Hatt (ftolkge of ^Agriculture At (SfarneU MniocraitB Htbratg Cornell University Library BF 131.P6 3 1924 014 474 112 Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924014474112 THE ESSENTIALS OF PSYCHOLOGY THE MACMILLAN COMPANY KEW YORK ■ BOSTON • CHICAGO • DALLAS ATLANTA • SAN FRANCISCO MACMILLAN & CO., Limitkd LONDON • BOMBAY • CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, Ltd. TORONTO THE ESSENTIALS OF PSYCHOLOGY BY W. B. PILLSBURY DIHECTOR OF THE PSYCHOLOGICAL LABORATORY PROFESSOR OF PSYCHOLOGY, UNIVERSITY OF MICHIGAN AUTHOR or " THE FUNDAMENTALS OF PSYCHOLOGY" REVISED EDITION THE MACMILLAN COMPANY 1920 jSll rights reserved Copyright, xgii and zgao. By the MACMILLAN COMPANY. Revised Edition. Set up and ^lectrotyped. Published January, tgso. Notbiooti T^ttiS J. S. Cushing Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. TO E. C. P. PREFACE TO THE FIRST EDITION The aim of this volume is to present clearly the ac- cepted facts of psychology.- Throughout, emphasis has been placed upon fact rather than theory. Where theories conflict, the better one has been chosen, the others merely neglected. This may seem dogmatic in places, but in a text dogmatism is preferable to con- fusion. The point of view is on the whole functional ; more attention is given to what mind does than to what it is. With this goes an emphasis upon the outward manifestations of consciousness and upon the behaviour of others to the subordination of the individual con- sciousness. Nevertheless, use is made of the results of structural psychology wherever they throw light upon function or are interesting for themselves. The position, it is hoped, combines the advantages of the rival schools. The content of a text-book in psychology is suffi- ciently agreed upon to require no comment. The general practice has been followed of introducing a brief exposition of the nervous system and its function. This is done with a full appreciation that it is no part of the task of the psychologist to teach neurology, but with the conviction that the beginning student in psy- chology is not likely to have acquired the knowledge elsewhere. In this treatment as little detail of structure VIU PREFACE has been given as is compatible with an understanding of function. Large use has been made of the hypothe- sis of the synapse. Its convenience in explaining habit and association outweighs any scruples about its final position in physiology. For the rest, I have deviated from traditional usage only in introducing rather more of the results of recent experiment. A body of knowl- edge has been developing in connection with memory and action that seems ripe for embodiment in a text. Similar considerations have led to the introduction of chapters on fatigue and on the transfer of training. The general arrangement followed is relatively novel. It consists in first developing a few simple principles and then making frequent application of them to the more complicated processes. Sensation, habit, reten- tion, and selection or control are fundamental and appear repeatedly in mental operations of all kinds. When they are once understood, it is only necessary to develop their applications and interconnections to master the more developed operations. The method involves much repetition, but not more than the expe- rience of the writer has proved necessary. What is not understood in one connection is made clear by the next application. My obligations to psychological writers are so gen- eral and so apparent as to need no special acknowledg- ment. Dr. Rowe of the Central Normal School,- Mt. Pleasant, Michigan, has read the manuscript and made many suggestions. Thanks are due also to my colleague, Dr. Shepard, for help at many points. I owe most to my wife, who has given constant advice in matters PREFACE IX of expression, and has been of great service in the me- chanical preparation of the book. I desire also to express my thanks to authors and publishers for permission to reproduce illustrations. I am indebted to The W. B. Saunders Company and Professor Howell for figures from 'The Text-book of Physiology' and the 'American Text-book of Physi- ology' ; to Dr. L. F. Barker for figures from his 'Ner- vous System ' ; to Henry Holt and Company and Professor Angell for cuts from his ' Psychology ' ; to Houghton Mifilin Company and Professor Jastrow for figures from 'Fact and Fable in Psychology'; to The Macmillan Company and Professors Titchener and Calkins, respectively, for figures from ' A Text-book of Psychology' and 'A First Book of Psychology'; to Professor Swift for a Curve of Learning, and to Professor von Frey for permission to adapt his Tem- perature Scale. Ann Arbor, Mich., April 25, 1911. PREFACE TO THE SECOND EDITION I HAVE made numerous changes in this edition to bring it abreast of the most recent results in the science, to improve the expression, and to increase its value for class-room use. A new chapter has been added on Types of Mind which introduces some of the more general results of mental testing, the chapter on Emotion has been largely rewritten, much new matter has been added to the chapter on Memory, and new paragraphs have been added or old ones rewritten in most of the chapters. For the convenience of the teacher and of the student who desires to review for himself, the questions and exercises have been revised and con- siderably extended. Although each teacher will desire to make a.Ust for himself, these will, it is hoped, be useful as a basis. It is with pleasure that I acknowledge numerous suggestions from many colleagues which have aided much in the present revision and in minor revisions in earher reprintings. I wish that I could mention all by name, but the Ust is too formidable. I am indebted to my colleagues Professor Adams and Dr. Grifi&tts and to Professor Hayes of Mount Holyoke for help with the questions. Professor Whipple has read the chapter on Types of Mind and made valuable sug- gestions. I desire now to thank aU for their help and courtesy. ^ B Pillsbtoy. Ann Arbor. November i, 1919. TABLE OF CONTENTS CHAPTEH PAGE I. Introduction i II. The Nervous System 17 III. Neural Action in Relation to Consciousness AND Behaviour 49 IV. Sensation 64 V. Selection and Control — Attention . .112 VI. Retention and Association . . . .141 VII. Perception i6g VIII. Memory and Imagination 204 IX. Reasoning 241 X. Instinct 267 XI. Feeling 288 XII. The Emotions 304 XIII. Action and Will 326, XIV. Work, Fatigue, and Sleep 358 XV. Interrelations of Mental Functions . -374 XVI. The Types of Mind 388 XVII. The Self 408 XIU ESSENTIALS OF PSYCHOLOGY CHAPTER I INTRODUCTION Psychology the Science of Behaviour. — Psychology is defined traditionally as the science of mind. This is the translation of the two Greek words from which ' psychology ' is compounded. The definition is now open to many objections. The most important of these is that the word ' mind ' has in the course of long use taken on many meanings and implications which do not concern psychology as a science. Various terms have been suggested to avoid these objections. Psychology has been defined as the ' science of consciousness,' or as the ' science of experience subjectively regarded.' Each definition has advantages, but no one so far sug- gested is free from objection. It is most satisfactory to give up the attempt to find a single word that will designate the facts covered by psychology, and to in- dicate the actual phenomena that it studies, — the evidences of mind. First of these is behaviour. We distinguish a man in the full possession of his senses from an imbecile by the character of his acts. We measure the intelligence of an animal by its accom- plishments. Mind is known from the activities of the 2 THE ESSENTIALS OF PSYCHOLOGY organism. Psychology may be most satisfactorily de- fined as the science of behaviour. We shall discuss human behaviour. This definition makes it possible to treat man as objectively as any physical phenomenon. It considers only what he does. Viewed in this way the end of our science is to understand human action. The practical end is to determine upon what human capacity depends and, in the light of this knowledge, to discover means of increasing man's efficiency. In many fields of in- dustry it is becoming more and more evident that an understanding of the laws of human efficiency is quite as important as a knowledge of mechanical laws, that it is quite as important to know what a man can do in a given time and how he should work to obtain the best results as to know the laws for the production of energy in boiler and engine. In fact, it is appreciated in many industries that further progress must wait upon increased knowledge of the human instrument. Psychology is concerned only indirectly with these prac- tical problems. Science always endeavours to under- stand the laws of nature for themselves and is indifferent to the applications that may be made of them. Psy- chology is interested in the conditions of learning and forgetting, of imagining and reasoning, and in the methods of acquiring skill in various activities without any thought of the use that may be made of the knowl- edge. It is probable, however, that all suggestions for improving the efficiency of individuals must be based upon these laws. Indeed, many rules have already been developed from psychological experiments and DEFINITIONS OF PSYCHOLOGY 3 more are foreshadowed in the general principles now estabhshed. If psychology is to be defined as the science of human behaviour, the term ' behaviour ' must be used in the very widest sense. It must include everything from the simplest movements of walking or of fingering the pen to the activities involved in swaying an audience by speech or in carrying to completion some great engineer- ing work. Certain of the very simplest acts, such as winking and other reflexes, are fairly within the range of physiology. But even these must be taken into consideration by psychology, because the most com- plicated act can be understood only when analysed into its components which are reflexes or closely related to reflexes. Even the simplest forms of behaviour must be studied by the psychologist if he is to know the laws that govern the more complicated forms. No form of human behaviour, from the simplest to the most com- plex, falls outside of the province of psychology. As a , science our knowledge of human behaviour must be organised and referred to a system of general principles. A science of human behaviour cannot be limited to a series of aphorisms or chance observations about man. ' Perseverance wins success ' is related to the psychology of conduct in very much the same way that ' an east wind brings rain ' is related to the science of meteor- ology. Each statement embodies the results of nu- merous observations, but it has no close cormection with other facts or general laws. In a science these observations must be related to other bits of knowledge and the whole organised into a consistent system that 4 THE ESSENTIALS OF PSYCHOLOGY sjiall harmonise with the results of other sciences. Scientific laws are based on carefully chosen data and in consequence possess wide validity and are not likely to be vitiated by popular prejudice or ill-founded tradi- tion. They give each particular fact a perspective and make it easy to recall and to use each new observation. Study of Behaviour Involves Consciousness. — To define psychology as the study of behaviour does not imply, as has been asserted at times, that we can neglect consciousness. For most individuals, consciousness is as much a fact as the existence of any external object. When a man acts he is aware that he is acting and also aware of the stimuli that produce the act. This aware- ness is what we mean by consciousness. While the reader might at this moment be observed by a friend to hold the book and move the eyes by jerks across thfe page with an occasional frown as a difficult sentence is met, the reader himself is aware of the sense of the ma- terial, and thinks in some part the ideas intended by the writer. The observer appreciates the behaviour, the reader, consciousness. In this case behaviour is the immediate outcome of consciousness and can only be understood through it. The frown is explained by the hesitation in getting the meaning of a sentence, and that is most evident to the reader. While many kinds of activity are best known from the inside, others may be as well known from the outside. Thus the capacity of an individual for assimilating the material of this chapter may be determined better by the instructor who assigns it and quizzes on it than by the student. This is particularly true if the reading is done under CONSCIOUSNESS AND BEHAVIOUR 5 the observation of the teacher. The differences in capacity to learn and repeat can be explained only through long study of the individual in the light of earlier training and habits of work. Consciousness an End. — Psychology, then, must study consciousness as well as behaviour. This is necessary first because much of behaviour is known only from the report of the actor and many of the conditions of behaviour can be studied only through consciousness. This holds particularly of the more complicated acts, of the lines of conduct determined by remote events in the life of the individual. In the second place, consciousness is worth understanding for itself. For the individual man, be he naive or erudite, nothing is* so interesting as the working of his own mind. Much of the consciousness of an individual is followed by relatively slight movements, while the consciousness itself is a matter of great moment. Had it no other value, to understand consciousness would be suflScient to warrant the existence of the science. Consciousness is at once an important means of understanding be- haviour and an interesting object of investigation for itself. Consciousness and behaviour are closely re- lated; consciousness in others is known only through behaviour, behaviour in ourselves and ultimately in others is known only through consciousness. If one is made the end, the other must be the means ; if either is understood in its completeness, the other will also be known. They are the inside and outside of the same organism. Even if in the present stage of development of the science it seems best to subordinate consciousness 6 THE ESSENTIALS OF PSYCHOLOGY to behaviour in the definition of psychology, for the sake of escaping ambiguity, we cannot eliminate conscious- ness from description and explanation. Psychology is the science of behaviour, but behaviour must be studied both through the consciousness of the actor and by observation of the acts of others. Mind, Consciousness, and Mental Process. — Before attempting any discussion of mental states it is necessary- to define certain of the terms that are to be used. Viewed from within, psychology seeks to explain the experiences of the individual as they run their course, — to under- stand the various perceptions, memories, imaginings, and so on which together constitute the mental life. Any one of the states that may be regarded as detached from the mass for separate consideration is designated a mental process. Your idea of this book as you read it is