound are really arranged in space, even with the eyes entirely closed. Orchestral leaders have been known to construct in this manner a genuine "field of hearing" similar to the field of vision. This projection is accomplished very rapidly, and entirely without deliberation ; it is just as direct and exact (that is, in accordance with the arrangement of the external stimuli) as the projection of sensations from the visual centre. It is very striking, especially in comparison with the localiza- tion of tones which are heard simultaneously, that our visual impressions are characterized by continuity. A gap between them never occurs ; in fact, even defects in the continuity of the nerve-ends of the retina, the so-called "blind spot" for example, are involuntarily repaired. We see the object, or the part of an object, corresponding to the blind spot, in the colour of its environment. An anatomical explanation of this continuity in the arrange- ment of projected visual sensations may possibly be found in the anastomosis of the nerve-ends of the visual fibres in the retina, or in the universal interconnection of the ganglion-cells of the visual centre by means of the nerve-processes. 1 The chief ground 1 In fact* according to more recent investigations, these connections are made not by the so-called protoplasmic processes, but by the axis-cylinder processes. Compare Golgi, "Sulla fina anatomia degli organi centrali del 126 Introduction to Physiological Psychology. for the continuity of sensations of sight, however, mast be sought chiefly in the continuity of the associated ideas of motion. The following facts in the sphere of visual perceptions are still to be investigated and explained in detail. First, the retinal image in the eye of the vertebrates is inverted ; that which is on the right and above in the real object, is on the left and below in the retinal image, and vice-versa. Still we do not see the object inverted, corresponding to the image on the retina, but right side up, corresponding to the object itself. How can we explain the fact that the retinal image is thus fittingly ^-inverted? In reply we may first observe that the spatial succession in which the visual sensations are projected is not altered at all ; it is simply a question of projection in its totality. So far as the pro- jection as a whole is concerned, the re-inversion of the retinal image is determined and controlled by sensations of touch. In general we project our sensations of sight so that they agree with the tactual sensations by which we are guided to a certain extent. This capacity has also been acquired phylogenetically and not ontogenetically. We should here call attention to the fact that the inversion of the image on the retina which necessitates to a certain extent a second psychical inversion, is specifically characteristic of the eye of vertebrates. The composite image in the compound eye of the glow-worm, for example, is not an inverted, but an upright retinal image. The glow-worm or fire-fly can therefore project its sensations of sight exactly in the position indicated by the retinal excitations. 1 A second question is suggested by the fact that we see with two- eyes, hence a double retinal image is produced by the majority of the objects seen. How is it that, notwithstanding this fact, an object generally appears single to us? Why does it appear double only in very rare cases, — for example, when we push on sistema nervoso," 1S85 ; and Flechsig, Arch. f. Physiolog. (Du Bois Kkymond), 18S9. 1 See EXNER, "Das Netzhautbild des Insectenauges." Sitzungsber. d. Wien. Akad. d. Wiss., 1889. The Sensations oj Sight. 127 the side of the eye-ball with a finger while gazing fixedly at an object? This question has given rise to numberless physiological and psychological investigations and discussions. It is sufficient here to notice that, physiologically, the union of the two retinal images is already accounted for by the peculiar partial crossing of the optic nerve-fibres. By this means the excitations produced in the left half of both retinas are conducted together to the right hemisphere of the brain, and vice-versa. The blending of the two images is provided for psychologically by the association of like ideas of motion, in general, with those points that are situated alike in the two retinas. It is for physiological optics to decide how far these two factors suffice, in a single case, to explain the blending of the two images. The final question is suggested by the fact that the retinal images are superficial or planiform. It asks, Whence do our visual sensations receive their stereometric character ? We see solids and not plane surfaces. In this case also it is obviously a question of association with ideas of motion and touch. It is at least very doubtful whether the two eyes, remaining wholly at rest, could ever achieve the construction of a stereometric image of space. 1 But our eyes are moved, there is a constant play of the muscles of accommodation (the ciliary muscle and the recti interni), the head is turned, the entire body is moved forward, the sensations of sight are controlled by the sense of touch. In this way a large number of new associated ideas of motion and touch is acquired. It is only by association with these ideas that our visual perception receives its stereometric character. Strictly considered, this perception in itself has neither a planimetric nor a stereometric character, since our sensations are at first projected merely in a definite direction, leaving it quite indefinite as to how far from us in that direction the object lies. For example, a person that is blind from birth and receives his eyesight later in life, conceives all objects to be directly in contact with the outer 1 As to possible physiological conditions, also concerned in this case, see Hering, I.e., Helmholtz, I.e., and others. 128 Introduction to Physiological Psychology. surface of the eyeball. He only learns by degrees to project his sensations of sight accurately also as regards distance and hence as regards stereometric relations. It is self-evident that experiments, applied for the purpose of ascertaining the degree of certainty with which sight-impressions are localized and distinguished in space, may also be employed in the case of vision in accordance with the Law of Weber. Such experiments have shown that, in general, an object can be no longer recognised, even by direct vision, when the visual angle in which it appears becomes less than one minute. As regards the estimation of magnitudes of extension, it has also been demon- strated that the Law of Weber is only valid for the medium dis- tances (e.g. lines). It appears, for example, that in attempting to determine one distance that will equal another given distance, the average error is about in proportion to the magnitude of the distance. 1 If the distances that are to be estimated become very large or very small, the " relative threshold of distinction " seems to be no longer constant. Furthermore, in the above experiment the individual variations are very great. We have now essentially completed our investigations of visual sensations. The senses of hearing and sight represent the culminating points of sentient life. In future chapters we shall also find that higher intellectual processes are chiefly dependent upon the sensations of sight and hearing. 1 This method is designated as the ' ' method of the average or mean error." CHAPTER VII. THE TONE OF FEELING AND THE SUCCESSION OF THE SENSATIONS. We distinguish three properties in each sensation : quality, in- tensity, and accompanying tone of feeling. To these are also to be added those characteristics of the sensations that have reference to space. The latter, and also the qualities and intensity of the sensations, have been discussed at length in the preceding chapters. In this chapter we turn to the last property belonging to every sensation, viz. the tone of feeling accompanying the sensation. We have already made use of the sign/ to indicate this property. As we have seen, this tone of feeling is nothing more or less than the feeling of pleasure or pain (displeasure) that accompanies our sensations with varying degrees of intensity. At this point, how- ever, we must beware of mistaking the words, " feeling of pleasure or pain." If we see a friend, we are glad; but this joy has nothing to do with the feeling of pleasure or pain accompanying the sensation, for it is not the sensation of seeing the friend in itself that produced the feeling of joy, but the idea associated with the sensation. The thought that he is our friend, that we can speak with him, etc., first awakens in us the feeling of pleasure. We must therefore make a sharp distinction between the tone of feeling which accompanies the sensation as such, and the tone of feeling that accompanies the ideas or images of memory whose activity has no direct reference to the sensations. We shall here refer at first only to the former. Let us cite a few simple examples of the tone of feeling accompanying sensation. If we strike the chord c-e-g, the sensation of sound is accompanied 129 K 130 Introduction to Physiological Psychology. by decided feelings of pleasure. We therefore speak of the chord as harmonious. On the other hand, if we strike c and d together, the sensation of hearing is accompanied by a lively feeling of displeasure ; in this case we speak of a discord. The feelings of pleasure are designated as positive, the feelings of pain or dis- pleasure as negative tones of feeling. These concomitant feelings of pleasure and pain vary greatly in intensity. The chord c-e7-g, the so-called minor chord, also produces a sensation of hearing that is accompanied by a feeling of pleasure ; but the latter is considerably less intense than in the case of the major chord c-e-g. A solution of quinine has a more or less unpleasant taste, accord- ing to the degree of concentration. Finally, there is a long series of sensations that to a certain extent occupy a neutral position as regards the tone of feeling ; that is, they are accompanied neither by a distinct feeling of pleasure nor by a distinct feeling of dis- pleasure or pain. To this class belongs by far the greater part of the sensations received through the highest senses. How many visual images, musical sounds and noises daily throng our con- sciousness ! How few of them are associated with any feeling whatever ! The few that do give us positive feelings of pleasure or pain do not possess this emotional effect in the mere sensation itself. The emotional effect is for the most part a result of the ideas with which the sensations are associated, as in the above case, when one sees a friend. The emotional tone, or tone of feeling, is therefore by no means a necessary property of sensation. Between the scale of pleasurable feelings and that of painful feelings there is a zero-point or point of indifference. Only a limited number of sensations rises above or falls below this point as regards the emotional tone. Let us now ask : On what does the emotional tone of a sensation depend ? The tone of feeling obviously depends mainly on the i?itensity of the stimulus, or, more specifically, on the intensity of the sensation. A simple tone, lightly struck, generally leaves us indifferent. Feelings of pleasure appear and increase slowly, in proportion to the gradual swelling of the tone. The pleasurable impression of the pure tone has reached Tone of Feeling and Succession of Sensations. 1 3 1 its absolute height as soon as the sensation has attained a medium intensity. If the intensity of the tone is further increased, the feeling of pleasure diminishes rapidly and finally passes into a feeling of pain. If the tone reaches the maximum of stimulus the piercing sensation of sound is accompanied by an intense feeling of the greatest pain and displeasure. Similar effects can also be produced in the case of any one of the other senses, The intense light that blinds us is unpleasant ; light of a medium intensity imparts the most pleasurable sensations. We can also express this dependence of the emotional tone on the intensity of max. Fig. 16. the sensation, diagrammatically by a curve. The unbroken lines of the above drawing (fig. 16), are already familiar to us They represent the relation of the intensity of sensation to the intensity of stimulation. The intensities of stimulation are re- presented by the axis of abscissas, E. E-min. designates the minimum, and E-max. the maximum of stimulation. The un- broken curve indicates the path described by the increasing in- tensity of sensation, following the increase in the intensity of stimulation. The intensity of the emotional tone accompanying the sensation is designated by a dotted curve. That part of the dotted curve lying above the axis of abscissas designates a 132 Introduction to Physiological Psychology. positive feeling, or a feeling of pleasure ; the part lying below the axis indicates a negative feeling or a feeling of pain. We see that at the minimum of excitation or upon the appearance of a barely noticeable sensation, the curve of feeling rises above the axis of abscissas. It reaches its height at the medium intensity of sensation. Thence the feeling of pleasure decreases rapidly and changes to an increasing feeling of pain ; the curve falls abruptly and sinks below the axis of abscissas. 1 In certain mental diseases the tone of feeling is very charac- teristically changed. Thus, for example, melancholia is charac- terized by a sudden conversion of the feeling of pleasure to one of pain, even in response to much slighter intensities of sensation. Finally the disease reaches a stage in which the curve of feeling no longer rises above the axis at all ; a feeling of pain is coupled with the slightest sensation. Everything that is perceived is accompanied by painful feelings. The dependence of the emotional tone on the quality of sensation is more complicated. Among the sensations of taste the quality of sweet is decidedly more closely associated with sensations of pleasure, and the qualities of sour, salt and especially bitter are more closely associated with sensations of pain or displeasure. More accurate observations, however, show that in this case also the intensity chiefly determines whether the sensations are pleasurable or painful. We like our food a little salty, and we find a slight taste of bitter or sour pleasant, while on the other hand the most concentrated solutions of sweet are distasteful to us. Thus pleasurable feelings are coupled with the 1 Horwicz (Psychologische Analysen, II, 2, S. 26), emphasizes several not unjust objections to this presentation, which has been essentially adapted from Wundt, He also emphasizes (with Beneke) that very weak sensations are not seldom associated with feelings of pain. Hence the curve of feeling, before rising at all above the line at the zero-point, would first sink beneath it a short distance, at least in the case of certain qualities of sensation. — An acceptable synopsis of the appertinent literature is to be found in Cesca, "Die Lehre von der Natur der Gefiihle." Vierteljschr. fiir wiss. Phil., 1886, X. Compare also in the same Ztschr., XI, O. Kulpe, " Zur Theoric der sinnlichen Gefiihle." Tone of Feeling and Succession of Sensations. 133 slighter intensities of sensation and painful feelings with sensa- tions of greater intensity. It is worthy of mention that bitter produces feelings of displeasure even in degrees of intensity that are relatively much slighter; sweet, on the contrary, awakens such feelings only when the degrees of intensity are relatively very much greater. It is obvious that this fact is to be under- stood as merely a product of phylogenetic development. The mother's milk contains a 4% solution of sugar, besides its fatty and albuminous constituents. The sucking babe, in which especial feelings of pleasure were coupled with the sensation of sweet, sought the mother's breast more zealously, was better nourished and consequently enjoyed better chances of growing up. This peculiarity has been nourished thousands of years until to-day it is universal. The tone of feeling accompanying sensations of smell has quite the same characteristics as in the case of sensations of taste. The intensity of sensation also chiefly determines the character of the emotional tone ; the most unpleasant smell is converted into a perfume by appropriate attenuation. The tone of feeling accompanying dermal sensations is of especial importance. In this case, indeed, the concomitant feel- ings of pleasure are considerably less pronounced than the feel- ings of pain. Tepidity, slight cold, a soft touch, impart but very slight positive tones of feeling. But the feeling of displeasure is just so much more pronounced when the sensation of warmth, cold, or pressure rapidly increases. In the case of heat, cold, and pres- sure, these intense feelings of displeasure are generally designated as pains. Pain, therefore, is no especial quality of sensation, but merely a special designation for the painful or unpleasant feeling that accompanies very intense dermal sensations. We also speak occasionally of a " painfully piercing tone," or a " painfully blind- ing light." It is worthy of mention in connection with painful dermal sensations, however, that the negative tone of feeling frequently obscures the quality of the sensation in consciousness. When very powerful effects are produced by heat, or cold, or by some very potent mechanical stimulus, as, for example, the thrust 134 Introduction to Physiological Psychology. of a sharp instrument, we are finally convinced that we feel only pain, i.e. we perceive the tone of feeling quite apart from the sensation. On this account some authorities have often desig- nated the sensation of pain as an especial quality of the dermal sensations. 1 But neither special " pain-spots " on the skin, nor a stimulus especially adapted in quality to cause sensations of pain have been shown to exist. It can be very easily understood also, why, on account of very intense stimulation, the feeling of pain has such an ascendancy only in the case of dermal sensations. As we shall find later, the voluntary action following a sensation is essentially dependent on the accompanying tone of feeling, as regards both its character and the rapidity with which it is exe- cuted. The more disagreeable a sensation, just so much more speedily and energetically do we seek to remove it ; we either flee or defend ourselves. Now in the development of the animal series, the earliest, greatest, most frequent, and most direct dangers to the animal organism consist of mechanical and caloric stimuli. The animal organism must be able to accommodate it- self to these stimuli, to respond with extraordinary rapidity by the execution of motions in defence or flight. Such reaction is in fact most fittingly attained by the association of a feeling of dis- pleasure, so completely dominant as that of pain, with all sensa- tions produced by intense mechanical and caloric stimulation. The claim has also been advanced that the sensation of pain is especially produced by irritating some part of the nerve-trunk or one of its chief branches, instead of the nerve-ends. This claim is sufficiently accounted for by the fact that irritation of the nerve- trunk of course affects a much larger number of fibres. It has also been thought that separate paths of conduction must be assumed in the spinal cord for sensations of touch and those of 1 Richet, " Recherches sur la sensibilite " ; Goldscheiber, Arch. Du Bois-Reymond, 1885, S. 90. The remarkable statement of the latter, that even the intense caloric stimulation of heat-spots and cold-spots produces but a relatively slight pain (at least considerably slighter than that produced by the stimulation of the cuticle between temperature-spots), still requires ex- planation and confirmation. Tone of Feeling and Succession of Sensations. 135 pain. The reasons for this assumption are twofold : (1) Schiff has observed isolated analgesia (insensibility to pain) in animals after having severed the grey substance of the cord, the removal of the sensibility to pain being accomplished without disturbing the sensibility to touch ; (2) in certain diseases, such as tabes, analgesia occurs without anaesthesia, i.e. without the loss of sensibility to touch. In fact it frequently happens in the case of tabes that the patient, on being pricked with a sharp instrument, first reports a sensation of touch and a few seconds later one of pain. Schiff's experiments in this line, however, are by no means free from all objections, and it is possible to explain all the other phenomena just quoted without assuming that there are separate paths of conduction in the spinal cord for sensations of touch and sensations of pain. It is sufficient to assume that, in the case of tabes for example, the nerve-fibres are sometimes altered by the pathological process so that they can still receive the weak stimuli and conduct the excitation to the cerebral cortex, although unable to transmit the more intense stimuli. If the latter produce any effect whatever, they are either first weakened before transmission, or the greater part is conducted more slowly. 1 Since we are almost entirely ignorant of the nature of the pathological changes affecting the conductivity of the sensory paths, however, it is difficult to see why this assumption should be rejected a priori. It is sufficient to explain both " analgesia without anaesthesia " and the separation of a sensation into two successive sensations, viz. a weak, painless sensation and a strong, painful one. As a result of these considerations we find that there is no ground whatever for regarding pain as a special quality of dermal sensation. On the contrary, we define that it is merely the strong feeling of pain accompanying the dermal sensations. The tone of feeling that accompanies sensations of simple tones 1 The more recent investigations by Golgi, Ramon y Cajal and Kolli- ker should be considered in connection with this question. According to these the sensory fibres, having entered the spinal cord, divide and also send off innumerable collateral processes further on. 136 Introduction to Physiological Psychology. having a medium intensity is not very strongly marked. There is a large number of qualities that exert no influence whatever upon the tone of feeling. Only very high or very low tones are generally more likely {ceteris paribus) to be accompanied by negative tones of feeling. The influence which is exerted by the quality of a tone-sensation is much more noticeable in the case of sensations of noise or musical sound, i.e. in the case of acoustic sensations that are produced by the combination of several simple tones. The most important fact for our consideration is that the irregularly periodic vibrations characteristic of noises, are, in general, not accompanied by positive tones of feeling; only the regularly periodic vibrations of musical sounds can impart a posi- tive emotional tone. As we have already mentioned, when a key is struck on the piano we really hear not a simple tone, but a musical sound ; that is, we hear a chord with very distinct over- tones, which decrease in intensity in proportion to their distance from the fundamental tone and the numbers of whose vibrations stand in a simple numerical relation to each other. Each pure tone of the piano generally imparts a slight feeling of pleasure, and is, in fact, as we already know, produced by the regularly periodic vibrations of the particles of air. But we also know that certain combinations, both of simple tones and of musical sounds (the chords of a piano for example) possess a consonance in- comparably more pleasant than that of either the simple tone or the simple musical sound. These are the so-called consonant chords. It is one of the most interesting and difficult problems to determine under what general conditions a combination of tones is consonant or dissonant, i.e. imparts a positive or negative tone of feeling. To begin with, it is conceivable, in fact obvious, that the consonant chords (for example, the common C-major chord, c-e-g) must consist of tones, the numbers of whose vibrations stand in a simple relation to each other. For we know it is only when this condition is fulfilled that a chord can be produced by a regularly periodic form of vibration. A regularly periodic form of vibration is the " conditio sine qua non " of strong positive emotional tones. In fact the numbers of vibra- Tone of Feeling and Succession of Sensations. 137 tions of the tones c-e-g t for example, stand in the relation of the simple numbers 4:5:6. Not all chords whose component tones possess numbers of vibrations standing in so simple numeri- cal relations, however, are consonant. For example, the simple chord c-d generally sounds quite dissonant, that is, it produces an entirely negative tone of feeling, despite the fact that it is a musical chord. The numbers of vibrations producing c and d, in fact, stand in the relation of the simple numbers 8 and 9. Hence not every chord of a regularly periodic form of vibration imparts the feeling of pleasure that accompanies a consonant chord. There are chords whose form of vibration is quite regularly pe- riodical, but which are nevertheless dissonant. Now, why is the cord c-e-g consonant and the chord c-d dissonant ? Both are not noises, but musical chords in the broadest sense; 1 both de- pend upon the regularly periodic vibrations of the particles of air. We might take into consideration the influence of the overtones that are mingled with each tone of the piano, for example, and refer the dissonant character of the chord c-d to the fact that in this chord the over-tones disturb the regularity of the form of vibration, which is not true of the chord c-e-g. This attempt at explanation fails however. C-e-g is consonant and c-d dis- sonant also when the chords are produced by tuning forks that have no overtones. Of the many answers that have been given to the above question, we shall consider only the one which Helmholtz has given in his noted " Theory of the Tone-Sensa- tions." In framing his theory Helmholtz proceeds from the fact 1 A musical sound (Klang) is in general any combination of tones that has a regularly periodic form of vibration or, in other words, a combination of simple tones whose numbers of vibrations stand in simple numerical relations. A tone of the piano is a special case of the simplest form of a musical sound. In this case the numbers of vibrations producing the separate component tones are in the relation 1 : 2 : 3 : 4, etc., and the intensity of the component tones decreases the higher they are above the fundamental tone. Conversely, the chord is a musical sound, or combination of musical sounds, whose component tones are all of approximately like intensity, and whose numbers of vibrations stand in the relation m :n : :fi, etc., the letters m, n, 0, p, representing only whole members in general. 138 Introduction to Physiological Psychology. that when two tones having but slightly different numbers of vibration sound simultaneously, numerous so-called " beats " l or " throbs " can be distinguished ; that is, the intensity of the sound alternately swells and diminishes. The number of these " beats" per second corresponds exactly to the difference between the numbers of vibration. These " beats " are also very unpleasant to the ear, especially when some twenty to forty of them occur in a second. The chord receives by means of these beats a pecu- liarly rough character. It can also be shown that the chord c-e-g produces no unpleasant beats, but that the chord c-d produces very unpleasant beats. In order to establish this separ- ately for each chord in each octave, it is necessary to take into consideration more exactly the overtones mingled in the chord, and also the so-called " summation-tones," " difference-tones," and those tones which Konig designates as "Stosstone." By this means, at least, Helmholtz thought to reduce the dissonance of discords without exception to the production of unpleasant " beats." It is probable, however, that still other elements act in connection with these beats to render one chord consonant, another dissonant to the ear. Perhaps, for example, the fact should also be considered that in dissonant chords the numbers of vibrations are generally in a more complicated relation (8 : 9 or 8 : 15), and that therefore the so-called " period " of the wave is considerably lengthened. In case of the combination of musi- cal tones into consonant chords, it is possible that the agreeable character of the latter is determined in part by a number of partial tones common to all the members of the chord, as urged by Wundt. The simple visual sensations having a medium intensity are accompanied only by a very slight positive tone of feeling. Even our joy in beholding the blue sky does not belong to the mere sensation. Associated ideas — such as the idea of the infinity of the blue vault above us, etc. — accompanied by their tones of feeling are also active to a great extent. Therefore the quality 1 The accepted term in acoustics is "beat." — 7" s. Tone of Feeling and Succession of Sensations. 139 of the visual sensations, colour, has almost no significance for the tone of feeling. It is true that older psychologists, such as George, attempted to compare each colour with a definite taste ; by this means they hoped to be able to ascribe a definite tone of feeling to each colour. Thus red was to correspond to salt, yellow to sour, blue to bitter and white to sweet. These are, however, mere subjective comparisons suggested by associated ideas (for example, "white," "sweet," "milk"). On the other hand, Goethe distinguished a plus and a minus side in the series of spectral colours. Red and yellow were to constitute the plus-side and act as excitative ; blue and violet, the minus-side acting as depressive. Green was to be the transition between the two sides. In view of this classification Italian psychiaters have proposed to bring individuals afflicted with melancholia into a room containing red light, and those afflicted with mania 1 into a room containing blue light, for the purpose of dampening the morbid inclination to extreme abnormal tones of feeling. It is obvious that these views are due to the association of certain colours with certain ideas and their tones of feeling. Red reminds us of flaming fire ; yellow of the life-giving light, etc. Hence in these cases the tone of feeling does not accompany a sensation but an idea. At most we may state perhaps that the qualities of sensation produced by dark colours, especially by those that re- present the transitions of the spectral colours to black, such as red-brown, are less easily united or associated with positive tones of feeling. The tendency of black itself to produce a negative tone of feeling is due, in part at least, to the idea of something dismal and dangerous with which it is associated. There are no "colour-accords" in the same sense that there 1 The reader should bear in mind that the term " mania " is used by German psychiaters in a much more restricted sense than by English psychiaters. The German alienist includes under the term "mania" only those mental diseases that are characterized by the presence of morbid, gay emotions. It is to be understood in this sense of course in this translation. See also Chapter XII.— T's. 140 Introduction to Physiological Psychology. are musical chords. Mixtures of colour produce sensations of colour that are just as simple as those produced by simple colours. We are unable to analyze the sensations produced by mixed colours. Therefore the consonances or dissonances of different colour qualities must be sought only in their spatial arrangement. In fact, a comparison of the paintings by the best masters of the Italian school shows beyond a doubt that certain combinations of colours are decidedly preferred. Thus Helmholtz calls attention to the triad, — red, green and violet, that are in fact combined in so many pictures with wonderful effect. However we know nothing as yet concerning the constancy and the exact conditions of this consonance of certain colours. Besides intensity and quality, the spatial arrangement of the sensations is an essential factor in determining the accompanying tone of feeling. In this connection we shall consider only sensa- tions of touch and sensations of sight as products of those senses that are characterized by the most highly developed and perfect relations to space. As regards the former, it is sufficient to men- tion that in general the positive tones of feeling accompanying sensations of touch produced by extended contact with a surface, are in proportion to the constancy and regularity of the surface. The unpleasant sensations of a rough surface are produced particularly when the tactual sensations arising from extended contact with a surface are irregularly distributed and of unequal intensity ; when some few ?