a mental process, your memory of reading the book yesterday or of the assignment for study is a mental process, as is the flitting thought that you would much rather be out for a walk than reading. Consciousness is the term technically used to designate the sum total of mental processes at any moment. Thus, the perception of the book, the background of tactual and organic sen- sations that are receiving no particular attention at the moment, the vague emotional dissatisfaction that you are kept indoors on a pleasant day, and many other more or less definite mental processes combine to con- stitute your consciousness at this moment. Mind is the word that designates the entire series of conscious states of an individual from birth to death. It is the most inclusive of the series of terms and covers all INTROSPECTION 7 processes, . active and passive. Experience includes practically the same mass of states, but it is a little more passive in its implications. All of these terms apply to the description of behaviour as observed from within, the mental antecedents and accompaniments of behaviour. The description of behaviour as it presents itself to the outside observer needs only the vocabulary of popular speech and requires no preliminary com- ment or definition. The Methods of Psychology. — As has been said, be- haviour can be studied in two ways : by observation of another's acts and by observation of one's own conscious states. Observation of another, or what in psychology is known as observation, requires no special comment as a method. In all essential respects it follows the rules of observation common to all of the sciences. Self-obser- vation, known technically as introspection, seems at first sight to offer more difl&culties and to require more safeguards. The question has been raised whether in- trospection is possible at all. The doubt arises from the assumption that the very observation of a mental state changes that state. One does not have the same mental state when questioning how one knows that the approach- ing footsteps are Smith's, as when one interprets the sounds to mean that Smith is coming. One cannot at the same moment wonder what one is doing and do it to the best advantage. This objection proves to be less serious in practice than in theory. AU mental states per- sist for a little time imchanged and it is possible to ob- serve them during this persistence. One does not ob- serve the mental state at the time it is happening, but 8 THE ESSENTIALS OF PSYCHOLOGY examines it a moment later in memory. Observation in memory is accurate and does not alter the process investigated. Observation in any natural science re- qiiires the same reliance on momentary memory. One cannot at the same time make an observation and record it. If one tried, mistakes would be made. A thermometer reading, e.g. is taken and held in memory until recorded, and then still later it is interpreted or used in the explanation of related facts. Introspection is no more difficult or uncertain than is observation of external phenomena. Experiment. — Within the last generation methods have been developed by which both introspection and observation can be carried on under experimental conditions and with the aid of instruments of precision. Experiment makes it possible to control accurately the conditions and antecedents of mental operations. It is possible now to remove from distracting stimuli the individual who is introspecting or being observed, to measure accurately the stimuli that are permitted to affect him, and to record his responses. It is a com- monplace that a man who is embarrassed will blush. Delicate physiological instruments used in the psycho- logical laboratory show that the blush is only a height- ened effect of the changes in circulation 'that take place in all parts of the body in coimection with almost all mental processes. Similarly it was first observed with the unaided eye that the eyes move by jumps during reading. Later it was found possible to photograph the movements of the eyes, and these results brought out important laws that could not have been known other- • EXPERIMENT IN PSYCHOLOGY 9 wise. Introspection has been aided principally by re- cording the times that elapse between different parts of a mental operation. The times required have been combined and the results emphasised relations that were unnoticed in introspection. While experiment is only a means of increasing the accuracy of observation and introspection, it has through its wide application made possible important advances in nearly every field of psychology. To its great benefit psychology has become an experimental science. But momentary introspection and observation com- bined, even with all the help that may be had from experiment, do not exhaustively explain behaviour or consciousness. The observer sees the occasion for action and notes the response ; the actor sees the object and feels the response, but neither knows what happens in between nor appreciates fully the conditions of the act. For example, a wasp approaches, the man draws back or strikes. The observer notes the occasion for the movement and the movement itself, but nothing more. The man attacked sees the wasp and knows that he is moving or has moved, but 'nothing more. Neither can know why the movement takes place. One sees the stimulus vanish into the physical organ- ism and movement result; the other sees the insect, moves, and all the time is perturbed by an emotion, bu£ neither can absolutely foresee the act, neither knows why it comes. These more fundamental ex- planations may be supplied in part on the basis of present knowledge. Two elements must be taken into consideration in the interpretation, — the character lO THE ESSENTIALS OF PSYCHOtOGY and nature of the action of the nervous system, and the past life and native endowment of the individual. One can understand what intervenes between the ex- citation and the movement only if one can trace the course of the impulse through the nervous system. The earlier history of the individual and of the race also plays a very large part in the determination of all sorts of behaviour. The man's responses will differ accord- ing to the amount and nature of his experience with wasps. The influence of earlier experiences can be traced in many more subtle ways in the interpretation - of any mental phenomenon. Both the nervous system and the effects of earlier life upon the acts of the in- dividual can be known only through observation and introspection, controlled and recorded, together with much experiment and reflection upon the connections of present with past activities. Human behaviour, then, can be understood by careful, long-continued observation of man in action from the inside and from the outside, and by relating the results of these observa- tions to the earlier experiences of the individual and to the facts concerning the nature and action of the nervous system established by the anatomist and the physiologist. Relation of Psychology to Other Sciences. — The re- lations of psychology to the other sciences are particu- larly close and important. The biological sciences shade over into psychology so gradually that it is not always possible to decide whether a problem belongs to psy- chology or to one of the biological sciences. The sciences that explain the nature and action of the hu- man body, the sciences of anatomy and physiology, PSYCHOLOGY AND BIOLOGY II merge gradually into psychology. One can under- stand behaviour only if one knows something of the living organism, of the sense organs that receive the impression from without, of the muscles that produce the actions, and of the nervous system that connects them. From the outside one can understand man's behaviour most fully and easily by comparing it with the behaviour of animals and tracing the gradual de- velopment of man's action in connection with the simpler forms of animal behaviour. Experimental biology gradually shades over into experimental psy- chology. The biologist has recently been devoting himself very largely to the problems of animal be- haviour. The light cast upon human conduct by these experiments is only less important than that cast upon the actions of animals themselves. Still more general results of biological science have been profoundly im- portant for the explanation of human consciousness. The very general acceptance in recent times of the doctrine of evolution has forced us to read the story of mind in the light of the development of the human organism from the lower forms of life. The result is a very much fuller understanding of many of the more fundamental phases of hmnan activity. All of the physical sciences furnish some material for the psy- chologist, since the sense processes can be understood only in connection with the physical forces that act upon the organism. The Social Sciences. — In addition to the sciences from which it receives material and methods, psychology has come into a position where it may offer help to 12 THE ESSENTIALS OF PSYCHOLOGY many sciences. If psychology can give information concerning human behaviour, it is evident that all the human and social sciences may look to it for aid in the solution of their problems. Sociology, or the study of man in the group, evidently must foimd its results upon a study of the individual. In less degree, history, when it seeks to trace coimections between its observed facts, must look to psychology for its fundamental principles. Economics, too, works with psychological materials. Its fundamental problems are essentially psychological. Values and human needs are largely mental. It must be said, however, that psychology is least well developed in the fields where it would be most helpful to the historian and to the economist. Last of all, the relations of psychology to philosophy are very numerous and are those of mutual helpfulness. Psy- chology was the last of the sciences to separate from philosophy, the parent of aU of the sciences, and the bond is still very close. The history of psychology is still very largely a part of the history of philosophy. The results of psychology constitute much of the foun- dation of philosophy, and on the other hand philosophy supplies the psychologist with general principles and sets very many of his problems for him. Practical Applications. — Of the immediately prac- tical subjects, education has probably made the largest demands upon the results of our science. Learning and teaching are both psychological operations. When any real attempt to understand either is made, education becomes an application of psychology. This is more and more appreciated in the modern schools, and in APPLICATIONS OF PSYCHOLOGV 13 them psychology and education are coming closer and closer together. The psychologist is paying more atten- tion to the problems of the educator, and the modern educational theorists are making more use of the results of psychological investigations. But the applications of psychology need not be confined to education. With the advance of knowledge all who have to deal with man will look to the psychologist to increase the knowl- edge that may be put at his disposal. The physician and the lawyer, the advertiser and the clergyman, are all dealing in one way or another with psychological problems. To the physician and the advertiser psy- chology has already given appreciable aid and it should be in a position at no distant day to offer help to the others. Too much of practical value is not to be ex- pected from the science, however. In all of these fields there is a great difference between principles and prac- tice. Often the rules that grow from daily practice are in advance of scientific principles. Science serves but to explain the truth of the practical precept. Theory does not always lag behind, and one can already see places in which psychological results point the way to improvement in practice. As a rule, however, all of the arts are more grateful for confirmation of the established custom than for the suggestion of improve- ments. This incomplete list of the relations of psy- chology may suffice to indicate how closely psychology is bound up with other fields of human knowledge. Any science that tells us anything of the nature of the physical vmiverse or of the nature of the living organism will throw some light upon the problems of psychology. On the 14 THE ESSENTIALS OF PSYCHOLOGY other hand, any science that deals in any way with human conduct, or that is dependent in any way upon human capacity (and what science is not?), can draw with profit upon the results of psychology. Either as creditors or debtors, aU the sciences stand in some rela- tion to psychology, the science of human behaviour. Divisions of Psychology. — Each of the sciences that furnish material for psychology has given rise to a differ- ent sort of psychology, or at least to a different name for a psychological work. Psychophysics grew out of an attempt by Fechner to determine the quantitative relations between the physical stimulus and the in- tensity of the mental state. Physiological psychology is the name Wundt gives to his work, that has for its primary object the explanation of the relation between mental states and the bodily organism. Each of these treatments has grown beyond its original scope to cover the entire field of psychology. The name now indicates nothing more than the attitude that is taken toward the subject. Other branches of the subject are named from the phase of behaviour that is discussed. Genetic psychology treats of the development of behaviour. The behaviour of animals has given rise to a flourishing science and in the last few years has made much progress. Child study has made numerous contributions to the more theoretical problems. Each has thrown some light upon the nature of adult human behaviour, as well as collected many facts in its own field. Abnormal psychology, the study of abnormal and imperfect individuals, has also been a rich field for the psychologist and has given many important results. Each of these partial sciences may BRANCHES OF PSYCHOLOGY 1 5 be considered by us only so far as it throws light on the behaviour of the adult normal man. A few years ago it was customary to classify psychological systems ac- cording to the methods of investigation. There was a rational psychology, an empirical psychology, an intro- spective psychology, and aii experimental psychology. Now it is seen that no science can be developed by one of these methods alone, and all are used by any psy- chologist worthy of the name. At the most it can now be said that there is an empirical and a rational method in psychology, a method of introspection and a method of observation, both aided by experiment. The results of each method shoula be the same if the methods are adequate. And as a matter of fact the results are the same although one method may be adequate for one problem, another for another. All the so-called branches of psychology, then, are closely related to the central science and at the most designate merely different fields for observation, or the preference of writers for different methods. Summary. — Our problem is to imderstand behaviour, and to investigate consciousness as the immediate ante- cedent and condition of behaviour. To understand either consciousness or behaviour it is necessary to know something of the character and action of the nervous system. As has been said, all knowledge of the world comes to consciousness through the nervous system and all expressions of consciousness in action are rendered possible by the nervous system. This is not psychology but is a necessary prerequisite for psy- chology. The psychological inquiry proper begins with l6 THE ESSENTIALS OF PSYCHOLOGY an analysis of the elements of behaviour and of con- sciousness, both structural and functional ; it involves a study of how these elements interact and imite in the constitution and control of the more complicated activities. The various partial problems will be, taken up in the order named : first, a brief statement of the facts of nervous physiology that have a bearing upon psychology ; second, an analysis of the facts of con- sciousness and behaviour to discover the elementary components, and third, a study of the more complicated activities in the light of these simplest forms. QUESTIONS 1. What are the evidences of mind (a) in an animal, (b) in another man, (c) in yourself ? 2. How far does knowledge of behaviour involve consciousness ? 3. What is a science ? Is it possible to have a science of mind ? of behaviour? 4. What is the method of introspecting? What question of its accuracy has been raised ? How can the objection be met ? 5. What is a psychological experiment ? Illustrate its applica- tion to observation and to introspection. 6. What sciences aid most in the solution of psychological problems? 7. Enumerate some of the divisions of psychology. What is the basis of division in each case ? REFERENCES Angell : Chapters in Modern Psychology. TiTCHENER : Textbook of Psychology. Chapter I. CHAPTER II THE NERVOUS SYSTEM Behaviour must be explained in large part by the action of the nervous system. It does not follow that the operation of the brain or of the nervous system is open to observation. On the contrary, one knows nothing directly of the nerves or of nerve-cells. Only consciousness and behaviour are known. The parts that act are altogether hidden, the effects alone are known. So completely is this true that even Arifetotle, the most acute observer of antiquity, had no suspicion that the brain had much to do with mental processes. He held that the brain was merely a gland for the secretion of tears and that its only function in thinking was to cool the animal spirits that originated in the heart and cir- culated through the brain. Dependence of Consciousness on the Nervous System. — If one cannot observe the workings of the nervous system directly, one may ask what right we have to assert that consciousness is related to it. Two facts bear most strongly in proof of the relation. The first is that behaviour increases in complexity with increase in the complexity of the nervous system. In the rudi- mentary organisms no nervous system can be distin- guished. The same protoplasm that cares for the nutrition of the body also receives the stimulus and c 17 48 THE ESSENTIALS OF PSYCHOLOGY contracts. All parts are alike and each does aU things necessary to its own welfare. The movements are correspondingly simple and the organism poorly ad- FlG. I. — Shows the development of pyramidal cells from the cerebrum of vertebrates. . (A-D) neurones from an ascending series of vertebrates, (a-«) the stages in the development of cells in man. {A) frog; (B) lizard; (C)rat;(D) man. (o) neuroblast without dendrites; (6) commencing dendrites; (c) dendrites further developed ; (d) first appearance of collaterals ; (e) further development of collaterals and dendrites. (From Howell: 'Text-book of Physiology,' Fig. 83, after Ramon y Cajal.) justed to its surroundings. As we go higher, nerve-ceUs are present, but they are few and the connections are relatively scant. Behaviour is more complicated as the nervous system is better developed. In the lower verte- THE NERVOUS SYSTEM I9 brates, a reptile for example, the nervous system is larger, the parts are more highly developed, and the connections between the elements are more numerous. The movements are also more mmierous, and they are more closely adapted to the environment. The animal is better equipped to live and to act. The climax of evolution, both in behaviour and in the structure and connections of the nervous system, is found in man. In short, mind or behaviour develops in the same degree as the nervous system, whether we measure the develop- ment of the nervous system by the character of the nerve unit, by the nature of the connection between nerve units, or, with few exceptions, by the ratio of nervous tissue to body weight. Defects of Brain and Mental Defects. — The evidence from pathology for the close relation of mind and body is even more striking. A slight injury to the head may destroy consciousness. Injury to certain small portions of the brain gives rise to paralyses of small groups of muscles, to other portions causes the loss of some sense. Injury to almost any portion of the nervous system impairs some capacity in some degree. Conversely if behaviour or consciousness is affected, some change in the nervous system is usually found. These two facts taken in connection with what we know of physiology, and what can be seen directly of the action of nerve in connection with muscle in the lower organisms, sufl&ce to make indisputable the very intimate relation between mind and brain. Development of the Nervous System. — It is perhaps easiest to xmderstand the nervous system if we consider 20 THE ESSENTIALS OF PSYCHOLOGY it in connection with the development of the animal organism from the lowest forms. AU higher organisms can be regarded as developed from the simplest of uni- cellular forms. The amoeba may be regarded as the type of the original simplest animal. The amoeba is a single cell. This cell is at once nervous system and muscle, mouth and stomach. When it moves, the cell contracts or expands or changes its form as a whole. When it is stimulated, the impression is received by part of the cell and the result is to call out a contraction iii the same and in neighbouring parts. When the stimulus is a food particle, it induces a movement of the cell or part of it toward the particle and about it until the particle is entirely surrounded. Then the same protoplasm that received the stimulus apparently acts as a digestive organ to assimilate the morsel. The original cell is thus possessed in some degree of the capacities of all parts of the human or higher organism. The development of the higher organisms may be re- garded as due to the coming together of many of these simplest cells to form a single whole or colony. Whether or not separate cells ever did combine in this way is a matter of indifference. It at least illustrates the nature of the relation of simple cells to the more complicated organism. The different cells take on different fimc- tions and, in many cases, different forms. No matter how changed, each cell of the body is regarded as a separate organism that has lost something of its in- dividuality, but is nevertheless descended directly from the independent amoeba-like prototj^e. The bone cells perhaps are most removed from the original ; the white PARTS OF THE NERVOUS SYSTEM 21 corpuscles of the blood have changed hardly at all. Next to the white blood corpuscles the nerve-cells probably have been least changed from the original type. Except for its dependence upon the other mem- bers of the colony for its food, and for the fact that the other cells serve to give it form, a nerve-cell is still independent. The function of the nerve-cells in the colony is to make* possible the coordination of the activities of the cells. When one cell is stimulated, a group of cells at a distance, constituting a muscle, may respond. The nerve-cells compel the parts to act to- gether and make the organism a unit for action rather than a mere mass of separate entities. The Divisions of the Nervous System. — As one looks at the central nervous system of man, one can observe three fairly distinct structures, (i) The largest is the cerebrum, enclosed by the skull. This is a mass roughly like a sphere much corrugated on its surface by irregular folds. The folds are known as convolutions; the de- pressions between, as fissures. Two of the fissures are most prominent. One, the median fissure, serves to divide the cerebrum into two parts throughout more than half its height. It is in the approximate centre of the mass. This division makes it customary to regard the halves as distinct, and hence we speak of the two hemispheres. The other, on the outer side of each hemisphere, is not so deep, and is known as the fissure of Sylvius. Slanting upward from the lower front part of the brain, it will be seen from the diagram to con- stitute a prominent landmark. (2) Below the cerebrum at the back are large masses of nerve-cells and connect- Cer. Fig. 2. — Shows the nervous system as a whole. The figure on the left repre- sents the relation of the nervous system to the body as a whole, that on the right the nervous system exposed and seen from the front. (Cer.) the cere- brum ; (Cb.) the cerebellum ; (Sp. C.) the spinal cord ; (P) the pons ; {M) the medulla. The other letters in the right-hand figure designate nerve trunks going to the central nervous system. (From Angell: 'Psychology,' Fig. 12.) 22 PARTS OF THE NERVOUS SYSTEM 23 ing masses of white fibre. These together constitute what is called the brain stem. Among them are the cerebellum at the back, the pons in front, and the medulla below. Each can be made out in Figure 2. The other structures in this region are too numerous to mention, and the action is too complicated to dis- cuss within the limits of our brief sketch. (3) Lowest is the cord. The whole mass is contained in a bony box. The cerebrum, the cerebellum, and the brain stem are within the skull; the cord, within the spinal column. From the central nervous system nerves extend to the sense organs and muscles. The sense organs in the head send their nerves to the brain stem. The sensory nerves entering the cord have enlargements near the cord, the spinal ganglia, which contain cell bodies. In addition to the central nervous system which alone we shall consider, there are masses of cells in many parts of the trunk and head with relatively few coimections with the central system. These are the ganglia of the sympathetic system. White Matter and Grey Matter. — Each of these large masses when cut across shows some tissue of a reddish grey colour, the grey matter, and other tissues of glistening white, the white matter. Isolated masses of grey matter are called ganglia (singular, ganglion). The grey matter is made up of cell bodies, the white matter of nerve fibres. In the cord the grey matter is in the centre, where it constitutes a butterfly-shaped central core. The butterfly shape is well marked in the sections, as can be seen in Figure 7. In the cere- brum and the cerebellum the cell bodies are for the 24 THE ESSENTIALS OF PSYCHOtOGY most part upon the cortex (bark), the outermost layer ; the white comiecting parts are within and below. In the medulla and brain stem, no law for the distribution of white and grey matter can be stated in a few words. Strands of fibres are interspersed with masses of cell bodies, — here one, there the other, is on the surface. The Growth of the Nervous System. — The architec- ture of the different parts can be imderstood most clearly from a study of the development of the system. In the early stages of the embryo the central nervous system is but a groove in the outer layer of the mass. This groove gradually becomes deeper, and the tops of the sides ap- proach imtil they grow together to form a tube. The different parts of the entire nervous sys- tem grow from different parts of the wall of the tube. The origi- nal hollow persists to the adult stage and is modified by the changes in the shape of the wall. The brain develops from the anterior, the cord from the posterior part of the tube. The anterior portion of the tube is first constricted in two places tc form three vesi- cles ; later the anterior and posterior again divide to make five vesicles in all. See Figure 3. The hemispheres of the cerebrum grow out at the sides of the anterior or head end and grow up and back until they cover the Fig. 3. — Development of the brain vesicles. The hemi- spheres are seen growing from the sides of the ante- rior end. The tube shows the first two constrictions and three vesicles. ELEMENTS OF THE NERVOUS SYSTEM 25 structures that develop from the other vesicles. The structures of the brain stem develop fsy the thickening of the walls of the four lower vesicles, or swellings of the tube, and the cord from the posterior part of the tube. The connections of the parts retain in the adult many traces of the earlier stages of development. The relation of the parts was not well understood until the development of the system was known. The Elements of the Nervous System. — We may represent the nervous system most clearly as a colony of some eleven thousand million amoeba-like organisms crowded together for the most part within the bony wall of the skull and spinal column with prolongations extending to all parts of the organism. The unit of the nervous system is the neurone. Each is connected with numerous othfer units, and also at innumerable points stands in close functional relations to the other cells of the body. To understand the action of the nervous system we must learn to know (i) the character of the single unit and (2) the connections the units make with each other and with other parts of the body. The neurone consists of a cell body and two sorts of pro- longations or processes, the axone or axis cylinder, and the dendrites. The axone is a long, hairlike extension that may reach more than half the length of the body. Most nerves are bundles of axones. The axone or- dinarily terminates by splitting into branches, — the end-brush. The dendrites are similar to the end-brush. They are made up of a number of branches of the cell protoplasm and are usually relatively short. The func- tion of the dendrite is to carry impulses to the cell 26 THE ESSENTIALS OF PSYCHOLOGY bodies; the function of the axone is to carry them away from the cell bodies. The end-brush of one cell is ordinarily in contact with, or very near, the dendrites of other cells. The points of contact are called the synapses. The form of the neurone varies greatly. In some cases the cell body is approximately round and Fig. 4. — A group of human nerve-cells drawn to the same scale, (o) small cell from ventral horn of the cord; (6) cell from Clarke's column, thoracic cord ; (c) small nerve-cell from tip of dorsal horn, thoracic cord ; (d) spinal ganglion cell, cervical root ; (e) three granules from cerebellum ; (J) Purkinje cell from cerebellum ; (g) small pyramidal cell from second layer of central gyri of cortex ; (A) giant pyramidal cell from the same region. (From Don- aldson, in the 'Amer. Text-book of Physiology,' after Adolf Meyer.) relatively smooth. In other cases it is more spindle- shaped, in