/mrritated nerve-ends always intervene between the /rritated nerve-ends. The spatial arrangement of the visual sensations is of much more importance for the tone of feeling. Let us observe a straight line for the purpose of desig- nating some point upon it that seems to us to divide the line into pleasing proportions. Fechner put this question to a large num- ber of persons. As a result it appeared that, besides the point bisecting the line into halves, one other point was especially pre- ferred, viz. the point that divides a line approximately in the ex- treme and mean ratio, or the " golden section." It is also exceed- ingly instructive to study the Italian works of architecture of older times ; their wonderful effect is due almost wholly to their Tone of Feeling and Succession of Sensations. 141 wonderfully symmetrical arrangement, i.e. to the division of the lines bounding the mass as a whole. However, regularity and especially symmetry in the spatial arrangement of visual sensations are by no means the only conditions of positive emotional tones. 1 As a rule the periodic recurrence of a certain spatial arrange- ment produces a positive tone of feeling. It is much more difficult to establish a universal rule for curved lines. No one believes any more in Hogarth's absolute curve of beauty. In the case of curved lines the constancy of the sensation is a very essential factor in the production of feelings of pleasure ; as a rule a straight continuous line makes a more agreeable impression than a row of points. The very minuteness of the interruptions in the sensations disturbs the impression. A crooked line con- stantly imparts associated sensations of motion ; to a certain extent the eye follows the entire course of the line. The ap- pearance of positive tones of feeling is largely conditioned by the constancy of the associated sensations of motion. The radius of curvature, therefore, should not change suddenly, particularly the constantly repeated slight. Irregular changes also have a very disturbing effect upon the sensations produced by crooked lines. The sensation must change either by a constant ratio, or if the change is very sudden it must also be very great. For this reason gentle arches play such an important role in ornamentation, and very flat angles are rarely found. But we have room here for only a very few short suggestions. As regards these same spatial forms, the aesthetical department of physiological psychology is still in its infancy. Finally, the emotional tone of sensations depends very essen- tially on those properties of sensation that have reference to time. We shall make use of this opportunity to discuss the time- characteristics of sensations, which have thus far been hardly mentioned. Each sensation has a definite duration which in general corresponds to that of the stimulation. In the case of the excitation Ec in the cerebral cortex, we must accept this 1 Fechner, " Vorschule der Aesthetik." Th. 1, Absclin. XIV. 142 Introduction to Physiological Psychology. statement as unconditionally valid. On the contrary, the state- ment that the duration of sensation corresponds to the duration of irritation is not quite correct as regards the excitation at the periphery, Ep. As an example taken from the sphere of visual sensations, let us call to mind the so-called " after-images " that appear in colours like, or complementary to, the colour of the primary image. If we observe a bright red disk and then close the eyes, we often see a red or light-coloured after-image which lasts some seconds after the external stimulus has vanished. This after-image then appears in blue-green, the colour comple- mentary to red, and is often very intense. This phenomenon is produced, as we know, by the after-effects of stimulation upon the retina ; the external stimulus E therefore was shut off by closing the eyes, but not the peripheral retinal excitation Ep. For this reason the sensation lasted longer merely as the result of a physiological phenomenon. Let us now ask first, In what relation does the intensity of a sensation stand to the original stimulation when the latter con- tinues for some time? We can easily employ an experiment to answer this question by listening to the approximately constant rushing of water through the faucet of a water-pipe. If we watch our sensations attentively, we observe that some seconds pass before they reach their greatest intensity ; then they retain this maximum intensity for some time with but very insignificant deviations, after which they very gradually but not altogether constantly lose their intensity. The constant increase noticeable at the outstart of the experiment is obviously to be explained by physiological adaptation, especially in the peripheral organs. To some extent the ear must first be placed in a position favour- able to stimulation. The quite unimportant variations in in- tensity during the maximum of sensation plainly have an ap- proximately rhythmical character. According to the experi- ments of Lange x the intensity of sensation swells regularly once in about every 2*5-4 seconds. The length of these periods 1 Philosoph. Stud., IV. Tone of Feeling and Succession of Sensations. 143 appears to differ for different sensations. We can perceive the fact most easily ourselves by holding a watch at such a distance from the ear as to render its ticking barely audible. By this means we are able to follow best the swelling and ebbing of sen- sation. It is very probable that these periodic variations in inten- sity are dependent on variations in the excitability of the auditory path from the labyrinth to the auditory centre in the temporo- sphenoidal lobe. Other slight variations are probably due to the fact that we cannot always regularly exclude other intercurrent sensations and ideas. The ultimate definite decrease in the in- tensity of sensation is undoubtedly due to a physiological fatigue that begins to be felt along the entire course of the sensory paths to the cerebral cortex, and to the simultaneous appearance of other ideas which constantly become more and more intense. A further question is as follows : How long must stimulation last at least in order to impart a sensation ? At first it would appear that, in general, an immeasurably brief duration is sufficient to produce a sensation. The intensity of stimulation, however, and in the case of optic stimuli the magnitude of the spatial image also, are of great importance. It appears further- more that stimuli of very short duration impart sensations that are no more distinct in quality than sensations produced by very weak stimuli. At least, when the change of stimuli is too rapid, it is impossible for us to recall correctly, by association, the quality of a sensation (whether colour, pitch, taste, etc.) after it has taken place. The quality was too indistinct to awaken the related image of memory, or, in other words, the term designating the colour, the pitch of the tone, etc. Thus at least eighteen vibrations are necessary in order that the pitch of a certain tone may be recognised. Since this law appears to be valid with approximate uniformity for high and low tones, the absolute duration of stimulation, in the case of the sense of hearing, is of less importance in the recognition of a tone than the absolute number of vibrations. It is very difficult to decide experimentally the degree of sensibility to differences in time, as in the case of acoustic impressions. It is worthy of 144 Introduction to Physiological Psychology. mention, however, that Mach 1 found the difference noticeable when a tone lasting -| of a second is compared with one -^q of a second longer. As far as these experiments have been carried at present, the Law of Weber does not appear to be valid in the above case. Two or more sensations that follow one after the other at very short intervals blend into a series of sensations in time in a manner very similar to the way in which sensations produced by adjacent stimuli in space blend into a line. The interval of time that must elapse in order that two sensations may be perceived as separate in time varies exceedingly, according to the quality of the sensation. For the eye an interval of at least -^ of a second is requisite, while only an interval of -^q of a second suffices for the ear. This blending of sensations that follow one after the other very closely, is probably due to physiological causes. On the other hand, however, let us call attention expressly to the fact that the projection and arrangement of our sensations with reference to time, the same as with reference to space, can- not be explained psycho-physiologically ; we must simply accept the fact for the present, although we shall touch upon the question again at the close of these lectures. In this connection let us call attention to an essential difference between the perception of space and the perception of time. We project our sensations into a space of three dimensions, while not only our sensations but also their mental images, the ideas, are arranged with refer- ence to time in but one dimension. We can now introduce the question as to how many sensations we can have in general at the same time. The number of sensa- tions possible from one sense at the same time is almost unlimited. We have already seen that co-existent sensations of sight and feeling are arranged together so as to produce an image of space and that co-existent sensations of hearing are blended to a complex of sound. But it is much more doubtful whether we can perceive a sensation of sight and one of hearing, i.e. two or more sensa- 1 Sitzungsber. d. Wien. Akad., Bd. 51. Tone of Feeling and Succession of Sensations. 145 tions from different senses, simultaneously. In this case the weaker cortical excitation produced by a slight momentary sound, for example, often remains without a concomitant psychical pro- cess or, as we may say, unnoticed in consequence of the pre- ponderance of another stronger cortical excitation, such as an intense stimulus of light acting at the same time. Therefore the sensations or, more properly, the sensory cortical excitations arrest one another, in very much the same way that, as we shall see in the future, the ideas check each other. This question must not be confounded with that as to how many simultaneously appearing sensations can be recognised or counted. Cattell * has made experiments for the purpose of investigating the latter question. He found, for example, that from 3 to 6 lines, visible o'oi second, can still be correctly counted. In this case it is obvious that the facts of sensation are not alone concerned, but also the association of ideas, especially of ideas of number. This association is only possible in the case of a limited number of simultaneous, momentary sensations. We can now return to our first question : How is the tone of feeling accompanying sensations dependent on their duration and succession in time? A long duration of sensation generally dampens both positive and negative tones of feeling. The manner in which several sensations follow one another in time only has an essential influence on the tone of feeling accompany- ing sensations of musical sound. A series of like sensations ot tone, following one after the other, generally becomes wearisome ; even when the quality of the tone changes an unpleasant feeling soon appears. In order to obtain the pleasurable feeling belonging to rhythmical division, either the intensity or the duration of the single tones must be subjected to a more or less regular periodic change. In musical tempo and the versification of poetry we have sequences of acoustic sensations in which certain sensations 1 Philosoph. Stud., III. Cattell's interpretation, however, cannot meet our approval. L 146 Introduction to Physiological Psychology. are especially accented or intense, and all together have a definite duration. 1 In this connection it is not necessary to consider that two quarter-notes or a triplet can take the place of a half-note, etc., or that two short syllables may be substituted for one long, or two unaccented for one accented short syllable. Such uni- formity, which we generally designate as tempo or verse, is constantly repeated with but slight change. At all events, the total duration of the sensations of sound and the arrangement of accentuation is constant for each new tempo or kind of verse. The qualities of sound, i.e. the notes and words, change, but the intensities of tone, the accentuations and diminutions, constantly recur at definite intervals or periodically. In poetry the close of such rhythmical periods can often be emphatically marked by choosing very similar tones with which to close the periods. In this form of emphasis lies the importance of the rhyme. As regards the succession of sensations, therefore, a regular periodicity is the chief condition for the appearance of feelings of pleasure. It is not mere chance that maniacs and those afflicted with emotional paranoia often speak in rhythm and rhyme. Such phenomena harmonize rather with the morbid, positive emotional states characterizing these forms of psychosis. From the preceding considerations we conclude that the ap- pearance of positive or negative tones of feeling depends on very different conditions. This conclusion brings us to a problem that is just as interesting as it is difficult to solve. It is the question as to whether these various conditions may be com- prehended under one common point of view, — the problem as to the nature of these tones. In answering this question it must be taken into consideration that, as mentioned in the beginning, not only the sensations, but also without doubt the ideas, have their emotional tones. Therefore we can first put the question as to whether the ideas borrow their tone of feeling from the 1 The old style of metrical composition places more weight on the duration, the new style more upon the accentuation. The Alexandrine regards merely ihe number of sensations of sound. Tone of Feeling and Succession of Sensations. 147 sensations, i.e. whether they have simply received the tones of feeling belonging to those sensations of which they are the images of memory. This supposition is undoubtedly to be granted in many cases. The idea " enemy " and the idea " hate," therefore, are only associated with feelings of displeasure because we have often felt the attacks of foes and the effects of enmity to be unpleasant. But, on the other hand, it cannot be denied that the reverse is also true. Ideas often transmit their tones of feeling to the sensations. Thus as children, or perhaps later, we have heard a certain musical combination produced frequently in connection with a certain mournful song. The succession of tones in the chord, as sensation, does not partake of a mournful character but because mournful ideas contained in the words so often accompanied it, the negative emotional tone gradually becomes associated also with the sensations of sound ; finally the chord itself is sufficient to produce a negative change in our tone of feeling that is quite independent of the mournful words. All attempts to assign certain constant tones of feeling to definite chords, rest upon just such a transmission of the tone of feeling from the idea to the sensation with which the idea is associated. 1 The sensation of black, as mentioned, probably produces a feel- ing of displeasure the more easily because the idea of something dismal or dangerous is associated with darkness. Hence, although the mere sensation of black is not necessarily connected with negative emotional tones, the colour of black has become the symbol of mourning among occidental peoples. It is probable that the quality of sensations, in general, originally influences the tone of feeling only in this indirect way by means of their association with pleasurable or painful ideas, and that therefore only the intensity of the sensations and their succession in time and space have any direct effect upon their 1 As regards chords, E. T. A. Hoffmann has probably taken the most extreme standpoint, since he believed that he was able to characterize each chord by a special state of feeling ; — for example the chord of B-major was to express harmless joy ; C-major, wild desire ; A-flat minor, longing. 148 Introduction to Physiological Psychology. tone of feeling. A universal rule has not yet been found which shall state just what intensity and what arrangement in space and time produce feelings of pleasure or feelings of pain ; and since the influence of these factors has been developed phylogenetically and will continue to so develop, no such rule can ever be formulated. As to the nature of emotional tones, it is obvious that they are to be regarded as qualitative characteristics of the sensations. Hence another quality, a feeling of either pleasure or pain, is often to be added to the qualities of sensation already discussed. This new quality, the tone of feeling, is capable of increase in intensity quite the same as the other qualities of sensation. To make use of an explanatory comparison, which is, however, somewhat inexact as to particulars, each sensation may be regarded as mixed with a certain proportion of black or white. The tone of feeling re- presents, as it were, a sixth sense which has only two qualities, — feelings of pleasure and feelings of pain or displeasure. One of these two qualities is united with impressions received from the other senses, and, under certain conditions, also with the ideas ; the emotional feelings never occur wholly independently of sen- sations or ideas. But, apart from their dependency on other psychical states, and their relation to ideas, these emotional feel- ings are essentially distinguished in still another important respect from the proper sensations. The common quality of sensation is determined (1) by the nature of the external stimulus E, and (2) by the structure of the sensory apparatus (including from the peripheral sensory organ to the cortical centre) that receives the stimulus and converts the E first into an Ep and finally into an Ec. The simplest illustration of this is furnished by the mechani- cal stimulus, which imparts a sensation of pressure when applied to the skin and a sensation of light when applied to the retina. Innumerable qualities of sensation correspond to the innumerable qualities of stimulus. But the tone of feeling has in general only two qualities, — the feeling of pleasure and the feeling of displea- sure or pain. The emotional quality of sensation is also depen- dent on the external stimuli and the sensory apparatus ; but only the two emotional qualities of pleasurable and painful feelings, in Tone of Feeling and Succession of Sensations. 149 their different degrees of intensity, correspond to the numberless qualities of stimulus and the different sensory apparatus. Each stimulus may be subsumed under one of these two qualities. Those properties of the stimulus and of the sensory surface receiving the stimulus, therefore, that cause the appearance of emotional tones, must be of a very general character. We must assume that indifferent stimuli merely produce an Ec in the cerebral cortex, while stimuli that are not emotionally indifferent (for example a too dazzling light) add something else to the physical process Ec in the irritated cortex of the cerebrum, the psychical correlative of which is the emotional tone. There- fore, properly considered, this emotional tone involves a re- action of the cerebral cortex upon the stimulus coming from without. This also explains the fact that like stimuli of the same intensity do not always impart the same definite tone of feeling. The qualities of sensation, sensu stricto, also depend in fact on the constitution of the cerebral cortex ; but they are determined by constant properties of the latter, while the tones of feeling are determined by its variable properties. For the sake of com- pleteness and perspicuity, let us cite once more the example of a light falling upon the eye. The excitant E is a light of medium intensity which produces a cortical excitation Ec and a sensation S corresponding to this excitation ; if the intensity of the light increases, both Ec and S also increase. It is only when a definite intensity of light is reached that Ec and S no longer merely augment. From this point, at the same time that Ec and »S are increasing, a new physical process is associated with Ec, •and an emotional tone with the sensation. Naive thought is therefore quite right in generally ascribing a more subjective importance to the tone of feeling, and a more objective import- ance to the common qualities of sensation. A phylogenetic factor of great importance should be included in the characterization of the emotional tone. Those stimuli that are associated with feelings of pleasure in many cases directly accompany the acts necessary for the nourishment and propaga- tion of animal life ; those that are associated with feelings of 150 Introduction to Physiological Psychology. pain often accompany situations in which animal life is en- dangered. Accordingly the stimuli of the first class generally incite approach to the stimulus, those of the second class urge withdrawal or flight. It is quite possible that this peculiar property of the cerebral cortex which enables it to react upon stimuli that are either generally injurious or useful with an entirely new psychical process, or, in other words, to add the so-called tone of feeling to the common sensation, has been developed phylogenetically to a higher degree of excellence from these motions of flight or approach. In the lowest stage of develop- ment the sensation directly imparts a motion that is generally fitting; in the highest stage the tone of feeling is introduced between sensation and motion. This tone of feeling, as we shall see, is of the greatest importance in voluntary action. It is of great advantage to us to possess the capacity for emotional tones, for the sensation itself generally furnishes the appropriate warning or allurement, but at the same time, by postponing the act of flight or approach, time is gained for the association of ideas and the play of motives. These conclusions will become more intelligible as soon as we have investigated the influence of the emotions upon the association of ideas and the motions of expression. CHAPTER VIII. SENSATION — IDEA — CONCEPTION. In the preceding chapters we have followed in detail the develop- ment of sensation from external stimulation. Now, what be- comes of the sensations which have appeared corresponding to the excitations of the cerebral cortex in the manner described, and which now become factors in the activity of association ? Let us at first assume one of the simplest cases. The complex sensation of a rose, for example, appears for the first time as the psychical correlative of an excitation in the cere- bral cortex. This sensation is followed at once by the conscious play of motives or the association of ideas. But at the same time an image of the rose seen is deposited in the memory, or, expressed in the language of physiology, a trace of the cortical excitation that has taken place, is left in the cerebral cortex. We are compelled to come to this last conclusion by the fact that we recognise the rose when we see it again, that we are able to remember it, and that we can reproduce its image in memory. This image of memory or mental image that is deposited by each sensation we have designated as an idea. 1 What are the psycho- logical elements of this image of memory, and by what excitation of the cerebral cortex is it produced ? The older psychology pronounced the ideas to be only copies of the impressions or sensations, and to be only distinguishable from the sensations by 1 The use of the German word " Vorstellung" in this more restricted sense was first introduced by Hegel and his disciples. It has since been used in the same sense, especially by Lotze. (According to the standpoint of the author, as expressed in his introduction, the corresponding English word is "idea." — Vs.) 151 152 Introduction to Physiological Psychology. their slighter vivacity. This view was emphasized most forcibly by Hume, whose noted " Treatise of Human Nature " cannot be too well recommended as a propaedeutic course in psychology. On the contrary, however, we must now emphasize that images of memory or ideas are quite different from the sensations them- selves. The idea of the sun, which is merely recalled to memory, has nothing of the brightness or splendour of colours which characterize the real sun, or the sun when seen. The idea of the sun is therefore by no means merely a faded sun ; in this respect the great English philosopher is mistaken. It is not a difference in intensity between the idea and the sensation, but above all a qualitative difference. 1 The sensual vivacity, characteristic of every sensation, does not belong at all to the idea, not even in a diminished intensity. The ideas of the slightest rustling and of the loudest thunder, therefore, exhibit no difference in intensity whatever ; in fact, all sensual vivacity is wanting in both. Hence we conclude that the different intensities characteristic of thun- der and rustling as sensations are lost in the ideas. We may easily have an idea of the greater intensity of one sensation, but the idea itself is no more intense on that account. If we try to imagine thunder ever so vividly we do not hear the slightest rolling. But in what does the qualitative difference between sensation and idea consist ? Or, to put the question in another form, what process takes place when a sensation disappears and its image is deposited in memory ? Apart from the rare phe- nomena of " after-images " the sensation generally disappears almost instantly upon the removal of the stimulus. But with this removal of the stimulus the cortical excitation is not wholly obliterated, for the cerebral cortex never fully returns to its previous condition ; some sort of material change still remains as a trace, a sign (o-^eioi/), as Plato calls it. 2 This so-called 1 Also Bain ("The Senses and the Intellect," 3rd ed.) denies the qualita- tive difference between the sensation and its image in memory. His views are not based on sufficient grounds, however. 2 Beneke ("Lehrb. der Psychologie als Naturwissensch.," 2nd ed., 1845, Sensation — Idea — Conception. 153 " deposition " of the image in memory takes place entirely un- consciously ; it has no concomitant psychical process whatever. We see a rose for the first time ; the sensation of sight causes a series of actions : we stop, perhaps, stoop to the rose and then pass on, other visual sensations soon occupying our attention. We are by no means aware that in the mean time a trace of the visual sensation of the rose has been deposited. This is accom- plished, as we say, latently, or without our being conscious of it ; we only conclude that a latent image was left in the memory by the first sensation, because we are able to recognise the rose when we see it again. Let us, therefore, guard against the rough conception that the mental images are deposited in the ganglion cells of the cerebral cortex as an indefinite psychical product, an unconscious idea. On the contrary, there is no psychical element left of the sensory excitation Ec corresponding to the sensation, but only a permanent material change which we designate as EL This El, the remanent material trace, has no psychical correlate whatever. We can conceive of this El most easily as a definite arrangement and constitution of the molecules composing the ganglion-cells; in other words, it is a latent disposition. This purely material trace only becomes psychically active as an image of memory or an idea when we see the rose again or when, by means of the association of ideas or the play of fantasy, some related idea occurs to us ; as, for example, the idea of red or of a fragrant flower. In order that the dormant image of memory, which is as yet only potential, may be aroused, therefore, the ganglion-cell having the disposition El, must first receive a new impulse from a new and similar sensation, or from some related idea with which it is associated ; that is, the El must be still further changed in some definite way, becoming an ideational excitation which we shall designate as Ei. Hence the ganglion- cell is trained to a certain extent for a definite idea. We can § 27) very aptly designates ii/ (latent excitation) as disposition ("Angelegt- heit ") but ascribes a psychical existence to the EPs without sufficient grounds. 154 Introduction to Physiological Psychology. illustrate this by comparing the ganglion-cells to the wheels, stars, monograms and other figures formed out of gas-pipes, as we see them used in illuminations. Unlit, they resemble the so-called latent images of memory ■ the disposition is already there in the form, structure, etc. But a spark must first light the gas that escapes from the innumerable holes of the pipes, in order that the latent form may become a living reality. It cannot be too urgently emphasized that the sensation in the psychical sphere corresponds to the excitation of the cerebral cortex imparted by the stimulus, but that nothing of a psychical nature corresponds to the residue of this material excitation. The designation " latent image of memory " is very convenient, but it contains a contradiction. Only either a new and similar sensation or the association of ideas can so change this residue of the material excitation as to produce a concomitant psychical process, a con- scious image of memory or an idea. In the future we shall often designate these material traces or dispositions simply as images of memory, but only for the sake of brevity, and always with the restriction just mentioned. Let us now follow the same process also physiologically. On seeing a rose, innumerable nerve-ends of the retina are irritated, and innumerable fibres of the optic nerve transmit the excitation to the visual centre in the occipital lobe of the cerebrum. It is very probable that the relations of the retina are to a certain ex- tent reproduced in the visual centre, so that the superior margin of the retina, for example, corresponds to the anterior margin of the visual centre, etc. When the rose is seen, numberless gan- glion-cells are excited in definite regions of the visual centre that correspond to the irritated portions of the retina. To this excita- tion of numerous ganglion-cells corresponds the visual sensation. But now where is the mental image of this sensation of sight deposited? In the same elements whose excitation produced the sensation ? Physiological psychology can afford to quietly await the answer of physiology and pathology to this question ; its conclusions harmonize just as well with the supposition that sensation and idea are dependent on the same cortical elements Sensation — Idea — Cotiception. 155 as with the contrary supposition. Nevertheless, for the sake of clearness, it is advisable to adopt one or the other of these two suppositions as a basis in the following researches. Therefore, if we assume in the future that sensation and idea depend upon different cortical elements, 1 it is because this supposition seems to correspond better to the physiological and pathological science of to-day. For example, it has been shown that the extirpation of a definite portion of the visual centre of a dog, or also the disease of definite parts of the human occipital lobe produces the condition of so-called mental blindness ; in other words the animal on which the above-mentioned operation is performed and the diseased human being still continue to see, as appears from the fact that they follow objects held before them with the eyes, and avoid obstacles placed in the way ; but they no longer recognise what they see. The dog no longer crouches before the threatening whip, nor dodges the stone thrown at him ; the man stares at the most familiar objects of his environment as if they were wholly unknown to him and recognises them only when he touches them. This condition of mental blindness 2 without physical blindness, as also the analogous condition of mental deafness without physical deafness, must in fact be explained by the assumption that the sensations and the images of memory are dependent on separate elements of the cortex. Those who wish to investigate this very interesting question more particularly can refer to the competent treatises of Munk, Mauthner, Nothnagel, Wilbrand and others. 3 1 The antiquated idea of Schroeder von der Kolk, which has recently been adopted again by the school of Meynert (Vienna), does not place the seat of sensation in the cerebral cortex, or at least only partly. It substitutes for the latter, either exclusively or in part, the corpora quadrigemina. The first of these two suppositions is wholly incompatible with more recent pathological experiences ; the second can only be made to agree with them with difficulty (compare also Chapters I and II). 2 The cases of the loss of visual phantasy, described by Charcot, are also worthy of mention. 