others again the surface is much broken by the processes. In certain parts of the cortex the cells are almost pyramidal in their general shape, with pro- cesses at each of the angles. In the spinal ganglia the cells that receive and transmit the impressions from the THE NEURONE 27 skin and muscles have dendrites and axones combined in a single process. The division is only recognizable some little distance from the cell body. All of these forms are to be regarded as departures from the type. But the character of the ceU has no demonstrable rela- tion to the function. The number of dendrites and the number of branches of the axone determine the number of connections that the cell may make ; the form of the cell depends upon the number and position of the processes, but so far as is known that is the only re- lation that holds between form and function. The Parts of the Neurone. — The neurone is a vital unit. The processes receive nourishment only from the cell body, and when cut off from the cell body, they die. The substance or protoplasm of the cell body is continu- FiG. 5. — Longitudinal and transverse sections of medullated nerve fibre from the sdatic nerve of frog. The myelin sheath is shown in black, the central proto- plasm shows its fibrous structure. (From Barker, Fig. 80, after Biedermann.) ous with the protoplasm of the processes. The central protoplasm of the neurone shows no important differences in the character of its parts. The only points worthy of mention are : (i) the sheaths of the axone, and (2) the nucleus of the cell body. Two sheaths may be distin- 28 THE ESSENTIALS OF PSYCHOLOGY guished, an inner or myelin sheath, and an outer, the neurilemma. The inner sheath is found in all except a few fibres in the higher centres, the second is present outside of the central nervous system. In the sympa- thetic system the outer sheath is usually the immediate covering of the protoplasm. The myehn sheath seems to have some importance for the function of the neurone, but just what has not been made out. The nucleus of the cell stands in some vital relation to the action of the cell. In fatigue the nucleus has been shown to become smaller and irregular in outline. Its exact function, however, has not been determined. Recently small fibrils have been traced within the substance of the nerve-cell, but their function also is not agreed upon. The Transmission of the Impulse within the Netoone. — What goes on in the neurone when it acts has not been definitely determined. Theories have varied at different periods from assuming that some fluid was transmitted through the nerves or that some wave was propagated along the substance of the nerve, to the assumption that the action was electrical in character. To-day a generally accepted theory is that the impulse is due to some form of chemical change which spreads through the neurone. This hypothesis is supported by several facts, (i) The rate of propagation, about one to two hundred metres a second, is altogether too slow for electrical transmission, but is within the Umits of chemical action. (2) The action of the nerve-cell is accompanied by electrical phenomena. Whenever a nerve is stimulated, an electric current passes from the cut end of the nerve to the uninjured sheath. If a THE NERVOUS IMPULSE 29 frog's nerve be dissected out and one end be connected to a point on the neurilemma through a delicate galva- nometer, the galvanometer will indicate the passage of an electric current when the nerve is stimulJated in any- way. Similar electric currents are induced, as is well known, by the chemical action in a battery. (3) The action of nerve-cells frees certain chemical substances, products of decomposition, that are removed by the blood. These three facts point to the assumption that action of the nerves is due to some chemical change. This assumption fits in with most of our detailed knowl- edge of the action of the nervous system. Our picture of the propagation of an excitation through a neurone is that it corresponds to the spread of chemical processes through its substance in very much the same way that a spark runs along a train of gunpowder. In the nerve the burning is but partial, and the materials used up are constantly replenished from the blood, but both processes are oxidations, — in each the destruction spreads from part to part within the mass. An alternative theory that is coming into favor re- gards the local electrical effects, excited by the chemical changes, as more closely connected with the nervous conduction. In the normal living organism the change is transmitted only in one direction. The stimulus is always received by the dendrite and is transmitted along the axone to the end-brush. It never runs in the reverse direction. One apparent exception may be noted. The cells in the spinal ganglia receive the im- pressions from the skin by a long process that extends to the surface of the body and is in its structure similar 30 THE ESSENTIALS OF PSYCHOLOGY to an axone. We may either call this a peculiar form of dendrite or regard it as an exception to the law that the axis cylinder does not receive, but always transmits, the impulse. Which of the alternatives for disposing of the exception is to be adopted is not as yet a matter of common agreement. Our picture of the nervous system is of a mass of ten thousand milHons or so of these minute organisms en- closed within a bony case, the skull and the spinal column. Each cell is structurally independent, but the terminals are in contact. In the mass we ordinarily distinguish three sorts of neurones, — the sensory, the motor, and the associating. The difference is one of connection and function rather than of structure. The sensory are receiving neurones; the motor send im- pressions out to the muscles, while the associating neurones serve to bring sensory and motor neurones into connection. As the sensory neurones always lead towards the centre, they are sometimes called centripetal or afferent, and for a similar reason the motor neurones are the centrifugal or efferent elements. There is no constant difference in structure between sensory and motor neurones. The difference in function is prob- ably largely dependent upon the connections. In terms of neurones the white matter is made up largely of axones, the prolongations of cell bodies; the grey matter is a mass of cell bodies. Neither can be under- stood apart from the other. The white matter is merely a bundle of transmitting fibres, the grey matter nothing more than a mass of central cells, but every fibre of the white matter is a prolongation of some cell body and cannot live without it. REFLEX AKCS 31 The Connec- tions of Neu- rones. — The action of the neurone is de- pendent upon its connections. A cell never acts alone. It is always a link in a reflex arc. All action of an- imal or man is excited by some stimulus in the external world, and every sen- sory excitation ends in some movement. The reflex arc in the nervous system always has its origin in a sense-organ and ends in a muscle. In be- tween there may be any number of asso- ciatory cells, Fig. 6. — Shows the first and third of the three leveb. B, the short path through the cord; A, the longest path through the cortex. The second level through the brain stem is not indicated. (From Van Gehuchten : ' Systeme nerveux de I'homme.') 32 THE ESSENTIALS OF PSYCHOLOGY but these beginning and tod structures must always be present. The problem of action from the side of nerve physiology is one of determining the paths of connection between the sensory and motor neurones. The course of transmission from neurone to neurone is determined by the openness of the paths. These connections are in part fully formed in the organism at birth, in part they are acquired through the activities of the animal during Ufe. Of these paths of connection we may rec- ognise three levels: first, the direct connections of the cord ; second, the paths through the brain stem, the medulla, and general midbrain region; and third, the more indirect and complicated lines of connection in the cerebral cortex. Each is to be looked upon as a path between sense-organ and muscle. They are dififerent ways by which the sensory impression may be trans- mitted to the muscle : they are different primarily in the directness with which the transfer is made; the higher paths permit more connections and make pos- sible the cooperation of a greater number of sensory impulses in the control of movement. The Action of the Cord. — In the cord impressions from the skin and from internal structures are carried across to the muscles of limbs and trunk. Through it appro- priate responses are made to stimuli of various sorts on the skin. Drawing back the hand when burned is primarily due to the nervous connections in the cord. The simplest reflexes of the cord involve two neurones only. The end organ in the skin is connected with the dendrite of the T-shaped cell in the spinal ganglion, the axone of that cell extends into the butterfly-like section REFLEXES IN THE CORD 33 mtlt of grey matter in the cord, and the end-brush comes in contact with the dendrite of a cell on the anterior side of the cord. This motor cell in its turn sends out an axis- cylinder to a muscle. The chemical change induced by the physical stimulus travels to the cell body, thence to the end-brush or synapse, where it excites an impulse in the efferent neu- rone that travels down to the muscle. The chemical change is trans- ferred at that point from nerve to mus- cle and excites the chemical change involved in the muscular contrac- tion. The diagram shows that the spi- nal cord consists of a mass of white fibres which sur- round a core of grey matter. In the latter are the cell bodies of the motor nerves, and the associating or connecting neurones. The surrounding white matter is divided by the exten- sions or horns of the grey matter into four parts or columns. Of these the posterior is made up of axones from the cells in the spinal ganglia, is sensory in func- Fio. 7. — Shows the simple reflex connection through the cord. C?, T-shaped cell in spinal ganglion; sN, long dendrite or feledendrion to A, sense ending in skin. C, motor-cell connecting by axone n with muscle M. 34 THE ESSENTIALS OF PSYCHOLOGY tion, while the others are both sensory and motor, out- growths of cell bodies in the central grey or from cell bodies in the cortex or brain stem. The Paths in the Cord. — If the central grey may be regarded as the transferring station, the surrounding white constitutes the transmitting paths by which the cortex and higher centres in general are coimected with the world outside. The sensory tracts bring impres- sions in from the periphery and transmit them to the cerebrum. The motor tracts serve, on the other hand, to connect the upper centres with motor cells in the cord, and thus with the muscles of the lower parts of the body. Not only do these outer fibre layers connect the upper portion of the nervous system with sense- organ and muscle, but they also connect the different levels of the cord with each other. A sensory impulse excites not only muscles that have their cells at the same level in the cord, but also groups of muscles at different levels above and below. If we return to con- sider the simple reflexes, we find that the sensory stimu- lus may spread not merely to the single motor neurone or group of motor neurones at the same level, but it may make connections with neurones that lie higher and lower in the cord, or more frequently, it extends to neurones lying in the opposite side of the cord and pro- duces movements of members on the other side of the body. If one destroy the brain of a frog or, by pith- ing, cut the cord off from the upper nervous system, it will be seen that all of these reflexes may still be called out by stimuli. If a bit of paper moistened with acid be placed upon the left foot of a frog, the foot will be drawn up. If CONTROL OP REFLEXES 35 now the foot be held so that it cannot be moved, it will be foimd that the other is brought over to remove the stimu- lus. If this is not successful, the muscles of the forelegs and trunk will contract and the contractions will continue until the stimulus is removed or the neurones exhausted. The first movement (of the left leg) is due to the transfer of the stimulus to the motor cell, or cells, on the same side of the cord. When the foot is held and the stimulus grows strong enough, the impulse is transmitted to the group of neurones on the opposite side of the cord, and muscles of the right leg are contracted. When the excitation becomes still stronger, the discharge spreads to neurones higher up, and the muscles of the trunk and forelegs are made to contract. Fig. 8. — Shows a ssmapse from the optic lobe of a chick. (From ' Amer. Text- book of Physiology,' Fig. 76, after Van Gehuchten.) Action of the Synapse. — Since there are evidently many possible lines of transmission, the question natu- rally arises, what decides which of the many paths shall be followed? The answer is found in a recent theory that the course of the impulse is determined at the point of connection between (neurone and neurone, the synapse. The end-brush of the receiving neurone is in contact with the dendrites of several motor neurones. Each of 36 THE ESSENTIALS OF PSYCHOLOGY these points of contact or synapses has a different resist- ance. The path to muscles of the same leg is most permeable; next in degree of permeability are the S37napses to dendrites of the motor neurones that control the muscles of the other leg, while the synapses that connect .with the muscles of the upper trunk open with still greater difl&culty. The lines of discharge depend primarily upon the openness of the synapses. In these lowest reflexes the ease of transmission depends upon the character of the sjoiapses as they are determined in the individual at birth, and thus the responses are pre- pared in advance of any experience. When the sensory excitation is weak, only the easiest paths are followed. As the impulse becomes stronger, more and more diffi- cult s)Tiapses will be crossed, and the motor discharge will become more and more diffuse. Reflexes of the Second Level. — ■ At the second level of reflexes the same general laws hold. The possibilities of connection are, however, very much more numerous. Many senses contribute impressions and the muscles over which the discharge may take place now include all of the muscles of the body instead of the muscles of trunk and limbs only. The sjoiapses for the reflexes of this level lie in the region of the central nervous system be- tween the top of the cord and the cortex. The anatomy of this region is too complicated to be described within our limits, but the connections are made in the numerous accumulations of cell bodies found in the structures of the medulla, midbrain, and on up to the lower ganglia of the cerebrum. Wherever the s}aiapses may be located, we may distinguish two general groups of connections. FUNCTIONS or THE BRAIN STEM 37 First each stimulus tends to excite certain movements immediately and directly. Thus in the eye, when a ray of light falls upon the retina, the pupil at once con- tracts. This movement is called out