3 Munk, " Ueber die Functionen der Grosshirnrinde," Berlin, 1881 ; Mauthner, Wien. med. Wochenschr., 1880 ; Wilbrand, " Die Seelen- 156 Introduction to Physiological Psychology. We assume, therefore, that the sensation of the rose is pro- duced in certain ganglion-cells, and that these numerous sensory cells transmit their excitation further to one other ganglion-cell, a )ne?nory-cell. x Hence if a, b, c, d, e,f represent ganglion-cells of the visual centre to which the fibres of the optic nerve lead, and if the rose, for example, excites only those fibres of the optic nerve which lead to the ganglion-cells 0, c, d, the visual sensation of the rose corresponds to the actual material excitation of the ganglion-cells 0, c, d. As soon as the rose disappears, the material excitation of the cells &, c, d is extinguished and at the same time the concomitant sensation vanishes. Only a part of the material excitations of 3, c and d is secured in the distant ganglion-cell /where it leaves a merely material trace or change, the image of memory. In a manner which we shall describe later more exactly, this image of memory becomes psychically active only when we see the rose again, or when it is reproduced by the association of ideas. Let us remember that this scheme is by no means the only one conceivable, but it is the one most in har- mony with present scientific knowledge. We shall ourselves be able to apply all the following discussions without difficulty to any other scheme, for they are essentially independent of this or any other physiological hypothesis. Let us now continue our discussion, still retaining some de- finite sensible object, such as the rose, for example, from which to proceed. The rose not only produces a sensation of sight and its proper image of memory, the visual idea, but its fragrance also produces a sensation of smell, and its soft leaves produce a sen- sation of touch. These sensations also leave images of memory, an idea of smell, and an idea of touch. Hence, at least three images of the rose, different in quality, are deposited in memory, corresponding to the number of sensual organs upon which the blindheit als Herderscheinung," Wiesbaden, 1887; NOTHNAGEL, Vortrag auf dem VI. Congress fur innere Medicin ; Reinhard, Arch. f. Psychiatrie, XVII and XVIII ; Lissauer, Arch. f. Psychiatrie, XXI. 1 The expression " memory-cells," so far as we know, originates with Uorwicz, Psycholog. Analysen, I, S. 287 ff. Sensation — Idea — Conception . 157 rose acted as stimulus. But the olfactory centre is far remote from the visual centre, and both of these are far distant from the centre of touch. Therefore, latent ideas are deposited in three ganglion-cells that are far remote from one another and in quite different parts of the cerebral cortex. The following sketch re- presents in rough outlines a hemisphere of the cerebrum. At V lies the visual centre, at i^the centre of feeling (in the restricted sense including touch), at Zf the centre of hearing, and at Sm the ms oeap Fig. 17. olfactory centre. Three component ideas of the rose have been deposited in the ganglion-cells a, b, and c. The ganglion-cell a is connected by the associative fibres with both b and r, and in the same manner b and c are connected with each other. Further- more a, b and c have been often incited simultaneously, — that is, we have often seen, touched and smelled the same rose at the same time, and the corresponding images of memory were ac- cordingly deposited in the cells a, b and c. As a result of this 158 Introduction to Physiological Psychology. frequent simultaneous appearance of the three component images, if b is excited, a and c are also always excited sympathetically. When we discuss the laws of association in a future chapter (IX), we shall learn why only the cells a and c are sympathetically excited by b with which they have often been simultaneously active, although b can be shown to be connected by associative fibres with many other ganglion-cells. For the present it is sufficient to know that the component ideas of an object of sense are deposited in different parts of the brain, that these component ideas are connected with one another by associative fibres, 1 and that there- fore, if one of these component ideas appears, the others are called into action by association. The totality of the component ideas thus associated with one another constitutes the idea of the object. The idea " rose," therefore, is not simple but complex, its unity depending merely on the reciprocal association of its component parts. But language furnishes us with another unity for these complex ideas of sensual objects. Thus far the ideas with which we have become acquainted are entirely independent of language, and therefore probably belong also to the lower animals. But man names his ideas; we articulate the word " rose " in connection with the complex idea above described. In other words, we execute a peculiar combination of motions of the larynx, lips, tongue, and palate with the result that another person hears us articulate the word " rose." We have already become acquainted with an idea of motion as the cause of every voluntary action. For example, the idea of a motion used in grasping the pen comes into the mind and without further impulse we seize the pen. In a similar manner we must conceive of the ideas of articulation as the cause of the motions of speech. These ideas of articulation are mental images that have been laboriously acquired by the repetition of the motions neces- sary for speech. 2 This assumption has received a very decided 1 Herbart designates this associative connection of component ideas, im- parted by different senses, as " complication." 2 The contradiction that seems to be contained in this statement will be explained in a subsequent chapter (XIII). Sensation — Idea — Conception. 159 confirmation from pathology. If the portion of the brain repre- sented by the hatched spot in the drawing is destroyed, we observe a remarkable phenomenon. The person thus afflicted still retains command of all his sensual ideas ; he still understands what we say to him ; he moves the tongue, the larynx, the lips, and the palate the same as before the appearance of the disease. But he has irretrievably lost the delicate combination of move- ments performed by the tongue, larynx, lips, and palate, necessary for the articulation of any word, — "rose" for example. The mental images or ideas of his motions of articulation have been destroyed. These ideas of articulation, which can be shown to be deposited in the posterior, inferior part of the frontal convolution (at d, fig. 17), are connected with the component ideas of an object of sense by the associative fibres. Thus for example, as the accom- panying illustration shows us, the ganglion-cells a, b, c, in which the component ideas, or images of memory, of the fragrance, colour, and form of the rose 1 are deposited, are not only connected with one another by paths, but also with a single ganglion-cell or complex of ganglion-cells situated in the frontal lobe and con- taining the complicated idea of motion, necessary for the articula- tion of the word " rose." In the drawing we distinguish all the cortical elements that stand in relation to speech by the shading. The same facts that characterized the component ideas a, b, c in their relations to one another also characterize the idea of articu- lation d in its relations to a, b and c. As soon as a, b or c appears, d> the word for the thing seen, smelt or felt occurs to us, and vice versa. The idea of articulation d is especially adapted to be a higher unity for the three component ideas, because it is uniformly and directly connected with these three ideas, without being itself a component idea immediately dependent on a special object of sense. Hence its general character. But the idea of articulation d does not constitute the sum total 1 In the case of an object acting also upon our senses of hearing and taste, of course, two more component ideas would be added. 160 Introduction to Physiological Psychology. of all the elements of speech related to the whole idea "rose." When we hear the word " rose," we understand what the word means, and the colour, form and fragrance of the rose occur to us. Therefore an image of this sensation of hearing the word which we have heard spoken by another must exist in the cerebral cortex and be in connection with a, b, c and d. It is obvious that this "acoustic image " of the word "rose," or the idea of the spoken word " rose " which we have heard, is to be sought in the auditory centre in the temporo-sphenoidal lobe. In fact there is quite a definite region in the superior temporal convolution at e, the destruction of which by disease leaves all the functions of the human brain, including speaking and hearing, intact with the exception that the ability to comprehend words is removed. A person in whom the region at e has become diseased still hears words that are spoken to him very well, but does not understand what he hears. Once familiar words sound to him as if they belonged to a foreign language ; but if he sees the same words written, he knows at once what they mean. Evidently this in- dividual has lost the acoustic images of memory that once gave him the power of recognising words ; in the language of anatomy, he has lost the acoustic memory-cells, but retained the acoustic sensation-cells ; he is mentally deaf to words. Hence the complex idea "rose" is still further aided by the " idea of the spoken word as heard " ( which are connected with each other by association. We remember that these three psychical elements correspond to the material process Ei\, Ei 2 , £i 3 . . . and that the J5i's originated in El's that had no concomitant psychical processes. Let us take, for example, the series of ideas : cloud, rain, umbrella. The associative connection between them is at once plain. Some one says to us, for example, that there are clouds in the sky. The idea of clouds causes us to think of the possibility of rain, which reminds us of our umbrella. In fact, however, we think much more rapidly ; the intervening idea of rain I 2 is very often entirely omitted. In this case the cloud reminds us at once of the umbrella, although the idea of rain does not expressly appear in our consciousness. The entire pro- cess is obviously the following. At first Ei\ is produced from El Y or, expressed in the language of psychology, the idea of the cloud (/"i) first appears. The material excitation is now transmitted still further and reaches E/ 2 ; but instead of changing the latter to £i 2 so as to produce the idea of rain (I 2 ), it either touches E/ 2 but lightly, or at least so little that Ei 2 and I 2 do not appear at all. But on the contrary, only as soon as the excitation has been conducted to El 3 , does the latter receive an impulse that is suffi- ciently long and intense to convert it into Ei s , upon which the idea of the umbrella (7 3 ) appears. There is no good reason for speaking of an unconscious idea of rain (I 2 ) in this case. As we already know, unconscious psychical processes do not exist. We must simply grant that the intervening idea, " rain " (I 2 ) has been omitted ; expressed with reference to the material processes that take place, the transformation of E/ 2 to Ei 2 has been omitted. El was touched by the excitation in the course of its conduction and undoubtedly influenced the latter ; at all events, it underwent certain changes, but these changes were either not sufficient or not of the right kind to convert El 2 into Ei 2 and produce the idea 198 Introduction to Physiological Psychology. I 2 . In the above process we recognise another very important form or way in which the acceleration of ideation may be accom- plished : intervening ideas may be omitted, and the association of ideas thereby abbreviated. Our thinking would be an im- mensely tedious 1 task, if we had to go through the process of re- collecting all the intervening ideas every time. In our usual thought we constantly skip numberless ideas ; in fact, the genius is distinguished from other less gifted individuals in that he omits greater series of intercedent ideas, and therefore, figuratively speaking, advances in seven-league boots. On the other hand, that which we call practice also frequently depends upon such an abbreviation of the association of ideas. The practised chess- player, for example, skips numberless intercedent ideas in his combinations or associations, while the amateur is compelled to think through the entire series according to the order in which the ideas occur. If we now conceive of this process of practice as still further perfected by the omission of all intervening ideas whatever, including ultimately also the idea of motion which imparts the final action, we have an automatic act. In this con- nection it is only necessary to recall what was said in a former chapter concerning the gradual development of automatic action from the so-called voluntary action. It is hardly necessary to emphasize that practice as such tends to directly facilitate the association of ideas besides exercising an indirect influence by abbreviating the process of thought. The shortening of the pro- cess of ideation is also often facilitated pathologically ; in such cases we often speak of thought as " incoherent." Thus far we have considered the association of ideas merely as a succession of discrete ideational elements. The only bond connecting the successive ideas f 1} f 2 , l 3 , etc., was, in accordance with the chief law of the association of ideas, either their frequent previous simultaneous appearance or their similarity. We have now to learn the more complicated forms of ideation. In fact, we 1 Ger. " langweilig," which in this case may also be understood in the apt literal sense, as signifying "great length of time." — T's. Rapidity of the Association of Ideas. 199 do not constantly think in simple, progressive series of ideas ; a higher stage of thought consists of the so-called judgments and conclusions. Let us now inquire whether these two chief logical functions of judging and concluding may also be subsumed under the processes of ideation, or whether we must regard them as entirely new, heterogeneous psychical faculties. Of course we shall decide in favour of the latter only in case of necessity. It will undoubtedly be more satisfactory if we are able to reduce logical thought, i.e. the judgment and the conclusion, also to the simple process known as the association of ideas. Let us begin with a simple judgment, — for example: "The rose is beautiful." In this judgment we have two ideas, (1) the idea "rose," and (2) the idea "beautiful." It is evident that these two ideas are not associated because of some merely incidental connection between them in the sense of the simple law of ideation with which we are thus far acquainted, but that the second idea stands in some much more intimate relation to the first. This more intimate relation is expressed by the word " is," it is true ; but even if we regard this " is " as an intermediate idea, we by no means avoid the fact that the judgment is not concerned with three ideas that are merely arranged in succession. On the contrary, we must correctly assume that the mediate idea " is " not only refers to the preced- ing idea "rose," but also to the succeeding idea "beautiful." Now is it quite impossible to explain the origin and development of this double relation of the mediate idea " is " physiologically ? By no means. Thus far we have not investigated the material process that takes place in the cerebral cortex during the associa- tion of ideas as a continous whole ; we have only selected a few single moments of the process in which certain phases correspond to separate ideas. It is evident that this is not quite correct. Between the material condition Ei x and the material condition Ei % there is a mediate material process, and we have no cause whatever for assuming that this intermediate process takes place entirely unaccompanied by a psychical correlative. On the contrary, it is highly probable that the foundation for the con- tinuity of our judgments, or, in other words, for the reciprocal 200 Introduction to Physiological Psychology. relation that exists between the ideas as combined in the judg- ment, is furnished by this process of conduction. It should also be considered that in the majority of judgments only the words, i.e. the motions of articulation, form a successive series, while the two ideas ('"'rose" and " beautiful" for example) appear simul- taneously as the component ideas of a complex idea. The separation of the ideas and their arrangement in a continuous series is only accomplished when they are expressed in language. Of course the above explanation is at present purely hypothetical. Furthermore, in view of the limited knowledge on this subject which we now possess, we need not yet attempt to give a really adequate psycho-physiological explanation of the continuity of our thought in judgment. On the contrary, it is sufficient to have demonstrated the possibility of such an explanation. We have shown that such an explanation is possible upon the grounds of physiological psychology and without exceeding the bounds of the association of ideas or fabricating a new, entirely hypothetical psychical faculty. From the above standpoint, therefore, the formulation of judgments is to be regarded as a higher stage in the development of that which we commonly designate as ideation or the associa- tion of ideas ; the former process is by no means wholly dissimilar to the latter. But what has thus far been said does not constitute a complete presentation of the psychological characteristics of the judgment. An essential feature of the judgment is its depen- dence on a much more intimate and abundant association of its component ideas. Supported by this close relation of its com- ponent ideas, we are able to claim for the judgment the right to be valued as correct. Psychologically " to be held as correct " simply means the absence of contradictory ideas. The common series of associated ideas, "rose — leaf — summer," depends on no other condition of association than some former incidentally simultaneous appearance of the ideas or their corresponding sensations. The judgment, "the rose has dentate leaves," is distinguished from the simple series of associated ideas just mentioned (i) by the thorough relation of the ideas to each other, Rapidity of the Association of Ideas. 201 (2) by the much more frequent former simultaneous appearance of the ideas contained in the judgment or of the sensations that produced them. In fact, contradictory ideas are entirely wanting in consequence of the very intimate association of the ideas composing the judgment; this absence of contradictory ideas (in the above case, for example, the idea of smooth-edged leaves) gives us the right psychologically to consider our judgments correct. The association, " rose — leaf — summer," rarely occurs without other intermediate members ; for this reason it bears the character of a chance association. On the contrary, the associa- tion of ideas in the case of the judgment is, almost without exception, an intimate association of simultaneous ideas, and an association in which conceptions of relation are of especial importance. Of all possible associations, a judgment is just that select association in which no contradictory ideas occur. 1 Hence we find that our conception of the association of ideas must be somewhat modified, if it is to include the judgment also. The association of ideas is not a process in which we consciously leap, as it were, from one discrete idea to another. On the con- trary, we must claim for the judgment, as a psychical process at least, the same continuity that the concomitant material process undoubtedly possesses. The association of ideas that are less closely related, with which we first became familiar, is therefore but one form, and the so-called judgment a second form of ideation. " School-logic " teaches further, that judgments are combined to form conclusions. Let us recollect the well-known, — Caius is a man — All men are mortal — Hence Caius is mortal. It is indeed without doubt an interesting fact that our logical 1 This selection is especially emphasized by Herbart. Lipps (" Grundthat- sachen des Seelenlebens," Bonn, 1886), has emphasized with undue partiality, as characteristic of the judgment, the fact that we are conscious of its reality and hence of its validity. 202 Introduction to Physiological Psychology. series of judgments can be arranged according to the above scheme, or any one of the other schemes familiar to the logicians. For certain purposes it may even be quite advantageous to arrange our series of judgments according to such a scheme. But we must decidedly oppose the idea, that our common, naive course of thought ever conforms to these syllogistic forms of the school- logic. When we think naturally, we know nothing of a major premise or a minor premise ; we simply make use of the associa- tion of judgments, — "Cams — man — mortal," and the conclusion has been reached. For example, we see " Caius " ; with the visual sensation is associated the idea iC man," with the latter the idea " mortal." Therefore every conclusion, the same as every judgment, is merely a form of the association of ideas : but as a distinct form of association it is of almost no importance whatever psychologically. It is of course impossible here to develop the entire structure of scholastic logic upon this psychological basis. We have only space for a cursory glance over the field of logic here, as formerly over the field of aesthetics. It is for physiological psychology to establish merely how thought actually takes place and what material processes accompany it. The problem of logic, as to which formal processes of thought lead to the so-called true judg- ment and which do not, does not belong to the sphere of psychology. The great problem of physiological psychology consists in the reduction of the many different forms of thought, including even the most complicated demonstration, all to the simple ideation or the association of ideas and its laws. But physio- logical psychology is still far from having reached a complete solution of this problem ; for this reason we have only been able to sketch in about what direction the solution is to be sought. It is probable that some of our deductions will undergo still further modification when the light of continued investigations is brought to bear on them. The fundamental conception that all processes of thought can be reduced psychologically to the association of ideas, will at all events endure. Of course we shall not attempt to disguise the fact that Rapidity of the Association of Ideas. 203 particularly in Germany another school of psychology is pre- dominant, that does not recognise this fundamental thought. Wundt x stands at the head of this school. He and his scholars claim that there is a large number of ideational combinations that cannot be explained merely by the association of ideas. They therefore assume a special psychical faculty, superior to the association of ideas, which they designate as apperception. The association of ideas constantly supplies this apperception with new- material for ideas, and the apperception itself selects from this material. It turns first to this then to that idea, and is then called attention ; or again, it combines one idea with another and forms a compound idea; finally it imparts volitional motor impulses through the nerves and is then called will. We see that this hypothesis is very convenient. All that cannot be easily ex- plained by the association of ideas is ascribed to the activity of a higher power or special psychical faculty. The latter, however, is an entirely unknown factor. All of the arguments that have so often and so justly been advanced against the theory which assumed so-called " faculties of the soul/' may be also directed against this metaphysical theory of apperception. The theory of apperception also arbitrarily assumes an active subject as the efficient cause of a series of conscious processes. Wundt has also given his theory a physiological tinge by adding the hypothesis that this apperception is located in the frontal lobes of the brain. In making this assumption, however, he only succeeds in placing the contradictory features of the entire conception in a still more glaring light. A supposed psychical faculty which, according to the very hypothesis in which it is assumed, acts independently of all mechanical causality, is thus localized in a definite part of the brain for the purpose of gaining some connection with the physiology of the brain and of rendering the theory more harmonious with the spirit of natural science characteristic of the 1 Wundt's "Grundziige der physiolog. Psychologie " ; besides in this work, a presentation of the theory in question is also to be found in Wundt's "Logik,"Bd. 1, S. 10 ff. 204 Introduction to Physiological Psychology. present age. But the physiology of the brain must reject this connection and with it the entire theory and hypothesis of ap- perception. The frontal lobes of the brain do not possess this function at all. Large portions of the frontal lobes of the brain may be destroyed without disturbing 1 that activity of the intellect which the school of Wundt ascribes to apperception. Changes in character and certain mental disturbances may appear in any disease of the brain, no matter where it is located. A great deal of argument has often been based upon the fact that part of the encephalon of lower animals corresponding to the frontal part of the human brain is relatively dwarfed. This fact has been used in attempting to explain the supposed absence of apperception in the lower animals. This application of the fact, however, is not justifiable. The motions used in speaking and writing, and finally also the motions of the trunk, are imparted by the cortex of the frontal brain ; accordingly speech, writing and upright locomotion are wanting in the animals below man. If we take the absence of these three characteristics into consideration, the frontal brain of the ape is, relatively at least, just as large as that of man. Therefore there is no ground whatever for assuming that this hypothetical apperception is localized in the frontal brain. Thus another prop, which was subsequently introduced for the support of the theory, falls. For reasons above discussed, we shall reject this metaphysical assumption of a psychical faculty. Instead we have attempted to explain the more complicated processes of thought, without apperception, by making use of the association of ideas. To do this requires, of course, much more pains than to simply refer or ascribe all of the more complicated processes of thought to a problematic apperception. Furthermore, in making such an assumption we make no progress toward an explanation of the processes that occupy our attention ; on the contrary, we deprive ourselves irretrievably of the possibility of understanding them in the light of psycho-physiological research. Let us repeat — many of our explanations may still need cor- 1 Compare L. Welt, Dissertation, Zurich, 1888. Rapidity of the Association of Ideas. 205 rection, but the way now opened before us is undoubtedly correct ; it is the only acceptable way for physiological psychology. Our explanations at least demonstrate that we can succeed with- out the assumption of a new psychical faculty, even though the progress of knowledge may correct them somewhat ; we have demonstrated the possibility of reducing all the so-called higher processes of thought to the association of ideas. In a certain sense we regard the ideational life as republican. All of the latent ideas enter into the contest, each one wishes to push its way into consciousness; but it is not a higher power which hovers over the ideas and determines the victory of one idea over another and thus fixes the order in which they appear, but merely the intensity, the accompanying emotional tone, the grouping and the associative relations of the ideas themselves. CHAPTER XI. ATTENTION — VOLUNTARY THOUGHT — THE EGO — MEMORY. In the last chapters we became acquainted with the chief char- acteristics of the association of ideas. We investigated the simple recognition and reproduction of mental images. We found that the reproduced images of memory appear together first in less compact series, then in combinations of a higher order, the judgments. Thus far in our discussions we have intentionally ignored one element which, however, plays an im- portant part in the processes of thought. This element is that which we commonly call " attention." We say that "we turn our attention now to this sensation now to that sensation," or that "we turn the attention now to this line of thought now to that." It seems to be left to our option; apparently we direct our attention to this or that sensation, this or that idea by preference. Hence we might fear that we shall yet be compelled to decide in favour of assuming an apperception, which is superior to the association, and which attends to, or disregards the sensations and ideas at will. This is not the case however. Let us first investigate the attention as directed to the sensations, making use for this purpose of a definite example. Suppose the left eye to be closed and the right eye to be open and motionlessly fixed upon the field of vision before us. Let the field of vision be designated by the circle, fig. 21, which contains a large number of objects. In the figure, but three of them are designated by letters ; one, situated somewhat apart from the centre of the field of vision and corresponding to the macula lutea of the retina, is designated by C, and two others, situated anywhere near the periphery, by P t 206 Attention — Voluntary Thought — The Ego — Memory. 207 and P % . Now it is an undoubted fact that we generally turn our attention to the object C situated in the middle of the field of vision. We fix the eye, as it is commonly expressed, on the object C, and we believe that we are able to do so with greater or less energy. Does this mean that an apperception generally prefas this C, to which it accordingly voluntarily turns the at- tention ? Certainly not. On the contrary the facts in the case are as follows : C is the point situated near the centre of the field of vision corresponding to the macula lutea of the retina ; hence, according to the teachings of physiological optics, it is much more distinctly seen than all other points situated nearer the Fig. 21. periphery. P 1 and P 2 in general cast but comparatively confused and indistinct images upon the retina. Consequently the sensa- tion produced by C, i.e. the material cortical excitation Ec corresponding to the sensation, will also be far more intense and correspond much more closely to former sensations produced by similar objects than the sensations produced by the objects P 1 and P 2 which are located nearer the periphery. In this case, therefore, we find several sensations active at the same time and, in a certain sense, entering into a contest for the privilege of awakening the next image of memory and determining the course of ideation. The result of this contest, as we have termed it, depends upon two factors, (1) the intensity, and (2) the distinct- ness of the sensation in question. It is obvious that the stronger sensations, or the more intense material processes accompanying 2oS Introduction to Physiological Psychology. them, possess a far greater ability for converting latent El's into EPs or, in other words, for awakening the images of memory and determining the course of ideation. But the distinctness or sharpness of a sensation is also essential. We have often dis- tinctly seen a tulip, for example ; hereafter it will be quite essential whether a new visual sensation of the tulip is like the former, i.e. equally distinct and sharp, or whether it is unlike former visual sensations, i.e. is indistinct and confused, the object, tulip, being too far off or being seen only by the peripheral parts of the retina. It is obvious that in the latter case recognition of the object will be more difficult; let us recall in this connection what was formerly said concerning the training of the nerve-paths necessary for recognition. The indistinct sensation of the tulip finds no path exactly trained for its purpose. For this reason, both the first reproduction, the awakening of similar images of memory formerly experienced, and the excitation of other ideas associated with the mental image of the tulip, will be rendered exceedingly difficult 1 Therefore distinctness and intensity are the most im- portant factors in determining which sensation will prevail in the contest with others, cause the reproduction of certain mental images and thus determine the association of ideas. This also explains why only the object situated in the centre of the field of vision generally determines the association of ideas; it is just the object that produces the most intense and distinct sensation. No "apperception" exercises any arbitrary control over the process whatever. The association of ideas is inevitably neces- sitated from the beginning to the end. Such are the objective facts accompanying the phenomena of attention. But whence arises the peculiar sensation of self-activity characteristic of attention? Self-observation teaches that this sensation is a sensation of motion produced by the innervation of numerous 1 Of course this important distinctness of visual sensations is very closely connected with the intensity of the sensations received from the macula lutea. The latter give rise to the greater number of associations because they are the most intense ; they are therefore the most distinct retinal images of the objects seen. Attention — Voluntary Thought — The Ego — Memory. 