by the sensory stimulus transmitted to one of the lower centres for vision. There the motor neurone connected with the muscles is excited and the pupil contracts. The visual impressions, too, excite and control the movements of the trimk and limbs through the midbrain centres and their connections with the motor tracts in the cord. A frog, for example, that has had its hemispheres re- moved will avoid obstacles in swimming or hopping and wiU give other evidences that its movements are guided by sight. In man the neurones of the brain stem are not so independent of the cortex, and it is difficult to demonstrate that they can act alone. The fimctions of these structures at the second level are : (i) to serve as reflex centres by which the senses at this level may be connected with muscles of the head ; (2) to connect the special sense-organs of the head with the motor neurones of the cord, and so with the muscles of trunk and limbs ; and (3) to connect the cortex with the sense-organs' and with the muscles. It is probable that all the sense- organs are represented in the brain stem by neurones, and that in every case the impulse from a sense-organ is transferred from one neurone to another in some ganglion in this region. The mechanism of the reflexes is the same as in the cord. The only difference is that the sources of excitation are more nmnerous and the pos- sibilities of connection are greater. Action of Cortex. — By far the most important divi- 38 THE ESSENTIALS OF PSYCHOLOGY sion of the nervous system is the cerebrum. In man the cerebrum is the largest of the nervous structures, con- stituting rather more than half of the total nervous sys- tem. It is also the part of the nervous system most Fig. q. — Localization of cerebral function. The figure opposite shows the outer surface of the right hemisphere ; the one above, the mesial surface of the left hemisphere. In both figures the motor areas are marked by horizontal shading, the sensory by vertical shading, while the associatory areas are unshaded. The doubtful or partially sensory or motor regions are indicated by dots. {S) is opposite the fissure of Sylvius; {R) above the fissure of Rolando. (Jlf) is above the motor region; (C) above the cutaneous and kinaesthetic area. (F) indicates the visual region ; (0) is below the olfactory area. The auditory closely related to consciousness. In fact, it is very doubtful if any consciousness at all accompanies the action of any other portion of the nervous system. Its structure and functions are very complex, but our guid- ing principles still suffice to explain its action. It, FUNCTIONS OF THE CEREBRUM 39 too, is made up of neurones in various connections, and the neurones act to transfer sensory impressions to motor neurones, and so to excite muscles. The only region is just below the fissure of Sylvius, above (H). (,FA) designates the frontal, {PA) parietal, and (,TA) the temporal association centres. There is some evidence that the dotted regions about the sensory and motor areas are areas in which particijar associations are formed with them. The diagram embodies the results of A. W. Campbell, but has been modified in one or two respects to agree with the results of Flechsig and Cushing. differences between it and the structures considered above are : (i) that it offers vastly greater possibilities of connection, and (2) that impressions received at an earlier period in the life of the individual play a large part in controlling the course of the movements. In 40 THE ESSENTIALS OF PSYCHOLOGY consequence the processes that intervene between stimu- lus and response may be regarded as much more impor- tant here than they are in any of the reflexes already considered. Localization of Cortical Functions. — Cell bodies are found for the most part only in the cortex or bark, a superficial layer of the cerebrum only a few millimetres thick. The inner mass consists of fibres, axones of cell bodies in the cortex or in the brain stem, which serve to connect different parts of the cortex, and the cortex with the muscles and sense-organs. We must distin- guish three sorts of areas or regions in the cortex. Cer- tain areas receive the impressions from the outside world and are known as the sensory regions. Others send out impulses to the muscles and are known in consequence as the motor regions. The remaining areas serve to connect the sensory and motor and constitute what are known as the association areas. The first two are often grouped together as the projection areas, since they represent regions of the body in very much the same way that parts of the screen may be said to represent the slide when a picture is thrown upon it by the projection lantern. The relation between these areas and the sense- organ and muscle is very close. Localization of Motor Areas. — The position of the motor region is more easily demonstrated. If the brain of a man be exposed for an operation and the motor area be stimulated electrically, some muscle of the body will respond and the same muscle or group of muscles will always respond provided the same region be stimulated in the same degree. The areas that CEREBRAL LOCALIZATION 4I correspond to the different muscles are sufficiently well known to permit the physician to decide what part of the brain is defective in case some group of muscles be paralysed. The motor area of the brain is shown in the diagram. It lies just in front of the central fissure, the fissure of Rolando, and extends upward from near the fissure of Sylvius to the median fissure and over to the mesial surface of the hemisphere, the wall of the median fissure. As is generally the case in the upper part of the nervous system, the right brain contains the motor centres for the left half of the body and vice versa. Sensory Areas. — The sensory regions are scattered and their positions are less certain than the motor regions. The part of the cortex coimected with the eye is in the back of the brain, the occipital region. The area to which vision may certainly be ascribed is in the cuneus, a wedge-shaped convolution on the mesial surface. It is marked in the diagram. The auditory region is in the temporal lobe, just below the fissure of Sylvius near its junction with the central fissure. The impulses from skin and muscle are received in the region just behind the central fissure. Smell is less certainly localized, but is probably on the mesial surface, as indicated in the diagram. Taste may be near it, but the localization is hardly more than conjecture at the present stage of knowledge. Association Areas. — It will be noticed that after all the regions with known relations to sensation and move- ment are enumerated, the greater part of the cortex is left without assigned function. It is the contention of 42 THE ESSENTIALS OF PSYCHOLOGY Flechsig, now generally accepted, that the remaining portions of the brain have as their function to make cross connections between the sensory and the motor regions, to unite sensory with motor, and sensory with sensory areas. For example, the axone from a cell body in the optic region extends to the intervening association region and there comes into contact with the dendrites of numerous association neurones, each of which in its turn will connect with other sensory or motor neurones, or with other association neurones. Each intervening asso- ciation neurone will increase the connections that a sen- sory neurone may make, and so increase the possible responses that the same stimulus may call out. Action of the Cortex during Speech. — If we turn from structure to function, we find that the nervous excitation transmitted from the sense-organ to the sensory cells in the cortex must sooner or later find its way to a motor neurone. In some cases the motor cell affected is in the same region of the brain. Thus movements of the eye may be excited by stimulating the occipital lobes, and it is probable that movements of the eyes evoked by visual stimuli may have a path in the cortex that does not extend beyond the wider limits of the optic region. More characteristic, however, are the interconnections that control the movements involved in speech. These are of interest because the disturbances of speech were among the earliest to receive an explanation. In ordinary repetition of spoken words, the excitation is transmitted from the ear by way of a lower centre to the auditory region, thence along the axones of sensory neu- rones to association neurones in the Island of Reil (the THE CORTEX IN SPEECH 43 bottom and sides of the fissure of Sylvius) and from there to the motor area for speech in the lower Rolandic region. Here the end-brushes of the association neurones come into functional union with the dendrites of motor neu- rones. The axones of the motor neurones end through the mediation of other neurones in the muscles of the vocal organs and the sound is repeated. That this is the approximate course of the nervous impulse we know from a comparison of the defects of speech with the injuries in different parts of the brain. If the auditory cells are destroyed in any way, the patient cannot repeat the words. The effect is the same as if the ear were destroyed. Again, if there is an injury to the associa- tion region in the Island of Reil, the ability to repeat words heard is impaired. Finally, if the motor centre for speech is injured, speaking of any kind will be im- possible. The condition is known as aphasia, — sen- sory aphasia is due to disturbance of the auditory region, motor aphasia to disturbance of the motor region. The existence of sensory aphasia is of- particular importance as an evidence that the action of the cortex is dependent, like the action of the lower centres, upon the excitations of sense, that all action is sensori-motor. There is no response unless an impulse is received from some sensory region. The relations of vision to speech, and of vision and audition to writing, follow the same general rules. When one reads aloud, the impulse is transferred from the visual area to the motor speech region through an association centre. Injury to the visual area or to the sight-speech association region may interfere with the process. The 44 THE ESSENTIALS OF PSYCHOLOGY resulting disease is known as alexia. Writing on dic- tation ordinarily disappears with speech in the sensory forms of aphasia. Each of these paths has been devel- oped through long practice and is relatively firmly es- tablished. Any other simple response to stimulation would take a corresponding course and would involve sensory, associatory, and motor regions. When the paths are less well established and the response is less completely prepared, as when one answers a question and several rephes are possible, the association regions probably play a larger part. There are more possible connections and-more open association paths, or at least the open paths in the association regions are more nearly on a par. In consequence there is smaller chance of prophesjdng in advance what course the response will take. The necessity for the cooperation of sensory, associatory, and motor neurones is none the less cer- tain. In addition to the connections between sensory and motor regions there are a number of cases in which two sensory regions must be connected. Thus when one touches a pencil in the dark, the picture of the object will present itself before the movement is made, or simultaneously with the movement. In this case the tactual neurones excite a visual neurone or group of neurones. In the perception processes such associatory transfers are the rule rather than the exception, as will be seen in a later chapter. Ordinarily the association leads finally to action of some sort, but so far as impor- tant action is concerned, that may be very long delayed. This fact of arousing other sensory processes raises the CORTICAL ACTION IN MEMORY 45 question as to the cortical seat of memory processes and imaginings. The most generally accepted answer at present is that the memories have the same cortical regions, in fact the same cortical cells, as the sensations, and that in remembering the same cells are excited as in seeing or hearing. Visual memories are in the visual region, auditory memories are in the auditory region, and so on. The process of arousing memories is one of retracing old paths, very much as habit depends upon the renewed action of a group of motor neurones. The details of the process must occupy us in the later chap- ters. Nerve Elements do not Act in Isolation. — One word needs to be added in this connection, and that is that the single parts of the nervous system probably do not act alone. When we speak of the action of a single group of cells it is probable that the group is merely the centre of excitation in a very wide region. The excitation that arouses that group spreads to very remote parts of the brain. Action is always of large masses of nerve- cells, but of the mass certain parts are emphasised, the others respond in very much sKghter degree. There is a complicated interplay of part and part throughout a very large portion of the mass of neurones, although only relatively few are in great activity. The interac- tions which themselves do not directly affect action serve to guide the course of the other responses. Each con- tributes its share to the total action, although one alone stands out prominently. The action of the nervous system, then, is always de- pendent upon a transfer of some sort of energy from 46 THE ESSENTIALS OF PSYCHOLOGY neurone to neurone. The original excitation is received from the external world and has its final outcome in some sort of movement. At least two sets of neurones are involved in every action. As the act becomes more complicated, a larger and larger number of neuron^ intervene, and a larger and larger number of stimuli contribute to the excitation and control of the movement. At the lowest level the stimulus is ordinarily single or at least of one sort, and the paths of motor discharge are relatively few. At the second level the neurones in- volved are still relatively few, but the stimuh are nu- merous and varied and the paths of discharge are more numerous. On the highest level in the cortex very many of the sensory and motor paths are concerned, and in addition the effects of the stimuh that were earlier re- ceived and are stored in the nervous system contribute their share to the control of action. Interaction between Cord and Cortex. — The different levels ordinarily interact in any response. Thus, when the hand is burned or pricked it will usually be drawn back reflexly. This means that the sensory impulse is transmitted to a spinal ganglion and thence to the anterior grey cells of the cord, and so down to the muscle. But suppose that the man is working in a bit of machinery with the hand in front of a knife, and the finger is burned. The reflex, if it is not too strong or if the stimulus is not unexpected, will be checked by the knowledge of the danger from the knife. This means that the visual impression of the knife has been carried to the visual area in the cortex by way of the eye and midbrain centres. The effect of the arousal of the visual INTERACTION IN THE NERVOUS SYSTEM 47 area is transferred to the motor region, and serves to inhibit the activity of the motor cells in the cord that would otherwise be involved in the reflex, or it may con- tract the muscles that oppose the reflex. In this way the impressions from the eye or the memories derived from the eye oppose and may overcome the effects of the excitation from the skin. The movement is con- trolled, not by the tactual sensations alone, but by tactual sensations together with any visual sensations and memories that bear upon the situation. At each level in the nervous system as we go upward from the cord, there are more neurones involved. The action is in the light of a constantly increasing number of sensations, and many more forms of response are possible. But the difference is one of complexity alone. The beginning and the end of the process may be identical. The impulse is propagated in the same way and the laws that govern the selection of the path are the same. Our first picture of the simple reflex explains the funda- mentals of the most complicated voluntary act. It is only necessary to add new stimuli and new possibiHties of response, — to recognise that many currents of nervous activity are adding their quota to the control of- action. QUESTIONS 1. What is the sheath of the axone? (a) neurilemma? (b) medullary sheath? 