209 muscles (particularly the muscles of accommodation and the musculi recti interni) which serve to fix the eye upon an object. By means of this fixation of the eye, the distinctness and intensity of the retinal images and hence of the corresponding sensations are increased. The feeling of a greater or less tension of the muscles regulating the eye, is itself produced by association ; it is imparted by the stimulus which acts upon the macula lutea. The tension thus perceived, in its slighter degrees of intensity, is the product of reflex action 1 ; in its greatest degrees of intensity it is voluntary action proceeding from the cortex. Particularly in the latter case, the innervation that has taken place imparts very numerous and intense motor sensations which are the cause of the exceedingly intense feeling of close attention. Therefore the feeling of attention is in fact merely a concomitant phenomenon. The essential objective characteristic of attentive or active sensa- tion, in distinction from the merely passive sensation, is the influence which the former exerts in determining the choice and order of ideas by which it is followed. This influence is not at all characteristic of a merely passive sensation to which the attention is not directed. We will now assume that P v one of the objects situated near the periphery, possesses a very unusual intensity of stimulation ; for example, a dazzling light suddenly appears near the periphery of the field of vision. What happens in this case ? It is true that P x is very unfavourably situated for producing an exact image on the retina and that C's situation is far more favourable ; but the greater intensity of light in the former case will more than equalize the unfavourableness of situation. Despite its peripheral location, P 1 will produce a stronger excitation of the retina and consequently a more intense sensation than C. Hence, in this more exceptional case, the attention is turned to the more intense sensation P x , despite its greater indistinctness. Again, this " turning of the attention " is strictly necessitated ; it means nothing more or less than (1) the sensation P x (and not C), by 1 According to Munk it is reflex action proceeding from the cortex. C .... 210 Introduction to Physiological Psychology. virtue of its greater intensity, reproduces the next following images of memory and thereby determines the further course of the association of ideas ; (2) either automatically or voluntarily (i.e. consciously) the eyes are turned to the dazzling light P t , and the motion of the eyes thus executed produces motor sensations which constitute the peculiar feeling of activity accompanying the change of attention. Therefore in this case also we discover nothing more than a process of association with certain muscular sensations. With some pains we can also occasionally succeed in directing the attention to the peripheral object P 1 without making the movement of the eye necessary to bring P x within the range of the macula lutea. But if we observe sharply during such an experiment, we perceive a constant inclination of the eye to move so as to bring the image of the object P t upon the macula lutea. Generally we are unable to entirely repress these motions ; our eyes occasionally deviate in fact toward one side or the other, although we again instantly correct each lateral deviation. Hence, in this very exceptional case also, motor sensations and motor ideas influence the feeling which accompanies attention. Let us now consider certain other factors, besides the distinct- ness and intensity of sensation, that help to determine the degree of influence which a sensation exerts upon ideation. Let us re- tain the example of the eye at rest, as used above. We shall suppose that the object P 2 , situated near the periphery of the field of vision, produces a stimulation of but very slight intensity; it therefore imparts a sensation that is but little fitted to draw the attention or to determine the association of ideas. Let us now, however, also assume that the object P 2 produces a very lively feeling of pleasure ; in other words, the sensation imparted by P 2 is accompanied by a very strong positive tone of feeling. For example, a star, faint indeed, but glimmering with the most beautiful colours, appears within and near the periphery of the field of vision. Despite its slight intensity of light and greater or less indistinctness, this retinal image will at once attract the attention. The eye is accordingly turned toward the star and the following ideas are determined by this sensation and not by that Attention — Voluntary Thought — The Ego — Memory. 211 imparted by C. The same thing is just as true of sensations that are accompanied by strong negative tones of feeling ; despite their slight intensity and distinctness, such sensations, by virtue of their strong accompanying feeling of displeasure, are able to divert the attention from sensations that are more intense and distinct, but that have a weaker emotional tone. In a certain sense they contest, as it were, with the latter for the influence upon the course of ideation. For example, a soft chord can fetter the attention in the midst of numerous louder noises. We hearken — that is, we tighten the ear-drum and turn the head in order to hear the chord as distinctly as possible, and our thoughts become occupied with the chord. In this case we again find all the elements characteristic of attention in general. A sensation, by virtue of certain of its properties (in the above case, for example, by virtue of its strong positive emotional tone) produces, either by reflex or conscious action, certain motions, and, what is still more essential, determines the course of ideation. The motor sensation produced by the motions gives the attention that peculiar feeling of activity by which it is characterized. A very similar process takes place when a slight, but very unpleasant } discord occurs in the midst of a number of tones or noises. It likewise attracts the attention very forcibly. Hence we rind that still a third factor also largely shares in the influence which the sensation exerts upon the association of ideas ; the i?itensity of the emotional tone is to be added to the distinctness and intensity of the sensation. But we have not yet exhausted all the factors that influence the attention. The decision of the question as to which sensation shall determine ideation is by no means wholly independent of the ideas that have preceded in the last few minutes or hours. It is not a matter of indifference as to which of these ideas are still very active and which are not, or as to which are mutually arrestive or mutually incitant. In brief, that which we formerly designated as the grouping of the ideas, likewise exerts an influence upon the attention. Let us take another simple example. While we are taking a walk, numberless visual sensations constantly throng our consciousness. If the idea of 212 Introduction to Physiological Psychology. meeting other strollers, for example, is in condition to be easily reproduced, the visual sensation of an approaching friend or stranger attracts our attention and determines our further move- ments and ideas ; but if this idea is checked by the predominance of other thoughts, we pass the approaching person in a state of absent-mindedness without heeding him ; we turn our attention to the landscape, for example, which happens to produce a visual sensation more favourable to the momentary grouping of the latent ideas. Under certain circumstances the visual sensation of a friend may be ever so distinct and intense and possess ever so strong an emotional tone, and yet in consequence of an unfavour- able grouping of the latent ideas, other sensations will prevail, and determine the course of ideation. The phenomena which we designate as " seeking " and " intense expectation " are typical cases of the influence exerted upon the attention by the grouping of the ideas. The visual idea of the object sought or expected constantly fills the mind ; numberless sensations appear, but de- spite their distinctness and intensity, none of them fix the attention. On the other hand, as soon as the image of the object sought but appears near, and within the periphery of the field of vision, be it ever so weak and indistinct, it is at once noticed and the atten- tion directed to it; it then determines further movements and ideas. In this case the grouping of the latent ideas is the factor that governs the attention ; it is aided especially by the feeling of pleasure which accompanies the desired sensation, and which is, in fact, the cause of the seeking. We shall designate the totality of all factors that decide whether a sensation shall become the object of attention and determine the following association of ideas or not, as the associative impulse of the sensation. We have seen that the associative im- pulse, or the associative power of a sensation is dependent on (i) the intensity, (2) the distinctness, 1 (3) the strength of the accom- 1 In this case the ''distinctness" of a sensation, as one of the conditions of the "associative impulse," might also be designated as the "associative relationship." A ttention — Voluntary Thought — The Ego — Memory. 2 1 3 panying emotional tone, and finally (4) the chance grouping of the latent ideas. These four factors decide in favour of one among several concurrent sensations. We have undoubtedly already noticed the analogy that exists between the contest of the sensations for the attention l and the contest of the latent ideas for the position I % . This analogy is easily understood if we recollect that the succession of ideas can be conceived of as the attention passing from idea to idea. There is, however, an essential differ- ence between the two contests ; the sensations that enter into a contest are all conscious, i.e. actually present as psychical pheno- mena, while the ideas that are struggling for the supremacy, with the exception of the one momentarily prevailing, are psychically latent. Thus far we have not especially mentioned the contrast of successive or simultaneous sensations among the factors that constitute the associative power of a sensation, although it un- doubtedly exerts some influence upon the attention. We find that a small black spot upon a white cloth is especially striking ; and the more suddenly an object appears with its full intensity upon a differently coloured background, the more forcibly does it attract the attention. It is obvious that this influence exercised by contrasting sensations, whether simultaneous or successive, can be reduced to the factors already mentioned above. As we have already seen, a sensation that is characterized by great uniformity or monotony in its relations to space or time, rapidly loses its intensity and the strength of its accompanying emotional tone. The activity of the ideational process is soon exhausted, the favourable grouping of latent ideas is expended. It can therefore be easily understood why each new sensation that suddenly appears in contrast with these monotonous sensations prevails over them in the contest for the attention. Generally, in the case of the contrast of simultaneous sensations, both the strong 1 In a certain sense, for the right of naming the first idea, I v 214 Introduction to Physiological Psychology. emotional tone and the grouping of latent ideas exert an influence in favour of the single contrasting sensation. Let us again emphasize that in by far the greater number of cases, the first idea to be imparted by the prevailing sensation is an idea of motion. In fact, it is generally the idea of just that motion which is fitted to adjust the organ of sense so as to receive the prevail- ing stimulus, thus heightening the distinctness and intensity of the sensation still further. We already know, furthermore, that the motor idea (its sufficient vivacity being assumed) is itself an ample, in fact, the only cause of the respective motion. Therefore the first consequence of most sensations to which we direct the attention, 1 is a motion which serves to place the organ of sense in a favourable position. These movements are most highly de- veloped for the eye and ear. When the attention is drawn to sensations of the skin, a general tonic contraction of the neigh- bouring muscles usually first appears ; only then does the associ- ation of ideas follow. According to these facts we may conclude that each sensation possesses a certain motor power or motor im- pulse. It is without doubt extraordinarily fitting and the outcome of a long process of natural selection, that this motor impulse always tends to render the sensation more distinct and intense by a more favourable adjustment of the sense-organ with reference to the stimulus. The sensation that is to occupy our thoughts is, to a certain extent, preparatively intensified before any thought occurs. We can easily imagine how the phylogenetic develop- ment of this expedient connection between the motor impulse and the subsequent association of ideas has been accomplished. 2 It is only necessary here to emphasize once more that many of these accommodative movements take place without our being conscious of them ; in other words, they are purely material processes, either 1 We designate those sensations to which the attention has been turned as perceptions (Wahrnehmungen). The word perception, however, has been used by psychologists in so many different meanings that its applicability has been impaired. 2 At first, especially because it renders possible more complicated and more exact defensive movements. A Mention — Voluntary Thought — The Ego —Memory. 2 1 5 reflex or automatic actions. The motor idea is omitted from consciousness; only the fact that the movement placing the organ of sense in a favourable position has been accomplished, makes us aware that a latent motor idea has been excited. For example, the turning of the head in the direction of a sound is in many cases an entirely unconscious act. Finally, there are certain movements by means of which certain organs are adjusted, such as those executed by the optic muscles of accommodation, which take place constantly, or almost constantly, as purely reflex acts. We have already become acquainted with the further course of the association of ideas after having been once excited by sensa- tions, in previous chapters. This further process of thought may be of two kinds. We generally distinguish between so-called voluntary thought and Involuntary thought. This is not a funda- mental distinction, however. Our thinking generally seems to us to be voluntary when we are occupied with those phenomena of consciousness which we designate as "reflecting," " trying to recollect," " making up the mind," etc The laborious mental occupation of the child with its puzzle, or of the adult thinker with his problem, are both simply varieties of that psychical pro- cess which we variously designate as "reflection," "contemplation," " meditation," and "cogitation." Now what causes the process of reflection to seem like a voluntary act P 1 Let us have recourse to accurate introspection. The so-called voluntary thought is characterized by the fact that the desired idea is always known to be already contained in the initial ideas that introduce the associative series, as well as in the following ideas ; the associations necessary for its discovery, however, are often very complicated. But there is still another important factor characteristic of volun- tary thought, as it is called. When we are occupied with deep reflections, a series of slight muscular innervations appears ; these are only to be discovered upon close introspection. This muscular innervation is seldom entirely absent whenever we are occupied 1 Compare the somewhat similar deductions in Mt'insterberg's m Die Willenshandlung," Freiburg, 18S8. 216 Introduction to Physiological Psychology. with so-called voluntary thoughts. We wrinkle the brow slightly, press the teeth somewhat more firmly together, and frequently there appears a slight tonic contraction of the lips and the muscles of the neck. 1 All these innervations of the muscles are gener- ally accomplished unconsciously. Furthermore, we have no isolated sensations of the single motions, but their combined action pro- duces that peculiar total sensation which we generally have when " trying to recollect," or when absorbed in so-called voluntary reflections. The English language very aptly designates this con- dition as "attention" (primarily from tendo, to stretch). 2 This combination of motor sensations often gives our thought the char- acter of attentiveness and an appearance of volition and self- activity which in fact do not belong to it at all. We cannot think as we will, but we must think as just those associations which happen to be present, prescribe. But there is still another circumstance which would seem to strengthen this appearance of volition. In the course of the ontogenetic development of the individual, a peculiar complex of associated images of memory is constructed, which we desig- nate as the idea of the " Ego." The child laboriously acquires the idea of its own body as distinct and separate from the rest of the world about it. In the beginning the child knows no difference between the hand touching and the object touched. The moon which it tries to reach, and its own foot which it grasps, seem to the child to be equally near to it. This condition 1 It is interesting to note that among the lower animals, particularly in the case of the ape, the wrinkling of the brow, as a motion expressive of attention, does not seem to occur. Darwin, however, observed a young orang-outang which undoubtedly produced motions expressive of attention by closing and protruding the lips. 2 It is very interesting to note that in the case of the observations made by Lange, already mentioned, the appearance of visual images of memory is fre- quently accompanied by slight unconscious movements of the eyes. For ex- ample, one thinks of a long street, and at the same time unconsciously moves the eyes slightly from one side to the other, as if following the line of buildings. The English expression "attention" corresponds exactly to the German " Spannung " — 'Ps. Attention — Voluntary Thought — The Ego — Memory. 217 of affairs changes but gradually. The child learns to distinguish between those objects, or spatial complexes of visual and tactual sensations, that are associated with active sensations of motion and those that generally appear without active motor sensations. The former, in their totality, correspond to the idea of one's own body; the latter, to the idea of all objects of the external world. Many other factors tend to fix and complete this distinction. When two complexes of visual sensations of the second kind, i.e. two external objects touch each other, no sensation of touch appears. If on the other hand two complexes of visual sensations of the first kind, i.e. two parts of one's own body, as the hand and face for example, touch each other, a double sensation of touch appears. Finally, if a complex of visual sensations of the first kind, (e.g. the hand) touch one of the second kind (e.g. any ob- ject), a simple sensation of touch appears. The totality of all sensations of the first class — in other words, the sum total of all the distinct and separate sensations of one's own body, leaves a composite image in memory, the idea of one's own corporeal ego. 1 At first this idea varies considerably. Primarily the ego of child- hood or babyhood is nothing more than alternate feelings of hunger and satiation, or pain and joy in beholding a light or in self-motion. The idea of the surface of one's own body as the limit of a definite portion of space, and with it the idea of one's own body as a whole, are only developed gradually. To the latter is also added by degrees the slowly developing idea of one's own mental ego — that is, a total idea of all the images of memory deposited at any given time in the cerebral cortex. This complex idea of the intellectual ego is much more laboriously acquired than that of the corporeal ego. At this point we must refer to what has already been said in a former chapter concerning the development of conceptions without an external or objective foundation in the sensations. We demonstrated that our entire psychical being is composed of sensations and ideas ; that the latter are primarily produced as a rule by the combination of sensations, 1 Compare Meynert, " Gehirn und Gesittung," Vienna (18S9). 2i8 Introduction to Physiological Psychology. but that combinations of ideas also take place within the mind itself, and in their totality correspond to no actually experienced combination of sensations. On the contrary, these ideas represent wholly subjective ideational combinations. In this manner a com- plex of ideas is also developed, in which our paramount, most intense lines of thought, accompanied by the strongest emotions, participate as elements. The sum total of our present inclinations and our actually dominant ideas constitutes an essential part of our idea of the ego. But besides the idea of one's present cor- poreal and mental ego, there is still a third member participating in the usual ego-idea. This is the very essential total idea that has been deposited in memory by the succession of one's most important mental and physical experiences in the past. It will seem striking to us, perhaps, that the ego-idea, which is designated by the short, small word " I," should be such a complex structure, composed of three chief members in which thousands and thou- sands of component ideas participate. But let us reflect ; the word is, indeed, short, but that its intellectual content must be very complex is readily shown by the fact that we should be at once embarrassed if called upon to state the mental content of our so-called "idea of the ego." We should at once think of the body, of our relation to the external world and our relations to family and to property, of our name and title, of our chief in- clinations and dominant ideas, and finally of our past experiences. In so doing we should demonstrate for ourselves how exceedingly complex this idea of the ego is. The reflective person, of course, reduces this complexity of the ego-idea to relative simplicity by placing his own ego, as the subject of his sensations, ideas and motions, over against all objects and other egos of the external world. To be sure, this simplification of the ego-idea by placing it as subject in opposition to the rest of the world as object, has a deep foundation in epistemology ; but regarded purely in the light of psychology, this simple ego is but a theoretical fiction. Empirical psychology recognises only that complex ego whose chief characteristic features we have just briefly described. When we are occupied with the common processes of natural thought Attention — Voluntary Thought — The Ego — Memory. 219 we pass from idea to idea and from judgment to judgment with- out the appearance of this complicated idea of the ego. It is very different in the case of the so-called voluntary thought to which we have already referred above. Here the idea of the ego often appears between the single ideas and judgments ; in this case we make a mental reference to the ego-idea as the cause of the series of ideas and judgments with which it is associated. However, the concomitant activity of the idea of the ego is not always present. In the case of very deep reflection or rumi- nation we often forget that it is we ourselves who are thinking. But in general it is true that the so-called voluntary thought is accompanied by the idea of the ego. Let us now recapitulate the three factors that characterize so- called voluntary thought. They are as follows : (1) The pecu- liarity that the idea desired and sought is known to be already contained in the initial series of ideas. (2) A complex of accom- panying muscular tensions that produces the kinesthetic sensa- tion characteristic of attention, and finally (3) the concomitancy of the ego-idea with the series of ideas that constitute thought. We have also seen that these three factors are all generally, but not always, present at the same time, and that they appear singly also in the case of involuntary thought. From what has been said, however, we may also conclude that this voluntary thought by no means occupies a unique or peculiar position among psychical processes. On the contrary it remains quite within the limits of the association of ideas with which we are already thoroughly familiar. Our thoughts are never voluntary ; like all events, they are strictly necessitated. The freedom, which we think to possess in the so-called voluntary processes of thought, is only semblance ; but this appearance of freedom is fully explained psychologically by the three above-mentioned factors. Both the common usage of language and of philosophical and psychological theories, have distinguished many other special forms of the association of ideas besides those that we have men- tioned. These special forms have received special designations, such as " understanding/' " reason," " power of judgment," 220 Introduction to Physiological Psychology. "sagacity," " fantasy," etc. At the same time there has always been a tendency to render these special activities, that may be distinguished more or less justly, independent entities by ascrib- ing them to just as many different psychical faculties. On the contrary, however, we shall hold to the fact that all these activities simply represent varieties of the association of ideas. It would not be at all difficult to reduce all these forms to the one funda- mental form of association by purely psychological reasoning. The difficulties that cling to these conceptions are due to their alli- ance with certain conceptions of metaphysics and epistemology and to the fluctuating applications in which the corresponding terms have been used by different peoples and philosophical schools. We shall now emphasize only one other phase of the association of ideas, the memory or faculty of recollection. In this example (the memory) we shall illustrate how such psychical activities are to be viewed as a rule and how they are to be reduced to the association of ideas. It is obvious that two things are necessary in order that we may recall the mental image of an object or sensation : (i) the image of the object in memory must be intact, and (2) the association as such must take place normally. The latter is abnormal only in cases of great fatigue or of mental disease. Under such circumstances the association of ideas may be so retarded that it is finally completely arrested ; no mental image or idea is reproduced. The latent mental image El is intact, but the material process, which should convert this El into Ei, and thereby bring the image of memory into consciousness, is not sufficiently vigorous to accomplish the task. This forgetfulness is but transitory. But the loss of memory, caused by the destruc- tion of the mental images themselves, is a very different matter. We have already heard in a previous chapter that during the first five minutes after their deposition the images of memory lose very little or nothing at all of their intensity and distinctness. Then the slow process of material change begins, gradually effacing the material dispositions — the El's. To express it in the language of psychology, the images of memory gradually lose their intensity and distinctness. The more seldom they are reproduced, the Attention — Voluntary Thought — The Ego — Memory. 221 more rapidly does this change progress. Also different individ- uals are very different in this respect. In one person the images are less firmly deposited and more speedily eradicable than in another. In this case we ascribe a " good memory " to the latter, and a " bad memory " to the former. But even with a due consideration of all these circumstances, "memory" and "loss of memory" still remain comparatively relative conceptions. Let us consider that the reproduction of an idea at any definite moment also depends upon both its associative relation to the preceding idea and the grouping of latent ideas. If these are un- favourable, even the most intense mental image may remain latent. We are then accustomed to say that this or that thought or idea " does not occur to us.' ; We see, therefore, that this apparently simple faculty of memory resolves itself into a much more com- plicated process. In all its variations, however, it depends on nothing more or less than the association of ideas and its laws, with which we are already familiar. 1 From the above we can judge how extraordinarily difficult it is to investigate experimentally either the retentive power or the forgetfulness of the mind. It is hardly possible, for example, in attempting to determine the influence of passing time upon the retentiveness of the memory, to retain all other factors, such as the state of feeling, grouping of ideas, attention, etc., entirely constant during the full series of experiments. However, in the case of the memory we have the very trustworthy, painstaking researches of Ebbinghaus. 2 Ebbinghaus arranged syllables in series of different lengths, but without regard to sense. He then memorized these series by repeatedly reading them aloud until he 1 Hering ("Ueber das Gedachtniss als eine allgemeine Function der Materie," 1876) has ascribed memory to all organized matter. In this case the word memory is also applied to processes that cannot be shown to be accom- panied by parallel psychical processes. We shall here exclude this expansion of the conception. Compare also Meinong, Vierteljahrschrift f. wiss. Philos., X. Joh. Huber, " Das Gedachtniss," 1878. Plato, "Theoetet." 2 Ebbinghaus, "Ueber das Gedachtniss." " Untersuchungen zur experi- mentellen Psychologie," Leipzig, 1885. Wolfe's dissertation (Philos. Stud., III.) contains a special investigation of the memory for tones. 222 Introduction to PJiysiological Psychology. was just able to reproduce them. After certain intervals of time (for example, 20 min., or 1 or 2 days) had elapsed, he deter- mined by experiment how many times he had to re-read the partly forgotten syllables in order to be able to reproduce them again. By this means he obtained a standard for measuring the degree of forgetfulness. As the result, it appeared that the process of forgetting progressed very slowly at first, then more rapidly and finally very slowly again. An hour after the series had first been memorized, the process of forgetting had advanced so far that more than half the time originally employed was requisite for committing the series to memory again. Eight hours later two thirds the original time was required for learning it anew, a month later about four-fifths the original time. These numerical rela- tions may be expressed, approximately at least, in the following law : " The quotients of the amounts retained by the amounts forgotten are to each other inversely as the logarithms of the various periods of time that have elapsed." The result obtained by the same author, in making use of series in which the syllables are arranged so as to produce sense, is worthy of mention. For example the verses of an epic poem can be ten times more easily retained than senseless series of syllables. Without investigating the correctness of the number ten, we see that it is undoubtedly true that the ideas composing a series are more firmly fixed in memory when they are more closely associated with each other, especially by means of judgments. Ideas thus thoroughly asso- ciated mutually assist one another in reproduction by means of that which we have designated as the grouping of ideas. As Herbart expresses it, they are " mutual aids " (Hiilfen). Ebbing- haus found further that one reading is sufficient to memorize a series of from seven to eight syllables, but that forty-four repeti- tions are necessary for a series of twenty-four syllables. Investigations that are just as exact as those supplied by Ebbinghaus for the memory, are wanting for most of the other pyschical processes. We must therefore restrict ourselves to re- peating once more that they may all be explained without diffi- culty by the association of ideas and its laws. CHAPTER XII. MORBID THOUGHT— SLEEP — HYPNOTISM. Thus far we have considered only the thought processes of the healthy man in his waking moments. Let us now descend, as it were, into the labyrinthic realms of insane or morbid thought. Right among these psychical anomalies we shall observe numer- ous phenomena that confirm the propositions thus far advanced. We remember that we reduced every psychical process to essen- tially the same simple scheme. An initial sensation £ is followed by a definite series of ideas, I v I 2 , / 3 , etc., in accordance with the laws of association. The sensation S is always conditioned by an external stimulus E ; the ideas I v / 2 , 7 3 , etc., originated in former sensations. These material dispositions, the El's that have been left by former sensations, are changed by the associative pro- cess into Ei's, or I's, and are thus reproduced, i.e. called into psychical life. Now what deviations. from this normal process occur in the conscious life of the insane ? Let us here first call attention to a peculiar phenomenon that has been termed " secondary sensa- tion." This phenomenon occurs when a sensation of one quality that has been normally produced by an adequate external stimu- lus, at the same time imparts a sensation of an entirely different quality for which there is no corresponding external stimulus. A simple example of this secondary sensation is as follows : We hear a very loud, shrill sound, and at the same time see a flash of light before the eyes. In this case the visual sensation of the flash of light has been produced without any adequate stimulating cause in consequence of a normal sensation of hearing. On the other hand, a bright light sometimes produces the secondary 223 224 Introduction to Physiological Psychology. acoustic sensation of a high tone besides the primary sensation of light. It is obvious that this phenomenon depends on the sympathetic excitation of the elements of the auditory centre to which the cortical excitation primarily produced in the visual centre has been transferred by means of the associative paths. This process differs from the process of association with which we are already familiar only in the fact that the latter is the associa- tion of mental images or ideas, while the secondary sensations, on the contrary, are produced by the association of sensations. The image of fire may remind one of a crackling noise ; the sound of a trumpet may recall the idea of yellow. In both cases, how- ever, the association is accomplished by means of ideas and only the mental image of red or yellow is reproduced. On the con- trary, in the case of secondary sensations the primary sensation directly imparts another sensation. We shall do better therefore to avoid the expression " associa- tion " in connection with secondary sensation and make use of the term " radiation." We are all aware that the pain caused by a carious tooth may often spread in a somewhat remarkable way until it finally attacks the entire half of the head. 1 The effect which prolonged pain produced in the case of one sense is transferred in the case of secondary sensations from one sense to another. Among the secondary sensations, "photisms" (i.e. secondary sensations of light or colour) are decidedly the most frequent ; " phonisms " 2 (i.e. secondary sensations of tone or noise) are considerably rarer. The quality of the secondary sensations is always the same in the same individual, but on the other hand, often different in different persons. For this reason it is only possible to formulate a few general laws. As a rule, bright photisms are produced by sensations of high tones, or also 1 The interesting observations of Urban tschitsch's upon the changes in the sensibility of the trigeminal nerves accompanying diseases of the ear, also present a certain analogy. Compare also Pfluger's Archiv, Bd. 42. 2 The use of the words "photism" and "phonism" has been borrowed from the German for the sake of brevity. Their meaning is parenthetically in- dicated above. — T's. Morbid ThougJit — Sleep — Hypnotism. 225 by intense pain and sharply defined sensations of touch ; dark photisms are produced by sensations of an opposite nature. In the same manner high phonisms are produced by sensations of bright light and sharply defined sensations of touch (small, pointed objects). The phonisms generally partake of the quality of noises ; the photisms generally appear in the colours of red, yellow, brown or blue. Sometimes a definite colour is associated with a definite pitch, vowel or noise. There is a case of one German lady 1 who is known to associate the acoustic sensation a with the sensation of the colour yellow, a with white, e with blue, 6 with red, and 66 with black. The same lady also sees the printed vowels glimmer in the same colours whenever she reads. In accordance with a proposition made by Fechner, the academic philosophical union in Leipzig instituted a collection of statistical data on a large scale. The result of these data showed that on the average, though not always, lighter photisms corre- spond to the vowels a, a and e, and darker photisms to the vowels 6 and 66. Both diphthongs and polysyllabic words appeared to the above-mentioned patient in mixed colours. French authors have very characteristically designated this as " audition coloree," or "coloured hearing." The localization of the secondary sensa- tions is also interesting. Photisms produced by sound, i.e. secondary sensations of light induced by sensations of tone, are generally localized in the field of hearing from which the primary sensation proceeds ; the rare photisms produced by sensations of taste are generally localized in the appropriate region of the buccal cavity, and photisms produced by sensations of smell, in the neighbourhood of the object smelled, or in the cavity of the nose. Much more rarely the localization is within the head (de Rochas, Ughetti). It is also well worth mentioning, that an un- pleasant emotional tone accompanying the primary sensation may be followed by an agreeable emotional tone accompanying the secondary sensation. In by far the majority of cases the second- ary and primary sensations seem to appear simultaneously ; in 1 A patient of the author's. — T's. 226 Introduction to Physiological Psychology. rarer cases an interval of some seconds has been observed to elapse before the appearance of the secondary sensation. The question now arises : are these phenomena pathological or normal experiences of the psychic life? Bleuler and Leh- mann 1 found such secondary sensations in one-eighth of all the men whom they investigated. The questions (Fragebogen) of Fechner 2 brought together 347 reliable cases in which colours were associated with sounds. Of course it is probable that not all of these cases are genuine, but that on the contrary, in a part of them, certain associations of ideas, originating partly in earliest childhood, are the cause of the secondary sensations. It cannot be doubted, however, that genuine cases occur. In these genuine cases, almost without exception, we find a neuropathic disposition. The above-mentioned lady suffered from severe reflex neurosis. At the time that Nussbaumer 3 first imparted his self-observations to Germany before the medical fraternity of Vienna, Benedict had already called attention to the psycho-patho- logical features of these symptoms. In very many cases there is an inherited disposition. Nussbaumer's brother had likewise had secondary sensations ; also several of Bleuler's relations besides himself. In mentally healthy individuals, who are free from all neuropathic disturbances, these secondary sensations are at least just as rare as the hallucinations that are to be considered pre- sently. There is no doubt that inherited associative paths of abnormal capacity for conduction are, in the above cases, the means of communication between the separate cortical centres of sensation. 1 " Zwangsmassige Lichtempfindungen clurch Schall und verwandte Er- scheinungen auf dem Gebiet der anderen Sinnesempfindungen," Leipzig, 1881. 2 Steinbrugge, " Ueber secundiire Sinnesempfindungen," Wiesbaden, 1887. In this work are also to be found further, though incomplete, literary re- ferences. To the above work should be added GlRANDEAU, " L'encephale," 1885 ; de Rochas, " La Nature," 1885 ; and numerous Italian authors. The first description was given by Lussana as early as 1865. 3 Wiener med. Wochschr., 1873. Fechner's first communication ap- peared independently of Nussbaumer's in the "Vorschule der Aesthetik," 1876. Morbid Thought — Sleep — Hypnotism. 227 Normally, the sensation should always cause the appearance of ideas only, and not of sensations ; the sensations themselves should not appear without adequate stimulation. The secondary sensation is not produced by adequate stimulation, but by the action of some other sensation ; it therefore departs from the nature of the normal or primary sensation. We shall now con- sider another case of morbid sensation — the hallucination. In this case not only the adequate external stimulus, but also the primary sensation are wanting. The persons subject to halluci- nations sees persons and landscapes in the cloudless sky, and hears voices in the most profound stillness. At the same time his visions are often so realistic and so true in colour, and the auditory hallucinations x that he hears are so loud and distinct, that it is absolutely impossible to distinguish them from the reality. They appear when the eyes and ears are closed the same as when they are open. They often correspond to the actual content of the invalid's thoughts ; in this case he complains that all his thoughts are at once " set in scene " and " illustrated," or that they " become loud." Again, the visions are often entirely strange and surprising to the patient himself; he sees faces that he never saw before, and hears words that have not the remotest connection with his thoughts or even combinations of syllables that he never heard before. In still other cases the invalid possesses the power of producing this or that hallucination at will, somewhat as Goethe relates of Ottilie in his novel, " Wahl- verwandtschaften." 2 Genuine hallucinations of taste, smell and touch are considerably more rare. Certain hallucinations in the case of motor sensation are highly interesting. One invalid told the author that he felt his larynx and tongue move as if he heard the word " parricide *' issuing from them.. It is not improbable that such hallucinatory motor sensations at times cause actual involuntary motions, thus producing the articulation of the respec- tive word. As regards localisation, the voices heard are occasion- 1 Ger. Akoasmen. — T's. 2 Natural or elective affinities. — T's. IS ... 228 Introduction to Physiological Psychology. ally, the visions very rarely located within the head ; much more frequently both are projected outward. Their location, when per- ceived as external to the invalid himself, appear to vary ; the variation is only in part dependent on the movements of the invalid's eyes while experiencing the hallucinations. Those cases are remarkable, in which the hallucinations are always heard with but one ear, or seen in but one half of the field of vision. The author also recollects a case in which the agreeable voices always spoke into the right ear, and the disagreeable voices into the left ear. Squinters often see their visions double. Sometimes it is necessary for the invalid to give especially close attention, in order to distinguish words among the indistinct hallucinatory murmur- ings. The hallucinations generally have a stronger influence upon the association of ideas than the concomitant normal sensa- tions, which are often, in fact, overshadowed. For this reason, when a large number of hallucinations continues many years they very rarely fail to beget insane ideas. In many cases of hallucination a disease of the invalid's organ of hearing or sight can be diagnosed • but in numberless cases no such disease of an organ of sense is present. Individuals whose optic nerves have been atrophied for a number of years can have visions. On the contrary no persons have ever been known to have optic or acoustic hallucinations, who were bom blind or dumb. 1 The stillness of solitude, as in the case of solitary confinement for example, favours the appearance of acoustic hallucinations ; the darkness of night or the bandaging of the eyes after an opera- tion for the removal of a . cataract, favours the appearance of visions. These two statements do not express entirely universal rules, however. On the contrary, there are even cases in which slight stimuli of sight or hearing, of any kind whatsoever, are sufficient for the appearance of hallucinations. It also appears in some cases that a normal sensation of one quality is requisite to produce hallucinatory sensations of another quality (Kahlbaum), so that in a certain sense a primary sensation is still necessary. 1 Leidesdorf, "Lehrb. d. psych. Krankh.," 1865. Morbid Thought — Sleep — Hypnotism. 229 Hence many hallucinations vanish when the eyes are closed ; many do not. Now, how shall we explain the origin of these hallucinations ; how can a sensation be produced without stimulation ? Let us remember the former distinction that we made between sensation-cells and memory-cells. We have already shown that the sensation and image of memory are probably not connected with the same material elements. We designated the material process in the sensory cells, corresponding to the sensation, as Ec ; the material disposition that remains in the memory-cells, as El ; the material process attending the awakening or repro- duction of the latent image of memory and corresponding to the conscious idea, as Ei. Normally, the sensation-cells are only excited by stimulation coming from the periphery ; Ec is only produced by a stimulus E that acts upon the sensory path. This is different in the case of hallucinations. . In this case it is the images of memory that produce lively sensations without external stimulation ; the El's or Ei f s are the cause of Eds. The process of sensation which normally always proceeds from the sensory elements to the memory elements, now takes the reverse course from the latter to the former. Generally, this only occurs under pathological circumstances. It is only when the sensory cells are morbidly irritable, that they react upon a stimulation from the memory cells, which, under normal conditions, would have no effect upon them, but which has been pathologically intensified. The sensation- cells are sympathetically excited, as it were. It is obvious that but two chief cases are to be distinguished. The ideas that sympathetically excite the sensory cells are either the ideas actually present in consciousness at the time (i.e. the Ei's), or the ideas that are psychically latent, i.e. more accurately expressed, the material dispositions that still lie below the threshold of consciousness. In the first case the hallucinations correspond to the momentary content of consciousness, as has already been described ; in the second case they emerge from among the latent ideas very suddenly, surprising even the invalid himself. It is evident that in general hallucinations of the second 230 Introduction to PJiysiological Psychology. class occur only when very considerable changes in the excita- bility of the sensation-cells have taken place, while the actual conscious ideas produce hallucinations even when the excitability of the sensation-cells has but very slightly increased. For this reason hallucinations of the second class are generally much more vividly perceived than those of the first class, since in the former case the sensation-cells are more affected by the morbid pheno- mena than in the latter. As we already know, both sensation- cells and memory-cells are located in the cerebral cortex ; the hallucinations are therefore decidedly of cortical origin. The assumption that the peripheral parts of the sensory nerve-paths (corpora quadrigemina, retina, etc.) are sympathetically excited to a certain extent in case of hallucinations, wants sufficient grounds. On the other hand it can be shown that in a large number of cases of hallucination, some external stimulation in the broader sense is not entirely wanting. It appears, in fact, that subjective sounds, produced in the peripheral parts of the organ of hearing, or entoptic disturbances in the vitreous body for example, and especially excessively augmented " mouches volantes " are very frequently the cause of hallucinations. Such subjective sounds, resulting from peripheral causes, may exist for years and be per- ceived in their true nature, i.e., for example, as a simple buzzing or humming in the ears. If, however, a mental disturbance is developed in the individual, these noises are soon heard as words and voices. In a similar manner the "mouches volantes" appear to one delirious from the use of alcohol to be numberless mice or bees swarming about him. It is very apparent that in this case, and in many other similar cases, the sensation-cells do not receive excitation from external stimuli in the narrower sense, that is, from such as are external to the body, but from those external stimuli that are situated in the sense-organ or in some part of the sensory nerve-path up to the cerebral cortex. Under normal circum- stances a very simple sensation corresponds to this excitation ; the individual hears a buzzing in the ears or sees dark spots in the visual field. Under abnormal circumstances the memory-cells act upon the sensation-cells in such a manner as to transform Morbid Thought — Sleep — Hypnotism. 231 the excitation into more complicated sensations ; the buzzing in the ears becomes words, the dark spots become forms. In many respects these hallucinations 1 already approach the illusions which we shall forthwith discuss more fully. Also, in this connection, we shall now ask whether the halluci- nations may occur in healthy persons, or whether their appearance is limited merely to mental diseases ? An exact investigation of this subject shows that in this case also the many individuals who have inherited tendencies toward mental diseases, although not mentally deranged themselves, experience hallucinations. Of still greater importance to us is the fact that even men who are very gifted mentally, particularly artists who possess a very vivid imagination, have hallucinations. The Italian painter, Spinello Aretini, is said to have copied his Madonnas, as it were, from a vision ; an Italian composer is said to have composed his sonata in imitation of music heard during hallucinations. The well- known vision of Goethe's — the rider in pike-grey mantle upon the Sesenheim ride — was probably a simple illusion. Halluci- nations are recorded of Schumann,Pascal, Cardanus, Mendelssohn, Jean Paul, Spinoza, Byron, Tieck, Johnson, Pope, and numerous others. To be sure, in many of these cases we have to deal with very doubtfully authenticated reports ; in many the phenomena may have also been mere illusions. In the normal man, at least, even the liveliest emotions generally produce nothing more than illusions, never hallucinations. Fechner and Henle report of themselves that at night objects with which they had been occupied during the day often appeared to them again as phantasms in the dark. The peculiar hypnagogic hallucinations 1 The literature upon the subject of hallucinations is extraordinarily com- prehensive. At the present moment extracts from over 300 works lie before the author. As a preparatory introduction to the theory of hallucinations, Hagen, Allgemeine Zeitschrift fiir Psychiatrie, Bd. 25, is to be especially recommended. Also Kahlbaum, ibidem Bd. 23. Lazarus, Zeitschr. f. Volkerpsychologie, Berlin, 1867. Kraepelin, " Ueber Trugwahrnehm- ungen," Arch. f. Psych., Bd. 14. Kandinsky, Arch. f. Psychiatrie, Bd. 11. A brief presentation of the doctrine of hallucinations is to be found in Mendel, Berl. klin. Wchschr., 1890. 232 Introduction to Physiological Psychology. that appear just before falling asleep are also very interesting. They have been most exactly described by Hoppe. 1 Almost every one can observe these in his own case occasionally. They appear only upon closing the eyes, and are, without exception, visions of but slight sensual vivacity, generally indistinct visages or landscapes. By illusio7ts we understand those sensations that are, in fact, produced by external stimuli, but that do not correspond to the same in quality. We are all familiar, perhaps, with the poem of Schiller's, which runs as follows : — " H6r' ich das Pfortchen nicht gehen ? Hat nicht der Riegel geklirrt ? Nein, es war des Windes Wehen, Der durch diese Pappeln schwirrt." " Seh' ich nichts Weisses dort schimmern ? Glanzt's nicht wie seidnes Gewand ? Nein, es ist der Saule Flimmern An der dunklen Taxuswand." 2 Or let us recollect the well-known example of an insane person who, while observing a real portrait, suddenly perceives the painted head protrude its tongue, the vision possessing all the sensual vivacity of the real act. Again, a lady who was mentally deranged once related to the author that as often as she travelled upon the railway, she heard a voice call out from the rattling of the wheels, " crazy Bremer, crazy Bremer," — Bremer being the patient's name. 3 Let us now inquire what processes lie at the 1 Hoppe, "Erklarungen der Sinnestauschungen," Wiirzburg, 1888. 2 The above selection is from Schiller's " Erwartung." The reader who is not versed in German will probably be able to derive greater benefit, so far as its specific application above is concerned, from a more literal translation in prose than from a free poetical translation. The former is as follows : "Do I not hear the wicket open ? Was it not the bolt that clicked ? No, it was only the wind sighing and murmuring through these poplars. . . . But do I not see something white, gleaming there ? Is it not the flash of a silken ix>be ? No, 'tis but the columns that glisten against the dark wall of yews." — T's. 3 The German words, when regularly repeated, bear more or less resemblance to the rhythmical, but monotonous noise of car- wheels in motion. " Verriickte Bremer, verriickte Bremer" (v-»— ^—^, w~^. — w). — T's. Morbid Thought — Sleep — Hypnotism. 233 foundation of these phenomena. It is obvious that at first a sen- sation is produced in the normal manner. The sighing of the wind in the tops of the poplar-trees, the white columns seen against the dark background of yews, the portrait, the rattling of the railway coaches, etc., are the external stimuli that impart sensations. But these sensations are transformed. The rustling of the poplar leaves sounds to the expectant person like the noise of an opening door ; the white column assumes the form and appearance of a white robe ; the head protrudes the tongue ; the rattling is changed into words. This transformation is produced by the influence of actual, or, in the last two cases, of latent ideas. The memory-cells, as it were, add certain hallucinatory elements to the sensations. Such transformed sensations are designated as "illusions." It should be carefully noted, however, that these are not merely cases of mistaken or deceived judg- ment. The rustling of the leaves in the wind is not falsely judged in the case of illusion, but the quality of sensation itself is directly changed ; it has a sound different from that corresponding to the stimulus. On the contrary, our judgment is often able to rectify such illusions. These illusions are of frequent occurrence, and appear in con- nection with all of the senses. In fact, we may say that the influence which the images of memory exert upon sensation is never entirely wanting. The proper nursery of the illusions, however, is the emotional life ; among the various emotions, ex- pectation, both when accompanied by fear and by hope, is of especial importance. We shall now understand also why we formerly designated those hallucinations, that depend upon entoptic and entotic stimuli, as illusions ; they are obviously merely the result of a transformation of sensations imparted by actual stimuli. Without doubt the illusions are also produced through the influence of a recurrent excitation of the sensation- cells by the memory-cells. We can dispose much more briefly of those pathological dis- turbances in which the images of memory themselves, and the association of ideas are affected. We shall very briefly mention 234 Introduction to Physiological Psychology. only the most important, and for normal psychology the most interesting phenomena. One of the chief among these is im- becility or dementia. We remember that the most probable anatomical basis for the association of ideas was found to consist of numberless so-called "associative fibres," which connect the ganglion-cells with one another by running through the white matter, partly in arcuate courses, from one part of the cerebral cortex to another. The ganglion - cells themselves are most naturally to be regarded as those elements which we have desig- nated as memory-cells, and in which the so-called latent images of memory are deposited. Now it is of the greatest interest that the investigations of pathological anatomy have furnished positive results in the case of that mental disturbance which inevitably leads to complete imbecility, the so-called softening of the brain, or dementia paralytica. It consists particularly in the destruction (i) of the ganglion-cells themselves, and (2) of the associative fibres uniting them. We find that these facts, to a certain extent, once more confirm all our previous deductions, a posteriori. The abnormal acceleration and obstruction of the association of ideas, and also its morbid incoherency have been already men- tioned above. It only remains for us to consider briefly two other psychopathic phenomena that deserve a very especial interest, — the delusive idea and the compulsory idea. The two phenomena are alike in being associations of judgment that have no sufficient foundation in the external world. They differ from one another in that in the former case the invalid believes in his delusion, while in the latter he is fully conscious of the incorrectness and morbid nature of the idea which is forcing itself upon him. A patient who believes that he is Jesus Christ is suffering from a delusion ; one who, while cutting his bread, is constantly harassed by the thought that he is cutting his brother in two, and who, although he recognises the idea itself to be false and laughable, is still unable to rid himself of it, and is driven to the point of refusing nourishment, is the victim of a compulsory idea, or an idea which forces itself upon him. How do ideas of these two kinds arise ? Normally the association of ideas, Morbid Thought— Sleep— Hypnotism. 235 especially association that produces judgments, develops under the constant influence of sensations, that we are always experi- encing anew from moment to moment ; the latter condition and determine the former. This influence of the sensations affords the possibility of a constant correction of the judgments that are being produced by the association of ideas. Incorrect judgments are suppressed in the very act of formation. Thus both fantasy and judgment are under the control of the external world, and may never become too contradictory to it. We com- mit "errors " of judgment, in fact, because our sensations them- selves do not always correspond exactly to the external excitants, and particularly because the chief law of the association of ideas, the law of simultaneousness, obviously permits or even causes at times quite illogical conclusions and unwarrantable generaliza- tions; 1 but such errors become neither delusive nor compulsory ideas. In general the parallelism of the associations of judgment and the series of external excitants or processes of the external world remains comparatively intact In invalids who are suffering from delusions or compulsory ideas the regulative influence of the sensations or of the external stimuli upon ideation has either been removed or has lost the persistency of its action. Hence the association of ideas produces judgments that are completely contradictory to the processes of the external world. In fact, in the case of these invalids the process is reversed ; the association of ideas influences the sensations. The latter are interpreted so as to harmonize with the existing insane ideas and remodelled accordingly ; a further stage brings illusions and hallucinations. It is not mere chance that illusions and hallucinations so very frequently accompany delusive or insane ideas. All three are symptoms that the ideational life has been wrested from the control of the sentient life. Delusive and compulsory ideas are only distinguished from each other as regards their origin. In the latter case correct judgments are still made as well as incorrect, 1 Munsterberg is right in declaring that the errors of judgment can be far more easily explained psychologically than its constant correctness. 236 Introduction to Physiological Psychology. and greatly exceed the latter in numbers, while in the former case, on the contrary, correct judgments are not formed at all, or at most only in very limited numbers. We must now content ourselves with these few hints con- cerning the theory of morbid disturbances in mental activity, and pass on to the psychological presentation of a condition that has often been directly compared, though of course without sufficient grounds, to the morbid mental conditions, viz. the condition of sleep with its dreams. We do not yet know with certainty what the physiological basis of sleep is, whether merely a chemical exhaustion of the cerebral cortex, or a universal or partial change in the circulation of the blood. 1 Psychologically, sleep appears to be a more or less complete removal of all psychical processes. One might designate this condition, if so desired, as uncon- sciousness. The Ec's of the cerebral cortex remain too weak to produce a concomitant psychical process or sensation, and the EPs are not aroused from their state of latency. Psychical processes appear in but one form during sleep, — in the form of dreams. The study of dreams is extraordinarily interesting, and urgently to be recommended as a subject for introspection. The results of our self-observations will only be exact, however, if we follow the example of Lazarus by laying paper and pencil beside us before falling asleep, so that, as soon as we waken in conse- quence of a dream, its contents can be written down at once. If we wait longer, till morning perhaps, the greater part of it will have vanished from memory. An accurate analysis of the process of dreaming shows that its elements are imaginative ideas (in the sense which we have already discussed above), but that these ideas are also often equipped with almost as great a sensual vicacity as the sensations themselves. On this account they may be regarded as peculiar somnial hallucinations that appear in longer successive series, but that are generally even more closely connected with one another than the hallucinations experienced 1 More recent investigations seem to indicate at least a partial aiiamia of the cerebral cortex. Morbid Thought — Sleep — Hypnotism. 237 when awake by those who are mentally deranged. It can be shown that in very many cases, at least, the somnial phantasms are more or less due to peripheral stimulation. For example, a severe neuralgia not infrequently causes the somnial sensation of a dagger-thrust in the neuralgic part of the body ; with this sensation the image of the murderer and his threatening words are then associated, appearing with all the vivacity of hallucina- tions. At first, therefore, an illusion, and not a hallucination, appears ; the hallucinations are only secondarily associated with the illusions. Generally those mental images are reproduced as somnial hallucinations, that participated in the association of ideas not directly, but some hours before falling asleep. This is not unexceptionably the case, however. It is often very striking that the somnial visions are colourless, although of course the most vivid colours occasionally appear. Above all, the almost complete absence of motor reactions is also characteristic of somnial phenomena. The muscular system seems to be lamed ; even in the deepest sleep the phenomena accompanying the activity of the tendons, otherwise so accurate an index of the existing muscular tone, have disappeared. We have, indeed, motor ideas ; in our dreams we believe that we are walking or fighting, and yet we scarcely move. It is only in the most vivid dreams that either men or animals (especially the hunting dog, for example) give a weak expression to the somnial ideas of motion by a few slight movements of the trunk and extremities. 1 In sleep, therefore, (1) the initial element of the psychical pro- cess, the sensation, is produced by ideational stimulation, and (2) the final element, the motor idea or the action, is almost entirely omitted. One characteristic of the dream, its speedy disappearance from memory, deserves an especial discussion. As a rule the repro- 1 It is of interest in this connection that Laura Bridgman, who was born blind and deaf, is said to have gesticulated with her fingers during sleep a great deal. In this case intensified motor ideas to a certain extent compensate for the absence of visual and acoustic ideas. 