2. Distinguish afiferent nerves, efferent nerves, ganglia, white and grey matter in terms of the parts of neurones or relations of neurones that compose them. 3. Describe the functions of the nervous system in the simplest and most general terms. 48 THE ESSENTIALS OF PSYCHOLOGY 4. What passes along the nerve as an impulse is transmitted? How is the action of the neurone like that of an amcBba? like that of a battery? 5. How are the acts controlled by the three levels of the nervous system similar ? how different ? 6. What level is involved in each of the following acts? Drawing up the foot when the sole is tickled. Sneezing as you breathe in dust. ' Winking as the eye is threatened. Turning a corner when thinking of something else. 7. What difference is there between the function of the anterior and posterior association centres ? 8. Why does injury to the left side of the cerebrum produce a paralysis on the right side of the body? EXERCISES 1. Draw neurones of three different types. Designate axones, dendrites, and end-brush of each. How many axones has a neurone? how many dendrites ? how many end-brushes? 2. Draw a diagram to illustrate the course followed by an impulse when you burn your finger. 3. Draw a cross section of the cord. Show the path followed by a simple reflex. 4. Draw the cerebrum in lateral and mesial view and indicate the sensory, motor, and associatory areas. 5. Trace on the diagram the path followed by an impulse as you copy a sentence from a book. 6. If possible examine neurones and their connections in a section of a cord under a microscope. 7. If opportunity offers procure the brain of an animal, sheep or cat, dissect it, and compare the structures with the diagrams. REFERENCES Howell : Physiology, Section II. McDouGALL : Primer of Physiological Psychology. QuAiN : Anatomy, vol. iii. Herrick : Introduction to Neurology. CHAPTER III NEURAL ACTION IN RELATION TO CONSCIOUSNESS AND BEHAVIOUR After a discussion of the structure and action of the nervous system the question of the relation between these physical processes and the mental processes or behaviour naturally arises. Popularly there is a tendency to con- fuse mind with brain. A man is said to have a good brain when it is meant merely that he is effective or unusually intelligent. This identification is altogether without warrant. On the contrary, there is little if any similarity between nervous activity and the mental state. If one could bring the processes that go on in the brain when one looked at a landscape side by side with the landscape itself and compare them, the two would not be at all alike. Where the landscape shows various forms and masses of colour, the nervous activity would show chemical reactions running here and there in the visual area at the back of the brain and in the nerves leading to and away from it. We have every reason to believe that the chemical changes stand in some essential relation to the mental processes, but it is obviously impossible to assert that the two are identical or even that they are similar in character. One of the problems most discussed in psychology and in philosophy is what is the exact relation between these E 49 so THE ESSENTIALS OF PSYCHOLOGY constantly shifting chemical changes in the nervous system as the landscape affects it and the mental image of the landscape; or, in general, between brain action and consciousness. While the answer makes little prac- tical difference for the treatment of psychological prob- lems, it is well before going farther to have a statement of opposing theories and a provisional working hy- pothesis. Relation of Mind and Body. — A large part of the difficulty in understanding the relation of body and mind grows out of the different ways in which one must ap- proach the explanation of behaviour. The observer sees only the stimulus or occasion for the action, the actor appreciates the mental states that follow the stimulus and precede the action, but neither can see both sides at once. Even if the observer calls anatomy and physiology to his aid and goes as far as he can by analogy from ex- periments on animals in the attempt to find an explana- tion of behaviour, he gets only nerves and their connec- tions ; he can never have a view of the consciousness of the actor. The actor from his side can never pass beyond consciousness ; he does not become aware directly of nerve or nervous activity, no matter how he may seek to penetrate beneath his immediate consciousness. The outside, observer sees excitations vanish into the nervous system and sees actions result ; the actor sees the occa- sion for his act approach, is conscious of the resulting sensation, and knows that he has acted, but knows noth- ing of the nervous system that intervenes. So far no one has been able to bring the two aspects of behaviour together in a single system of explanations, either by BODY AND MIND 5 1 direct observation or in theory. At present it is uni- versally accepted that mental state and bodily or nervous activity are always found together, but care is taken not to assert that one is the cause of the other. The imphcation is that they are related in some essential and fundamental way, but what that relation is, is not stated. It is customary to explain any mental process in terms of other mental processes, and to explain all nervous action by other nervous activities, but no attempt is made to explain one in terms of the other, further than to say that the two series are always found together and run on side by side. For our purposes it is not necessary to discuss the theories that have been developed to explain the connection. We may leave the whole problem open, as the facts of psychology are the same whatever theory may ultimately prevail. For convenience we shall often seem to imply that activity in sensory neurones produces changes in con- sciousness and that ideas start the motor discharges which lead to action. This is not to be regarded as committing the author to any theory of the real connec- tion between body and mind, but as a lapse into popular speech. The Connections of Neurones. — While it is assured that consciousness is dependent upon the activity of the nervous system, and that certain conscious processes are connected with the activity of certain nervous structures, it is also important to know what change there is in the elements of the nervous system as a result of action. Upon their changed character as a result of earlier action depends most of the possibility of educa- 52 THE ESSENTIALS OF PSYCHOLOGY tion and of improvement in behaviour. Formation of habits and the acquirement of memories are the most striking of the mental and physical capaci- ties directly re- ferred to the nervous system. At present the tendency is to explain aU learn- ing as due to a change at the point where two neurones come together, where the end-brush of one comes into contact with the dendrites of an- other. This point, as was said, has been called the syn- apse. As was seen in the pre- ceding chapter, the synapse gov- erns the course of the impulse. Each sensory path makes connections with several motor and associating paths or neurones and any impulse wiU take the path Fig. 10. — Shows the complexity of interconnections (number of synapses) between neurones in the cortex. (From Barker, Fig. 655, after Ramon y Cajal.) THE SYNAPSE S3 that offers least resistance. The ease with which the synapses may be crossed determines the path, and this in turn is determined first by inheritance, second by use. The reflexes of the cord run their course through synapses already prepared at birth. The course of an impulse through the cortex is largely controlled by synapses whose degree of resistance depends upon the frequency with which they have been used. Evidently, then, the most important question of nervous physiology for the psychologist is what is the nature of the synapse and of its action. The Amoe1?a Theory of the Sjmapse. — The details of the mechanism of the synapse are still altogether lacking, although numerous theories have been developed to explain it. All agree that whenever two neurones are active at the same time some change is induced in the synapse that makes it act more readily later. The two neurones become more nearly a single unit for action. Two suggestions as to what the change is may be mentioned as typical. The older, and in many ways the simpler, regards the neurones as living organisms that still possess at their extremities the power of motion in- herent in the amceba-like prototype. When both cells are active, the processes extend and come into contact, and the chemical action of the one in some way excites a similar activity in the other. The action of the pro- cesses, particularly of the dendrite, leaves behind it a disposition to act again more easily in the same way. As a result of this disposition, the same extension is repeated on suitable occasion and the connection be- tween the cells and their simultaneous action is renewed. 54 THE ESSENTIALS OF PSYCHOLOGY What the nature of the change may be is not made very clear. It may be an actual physical bond that persists when the end-brush of one neurone has once been brought into contact with the dendrite of another, or it may be that one or the other of the processes takes on a habit of extending in the way that brought it into contact with the other. The original obstruction to the transfer of the action from one neurone to another is spatial, and this original gap is bridged by the move- ment of processes, a movement, which when once made, leaves a permanent tendency to the union of the neu- rones. Sherrington's Theory of the Synapse. — The more recent theory, proposed by Sherrington, the English physiologist, is that the synapse opposes the passage of an excitation in much the same way that a mem- brane opposes the transfer of fluids. At first this resist- ance is very great, but it is lessened with each act. On this theory the change in the synapse is chemical in character. Here again the exact nature of the change is not asserted. On either theory the synapse is the point where action leaves its impress upon the nervous system, — it is here that learning has its effect. The change that comes with action is a lessened resistance at the synapse, whether it be due to the coming closer of the processes or to a chemical change that makes more per- meable the relatively impermeable membrane that at first separates the neurones. On either theory it is pos- sible to picture the synapse as a valve that controls the interaction of nerve elements, — that governs the passage of the nervous impulse from unit to unit. At first the THE SYNAPSE 55 valves are stiff and open only to strong currents ; with use they work more easily until those most difi&cult at birth may become as delicate in action as those that were at birth most permeable. It should be emphasized to avoid giving a wrong impression that there is no real valve ; it is only that the action is like what might be expected were there a valve at the synapse. As the out- come of our discussion, we have a picture of the nervous system as a mass of relatively independent amoeba-like cells that are held in a definite position and relation to one another by a cage of bone. At the beginning certain of the neurones constitute a path for an impulse from sense- organs to muscles. These original paths are few and make possible only the activities most essential to the continu- ance of the life of the individual. Additional paths of con- nection are formed by each activity, physical and mental. Whenever any two neurones chance to act together a connection is formed between them, the original gap is bridged, and they come to form part of a new pathway from sense-organ to muscle. This holds also for the action of the neurones within the cortex, when the learning that results is primarily of ideas rather than of movements. Learning, whether of new movements or of new ideas, is a process of making easier the passage of an impulse from neurone to neurone and is funda- mentally the same everywhere. Reflexes Determined by the Synapse. — ■ When the connections in the nervous system have once been formed, the course of a nervous impulse is determined by the intensity of the stimulus and the openness of the synapse. The course of a reflex through the nervous system depends 56 THE ESSENTIALS OF PSYCHOLOGY upon the innate connections of the synapses. In the cord, for example, a slight stimulus on the hand arouses the muscles of that arm; a stronger one excites the corresponding member of the opposite side ; still stronger impressions cause contractions in the legs, and finally contractions will spread to all of the muscles of the trunk. Translated into terms of neurones and synapses, this indicates that the synapse which opens most readily is the one between the sensory neurone and the motor neurone at the same level and on the same side of the cord. Slight stimuli are strong enough to force their way across this gap. As the stimulus becomes stronger, the synapses which lead to the opposite side of the body open, then those that lie at the higher and lower levels. The course of the impulse and the selection of the movement depend altogether upon the ease with which synapses open and the strength of the stimulus. Habit a Change in the Synapse. — The same factors determine the selection in the more compUcated reac- tions of the higher brain centres. In man the action that will be called out by a situation depends upon the habits he has formed, and these in turn are due to con- nections between neurones in different parts of the brain. In a soldier trained to answer to the word of command the readiest response is to obey, however that action may conflict with his instincts. The synapses have opened so frequently between the centres for hear- ing and the movements evoked by the order that the stimulus leads to action at once, however unfavourable the other circmnstances. In these responses, too, stronger stimuli arouse more diffuse responses. Where HABIT AND THE SYNAPSE 57 a single command when in ranks meets with immediate response, the sudden charge of an enemy when the ranks are broken and the men are in disorder may cause sudden diffuse responses that will overcome the effects of the long drill. Similarly, in a game of baseball the habitual response will be made immediately and accurately when the stimulus is slight and the circumstances nor- mal, but when some strong stimulus or some emotionally disturbing event takes place at the moment, the suitable habitual response is frequently lost in the general over- flow to neighbouring muscles. The ball is often thrown over the first baseman's head at a critical moment. While in the higher habitual responses more compli- cated factors must be taken into consideration, the char- acter of the response still depends upon the openness of the synapses at the moment and the intensity of the stimulus or its appeal to the individual. In essen- tials, the response of the higher neurones and paths of connection follow the same laws as the lower. The Formation of Habits. — One of the most impor- tant facts that can be referred to the action of the nervous system is the formation of habits. This, as has been said, is due primarily to the opening of synapses by use. Habit, whether for good or ill, is one of the most striking elements in any explanation of behaviour. As it is fundamental for many of the psychological explana- tions, we may begin our discussion with a brief sum- mary of itS' laws and applications. In popular speech habit, for some reason, implies bad habit, but this re- striction of the term is altogether unjustifiable. Absence of habit would mean complete loss of efficiency. Most of S8 THE ESSENTIALS OF PSYCHOLOGY eating, walking, talking, and all of the frequent and im- portant actions of everyday life are habits in whole or in part. Dressing is a habit. You do not think as you put on your garments. Your hands find their way to the buttons without thought and without your being con- scious that they are moying. The tie is adjusted with no knowledge of the separate movements. Were you asked to describe the movements made in tying a cravat, you probably could not do so, although the operation is run through daily without mistake. If we turn from a dis- cussion of the omnipresence of habit to the question of what goes on in the nervous system when a habit is ac- quired, we get back to our problem of the synapse and its relations. Each time an act is performed, it matters not how, there is some change in the sjoiapses between neurones. The effect of the act persists and becomes stronger with each repetition. After several repetitions the cormection between the cells becomes so close that whenever the particular sensory cell is excited, the im- pulse spreads to the motor cells active with it before, and the neurones grow more and more to constitute what is practically a single structure. The formation of habits is thus a process of decreasing the resistance of the syn- apses in the different possible paths of transmission. Ul- timately it is due to a change of some kind in the synapse. When a sensory neurone is excited, one of the sjoiapses is more open than the others. This is traversed by the impulse and the corresponding muscle responds. The opening of the S3aiapse has in every case been brought about by the simultaneous action of the two neurones. The Omnipresence of Habit. — The process of form- HABIT 59 ing a habit is relatively simple, but the effect of habit for- m3,tion has the most far-reaching importance. Every act of any kind is the forerunner of other acts of the same kind. At first the habit is easily changed ; but if fre- quently persisted in, the time comes when that movement must be made whenever the particular occasion presents itself, without reference to the other circumstances of the moment. Obviously when the movements are repeated until they are so completely fixed, it is essential that the movements chosen for fixation shall be helpful or harm- less. The useful man is for the greater part marked off from the useless and the vicious by the nature of his habits. Industry or indolence, good temper or bad temper, even virtue or vice, are in the last analysis largely matters of habit. One forms the habit of work- ing at certain times of the day, and soon if one is not busy at that time one experiences a lively sense of dis- comfort. Or, on the contrary, one forms the habit of loafing all day. Work then becomes distasteful and indolent irresponsibility is estabhshed. Losing one's temper is largely a habit, as is self-control. Each time one is provoked by a trifle, it becomes the more difficult to look calmly at an unpleasant episode ; while each time one remains calm under difficult circumstances, strength is gained for later difficulties. Similarly, whenever temptation is resisted, virtue gains a victory; when temptation is yielded to, new weaknesses develop. Frequent yielding makes resistance practically im- possible. A bank president of estabhshed morals could no more step out and pick a pocket that was ter^iptingly unprotected than he could fly. The habitual drunkard 6o THE ESSENTIALS OF PSYCHOLOGY can no more resist the invitation to have a glass than he can resist the action of gravitation while faUing freely through space. Frequent giving in has entirely de- stroyed his original freedom of choice. We are all constantly forging chains of action in our nervous system that we shall never be able to break. Fortunate is the man whose chains are all suited to the life he is compelled to live. He was once free in the sense of our present problem, but after a few experiences he becomes bound to his past by chains that only the strongest impulses can break. Habits are riot restricted to action, but show, themselves even in the features. Much has been said, particularly in semi-popular writ- ing, of the ability to determine character from the face. Each movement of the muscles of the face has left its impress upon the muscles and the skin, just as each action has left its impress upon the nerve-cells. One can tell at a glance at the face, even in repose, what its most characteristic responses have been and can form some idea of the character of the man, of the effects that have been left by the same actions upon the nerve-cells which show themselves when the man is called upon to act. A weak man, a strong man, even more truly a jovial man or a crabbed man, carries the marks upon his face. These marks are but evidence of the changes that the same set of acts has left upon the synapses of the nervous system everjrwhere along the paths of action. Habits Essential to Action. — Habit not only limits choice but through early training makes choice possible. The adult ordinarily chooses one habit rather than an- other ; he does not choose between some habitual action HABIT AND MEMORY 6 1 and something never done before. What has never been done is ordinarily not within the power of the individual. For example, you cannot speak the Russian word for prince and could not if some one should first pronounce the word for you. You cannot because you have never developed the habit. When you do choose to speak an EngHsh word, you do it because you have that habit fully developed. Had you never formed habits of speaking you would be as powerless in English as in Russian. As all of our intellectual operations are expressed in language, habit is in the highest sense a powerful, an indispensaljle tool of thinking. But that is not all. If you ehminate from the various intellectual activities all that belongs to habit, most of the higher mental operations become impossible. Habit, like fire, is a cruel master but an invaluable servant. Without it all action would cease or at the best become but a painful process of feeling one's way through even the simplest act. Association of Ideas a Form of Habit. — The associa- tion of ideas, fundamental for thinking, is similar to habit. The recall of any memory necessitates the stimulus of some earlier connected event. An old experience returns only in connection with some other event now revived in consciousness. On the nervous side this means that the cells in the cortex corresponding to the two ideas have been active together and that the resistance of the common synapse has been reduced by the simultaneous action of the two neurones. When one presents itself, the impulse spreads through the synapse of least re- sistance to the related cell and the old idea is recalled, 62 THE ESSENTIALS OF PSYCHOLOGY All recall is dependent upon the connection of ideas, and ideas are connected only as the neurones are united through the reduced resistance of the synapses. The association processes are thus in every particular similar to habits. They might be called habits of neurones in the cortex. The only difference worth emphasising is that in this case there is no movement of muscles accom- panying the activity of the cortical cells. Even this difference is not always present; for the cortical cells, whenever active, tend to call out movements, often very slight, sometimes nothing more than the tendency to movement. If we include association among the habits, we may say with complete assurance that no intellectual activity of any kind goes on except on the basis of habit. Habit and association are the two fundamental facts upon which all of our activity, mental or physical, depends. That either should be lacking is inconceivable. Were they lacking, man, either as a mental or as a physical being, would not be what he is. QUESTIONS 1. Describe the nervous processes that accompany seeing a landscape. How are they different from the perception? 2. When the idea initiates the act of writing a description, can you say that the idea causes the movement ? 3. Discuss the two theories of changes in the synapse. 4. Give acts that are determined (a) by heredity, (b) by use. 5. What elements of character may depend upon habit? EXERCISES 1. List ten acts of the day that you may be sure are habits. 2. Trace the different steps in forming the habit of adjusting some new article of attire, e.g. adjusting a new tie. HABIT 63 3. Try to break some undesirable habit and keep a daily record of progress. REFERENCES James : Principles of Psychology, vol. i, ch. iv. TiTCHENER : Textbook of Psychology, sec. 4. JUDD : Psychology, pp. 61-64. Pillsbury: Attention, pp. 129-225. McDouGALL : Primer of Physiological Psychology, pp. 14-107. Angell : Psychology, ch. iii. CHAPTER IV SENSATION Since all acts and all conscious processes are initiated by sensory stimulation, it is necessary to have a full knowledge of the different stimuli which affect man and of the sensations they produce. We might deter- mine without the use of introspection what stimuli are efifective by stud3dng the responses of the organ- ism. In man, however, it is much simpler to study the direct effects in consciousness. This has the added advantage of revealing the qualities of sensations. Knowledge of behaviour is dependent upon a know- ledge of the stimuli, and sensations are interesting and important in themselves. We may turn then to our first task, a study of the character of conscious- ness. Components of Consciousness. — We may follow tra- dition and begin our study of consciousness by attempt- ing to discover its elementary components. At this moment the consciousness of the reader is made up of a number of processes. Experiences are received through the eyes that constitute or suggest the book with its physical appearance. At the same time you acquire certain elements of knowledge from the words 64 SENSATION 65 on its page. Your mind wanders now and again to the thought of the game you would like to be having or of the recitation that you would like to make on the morrow, or to the entertainment of the evening, or to some other topic. Accompanying each of these pro- cesses are feelings of pleasure or displeasure, and in many cases emotions of greater or Ijess intensity. Obviously even the simplest consciousness is a very complex affair. To attempt to describe or to classify the different sorts of consciousness taken in this concrete way would evidently be an endless task. In practice the undertaking is made easier by the fact that the memory processes and the immediate sensation processes have approximately the same qualities. A remembered or imagined red is of the same quality, approximately, as the red that is seen directly. Leaving aside the feeling processes for the moment, we may say that the qualities of consciousness are the qualities of sense. Since Locke it has been an axiom of psychology that there is nothing in mind that was not previously in sense. It is true undoubtedly that one cannot think of a colour that has never been seen. Try to picture to yourself what the ultra-violet waves would be like to an eye that had developed a capacity to see them, and you will find that each colour you call up is compounded out of th,ose already familiar. All attempts to produce an imaginary quality that has not been received through some sense-organ are fruitless. Every quality, of memory and imagination is received through the senses. New things may be compounded out of these qualities, but the niunber of qualities is fixed by these elementary sensations. Evidently, then, 66 THE ESSENTIALS OF PSYCHOLOGY the first task that confronts us as we undertake a de- scription of the nature of consciousness or of its com- ponents is to determine the number of simple sensations. We approach this task confident that its solution will determine, not merely the number of sensory qualities, but the number of qualities that may be remembered or imagined as well. Doctrine of Specific Energies of Sensory Ends. — The enumeration of sensory qualities is not so simple and easy as might at first appear. Whether one shall call each distinguishable colour in the spectrum a single sensation or shall regard them aU as compounded of a few simple qualities, is a question that cannot be decided by direct observation. A theory that was first suggested by Johannes Muller, the pioneer in modern physiology, offers perhaps the most convenient principle to guide us in our task. Briefly, this law asserts that any sense- organ must always give its own quality of sensation, no matter how it may be excited. Simplest evidence of this may be offered by pressing the eyeball with the finger. You will notice about the circle of pressure a ring of light of a quality that might have been induced by a ray of Ught. An electric current passed through the eye will also produce a visual sensation, as will jarring the optical apparatus by falling (' seeing stars'). Con- versely, it may be said that there can be no more qualities of sensation than there are different kinds of sensory end organs. If the quality of the sensation depends upon the character of the sense-organ that receives it, and not upon the nature of the stimulus, the number of sense qualities must be as great as, and no greater than the SENSATION DEPENDENT ON ORGAN 67 number of sensory ends. Since the same stimulus often gives different results , upon several different