238 Introduction to Physiological Psychology. duction of even a vivid dream is no longer possible with any degree of completeness five minutes after one has wakened. But we are also unable to reproduce a long series of sensations or ideas that have been experienced in waking moments entirely without omission. Let us remember that the association of two ideas which have no other connection than that of mere suc- cession in time is very loose ; on this account we reduced the association of ideas by succession, in so far as the latter is not quite direct, to the association of simultaneous ideas. Such associations as the latter are never entirely wanting. Hence we are able to reproduce even the long series of our experiences that we have when awake, passably well. In so doing we are also aided especially by the vivacity which the images, left in the memory by the successive sensations, possess in different degrees and by the complete and close relation existing among the successive sensations or ideas. The series of somnial sensations or ideas offer much less favourable relations for reproduction. The sensations in dreaming are always less intense and much more disconnected ; they are characterized by many abrupt transitions. The separate successive ideas are but rarely com- bined into conceptions, and conceptions of relation are rarely introduced. Finally a sudden awakening produces abrupt changes in the circulation of the blood which are followed by immediate and important changes in nervous excitability that are probably not the same for all parts of the cerebral cortex ; numberless stimuli act at once upon all the sensory organs, and produce an equal number of sensations. By this means that which we designated as the grouping of latent ideas is wholly changed ; the new grouping is in all respects unfavourable to the mental images that have been deposited by the somnial sensations. This explains the difficult reproduction of the images of a dream, or, as it may also be expressed, the amnesia of somnial processes. However, the nature of the dream-images is by no means less psychical than the series of sensations and ideas that are ex- perienced when one is awake. If we have entirely or almost Morbid Thought — Sleep — Hypnotism. 239 entirely forgotten a small occurrence that happened while we were awake a short time ago, we are not on that account justified in concluding, however, that we had no proper psychical process, and were hence unconscious. The same is true in the case of dreams. The fact that we have forgotten them is not sufficient ground for the conclusion that during the dreams we were not fully conscious or that we were unconscious. 1 The psychical phenomena of the dreams and the conscious life of waking hours are different, but the two do not have a different psychical value. A removal of psychical processes, i.e. unconsciousness, occurs only in the case of sleep without dreams, which is comparatively rare. Besides sleep there is still another series of different alterations in the psychical life, all of which are characterized by a greater or less derangement of the conditions attending normal excita- bility of the cortex, and by a consequent more or less complete amnesia. To these belong particularly the dazed or stupefied conditions of many epileptics, in which they perform the most complicated actions, or sometimes even commit crimes, that they are afterwards totally unable to recollect. 2 In very rare cases it sometimes happens that both phases of psychical life, with their different groupings of latent images of memory, alternate; each phase is characterized by amnesia of the preceding unlike phases but by recollection of all former like phases. This morbid phe- nomenon has received the very unsuitable designation of double consciousness." 3 Hypnotism is another phenomenon that claims especial interest. Under this term we shall comprehend all those data that remain after a thorough critical elimination of the phenomena of animal 1 The use of the word " unconsciousness " also in forensic psychiatry, and especially the conclusion that there must have been zmconsciousness because ■ there was amnesia, are thus placed in a very unfavourable light. 2 Compare Samt, Arch. f. Psychiatrie, Bd. 5 and 6, and also the manuals of psychiatry by Griesinger, Krafft-Ebing, and Schule. 3 Compare EMMINGHAUS, " Allgemeine Psychopathologie." Ribot, " Les maladies de la personnalite," etc. 240 Introduction to Physiological Psychology. magnetism, mesmerism, etc., and that have now become an object of exact scientific investigation. Hypnotism depends chiefly on the fundamental fact that certain individuals may be placed in a remarkably changed psychical condition. This condition is itself designated as Hypnotism. It is produced either by requiring the person that is to be hypnotized to gaze at a glittering object and then by gently stroking his forehead, or by constantly telling the subject, "you must sleep, you shall sleep." The first-named method we designate as the physical method ; the second method is commonly known as "suggestion." Both methods can be still further modified in various ways. In general " suggestion " is the more effective. Bernheim has recently attempted to re- duce all hypnotism to " suggestion," and to this end has sought to show that a hidden indirect suggestion of sleep is always con- tained in the acts of fixedly gazing at an object or stroking the forehead. Success is most rapid when one makes use of both methods, the stroking of the brow and the suggestion of sleep. But the essential peculiarity of the hypnotic condition, without regard to the manner in which it is produced, in fact, probably the only peculiarity common to all hypnotic conditions, is the power of suggestion. We may command the hypnotized person to perform any actions we please ; he performs them like an automaton. We may suggest any sensations whatever to him and he has them at once, just as vivid and realistical as if they were hallucinations. If we tell him that his left arm is insensible to pain, he does not feel or notice the severest thrust of a needle into that arm. We may suggest any idea to him that pleases us, for example, the delusion that he is king ; the subject conducts himself at once as a king. If we fold his hands as if in prayer, these passive motor sensations at once produce the hallucination of a church, a priest, etc. In short, the person who is hypnotiz- ing excites in the brain of the hypnotized individual, either by speaking to him or in some other manner, any idea that he de- sires, and the idea thus aroused at once assumes sway over the association of ideas. All contrary ideas and even the sensations that are actually present are suppressed, and the ruling idea Morbid Thouglit — Sleep — Hypnotism. 241 almost alone determines the course of association, while, at the same time, the mental images reproduced acquire a sensual vivacity amounting to hallucination. If the delusive idea of being king is suggested, the hypnotized patient forgets his real title and beholds himself clad in the coronal robes instead of in his own simple garments. It is obvious that this condition in which the subject can be swayed by the power of suggestion, presents a peculiar change in the cortical conditions of nervous excitability, This change is manifest chiefly in the disarrange- ment of the grouping of ideas, in the alteration of the intensity of latent mental images, and in the abnormal receptivity of the sensation-cells for stimuli imparted by the memory-cells. It is impossible here to give even an approximate idea of all the num- berless variations of the hypnotic condition. 1 In what manner the above-mentioned methods produce this condition is as yet entirely unknown. 2 The hypnotic condition is followed by a more or less complete amnesia of all its processes. Of course, when the amnesia is complete, it is still a matter of doubt (as also in the case of the total amnesia of acts that occur during the stupefied condition of epileptics), whether despite their compli- cateness, all the acts of the hypnotized individual are not motions accomplished without any concomitant psychical process. Since the person who has been the subject of experiments is unable to give any account whatever of possible conscious processes during the hypnotic state, the criterion which we formerly employed in distinguishing between voluntary actions and automatic actions now leaves us in the lurch. We cannot decide with certainty whether actual, i.e. psychical or conscious images of memory have 1 A good introduction to the subject of Hypnotism is given in the two articles upon hypnotism by Preyer and Binswanger in the Eulenburg " Realencyklopadie der medicinischen Wissenschaften." Max Dessoir (Ber- lin, 1889), has furnished a very complete summary of the entire literature upon the subject of hypnotism. 2 Perhaps a dim light is thrown upon the subject of the production and nature of the hypnotic condition by the experiments of Bubnoff and Heidenhain ; Pfluger's Archiv, Bd. 26. R 242 Introduction to Physiological Psychology. accompanied the psychical acts or not. It is sufficient here to state the problem ; in the closing chapter we shall meet it again in a general form and attempt to solve it. At all events the amnesia as such cannot be cited as an argument either for or against the existence of concomitant psychical processes during the hypnotic state. 1 It is equally probable that the sudden change in the cortical excitations, as soon as normal conscious- ness returns, renders the association of the ideas experienced in the normally conscious condition, with those of the hypnotic con- dition impossible, or that both ideas and sensations are entirely absent in the latter state. We are now familiar with the most essential deviations from the normal association of ideas, and can therefore turn to the final element of the psychical process, action, in the following chapter. 1 Even the recollection of the hypnotic psychical processes would not necessarily argue in favour of their existence during the hypnotic state. Let us call to mind a former example, — that in which we pass a friend without noticing him ; it only occurs to us subsequently that we have seen him. For obvious reasons, however, this subsequent appearance of the psychical process is only possible within a very short interval of time after the appearance of the stimulus- CHAPTER XIII. ACTION ! — EXPRESSIVE MOTIONS — SPEECH. The psychical process began with the sensation. The associa- tion of ideas, i.e. a series of successive ideas, followed the sensa- tion. The result of this association of ideas may be a motion, and such a motion we call " action." The association of ideas immediately preceding an action we generally prefer to designate specifically as the " play of motives." Let us begin by asking, How has this new element, the motion or the motor innervation, been added to the sentient and ideational life ? How has man acquired his motions — motions that are, in fact, advantageous, that in general correspond with remarkable accuracy to his ideas, and show the highest degree of fitness ? That much neglected department of psychology which seeks to establish some theory as to the evolution of the child's soul, is alone able to assist us in obtaining the correct answer. The new-born child, the same as the new-born animal, at first executes very few, if any, movements that could be designated as voluntary motions or actions. It performs only reflex or auto- matic acts, although part of these are already extraordinarily com- plex. This statement agrees well with the fact of physiology and anatomy, that the nerve-fibres leading from the thalamus opticus to the periphery are already fully developed in the new-born child, 1 By "action" the author signifies that which has generally been termed "voluntary action." The latter expression in the present work is only ac- ceptible when understood in the sense of "conscious" or "desired action as the result of ideation," not " willed action," See pages 25-29, 247 and 265-269.-7^. 343 244 Introduction to Physiological Psychology. i.e. in particular, they are already encased in medullary sheaths ; while the large nerve-path, which extends from the so-called motor region of the cerebral cortex to the anterior horns of the spinal cord and thence to the different parts of the muscular system, and which, as has been demonstrated, conducts the in- nervating excitations to the muscles in the case of voluntary acts, 1 has not yet been provided with medullary sheaths. It also agrees with the further fact that electric stimulation of a definite part of the motor region in the adult cortex always produces movements of the opposite arm, stimulation of still another part movements of the opposite leg, and stimulation of a third part motions of the opposite facial muscles ; but that electric stimulation of all these parts of the motor region, in the case of the new-born animal, produce no results whatever. From all these facts we must con- clude that during the first months of its life the child gradually learns to make use of voluntary motions, or, as it may be more correctly expressed, of motions that are conditioned by psychical activity. We shall now inquire into the particulars of trie process by which these actions are acquired. From the moment of birth the brain of the new-born animal, at first only capable of impart- ing "infracortical" reflex and automatic motions, is thronged with numberless sensations, produced by the numerous stimuli that stream in through all the sensory avenues. These sensations leave in the cerebral cortex (particularly in its sensory regions) 2 mental images which correspond to the material processes of excitation. At once the association of ideas begins. The sensory excitation is propagated along the paths of association and every- where reproduces images of memory in the cerebral cortex. The material excitation thus propagated in the cerebral cortex also 1 This is shown simply by the fact that if this path is broken at any point by disease all voluntary motions of the corresponding half of the body are no longer possible. 2 In this connection it is not necessary to take into consideration the state- ment of many authorities on the physiology of the brain, that the size of the cortical centre for dermal sensations, the so-called " centre of feeling," cor- responds to the size of the motory region. Action — Expressive Motions — Speech. 245 reaches the motor region by means of associative paths and is discharged toward the periphery along the great motor path, the so-called pyramidal tract. At first this motor " discharge " is quite irregular. Certain paths of association, however, will have inherited specific capacities for conduction, which render them better prepared than others to receive certain specific stimuli. On this account the excitation will be directed along these paths from the beginning. These statements explain the fact that the chick, which has just been hatched, is able to pick up corn at once, 1 It is not necessary in this case, however, to assume that the chicken has inherited ideas of the kernels of corn ; on the contrary, it is sufficient to suppose that at birth it already possesses an inherited associative path which is especially fitted for con- duction between the visual centre and that part of the motor region from which the innervation is discharged to those groups of muscles active in the motions of picking up food. But apart from such dispositions as these, which the child possesses from birth, its first movements are in general fitting. The selection of fitting motions is only accomplished gradually and by practice ; it acquires these motions in very much the same way that the adult, later in life, acquires a new motion or a series of motions, as those necessary in playing of a selection on the piano, for example. The extraordinary rapidity with which a child learns to execute so many and so complicated motions is to be explained simply by the inheritance of a favourable disposition in the associative mechanism. The exercise of this mechanism consists in the constant repetition of motor discharges until the irritant is removed. The child continues to reach after an object that acts as an irritant upon his sense of sight, until, after numerous un- suitable motor discharges, the fitting motion is at length hit upon. As soon as the object is seized the stimulation disappears and the motions just previously executed in trying to grasp the object cease. More correctly stated, the stimulation changes as soon as the object is seized, its position changed and the consequent 1 Not excluding the possibility of an automatic act in this case, however. 246 Introduction to Physiological Psychology. sensations of touch appear; then the child is at once occupied in attempting to execute new motions that have different ends in view. In this manner a gradual process of selection, that is in fact astounding, produces the thorough fitness of our so-called voluntary motions. They are gradually adapted with extraor- dinary exactness to the stimuli of the external world, or — which is the same thing — to the sensations. In the meantime, however, another still higher stage of perfection is gradually effected in the cortical motor apparatus. The motor discharge that has just been described, is at first accomplished entirely without a con- comitant psychical process. It is true that sensations and ideas may precede the motor discharge, but primarily they contain no element that is concerned in the resulting motion. It is only after the motion has taken place that the child acquires any knowledge of its own motor act. This knowledge is acquired by means of the sensations of active motion that we have already described in full. The active motions stimulate the neryes of the joints, tendons, ligaments, and skin, and the complex sensation thus produced we briefly designate as a motor sensation. Also the visual sensation, by which we are made aware that the position of the limbs has been changed by the active motion, blends with the motor sensation ; by the latter term we shall hereafter desig- nate a complex sensation which includes both the sensation of sight and the feeling of motion. Therefore the sensation of motion, which informs us that a series of ideas has resulted in a definite motion, directly follows the ideas immediately preceding it without the aid of any intervening element. An idea is now deposited by this motor sensation, just as mental images or ideas are deposited by all sensations. Hence we have also designated the image of a motor sensation in memory as a motor idea. Like all other ideas, these ideas of motion also participate henceforth in the association of ideas ; like all other ideas, they also acquire the ability to produce motor discharges. At first only the visual sensation and idea, or the tactual sensation and idea of an object produce the motion which is executed in grasping it. After the motion of grasping has frequently taken place the motor idea of Action — Expressive Motions — Speech. 247 grasping the object is itself able to impart the motion. The complete associative connection that exists between the initial elements of the voluntary motor path and all cortical elements, is of just as much advantage to the motor ideas as to the ideas pro- duced by any one of the senses ; in other words, an especially intimate associative connection is established between the motor ideas and the excitations in the initial cells of the motor path. In fact, every single movement produces a synchronous association between the ideas and the excitations in the motor path, thus specifically training the associative path for conduction. Hence the motor ideas that were entirely secondary products, and that were only associated with the motor elements secondarily, finally acquire an almost complete sway over these motor elements. Later, when a series of ideas, T lt I 2 , I 3 . . composed of ideas of sight, hearing, and touch, appears, they generally do not directly impart the motor innervation ; on the contrary, the asso- ciation of ideas first produces the appropriate motor idea, and only the latter causes the motor innervation. Recently Miinster- berg 1 has justly called attention to the fact, that it is this pre- cedence of the motor idea, indeed, which causes the motion to seem voluntary. " We will execute a certain motion " properly signifies, " we are conscious of the idea of the motion," or, " of the motor idea." The feeling which leads us to suppose that we are exercising a will-power is strengthened by the simultaneous innervation of certain muscles of the body, the musculus frontalis for example. This muscular innervation accompanies the volun- tary movements the same as every effort of attention, and gives rise to peculiar concomitant kinaesthetic 2 sensations. The results of modern investigations in the field of cerebral physiology also harmonize well with the above presentation of the subject. The so-called motor-zone of the dog, that region of 1 The above presentation of this subject agrees with Munsterberg's writ- ing, "Die Willenshandlung " (Freiburg, 1888) in the most essential points, although it deviates from it in some of the less essential particulars. 2 Motor sensations in the restricted sense. •c .... 248 Introduction to Physiological Psychology. the cerebral cortex which produces contractions of the muscular system when electrically irritated, contains the primary elements of the motor path. In the dog the motor sensations and the motor ideas also appear to be located in this same region. At least this conclusion may be drawn from the experiments made by Munk ; according to these experiments, the extirpation of the motor region from one hemisphere removes all ideas of move- ments performed by the opposite half of the body. In fact, ac- cording to Munk, both sensations and ideas of active and passive- touch and of position, in the case of the dog and ape are de- posited in this same region. If the motor region governing the muscles of the dog's fore leg be extirpated from the left hemi- sphere, the right fore leg may be placed in the most uncomfortable position, and the animal makes no attempt to correct it. In descending a flight of stairs it misses the steps and frequently slips with the right fore foot. If it was trained to offer the right fore paw in response to one definite signal and the left in response to another, the latter is offered as before, but not the former. The dog that has thus undergone vivisection only reaches for a piece of meat with the left foot, never with the right foot, the cortical centre of which has now been extirpated. We see, there- fore, that in these animals the different ideas of position, touch and motion are located in one and the same cortical region. In the case of man a greater local separation of these functions seems to have been effected. We should also consider that the motor idea is complex and that it contains a visual element besides the tactual. From the facts that we have thus far presented, it is at least obvious that the material process which takes place in the large initial cells of the motor path during innervation, occurs without a concomitant psychical process ; psychical processes only accompany those physical processes that correspond to the antecedent motive sensations and ideas and to the motor idea following these and immediately preceding the motor innerva- tion. Only sensation and idea are psychical processes ; the motion or motor innervation has no psychical concomitant and is onl/,'the effect of a psychical process. Action — Expressive Motions — Speech. 249 Of course a great deal of interest centres in the question as to how great the velocity of the nerve-process is in certain simple cases of action. We remember that, in connection with our ex- periments for determining the velocity of the association of ideas, and in anticipation of future investigations, we have already em- phasized the importance of exhaustive researches in this sphere. In fact a large number of experimental works upon this subject have appeared, the majority of which are productions of the Wundt school. We shall here present the results of these investi- gations briefly, although the interpretation of the numbers given by the Wundt school will have to be greatly modified of course in order to harmonize with our standpoint. When a very simple sensation imparted by a momentary excitant, produces a movement that is as simple as possible — a movement of the hand for example — we have the simplest case of action. In accordance with the precedence of Exner and Wundt, we designate the time that elapses between the stimula- tion and the resulting motion as the simple reaction-time. 1 It is of course very important that this simple reaction-time should also be determined when the person who is being tested does not know beforehand what stimulus will probably act upon him and when he has not been previously told to react with a certain movement. However such an arrangement of the experiments, especially as regards the second point, is obviously difficult to attain. On the contrary, the experiment is generally so arranged that the person who is being tested knows beforehand the stimulus which he has to expect and a definite movement which has been previously determined. The experiment is further ar- ranged so that both the moment in which the stimulus takes effect, and the moment in which the reactionary movement is executed, are registered upon a rotating drum. We cannot here enter into a description of the numerous apparatus that have been applied in ascertaining the reaction-time ; it is sufficient to name 1 In accordance with our nomenclature, we should prefer the designation "simple action-time." (Also called " physiological time." — T's.) 250 Introduction to Physiological Psychology. simply Hipp's chronoscope and Wundt's chronograph. 1 The reaction-time is generally stated in thousandths of a second (a). These experiments for measuring the reaction-time very soon showed that the latter varies considerably, according to whether the tested person directs his attention to the expected sense-im- pression or to the hand which is to perform a certain movement. In the first case we speak of a sensorial reaction, in the latter case of a muscular reaction. The muscular reaction is always con- siderably quicker than the sensorial, the difference being 2 about yV second or 100 o\ The muscular reaction is therefore designated also as the shortened, and the sensorial as the complete reaction- time. According to the experiments of Ludwig Lange, the simple reaction-time in the case of stimulation by light, electricity and sound, amounts, in round numbers, as follows : — Stimuli of — For sensorial reaction. For muscular reaction. Light Electricity (on the skin) Sound 2900- 2I0(T 2300- 1700- IOC<7 I20CT The most noticeable fact, at all events, in the above table is that the reaction upon impressions of light is considerably slower than in the other two cases. Individual differences are strikingly slight as soon as each person tested complies with the proper conditions, and turns his attention either exclusively to the sense- impression or exclusively to the movement. The reactions of one who undertakes to become the subject of experiments for the first time without preparation, are at first half muscular and half sensory, the attention is divided and fluctuates between the ex- pected sense-impression and the movement agreed upon. On this account the reaction-time in this case varies greatly also ac- cording to the point toward which the attention is chiefly 1 Compare Ludw. Lange, Philosoph. Stud., Bd. 4, S. 457. 2 Wundt, "Physiol. Psychol.," Bd. 2, S. 267; L. Lange, Philos. Stud., Bd. 4, S. 479. Action — Expressive Motions — Speech. 251 directed. In registering the time of astronomical phenomena, this vacillation of the reactions has been found to affect the accuracy of observations. A slight difference in the time of registration appears when two observers view the same pheno- menon ; it is in this case necessary to make use of especial so- called " personal equations *' for the purpose of eliminating the error. Only a few trustworthy series of experiments have been made with the other qualities of sensation. The statement made by v. Vintschgau and Honigschmied is very interesting ; accord- ing to this, the time of reaction is greater when the tip of the tongue is stimulated with quinine than when stimulated with sugar, while the relation between the two reaction-times is re- versed when the back part of the tongue is tested. This recalls the fact already mentioned, that the nerve-fibres which impart the sensation of sweet are located chiefly in the anterior third of the tongue, and those that impart the sensation of bitter, chiefly in the two posterior thirds of the tongue. There are as yet no con- cordant experimental results in the case of olfactory irritants. v. Vintschgau * and Steinach have determined the reaction-times in the case of mechanical and thermic stimulation of the skin. For pressure the reaction-time amounts to about 120-1500-. When the stimuli are applied to one and the same region on the skin, the reaction-time in the case of heat-stimulation is longer than in the case of stimulation by cold, and the reaction-time in the latter case is longer than for stimulation by pressure. The reactions appear more quickly when stimulation by heat or cold is applied to the right half of the face than when applied to the left half. The fact that individual differences are very consider- able, as mentioned above, is of great interest. Now what do these numbers signify ? It is obvious that the action-time as just determined is occupied by three processes : (1) the centrifugal conduction of the stimulation from the peripheral sensor}' organ to the centre of sensation in the cerebral cortex, (2) the intercentral process of association which takes place within the 1 Pfluger's Arch., Bd. 43. 252 Introduction to Physiological Psychology. cortical elements, (3) the centrifugal conduction from the motor region of the cortex to the muscle. We shall disregard any possible periods of latency or inhibition at present, for the sake of simplify- ing our investigations. Only the second of these three processes is accompanied by a concomitant psychical process. Since the dura- tion of the first and third are known to us through physiology;, at least approximately, the duration of the second process may also be computed with comparative accuracy. Thus, for example, in the case of electric stimulation of the skin, some 60-800- of the 2100- complete reaction-time, may be calculated for the sensory and motory conduction, leaving only about 0T-0T5 sec. for the psycho-physical process of association. In the case of muscular reaction a still smaller fractional part of a second remains. This last statement harmonizes well with the fact that reactions often go astray in the latter case ; the tested person often executes the movement agreed on before the stimulus has taken effect at all. Now in what particulars are the two forms of reaction to be dis- tinguished from each other ? It is obvious that the direction of the attention to the expected sense-impression means nothing else than that, before the sensation appears, ideas which bear some relation to the impression, are already present in the mind of the person upon whom the experiment is being made. Among these ideas is especially the mental image of the expected sense-impres- sion, which is already familiar from the fact that its effects have been previously experienced. This psychical state is very closely connected with a corresponding physical phenomenon, the inner- vation of the muscles of accommodation governing the respective organ of sense, particularly of the musculus ciliaris and the tensor tympani. These phenomena are changed in the case of muscular reaction. Here the attention is directed to the motion that is to be executed, — in other words the motor idea, specifically the idea of the movement of the hand agreed on, occupies the mind of the person who is being tested at the time the sense-impression appears. This psychical state generally manifests itself in a slight, constant, tonic contraction of the muscles of the hand and arm Action — Expressive Motions — Speech. 253 which is present long before the reaction takes place. Hence the difference between the two reaction-times is very satisfactorily- explained. The predominant mental image of the stimulus, in the case of sensorial reaction, acts almost as a direct check. The especial reproduction of this image is not at all necessary in the entire process of association, — in other words, an especial recog- nition of the excitant is superfluous. Therefore, while the tension of the muscles of accommodation in sensorial reaction can, in fact, generally facilitate the process of reaction, the image of memory which is present in consciousness at the same time com- pels the association to take an indirect course, as it were, or to introduce a superfluous, intercedent act of recognition. In the case of muscular reaction the reception of the stimulus is neither facilitated nor delayed ; but by means of the dominant motor idea the intercentral paths of conduction, the motor centre, the motor paths of conduction, and finally even the muscular system are to a certain extent adjusted and prepared for the coming stimula- tion. The stimulus only needs to barely tilt the full vessel, as it were. The excitability of the paths of conduction is heightened by the idea of motion. This very favourable disposition of motor elements explains the remarkable abbreviation of the process which characterizes muscular reaction. x Muscular reaction is very apt to become an automatic action, that is, a reaction in the proper sense ; after some practice the concomitant psychical process is easily omitted and the movement of the hand is mechanically executed. This is much more seldom the case with sensorial reaction. This fact is easily explained by what has been stated above ; in the case of purely muscular action the psychical act is to be regarded as of minimum duration, since the innervation, as such, has no psychical correlate what- ever. In muscular reaction also the sensation exerts a much less essential influence ; it merely imparts the reaction. Many psycho- logists assume that in such cases, where the voluntary action be- 1 There are no sufficient grounds whatever for the subcortical or cerebella localization of muscular reaction assumed by Lange. 254 Introduction to Physiological Psychology. comes automatic by practice and the psychical process is at the same time lost, the material process of excitation gradually takes another shorter path. They imagine that the intermediate cortical centre is entirely omitted from the process, and that the trans- mission of the excitation from one sensory centre to another motor centre is accomplished below the cortex. This assumption unavoidably leads to contradictions. In those cases where the psychical acts become automatic, the path leading across the cortex is more and more thoroughly trained in consequence of constant practice ; now the same thing occurs that we have already met in the case of the association of ideas, — intercedent ideas are omitted in proportion as the process is more and more facilitated. If the process is constantly developed, one intercedent idea after another is omitted until the last one finally drops out. Thus, when a high degree of practice and facilitation has been attained, the entire psychical process is omitted, especially if at the same time the intensity of the initial sensation is reduced by other more intense sensations or ideas approximately to zero. The path of ex- citation in this case probably remains quite the same; it is simply more rapidly traversed. In this manner reactions and even reflex actions are developed from psychical acts. The above-mentioned psychical omission of a cortical centre as an element in the pro- duction of action is only accomplished phylogenetically. But let us return to our experiments for measuring the time of actions. Thus far we have only investigated the simplest form of action. We shall now consider some more complicated cases. We next require the person whom we are testing, to execute the con- certed movement of the hand only when he has expressly recognised the sensible stimulus, i.e. when a complete recognition has taken place. The reaction-time will, of course, be rendered consider- ably greater by this means. Apart from the special reproduction of the mental image, another process, a judgment, is generally introduced, for the person only reacts after having made the judg- ment " now I have recognised the light " or " the sound." We must observe, however, that no well-defined distinction exists be- tween this act of recognition and the simple sensorial reaction ; Action — Expressive Motions — Speech. 255 for (1) in the case of sensorial reaction in its most complete form, the appearance of the mental image and the introduction of a judgment similar to the one just mentioned, are hardly to be avoided ; (2) in the case of reaction after recognition the attention of the person who is being tested is generally directed chiefly to the expected sense-impression. As may be easily seen, those experiments employed to determine the reaction-time in the case of recognition are best in which there is a constant change of sense-impressions selected from a definite number. By this means the person who is the subject of the experiment is most easily compelled always to introduce the above-mentioned deliberation and recognition, instead of simply reacting. Thus the recog- nition-time becomes also the " discernment-time " or " distinction- time." A still further complication of the process may be presented by so arranging the experiment that upon one definite sense-impres- sion reaction always takes place with the middle finger, upon another always with the fore-finger. In this case a choice must be introduced in addition to the distinction or recognition ; accord- ingly the reaction-time becomes still greater and is designated as the "selection-time." For obvious reasons it is difficult to obtain either purely sensorial ox purely muscular reactions ; in experiments of this kind the mode of reaction is generally more or less mixed. Finally, if we introduce one or several more ideas, i.e. a complete association of ideas, between the sense-impression and the move- ment, we obtain an example of action in its most complex form and return once more to the problem of the velocity of associa- tion which we have already discussed in full. We shall purposely avoid stating more exact numbers for the so-called " complex reaction- times " just discussed, for the reason that the experi- mental investigations made by Cattell, 1 Friedrich, 2 Munsterberg, 3 1 " Psychometrische Untersuchungen," Philosoph. Stud., Bd. 3, S. 305 and 452, Bd. 5, S. 241, Bd. 2, S. 635. 2 " Zur Methodik der Apperceptions versuche, " Bd. 2, S. 66, and Bd. 1, S. 39. 3 " Beitrage zur experimentellen Psychologie," H. 1. 256 hitroduction to Physiological Psychology. and others in this field, despite their numerousness and the care that has been devoted to them, are not yet sufficiently concor- dant. On the other hand, we shall find still another question of interest. How does the simple process of reaction vary when the different psychical factors vary ? The most important fact bearing upon this question is that the reaction-time decreases as the intensity of the sensation increases. Furthermore, the reaction-time is always considerably lengthened by the simul- taneous presence of other sensations or ideas which, as it is ex- pressed, divert and distract the attention. Wundt has also established the interesting fact in particular, that the disturbing effect of synchronous sensations is greater when the stimuli are disparate than when they are of the same kind. Therefore if the subject of the experiment is to react upon a spark of light, a synchronous noise is more disturbing than a synchronous light. Finally, the state of feeling which is dominant in the subject at the moment of experimentation, is not without influence upon the reaction-time, as may be easily understood from former dis- cussions. By " state of feeling " we understand the resultant of the positive and negative emotional tones that appear at any definite time. The more the positive tone of feeling predominates in the state of feeling, the more rapidly, ceteris paribus, do all the reactions take place. Among other things this accounts in part for the abnormal acceleration of motor reactions, the so-called motor excitement, accompanying mania, which, as we have already mentioned, is characterized by the predominance of positive emotions. The reaction-time is also changed by the use of toxicants. For example, Kraepelin x found that certain drugs, such as nitrite of amyl, ether and chloroform, first increase and then shorten the reaction-time, while alcohol, on the contrary, first shortens and 1 Philosoph. Stud., Bd. I, S. 417 and 573 ; also recently a discourse before the Jahresversammlung des psychiatrischen Vereins, 1 889. Compare also Dietl and v. Vintschgau, Pfluger's Archiv, Bd. 16. Action — Expressive Motions — Speech. 257 then lengthens the reaction-time. In these experiments of course the difference between muscular and sensorial reaction has not yet been considered. Furthermore, in proportion as the doses of alcohol are increased, that phase of its effect which is char- acterized by an abbreviation of the reaction-time becomes less and less pronounced and noticeable. We shall now turn from these experiments for measuring the time required for the discharge of an action to the different forms of action that may be distinguished. Here it is psycho- logically most important to determine whether the initial sensa- tion, or the total content of the mental images participating in the play of motives, or the emotional tone of both sensations and ideas has had the predominant influence upon the character of the resulting motion. In the first case we speak of an "im- pulsive action " or an " action from impulse," 1 in the second of an "intellectual action " or an "act of calm deliberation," in the third case of an " emotional action." The movement of defence that one makes in response to the visual sensation of a threaten- ing blow is an impulsive action. The numberless actions that are daily and hourly performed for the satisfaction of some desire are emotional actions. Most deliberate actions are intellectual actions in the sense in which we understand them. This dis- tinction, however, is by no means always so sharp as may appear from the above statements. Most actions are affected by all three factors ; the impulsive acts are always more or less deter- mined also by some emotion. The voluntary motion in the narrower sense, i.e. that motion which is accompanied by the most deceptive feeling of free and voluntary choice, finds no especial place in this classification. We have already mentioned the characteristic features of this voluntary action. We may here add that in the most pronounced cases such action is always chiefly emotional ; in fact, the predominant factor is the positive 1 Wundt designates as impulsive actions those movements that are un- equivocally determined by a single motive. It is obvious that the two defini- tions only partially agree. S 258 Introduction to Physiological Psychology. tone of feeling accompanying the motor idea that precedes the motion. The impulsive act approaches most closely, of course, to the automatic act ; * the intellectual action is furthest removed from it. Of far greater importance than the classification just given is the distinction of a definite group of actions from another stand- point. This group is composed of the " motions of expression" or "expressive movements." All movements of expression are alike in being the motor discharge of a psychical process, but the chief effect of this motor discharge consists merely in betraying the psychical process to other individuals. Every other move- ment has some Other definite external effect, and only incident- ally and indirectly betrays the psychical state of the person who is acting. But on the contrary, in the case of motions of ex- pression, any further external effect is merely incidental. If we seize a glass of water, it is simply incidental that others perceive in this movement of the hand our intention to drink. On the other hand, if we laugh, the chief effect is the expression and ultimate betrayal of our state of feeling to others. We designate the grasping of the glass of water as an intended or voluntary- action, while many expressive motions, such as laughing, crying, etc., we generally designate as more or less involuntary. Finally, there is a series of expressive movements also that are produced by non-striated muscles, which, according to the common termin- ology, are never subject to the will at all ; among these are blushing, crying, the bristling of the hair, the ruffling of the feathers, and other movements affecting the various cuticular appendages, etc. These expressive movements of the face and of the dermal appendages do not of course exhaust the series of expressive motions. The gesticulations of the hand, the shrug- ging of the shoulders, the bowing of the head, the bending of the body, and others are all also to be regarded as expressive move- ments. 1 Meynert (" Psychiatrie," Wien, 1888) has attempted to demonstrate that all voluntary motions develop from automatic motions ; such a develop- ment in fact seems to be conceivable for many impulsive motions. Action — Expressive Motions — Speech. 259 The most important group of expressive movements is that which comprehends the movements of speech. As we know, these motions represent the sum of extraordinarily complicated, co-ordinated muscular movements of the lips, palate, tongue and larynx. While the expressive motions first mentioned — laughing, crying, etc. — generally express especial emotions, the movements of articulate speech become the expression of our sensations and their images of memory the ideas. The enormous number of actual sensations and ideas naturally requires a correspondingly large variety of articulative movements. Both speech and thought are the result of a parallel development ; each one is developed in and with the other. The importance of the articulative move- ments for the combination of component ideas into uniform con- ceptions we have already discussed in a former chapter. We shall now understand also why the expressive movements of speech have so great an influence in determining the higher development of man. This fact may be further shown in the anatomical structure of the surface of the brain. If we compare the brain of the ape with that of man, we find in the latter a complex con- volution on the back part of the lower frontal convolution, that is as entirely wanting in the brain of the ape as if it had been scooped out with a gouge. At this place, as science has known for fifty years, lies the cortical centre of articulate speech. If this so-called "convolution of Broca" is destroyed in the left hemisphere in consequence of having become the seat of disease, the invalid is still able to execute the grosser movements of the lips, tongue and larynx, but has lost the finer complex movements of these organs that are necessary for speech, and will never recover the control of them. The function of the corresponding place in the right hemisphere of the human cerebrum is not exactly known. It is probable that it is more or less concerned in the articulation of interjections, such as, " my God ! " "yes," and " no." x At the same time that the development of this 1 Compare Gowers, " Vorlesungen uber die Diagnostik der Gehirnkrank- heiten," Vorl. 9 and 10. 260 Introduction to Physiological Psychology. motor-centre of articulate speech is taking place an auditory word-centre, in which the mental images of words that we hear articulated are deposited, is developed in the auditory centre of the cerebrum in the temporo-sphenoidal lobe. If the so-called region of Wernicke in this centre be destroyed in the left tempo- ro-sphenoidal lobe, words are still heard, indeed, but not under- stood. Finally in the case of the civilized and cultivated man a new stage of expressive movements appears in the motions of writing to which the visual ideas of reading correspond in the sensory sphere. It is only possible here to cast a very hasty glance at these highly interesting relations of the cerebrum to speech ; the study of the respective writers on this subject is to be urgently recommended. 1 The development of expressive motions is a question of para- mount interest. Duchenne, the celebrated author of " Physiologie des mouvements" and "Mecanisme de la physiognomie humaine," still considers the expressive movements to be a gift with which God has especially endowed mankind. Either the divine wisdom or the divine fantasy, according to this conception, has arbitrarily designated this or that muscle as the means by which mankind is to give expression to a definite emotion. Darwin 1 was the first to open the way for a phylogenetic explanation of this subject. The expressive movements of man are also developed through thousands of years from the expressive movements that are found in the lower animals. It is very probable that almost all motions of expression have only developed secondarily from the common inexpressive psychical actions. Let us take a definite example : The facial expression of rage and hate in man is manifested chiefly in the retraction of the lips and the exposure 1 Wernicke, " Der aphasische Symptomencomplex," Breslau, 1874, and also especially the more recent compositions of the same author in Fried- lander's Fortschritten der Medicin, 1886. Further Grashey, Arch. f. Psychiatrie, 1885. Lichtheim, Deutsch. Arch. f. klin. Med., Bd. 36. 2 "The Expression of the Emotions in Man and the Lower Animals." 9th Edition, 1876. Action — Expressive Motions — Speech. 261 of the teeth j particularly the corners of the upper lip are elevated so that the canine teeth become visible. This move- ment is undoubtedly inherited from the lower animals. In quite the same way the dog, cat and ape expose the canine teeth in the presence of a foe whom they intend to attack, or by whom they expect to be attacked. Originally this movement is not an act expressive of passion in these animals at all ; on the contrary, it is a highly fitting preparation for the impending battle. Be- cause of its fitness, this motor discharge, produced by the unpleasant sensation of seeing a foe, has been fostered by a process of selection until it has become a universal phenomenon in this series of animals. In the case of man the original advantage accompanying the movement has disappeared, since, in fact, the teeth rarely serve mankind as a weapon in battle at the present day; but the movement has been retained as the expression of the specific painful emotion which accompanies the seeing of a foe. But still further, other sensations that resemble the visual sensation of a foe as to their tone of feeling, or that are associated with the idea of a foe, also impart this same movement of expression. This is true also in the case of the lower animals very often when the possibility of battle and of using the teeth is entirely excluded. A passionate person also often shows his teeth when fortune has failed to fulfil some desire. We should also mention that in the large majority of cases, in fact, these expressive motions lose their original and immediate advantage (defence, etc.), but at the same time gradually gain another just as great advantage. The young animals' cries of distress call the mother to their side ; the adult animal's cry of rage terrifies the intruder. In by far the greater number of cases it is useful to animals thus to become cognisant of one another's passions. In man the development of these expressive movements reaches its highest stage. Since language has a special word, i.e. a special expressive movement executed by the muscles of the larynx and mouth, for each sensation and each idea, and not alone for the emotions, as is the case with the expressive movements of the lower animals, social community 262 Introduction to Physiological Psychology. and culture are possible, and man gains an immeasurable advan- tage in the struggle for existence. It is still very uncertain from what special expressive move- ments language or speech has developed. It is by no means a human invention, as has been recently asserted, that has come into use in consequence of a universal agreement. On the other hand, the construction of words appears to have taken place chiefly in two ways : (1) by development from the animal's cry, (2) by so-called onomatopoeic development. The animal's cry already expresses manifold psychical states, although they are chiefly of an emotional nature. As the enticing call of the male, it expresses sexual feelings ; as the cry of distress, it expresses the fear of impending danger ; as the cry of rage, it expresses hate, etc. Particularly the suddenly appearing visual stimuli (a passing animal in flight, lightning, etc.) impart a cry that ap- proaches very closely to the nature of reflex action. By the process of selection these cries become differentiated more and more, in the manner that we have so often noted, until finally they become the colossal treasure of words that constitute a language. Onomatopoeia has exerted a more secondary modify- ing influence upon language. It is especially 1 important in the case of acoustic stimuli. A sound that is often heard in nature, is imitated ; in other words, the motor discharge which is imparted by the acoustic sensation of a roll of thunder, for example, is gradually modified until the movements of the organ of speech finally produce a sound resembling thunder. We are as yet far from having arrived at an understanding of this imitative impulse from the standpoint of the Darwinian theory, but its importance in the development of language is not to be doubted. That many individuals are able to understand a large number of words thus developed may be easily explained in both cases by laws of association with which we are already familiar. Let us con- sider that both the reflex cry and the onomatopcetic imitation, 1 But not exclusively; compare Lazarus, " Leben der Seele." Steinthal, Abriss der Sprachwissenscliaft." Action — Expressive Motions — Speech, 263 in the case of one and the same sensation, would necessarily result the same, in different, but similarly constructed individuals. The great influence which heredity exerts upon the movements of expression is most forcibly revealed by the fact that persons who are born blind and deaf (as Laura Bridgman for example) express their joyful emotions by the typical form of laughter. In the development of the normal child, most of the expressive motions only appear comparatively late ; for example, weeping seldom appears before the third month after birth. 1 It is very interesting to note that in almost all the races of mankind the mimic motions expressing feeling are very nearly identical. As regards the movements of expression in speech, we know that comparative philology has already established very great analogies between the different languages. We have already mentioned above that the lower animals also exhibit numerous expressive movements that resemble those of man in a high degree. Another very interesting part of this subject is the anatomical localization of the nerve-paths and nerve-centres for motions of expression. As we have already heard, the centre for the most complicated expressive movements, those of speech, is un- doubtedly located in the cortex. The path that conducts the motor impulse of speech from the cortex to the muscles of articu- lation appears to be contained chiefly in the pyramidal tract ; no interruption of this path whatever takes place in the large ganglia. This is different in the case of the mimic movements of expres- sion. Their centre is probably located in the Thalamus opticus. After the entire cortex of the cerebrum has been removed from a rabbit, it still performs its characteristic movements of expres- sion — the bobbing of the tail for example. 2 According to the more recent clinical observations of Nothnagel's, 3 the Thalamus 1 Compare Preyer, " Seele des Kindes." Binswanger has observed laughing already in the 15th week after birth; smiling appears in the 7th and 1 Oth weeks. 2 Bechterew, Virch. Arch., Bd. 101. Ziehen, Arch. f. Psych., XX. 3 NOTHNAGEL, Zeitschr. f. klin. Med., 18S9, Bd. 16, H. 5 and 6. 264 Introduction to Physiological Psychology. opticus seems to be undoubtedly of great importance also in the case of the mimic expressive movements of man. This infra- cortical localization is also justified by the psychological fact that the mimic motions of expression — laughing, for example — are imparted by a psychical factor, indeed, but that they are very little subject to the process of association. In fact, we may say that they take place almost involuntarily. It is obvious, however, that there must be still another path to impart to the Thalamus opticus the cortical excitation which corresponds to the psychical state of the gay mood. Such internuncial fibres are, in fact, known to exist in large numbers between the Thalamus opticus and the cortex of the cerebrum. Finally, certain expressive movements, such as the bristling of the hair, blushing, 1 etc., probably have their centre in still deeper parts of the brain, particularly in the Medulla oblongata. This again harmonizes with the fact that these expressive movements also result from psychical causes, but are virtually not subject to the volition or, more properly, to the process of association at all \ they cannot even be voluntarily suppressed. We must now content ourselves with this hasty view of "actions." The task next awaits us of determining what place in our psychology shall be assigned to the so-called will. 1 In a certain sense, the peculiar changes of the pulse that accompany the emotions of excitement belong to this class of expressive movements. Com- pare Ziehen, " Sphygmograph. Untersuchungen," 1887. CHAPTER XIV. WILL — GENERAL CONCLUSIONS. We have traced the cortical excitations back to the numberless material stimuli of the external world ; in the psychical sphere the sensations correspond to the cortical excitations. We also followed the cortical excitation in the cerebrum by way of certain associative fibres to the motor centres. From these the excita- tion is again conducted toward the periphery to the muscular system, and imparts certain muscular contractions. Psychically the process of the association of ideas corresponds to the material process of nervous excitation that takes place in and across the cortex i to the resulting motion we gave the psychological desig- nation of " action." We were able to deduce action very satisfactorily from the sensation and the mental images of former sensations, the ideas, in accordance with the laws of association. In so doing we had traced the psychical process to its close. At this point, however, we meet a hypothesis that has been taught by all former psychologies almost without exception, — a hypothesis at which, as it would seem, the common understanding of humanity has arrived naively and unconsciously. This is the assumption of an especial will as the cause of our actions. This hypothesis introduces between the process of ideation and the ac- tion the further activity of a special psychical faculty. The associ- ation of ideas only supplies the motives ; it is the will that finally decides which of these motives shall prevail. While the other faculties of the soul (understanding, judgment, etc.), as such, have rapidly lost ground since Herbart, the doctrine of the existence of an especial will-faculty still obtains with the greatest pertinacity. 265 266 Introduction to PJiysiological Psychology. Now, as we have already seen, nothing has as yet compelled us to assume a new and entirely hypothetical factor in the conscious life. We can therefore with complete justice shift the onus pro- bandi on to the shoulders of those who champion the doctrine of a special faculty of the will. We have explained all psychical, processes without it ; they would not be rendered any more intelligible by using it, What does it mean when we say " I will go"? or, to state the question more correctly, what psychical content do the movements of speech producing the words, " I will go,' ; express ? Obviously they only express the fact that the motor idea of going occupies the consciousness with great inten- sity, and is accompanied by a very pronounced positive tone of feeling. At the same time the grouping of latent ideas is such that those ideas which aid the appearance of the motor idea of going predominate over those ideas that would arrest its appearance. When we imagine how fine it would be to climb yonder mountain, this idea may be very vivid and yet we may not come to the conclu- sion that we will go up there. In this case a visual idea accompanied by a positive tone of feeling almost exclusively occupies the attention ; there is only a very weak idea of the motions to be performed by the limbs. Numerous arrestive ideas, as that of the remoteness of the mountain, etc., do not permit the motor idea to gain strength. We go one step further and say, " I would like to climb yonder mountain." What does this " would like " — this " desire " mean ? In this case also the content of the idea remains the same ; the motor idea is still checked despite the great increase of its positive emotional tone. Finally, the last step is taken when we say, "I will climb yonder mountain." The motor idea has become extraordinarily intense, the positive tone of feeling has reached its height, and, above all, the assistant ideas predominate over the arrestive. The expression "I will" desig- nates not only the subjective sensations at a definite moment, but also the objective status quo of the brain, in particular the grouping of latent ideas. Here we may distinguish three cases. If another person says of us that we will do this or that, he means properly that the grouping of our latent images of memory is Will — General Conclusions. 26 7 favourable to the appearance of this or that idea of motion accompanied by a strong positive emotional tone, or to the ap- pearance of the appropriate action. On the other hand, when we will do something, o?tr own psychical content at that moment is only distinguished from other psychical contents by the fact that the idea of a desired action, accompanied by a positive emotional tone, is already contained among the sensations and ideas that are then actually present. In addition to this also, those peculiar oft-mentioned motor sensations appear, which are produced by the unconscious innervation of the appropriate muscles correspond- ing to the increase in attention. Finally, still a third case is to be distinguished, — our own psychical content when we say, "I will do something" i.e. when we interrupt the voluntary action for a moment and reflect upon it. This " I will do something," when spoken, is a series of motor ideas of speech with which are associ- ated (1) the Ego-idea in the sense formerly discussed; (2) the idea of a future act, accompanied by a positive emotional tone ; (3) motor sensations accompanying attention ; and (4) the idea of a causal relation existing between the Ego-idea and the desired action. 1 All of these elements are already known to us ; none of them is new. The idea of a causal relation is an idea of relation quite the same as the idea of similarity, formerly discussed as a paradigm of all ideas of relation. Therefore this analysis also gives no ground for the assumption of a special faculty of the will. Psychiatry also furnishes an interesting confirmation of the above conclusion. It has arrived, quite empirically, at the assumption of two chief forms of psychosis, the one originating in the intellectual sphere, the other in the emotional sphere of psychical life. Psychiatry knows of no special psychosis of the will. The attempts to set up special diseases of the will under the name of monomania, or a general disease of the will designated as moral insanity, have all been recognised failures. All disturbances of voluntary action that we find in cases of mental disease, without 1 Compare the discussions of Th. Waitz, " Lehrbuch der Psychologie als Naturwissenschaft," that in many respects already anticipate this standpoint. 268 Introduction to Physiological Psychology. doing violence to or neglecting any facts, may be reduced either to disturbances of the sentient life, especially of the emotional tone, or to intellectual disturbances, i.e. disturbances of the ideas or of the association of ideas. The so-called loss of volition (abulie), the inability to come to a decision, for example, is a frequent symptom of mental disease; but this so-called loss of will-power may always be reduced either to the exceeding sluggishness of of the association of ideas, to the abnormal negative tones of feeling, or to other similar afflictions. Pathology also argues against the assumption of a special faculty of the will. 1 We have yet to discuss the question as to how we come to regard the idea of our ego as the cause of our actions; and finally, whence the feeling of freedom that accompanies our actions arises. It is obvious that we finally come to regard the ego-idea as the cause of our actions because of its very frequent simultaneous appearance with each action. It is almost always represented several times among the ideas immediately preceding the final movement. But the idea of the relation of causality is an empirical element that always appears when two successive ideas are very closely associated. The feeling of freedom in actions is to be explained the same as the feeling of freedom in the association of ideas formerly described. We must here emphasize once more that this feeling of freedom depends upon the absence of external compulsory motives, and therefore upon the fact that not the sensations alone, but also the images of memory, determine our movements. This notion of a free will is also furthered by the fact that the idea of " not performing " a movement, or the idea of another movement than the one which is accompanied by the stronger tone of feeling, and which is finally actually executed, appears and takes part in the play of motives. But that which finally causes the latter idea to prevail and suppresses the former is not a special faculty exercising free will, but only the stronger emotional tone 1 Compare Ribot, " Les maladies de la volonte," a work, however, that ascribes decidedly too much importance to the ego in acts of the will. Will — General Conclusions. 269 and greater intensity of the prevailing idea, combined with the favourable grouping of the latent mental images. Our actions are as strictly necessitated as our thoughts ; l we cannot but come to this conclusion, for both action and thought are in fact quite identical when viewed in the light of their fundamental psychical characteristics. Thought consists of a series of ideas, and the psychical element of an action is likewise a series of ideas whose sole specific characteristic is that its last member is an idea of motion. Both are governed by entirely the same laws ; both are associations of ideas. The final motor effect in the case of action, according to this standpoint, is rather an incidental accession which in itself has no concomitant psychical process. We should not forget, furthermore, that slight motor elements — the slight muscular tension accompanying attention, for example — affect the process of thought. On this account thought has also been very suitably designated as inner actio?i ; and action that is manifested in the contraction of the muscles, as external action. In this connection we must consider another reason that many seem to regard as of especial importance in arguing the freedom of the will. It is a common belief, in fact, that if the will in general and the freedom of volition in particular are denied, all ethical distinction between actions and all accountability for actions are thereby removed. Let us consider the two arguments separately. Psychologically an " ethical distinction " means that certain actions (for example, murder) produce a negative tone of feeling, others a positive tone of feeling. This difference between the accompanying tones of feeling is by no means destroyed by any of the doctrines that we have advanced. In the sphere of ethics "good" and "bad" designate respectively positive and negative tones of feeling, just as " beautiful" and " ugly " express respectively positive and negative emotional tones in the sphere 1 The memorable expositions of Spinoza (" Ethik," P. II, Propos. 49, and especially the following Scholium) should also be compared with the above conclusions. 270 Introduction to Physiological Psychology. of aesthetics, or the sphere of sensation. The ethical feelings, the same as the aesthetic, cannot be reduced by the empirical psychologist to a certain chief formula. It can be shown that almost all actions, which we now regard as crimes, have at some time been regarded as good by human beings of other ages or of other places, i.e. they were accompanied by positive emotional tones in mankind. Absolute ethical laws are as little to be expected from psychology, as absolute gesthetical laws. Both the ethical and gesthetical emotional tones fluctuate, (1) historically: they are the product of an historical, if not phylogenetic, develop- ment; and (2) also among the same people at any definite time ; they are fully agreed upon only by a large majority and not by all. We shall certainly not condemn empirical psychology for not establishing ethical laws, for of what assistance would any possible laws which the psychologist might establish be to the moral philosopher ? They could only have an empirical charac- ter, and not that absolute character customarily required by the ethical philosopher. In this work we are only concerned with laws in us, and not laws above us. It is very different with the conception of moral accountability or responsibility. This conception, in fact, is contradictory to the deductions of physiological psychology. The latter teaches that our actions are strictly necessitated ; they are the necessary product of our sensations and ideas. Therefore, according to physiological psychology, we could no more hold a man guilty and accountable for his bad action than a flower for its ugliness. Hence the action remains bad, even when viewed psychologi- cally, but in itself does not impart guilt. The conceptions of guilt and accountability are — to designate the antithesis briefly — either religious or social conceptions, and on that account may be disregarded here. Psychology, let us repeat, does not deny absolute sesthetical or ethical laws in so far as they can be de- monstrated from some other standpoint ; but psychology itself, limited to empirical data, can only establish empirical laws. 1 1 The following authors are to be especially recommended for a further, Will — General Conclusions. 271 Hence the investigation of the so-called voluntary processes has given us no grounds whatever for the assumption of another psychical " something " in addition to the series of sensations and ideas. The metaphysician can perhaps arrive at the theoretical fiction of a being which is the subject of the sensations, ideas, and actions, and may name this subject Ego or Soul. Physiological psychology, however, cannot exceed the bounds of its empirical data ; at the close of its investigations we have simply to ask whether it can offer us any further empirical facts that will throw some light upon the nature of that parallelism which, from the beginning, we have supposed to exist between the psychical processes and the material physiological processes of the brain. Let us now briefly consider how science has hitherto accounted for this parallelism, which primarily means simply a regular coexistence. For this purpose we distinguish dualistic and monistic theories. The dualistic theories all accept the dualism of the two series (material and psychical), and avoid every attempt to resolve it. In so doing the complete interdependence of the two series, in fact the very thing that we have called parallelism, remains wholly unintelligible. On this account Leibnitz, one of the chief champions of the dualistic theory, was forced to have recourse to the theory of a pre-established harmony. Geulinx's occasional- ism also belongs to this class of theories. Of course the fact that the psychical series of phenomena is much shorter than the material or physical series is somewhat unfavourable for this more exact study of the theory of the will : Herbart, " Psychologie als Wissenschaft " ; Spencer, "Principles of Psychology"; Lipps, "Grund- thatsachen des Seelenlebens " ; Steinthal, "Einleitung in d. Psychologie u. Sprachwissenschaft " ; Bain, "The Senses and the Intellect," and "The Emotions and the Will." The views of Wundt, which are in general diame- trically opposed to the views of these researchers, and which agree with older authorities in the assumption of a special faculty of the will, are to be found in his " Grundziige der physiologischen Psychologie," and also in his " Ethik." 272 Introduction to Physiological Psychology. dualistic theory. Experience demonstrates parallel psychical processes for only a small part of the material processes, namely, for the physiological processes of the brain. For this reason the attempt has been made to equalize this difference in " length " — if we wish to preserve the comparison with lines — by hypotheti- cally lengthening the psychical series. Hence certain philosophers came to assume parallel psychical processes, not only for all physiological processes of the brain, but also for all organic material processes. This hypothesis may be designated as the animistic theory. Among its champions is Wundt. Finally the doctrine of hylozoism goes still further, and ascribes life, and hence parallel psychical processes, to all inorganic processes. Fully and logically applied, this theory views each atom and each molecule as the possessor of a concomitant psychical substance. In opposition to all these theories, it should be remembered that they all lead unavoidably to the assumption of unconscious psy- chical processes, an assumption that is in itself contradictory, as we have already seen. Among the monistic theories we shall consider those first that assume the subordination of one series to the other. Here but two theories are possible ; either the material series of pheno- mena is to be regarded as a function of the psychical, or the latter as a function of the former. Neither the first-mentioned spiritualistic view, nor the last-mentioned materialistic view is able to give any sufficient ground whatever for the subordination of one series of phenomena to the other which it assumes. Those monistic theories that preserve the co-ordination of the two series, but would still establish their unity, have sought to accomplish the task by regarding both series as attributes of one substance. Accordingly Spinoza ascribed the two attributes of extension and thought (extensio and cogitatio) to his one absolute substance, the Deus sive mundus. This view of Spinoza's is in harmony with that of many natural philosophers who ascribed (1) extension and (2) a psychical property, as memory for example, to their molecules, in that it merely creates a formal logical unity for the two separate series. But these undemonstrated hypotheses do Will — General Cone Ins ions. 273 not give us any insight whatever into the connection that exists between the two series. Another variety of the monistic theory likewise accepts the two series as co-ordinated, but attempts to remove their difference by more or less sophistical arguments. The two series are supposed to be originally and properly identical " in the absolute," and to have become differentiated only by a " disunion of the absolute." The metaphysical histories of creation, found in the " philosophy of identism," or the "doctrine of identity," belong to this class of theories. The last of the monistic views may be designated as the critical. It is the only one that remains within the bounds of empirical psychology as a natural science. This critical view does not accept the two series without further test; on the contrary, it investigates the manner in which we have come psychologically to assume the existence of two series and endeavours to deter- mine whether the material and psychical data are equally primary or not. Such a critical test demonstrates quite irrefutably that our first data are only those contained in the psychical series of phenomena. 1 We shall now discuss somewhat more thoroughly this last and most important proposition of empirical psychology, a proposition that is too easily ignored, especially on the part of the natural sciences. We first became familiar with reflex and automatic acts. Neither is accompanied by a psychical process. Such a process appeared first as a concomitant of action. We should not forget, however, that action is not produced because a concomitant psychical process is introduced. By no means. On the contrary, the material process that lies at the foundation of an action is complete in itself, exclusive of the concomitant psychical process; it can be perfectly understood also without the aid of sensation or ideation. On the contrary, sensation and ideation to a certain 1 That strictly speaking only the psychical series of one individual is primarily given, may here be disregarded. The exclusive consideration of this fact leads to so-called solipsism or egoism in epistemology. Comp. v. Schubert-Soldern, " Kampf um die Transcendenz." 274 Introduction to Physiological Psychology. extent present complications of the process. The unintelligible fact which requires explanation is that, contrary to the automatic and reflex acts, the action is found to be accompanied by an entirely new element, the concomitant psychical process. The material elements of the action are in themselves quite clear. The action would not be any different even if the excitation of the sensory cell should not produce its correlate, the sensation, nor the material disposition left in the brain (the El or Ei), its correlate, the image of memory or idea. We could render the general fitness of our actions just as intelligible as the fitness of automatic and reflex acts, or the fitness of a bird's plumage. In both cases the process of selection is the essential factor in the development of this fitness. In the case of the bird's plumage, of reflex action, and to some extent of automatic 1 action this selec- tion is essentially a phylogenetic process ; in the case of actions it is an ontogenetic process. Strictly considered, all actions must first be attained by practice during the ontogenesis of the indi- vidual, — for example, the practising of a selection for the piano. Only the cortical mechanism, an apparatus highly adaptable to the training of voluntary actions, is phylogenetically acquired, i.e. inherited. Therefore the fitness of actions is quite conceivable, at least, as the result of material laws ; as a simple matter of ex- planation, the parallel psychical processes are useless and super- fluous. Let us repeat that, according to the above statements, the appearance of concomitant psychical processes themselves is the only fact that needs explanation. Accordingly the question arises : What material processes are accompanied by these psy- chical processes ? It is not sufficient to answer that the cortical 1 The above throws new light upon the nature of the automatic act, the intermediate position of which has already been mentioned. In fact, apart from the absence of concomitant psychical processes in the case of automatic action, and their presence in the case of action, there is no well-defined dis- tinction between many automatic acts that are ontogenetically developed and pure action. The unconscious automatic playing of the piano, acquired by practice, as a material process, is hardly to be distinguished from the conscious act in any essential point. [ / 7// — General Conclusions. processes alone are accompanied by psychical processes. Num- berless material processes of the cortex take place without the concomitance of psychical processes. One and the same Ec produces a sensation to-day, but none to-morrow, according to the variations in the grouping of the latent ideas. There is no answer to the above question whatever. But empirical psycho- logy now raises that critical and decisive question, by means of which it tests its own foundations : How do we come by this separation of the empirical data into two series, the material and the psychical ? With which series are we directly and primarily furnished ? Let us test the matter upon ourselves. We see a tree, for example. Apparently in this case both series of data are already present, the seeing and the tree. But is this an exact statement of the facts in the case ? By no means. That which is empirically furnished us is simply and alone our visual sensa- tion, tree, i.e. merely a psychical process. We only employ this sensation in a very remarkable way by constructing an idea of the object tree as the cause of our sensation tree. The same is true of all objects of the external world. In every case we have only the psychical series of sensations and their ideas. We only adopt a universal hypothesis, when we assume that a material series exists in a casual relation to the psychical series. Epistemology and metaphysics, in so far as there is such a science, must decide as to the justice of this hypothesis. The proposition itself, that the material and psychical series of phenomena are not equally direct and primary as factors in cognition, contains all that is ot importance to us here. We are only directly and empirically furnished with the psychical series of phenomena; the other series is simply inferred. The material series may be regarded as an idea that we have abstracted from our sensations and their ideas. Modern physics harmonizes well with this view. Ulti- mately nothing of the so-called matter is left to the natural scientist but infinitesimal points in space, that are conceived of as possible centres of power, i.e. that can effect sensations. This so-called matter, apart from its hypothetical causal relation to the sensations, is otherwise an entirely unknown element. Now the 276 Introduction to Physiological Psychology. same thing is true of the material cortical processes that is true of all material processes. They are also merely inferred, and not primary, empirical data, as are the psychical processes. Strictly speaking, we arrive at the inference of a material series of pheno- mena as follows : We have numerous sensations, and by means of these we acquire ideas ; we then assume external objects as the causes of these sensations and ideas. Among our sensations are also those with which we have met in our anatomical and physi- ological investigations of the cerebral cortex. Here, the same as in the case of all sensations, we also assume that a material cause, the cerebral cortex, produces the sensations which we have in seeing and investigating the same. Further research shows that just these material cortical processes also have a very special relation to all psychical processes ; that, in fact, the former never occur without the latter, nor the latter without the former. Em- pirical psychology does not need to occupy itself with a further solution of this complicated problem. Every attempt to reach a complete solution would necessitate its departure from empiri- cal grounds. It therefore relegates the further handling of the problem in so far as it is capable of any solution whatever, to a possible metaphysics, or to epistemology. On the other hand, our science must depend so much the more upon the empirical fact itself, that primarily we have only psychical data, and nothing outside of or beyond these. Thus far psychology remains within the bounds of natural science, and is quite true to its empirical character. It is of interest that in this last proposition our science stands in the closest harmony with the founder of the critical philosophy, Kant. Locke, Berkeley, and Hume had pre- pared the way for the great truth which Kant finally expressed, that primarily we have only the psychical series, the series of appearances or "phenomena," as he called them. The hypothet- ical "cause" of the "phenomena," or of the psychical series, is ( i ) merely inferred, and (2) a factor of which we know absolutely nothing. Thus the psychophysical dualism or parallelism finally proves to be only a semblance. Will — General Conclusions. 277 Hence, since the psychical series is the primary series, we can also understand why we frequently met with psychical factors in our previous researches for which there was no material basis. Let us recollect, for example, the projection of our sensations into space and time, a psychical fact for which we were unable to obtain any psycho-physiological explanation. With this last proposition our task is completed ; the sphere ot empirical physiological psychology is brought to a close. Each further step would be a metaphysical procedure, and would in- evitably lead to a problematical metaphysics. Physiological psychology, however, must remain a natural science or betray its cause. INDEX. Actinospharium, reflex action of, 8. Action, contrasted with reflex and automatic action, 22-25, 3 1 > def, 243 ; nature and development of, 243-249 ; forms and kinds of, 249-258. After-images, 142. After-sensations, 189. Amnesia, of somnial processes, 238 ; following the hypnotic condition, 241. Amcebce, nervous processes of, 6. Animistic theory, see Theories, etc. Apperception, no special faculty of, 184 ; arguments against Wundt's assumption of, 203, 204. Aronsohn, 65, footnote. Associative relationship, def. of, 212, footnote. Association, def. of, 24 ; of ideas, 172-189 ; laws of, 173 ; as recog- nition, 173-178 ; chief law of, 178 ; forms of, 178-183; physiological basis of, 173-176, 179, 180; as choice, 183-188; rapidity of, 190- 198 ; as judgment, 198-201 ; other forms of, 201-222. Attention, def. of, 206 ; as directed to sensations and ideas, 206-215. Axidition coloree, 225. Anerbach, II, footnote. Automatic Action, defined, 13, 14 ; non-psychical character of, 14, 18, 19 ; distinguished from reflex- action, 13 ; examples of, 13, 15-18 •; anatomical localization of, 35, 36. Bain, footnotes on pages 152, 182, 271. Beats, def. of, 138. Bechterew, 263, footnote. Benedict, 226. Beneke, 152, footnote. Berkeley, 276. Bemheim, on hypnotism, 240. Biedermann, on discriminative sensi- bility, 71. Binswanger, 241 and 263, footnotes. Blenler, 226. Blix, Magmis, on specific energy, 65. " Brain," 65, footnote. Brentano, on interpretation ot Weber's Law, 52, 53. Bridgman, Laura, 263. Br oca, convolution of, 259. Brodhun, 115, footnote; on discrimi- native sensibility, 119. Bubnojf and Heidenheim, 241, foot- note. Byron, Lord, 231. Camerer, 64, footnote. Cardanus, 231. Cattell, on counting sensations, 145 ; on reaction-time, 255. Ccsca, on unconscious psychical con- 278 Index. 279 ditions, 5, footnote ; also 132, foot- Ducheune, on movements of expres- note. sion, 260. Charcot, 155, footnote. Chesseldens, 81. Ebert, 120, footnote. Chord, def. of, 137, footnote. Eccentric projection ,97- Caienterata, 6. Ego, 216-219. Cold-spots, on the skin, 68. Emminghaus, on double conscious- Colour, 1 03-1 12. ness, 239, footnote ; on memory, Colour-blindness, 1 14. 221, 222. Compulsory ideas, 234, 235. Empirical psychology, I . Conception, formation of, 154-160 ; Energy, of the idea, 171. sensual or concrete, 161 ; general Engelmann, on reaction, 16. concrete, 163 ; abstract, 165. Entoptic stimuli, 230-233. Conclusion, 201, 202. Entotic stimuli, 230-233. Conscious action, see Action. Erdmann, 176, footnote. Consciousness, def. of, 29, footnote. Eulenburg, 74, footnote. Conscious phenomena, 26. Excitation, def. of, 8 ; see also Stimu- Contiguity, 182, 183. lation. Corti, organ of, 88, 89, 97, footnote, Exner, 64, 126, footnote. 112. Critical theory, see Theories, etc. Fechner, on the application of Weber's Law, 51, 97, 119 ; on the "golden section," 140, 141, and Dahl, 64, footnote. footnote ; on audition coloree, 226 ; Darwin, on inherited acts, 17, 216, on hallucinations, 231 ; his funda- footnote ; on interpretation of mental formula, 52, and footnote. motions of expression, 260. Feeling, def. of, 61, footnote; see Darwini sm, applied to the theory of Sensation. the origin of language, 262. Fischer and Penzoldt, 65, footnote. Delbauf, on interpretation of Weber's Flagellata, reflex action of, 8. Law, 59. Flechsig, 32 and 126, footnotes. Deliberation, see Play of motives. Flight of ideas, 196. Delusive ideas, 234, 235. Forel, 32, footnote. Dessoir, 241, footnote. Franz, 89. Diet I and v. Vintschgau, 256, foot- Friedrich, on reaction-time, 255. note. Discriminative sensibility, 71, 72, 93, Galton, on rapidity of association, and footnote. 192. Discernment-time, or distinction-time, George, 139. 255- Geulinx, dualistic theory of, 27 1. Distinctness, of the idea, 171. Giraudeau, 226, footnote. Dohrn, on the discriminative sensi- Gladstone, on colour-blindness of the bility, 71. ancient Greeks, 114. Dreams, 236-239. Goethe, on colour, 139. Drobisch, on the colour-scale, 104. Golscheider, footnotes on pages 38, 280 Index. 40, 74, 75, 134 ; on a general sense of feeling, 68 ; on sensations of motion, 69 and 74- Golgi, 32, 125, footnotes. Goltz, on reflex motions of the frog, 12 ; on automatic movements, 14, 15 ; also footnotes on pages 12, 13, 14. Gowers, 259, footnote. Graskey, 260, footnote. Griesinger, 239, footnote. Grouping, of latent ideas, 186. Gustatory bulbs, flasks, or knobs, 62. Hagen, 231, footnote. Hallucinations, 227-232. Hamilton, 5, footnote. Hearing, see Sensations of Hearing. Heat-spots, 68. Helmholtz, on Weber's Law, 53 ; on timbre, 94 ; on sensations of sight, 104, 113, 137, 138, 140. Henle, on hallucinations, 231. Herbart, his mathematical computa- tions as applied to psychology, 187, 188. Also footnotes on pages 80, 158, 176, 178, 201, 271. Hering, his law, 56, 57 ; on caloric stimulation, 68 ; on sight, 113, 122 ; also footnotes on pages 58, 75, 221. Hermann, 39, footnote. Hipp, his chronoscope, 250. Hoffmann, E. T.A., 147, footnote. Hogarth's curve of beauty, 141. Hbnigschmied, on reaction-time, 251. Hoppc, on hypnagogic hallucinations, 231, 232 ; also 232, footnote. Horwicz, 132, footnote. Huber, 221, footnote. Hume, on ideas, 151, 152 ; as prede- cessor of Kant, 276. Hydra, 6. Hypnagogic hallucinations, 231, 232. Hypnotism, 239-242. Idea (mental image or image ot memory), 24, 25 ; of motion, 26 ; use of term, 151, footnote ; for- mation and nature of, 151, 152 ; physiological basis of, 152-154 ; of articulation, 158, 159 ; of a word as heard, 159, 160 ; imaginative, 166; qualities of, 167-169; de- struction of, 171. Idealism, see Theories, etc. Illusions, 232, 233. Incoherent thought, 198. Jean Paul, 231. Johnson, 231. Judgment, 198-201. Kahlbaum, on hallucinations, 228 ; also 231, footnote. Kandinsky, 231, footnote. Kant, on the science of psychology, 3 ; on the critical philosophy, 276. Kolliker, 135, footnote. Konig, on discriminative sensibility, 119. Konig and Dieterici, 115, footnote. Krcepelin, on reaction-time, 256, 257 ; also 231, footnote. Krafft-Ebing, 239, footnote. Krause, on the regio olfactoria, 64. Kiilpe, 132, footnote. Lange, L., on association, 27, 28 ; on duration of sensation, 142 ; on re- action-time, 250, and footnote. langley, 120, footnote. lazarus, 236, and footnotes on pages 231 and 262. Lehmann, 177, 226, footnote. leibnitz, his dualistic theory, 271. leidesdorf, 228, footnote. lewes, footnotes on pages 5 and 10. lichtheim, 260, footnote. lightness, or light, distinguished from white, 107, 108. Index. 281 IJpps, footnotes on pages 201 and 271. Lissauer, 155, footnote. Local stamp or sign, j6, 83. Locke, as predecessor of Kant, 276. Lozait, on discriminative sensibility, 71. Luft, E., on discriminative sensibility, 92. Lussana, 226, footnote. Lustig, on the regio olfactoria, 64. Much, on the barely noticeable differ- ence in the duration of tones, 144. Mania, as understood by the German alienist, 139, footnote. Masje, 38, footnote. Masson's disks, 118. Materialistic theory, see Theories, etc. Maudsley, 5, footnote. Mauthner, 155, footnote. Maximum of excitation, 46-53. May, on sense of smell in crabs, 64. Medusa, 6, 7. Meinong, 221, footnote. Memory, 220-222. Memory -cells, 156. Mendel, 231, footnote. Mendelsso/m, 231. Mental blindness, 155. Mental deafness, 155. Merkel, on Weber's Law, 59 ; on dis- criminative sensibility, 71 and 119; on the method of mean gradations, 96, and footnote. Method, of the average or mean error, 128, and footnote ; of average or mean gradation, 59, 60, 96 ; of correct and false (mistaken) cases, 63 73i 74- Meynert, footnotes on pages 17, 161, 217 and 258. Mill, James, 5, footnote. Mill, J. S., on abstract and concrete conceptions, 165 ; on laws of asso- ciation, 182, footnote. Minimum of excitation, 46-53, 63, 65, 71- Monistic theory, see Theories, etc. Morbid thought, 223-239. Motions of expression, 258-264. Motives, see Play of motives. Motor ideas, see Idea of motion. Motor sensation, see Sensation of motion. Monches volantes, 230. Movements of speech, 259. Mnnk, footnotes on pages 35, 40, 124, 155, 209. Miinsterberg, footnotes on pages 17, 23, 176, 195, 215, 247. Muscular reaction, see Reaction. Muscular sense, 70. Musical sound, def. of, 86 and 137, footnote ; nature of, 85-88. Noise, 86-88. Norr, 96, footnote. Nothnagel, on the optic thalamus, 264; also footnote, 155. Nitssbaitmer, on secondary sensations, 226. Oehrwall, on the papilla? fungiformes, 63. Ontogenesis, of automatic acts, 17. Paneth, 168, footnote. Pascal, 231. Perception, distinguished from sen- sation, 25. Pfeffer, 54, footnote. Pfiiiger, on "a soul in the spinal cord," II. Phenomena, the material and psychi- cal, 1, 2, 167. Phouisms, 224. Photisms, 224. Phylogenesis, of automatic acts, 1 7. U 282 Index. Physiological psychology, relation to psychology, 1-3 ; province of, 22-25. Physiological lime, see Simple re- action-time. Pitch, 90. Plateau, on Weber's Law, 52, 53, 97 ; also footnote, 59. Plato, 152. Pope, 231. Poteriodendron, 6. Press7ire-spots, 67, 82. Preyer, on the Ophiurae, 15; foot- notes on pages 99, 241, 263. Processes 1 material, 2 ; nervous, 10, 31-36; physiological, 2; psycho- physiological, 21, 22, 29. Projection, eccentric, 77. Protista, J. Psychical phenomena, 4-6. Psychology, as a science, 3. Psycho-physics, province of, 3. Radiation, 224. Ramon y Cajal, 135, footnote. Reaction, muscular, 250 ; sensorial, 250. Reaction-time, 249-253 ; simple, 193, Recognition, 173-176. Recognition-time, 254-257. Reinhard, 155, footnote. Reflection, 31. Reflex action, clef, of, 7 ; nature and development of, 7-13; as instinct, 17, 18; anatomical localization, 34-36. Reproduction of ideas, def. of, 172. Ribot, 239, 268, footnotes. Richet, 134, footnote. de Rochas, 226, footnote. Romanes, on the Medusae, 6. Romanes and Ewart, on starfish, 15. Samt, 239, footnote. Sanders-Ezn, 11, footnote. Schiff, on sensations of touch and pain, 135. Schroeder von der Kolk, 155, footnote. z\ Schubert- Soldern, 273, footnote. Schiile, 239, footnote. Schumann, 231. Secondary sensations, see Sensation. Selection-time, 255. Sensation, production of, 23-24 ; properties of, 43-44, 129 ; inten- sity of, 44-49 ; Law of Weber, 49-60; quality of a, 61 ; five chief groups of, 61 ; time characteristics of, 141-145 ; secondary, 223-226. Sensation-circles, def. of, 82 ; signi- ficance and characteristics of, 82-83. Sensations of feeling, development of, 66 ; stimulation of, 66 ; number of qualities of, 66, 67 ; cortical centre of, 68 ; organic, 68. Sensations of hearing, stimulation of, 85-88 ; organ of, 88-90 ; quality of, 90-95 ; intensity of, 95-97 ; time as an element of, 93-94 ; localization of, 97-100. Sensations of motion, def. of, 69 ; passive and active, 69, 70 ; 246. Sensations of position, def. of, 68, 69. Sensations of pressure, 71, 72, 73. Sensations of sight, 101-128 ; stimu- lation of, 101 ; organ of, 101-103 ; qualities of, 103-116; intensity of, 1 1 6- 1 20; arrangement and locali- zation of, 120-126 ; correctness of, 126-128; nativistic and genetic theories of, 122. Se?isations of smell, 64 ; qualities of, 64-65 ; organ of, 65 ; stimulation of, 65 ; intensity of, 65 ; localiza- tion of, 65, 66. Sensations of taste, 62 ; stimulation of, 62 ; qualities of, 62 ; organ of, 62, 63 ; general characteristics of 63, 64. Sensations of temperature (of cold and Index. 283 of heat), stimulation of, 66, 67, 68 ; intensity of, 74, 75. Sensations of touch, organ of, 66; see also Sensations of pressure ; of active touch, def., 70. Sensorial reaction, see Reaction. Simple reaction-time, 193. Sleep, physiological basis of, 236. Soul, in the spinal cord, Pfliiger, 10. Sound, 85-88 ; musical, 86, Sy, 137 ; noise, 86, 87. Spaceperception, by touch, 77-84 ; by sight, 121-128. Specific energy, of sensory nerves, 40-42. Spencer, 271, footnote. Spinello Aretini, the painting of his Madonnas, 231. Spinoza, subject to hallucinations, 231 ; his monism, 272 ; also 269, footnote. Spiritualistic theory, see Theories, etc. Spontaneous motions, def. of, 36. Starke, 96, footnote. Steinach, on reaction time, 251. Steinbriigge, 226, footnote. Steinthal, 262 and 271, footnotes. State of feeling, def. of, 256. Stimulus, kinds of, 37-40 ; of taste, 62 ; of smell, 65 ; of touch, 66, 67 ; of hearing, 85-8S ; of sight, 101- 112. Stimulation, 40-43. Strassburger, on phototaxis, 124. Successive contrast, 189. Sumtnation-tones, 138. Sympathetic vibrations, 162. Temperature-spots, see/feat- and Cold- spots. Theories as to the parallelism of material and psychical phenomena, 271-277 ; the dualistic (Leibnitz- Geulinx), 271-272 ; animistic (Wundt), 272 ; monistic, 272, 273 ; Spinoza's, 272 ; spiritualistic, 272 ; materialistic, 272 ; of identity, 273 ; critical, 273-277. Thoftisen and Ttimlirz, on the mea- surement of vis viva, 45. Thought, the distinction of voluntary and involuntary, 215-219. Tieck, 231. Tiedemann, on the movements of star-fish, 15. Timbre, 94. Tone, def. of, 86. Tone of feeling, 129- 14 1, 145-150. Touch, distinction between active and passive, 70, footnote. Trautscholdt, on rapidity of associa- tion, 192-193. Ughetti, on secondary sensations, 225. Uhthoff, 115, footnote. Urbantschitsch, 224, footnote. Venable, on stimulation by strych- nine, 63. Vey-worn, on the Protista, 8. Vierordt, on caloric stimulation, 68. Vibrations, sympathetic, 162. Vintschgau, on mechanical and ther- mic stimulation, 251 ; also foot- note. Voluntary actions, def. of, 28 ; see also Actions. Vulpian, on reflex motion, 12 ; also 15, footnote. Wahle, on the "grouping" of latent ideas, 187. Waitz, 273, footnote. Weber, E. H., on caloric stimulation, 6S. Weber' 's Law, 50-53 ; Fechner's inter- pretation, 53, 54; Pfeffer's, 54, 55 ; Wundt's, 55 ; Ziehen's, 55-59 ; for sensibility of skin, 71 ; for hearing, 96 ; for sight, 118, 128; for sensi- 2S4 Index. > hility to differences in time, 143, 144. Welt, L., 204, footnote. Wernicke) footnotes, 161 and 260. Wilbrand, on hemianopsia, 105, 155, footnote. Will, 265-271 ; the theory of, 28, 265-267 ; as viewed by psychiatry, 267, 268 ; whence the idea of the, 28, 29, 268 ; as related to ethics, 269, 270. Wolfe, 221, footnote. Wundt, on the specific energy of sensory nerves, 40, footnote ; on the method of average gradations, 59 ; on lowest tones, 90, footnote ; on apperception, 203, 204 ; his chronograph, 250 ; on reaction, 250, footnote ; as champion of animism, 272 ; also 257 and 271, footnotes. Ziehen, 264, footnote. Zuckerkandl, 65, footnote. Butler & Tanner, The Sclwood Printing Works, Frome, and London. 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