sense- organs, the difference must be due to the organ, not to the stimulus. Many instances may be cited. A vi- bration of ether excites the sensation red upon the retina of the eye, a sensation of warmth upon the skin. The electric current gives a different sense quality for each sense-organ, — pain on the skin, taste on the tongue, and so on. If we accept this law, it follows that we can determine the number of different kinds of sensation if we can discover the mmiber of distinct sensory end organs. The Development of Sensations. — The development of the sense qualities depends upon and goes hand in hand with the development of the sensory endings. In the simplest organisms there is no differentiation of sen- sory tissue, and consciousness perhaps shows no dif- ferences whatever. AU stimuli give rise to exactly the same effect. Taste is not different from touch, sight from hearing, — if hearing be present at all. All forms of stimuli excite the same organ and in consequence must give the same effect. As differentiation takes place in the animal series, new organs are developed and new sense qualities make their appearance. At the level of insects most of the senses found in man are pretty well differentiated. Even in man, however, not all of the physical stimuli have corresponding sensations. The electric and magnetic forces have no sense-organs and are not recognised as separate qualities. For that reason, too, knowledge of electrical and magnetic phenomena developed relatively late. Indirect evi- 68 THE ESSENTIALS OF PSYCHOLOGY dence obtained through the other senses alone gives knowledge of their existence.. Our problem in this chapter is to determine the nimiber of different kinds of sensory ends that the human organism presents to the ex- ternal world, confident that this will also give the number of distinct conscious qualities. Sensations of Temperature. — We may begin with the sensations derived from the skin, since the skin is probably the simplest of the sense-organs, although far more complex than one is inclined to believe. The ordinary assumption seems to be that the skin is a com- paratively homogeneous surface with but one sense quaUty. Recent investigation, beginning in the early eighties of the last century, has shown that the skin has four senses and that each is distinct in quality and in sensory ending. Two of these respond primarily to mechanical stimulation, two to temperature. The mechanical senses are pressure and pain, the temperature senses are warmth and cold. Evidence for the two temperature senses is most readily obtained by the beginner. If one will but run over the skin with the point of a rod heated above the body temperature, one will notice that the rod feels warm only here and there at points well separated. These spots were foimd by von Frey to average about one and one-half to the square centimetre. If the rod be cooled below the temperature of the skin, cold is noticed at many more spots, about thirteen to the square centimetre, but still wide areas without temperature sensations intervene. While, then, the physicist assures us that cold is nothing but the absence of heat so far as energy is concerned, it is un- SENSATIONS OF TEMPERATtIRE 69 doubted that, physiologically and psychologically, cold is just as truly a distinct sensation as warmth. Not only is it proved by mapping the spots that the temperature senses are distinct, but the result is confirmed by a mun- +•••• • + • • , + ++ + -I- . + . Fig. II. — Map of warm and cold spots on volar surface of forearm. The dots represent warm spots as tested at a temperature of 4i°-48° C. ; the crosses, cold spots as tested at 10°. (From Howell, after von Frey.) ber of related facts, (i) Stimulation of a well-marked cold spot always gives cold only, no matter what the source. Pressure, the electric current, even the warmth obtained by concentrating the sun's rays upon the spot by a small lens, all give the same sensation of cold. 70 THE ESSENTIALS OF PSYCHOLOGY Warm spots may also be aroused by inadequate stimuli but they require greater intensity than the cold spots. (2) Certain parts of the body, the cornea of the eye, e.g., lack warm spots altogether, and there are relatively large areas where cold spots are lacking. (3) Certain chemicals, e.g. menthol for cold, carbon dioxide for warm, wiU excite one sort of spot, but not the other. All these facts go to show that cold and warmth are inde- pendent senses with independent nerve ends in the skin. Physiological Temperature Scale. — The response of the nerve ends to the different changes in temperature is indicated in the accompanying diagram. The physi- ological zero point lies somewhere in the neighbourhood of 30° C. The variation is from 28° or below to 34° or above, according to the temperature to which the body has been adjusted. At any one time the limit will be only a fraction of a degree. Below this point all tem- peratures excite the cold organ; above, all excite the organ of warmth. Very low temperatures, from 12° downward, also excite the nerves of pain which give the sensation of burning or biting cold. Above the neutral point, at about 45° C, warm becomes hot. In con- sciousness it is marked off from warm by a very sharp line. Physiologically, the difference is due to the presence of the sensation of cold. Hot is a compound of warm and cold. This excitation of cold spots by heat has been called the paradoxical cold sensation. Beyond this, at some 50° C, pain is also aroused and gives burn- ing heat. All the temperature effects are produced by combinations of the excitations of the three sense endings of cold, warmth, and pain. SENSATIONS OF PRESSURE 71 Fig. 12. — Shows the sense-organs stimulated, and approximate degree of stimu- lation at the different temperatures. The figures on the base line indicate the temperature in centigrade, the height of the line the amount of stimulation. (After von Frey : 'Vorlesungen ilber Physiologic,' Fig. 50.) Cutaneous Sensations from Mechanical Stimuli. — Two sense qualities may be excited mechanically, pres- sure and pain. Somewhat the same differentiation must be made between them as between the tempera- ture senses. Gentle pressure upon the skin with a sharply pointed wooden rod or a short hair is felt only here and there. These points are known as the pressure spots. They are found closer together on the average than either class of temperature spots. They vary from about nine to some three himdred to the centimetre. 72 THE ESSENTIALS OF PSYCHOLOGY These pressure spots are relatively easy to excite, — they are affected by hairs that exert a pressure of little more than a milli gram. The pain spots are much closer Fig. 13. — Nerve endings in skin and about hair follicles, (c) the most super- ficial plexus of fibres in the skin, free nerve endings still nearer the surface ; {h) the hair with nerves about root. (From Barker, Fig. 227, after Retzius.) SENSE-ORGANS IN THE SKIN 73 together and require greater pressure for their stimula- tion. They are most easily found by pressing upon the different points on the skin with a well-sharpened horse- hair. It has been shown that 200 or more points to the centimetre give rise to the pain sensations. That pain is not merely a more intense pressure, as was thought for a long time, is proved (i) by the fact that a pressure spot always responds more quickly than a pain spot, and (2) that certain parts of the body are sensitive to pressure but not to pain, e.g. the inner membrane of the cheek, while the cornea of the eye always responds with pain, never with pres- sure, no matter how slight the excitation. Again, (3) certain drugs destroy one sense quality and leave the other unaffected, e.g. cocaine when first applied de- stroys the sensitiveness to pain but not to pressure; a rare drug, saponin, destroys sensitiveness to pressure but not to pain. It is now generally held that pain and pressure are distinct senses with distinct kinds of sensory endings in the skin. The Organs of Cutaneous Sensation. — Pressure and pain may with some certainty be referred to particular sense-organs. The nerves of pressure for the greater part of the body are the nerves at the roots of the hairs, as illustrated in the accompanying diagram. On the palms of the hands and the soles of the feet where hairs are lacking, the organ of pressure is the touch corpuscle of Meissner found in the papillae of the skin. (Figure 14.) The nerves of pain are the free nerve ends that extend into the outer skin. They too may be seen in Figure 13. That pain has a very superficial organ is evident from 74 THE ESSENTIALS OF PSYCHOLOGY the fact that an acid will give rise to pain before it affects any other of the sense ends. It needs only to eat into the most superficial layer of the skin, and the sensation of pain is aroused. The organs of warmth and cold have not been made out with any certainty. The skin, then, is not a single sense-organ, but a mosaic in which four separate senses may be distinguished, each with a special end-organ. These are pressure, pain, warmth, and cold. With their combinations they give rise to all knowledge of the outer world obtained through the skin. The Gustatory Sensations. — The principles established for touch can be readily transferred to taste. As every one knows, the chief organ of taste is the tongue. More particularly the sense endings of taste are to be found on the sides of the foliate, the fungiform, and the circum- vallate papillae on the tongue. Essentially the papillae are folds of skin on the surface of the tongue. The sense endings proper are the taste beakers which are arranged along the sides of the depressions formed by the papiUae. The beaker itself, as may be seen from the diagram, is a group of nerve ends interspersed with supporting cells. The whole looks not unlike a flower bud. The papillae are scattered fairly thickly over the tip, sides, and back of the tongue. They can be seen Fig. 14. — Tactile corpuscle of Meissner from the skin of toe. (N) nerve fibre. (From Barker, Fig. 242, after ScMefferdecker.) SENSATIONS OF TASTE 75 on the tip of the tongue as httle bright red depressions. Four separate taste qualities are distinguished, — sweet, salt, sour, and bitter. The different qualities cannot be so easily connected with different spots on the tongue as can the touch qualities with spots on the skin. Subyemmal cell IntergemmiU fibrils Fig. IS- — Taste-buds and endings of gustatory nerves, (a) shows taste cells about a central supporting cell; (6) fibrils around and between the taste- buds. (From Barker, Fig. 348.) The taste-buds are well concealed in the papUlse and a single papilla often possesses more than one quality. It is assumed, however, that each taste beaker responds to but one quality, although several beakers of different kinds may be present in the same papilla. In general. 76 THE ESSENTIALS OF PSYCHOLOGY sweet is perceived on the tip, sour on the sides of the tongue, bitter on the back, while salt is pretty evenly distributed. At the most this arrangement is only partly carried out, and there are many exceptions. The best evidence for the doctrine of specific energies is the fact that different drugs dull or destroy the capacity to discriminate different tastes in different degrees. Cocaine, for example, first destroys the sensitiveness to bitter and affects the other tastes more slowly. Gym- nemic acid first destroys the sensitiveness to sweet. The time required for the nerves to respond is also dif- ferent for each taste. These facts together seem sufficient to justify the statement that the four taste qualities have each a special sort of taste beaker, although several different sorts of beakers are usually found in a single papilla. Combination of Taste with Other Sensations. — One may be inclined to question the statement that only four taste qualities can be distinguished, for certainly or- dinary experience seems to show a large munber. This objection must be admitted. The other qualities are, however, not tastes but additions from other senses. The most evident are the ordinary cutaneous sensations. Temperature seems to modify taste, as is seen in the peculiar effect of the cold of ice cream or the heat of coffee. Melted cream seems to have a different taste from the frozen; cold or lukewarm coffee, from hot. Roughness or smoothness adds a quality not easily distinguished from taste. Witness the difference be- tween granulated and pulverised sugar. Other instances will be recalled by the practical housewife. By far the OLFACTORY SENSATIONS 77 most important additions are those that are made by smell. Most of what we seem to taste we really smell. All of the delicate tastes, so called, are largely odours that reach the sensory region in the nose by way of the inner air passages. That much of the taste of food is really received through the nose is evident from the fact that a cold destroys nearly all taste. Moreover, if the nostrils be closed, substances will be confused that ordinarily are easily distinguished. Cinnamon is said not to be distinguishable from flour under these cir- cumstances. In short, in what is ordinarily called taste we have a mixture of the four simple tastes with the qualities of cutaneous sensation and with odour. The stimulus for taste is some chemical dissolved in a liquid and brought into contact with the taste-buds by being caught in the papillae. A substance to be tasted must be dissolved either before it is taken into the mouth or by the saliva. Sensations of Smell. — Of the sense of smell we know practically nothing. All that can be determined is that the organ of smell is the olfactory membrane in the upper nasal cavity. The sense nerves are simple cells with hairlike projections that come to the surface of the mem- brane between supporting cells. In their structure they are the simplest of the sense-organs. The stimulus for odours is some chemical substance carried to the olfactory membrane in particles. It produces some chemical change in the sense ending and this starts the nervous impulse toward the brain. No definite answer can be given to the question of the number of different organs and the number of different 78 THE ESSENTIALS OF PSYCHOLOGY olfactory qualities. Zwaardemaker has suggested that there are nine, but his results cannot be accepted as conclusive. Certain facts connected with pathology and with fatigue indicate that there are different organs for the different odours. In diseased conditions a patient Fig. i6. — Scheme of the olfactory apparatus of mammals. (ZJ) the olfactory membrane; (J) the olfactory neurone. Above are shown the more central neurones coimecting with the olfactory lobe. (From Barker, after Ramon y Cajal.) may lack one class of odours alone. Also the nose may be fatigued for one odour and remain sensitive to others. After one has smelled camphor for some time, alcohol will not be noticed, but iodine will still have its usual effect. While these experiments are suggestive of the AUDITION 79 presence of distinct sense-organs for different odours, they have not been carried far enough to determine the number of qualities. The uncertainties of science are reflected in the popular speech. There are no names for odours other than those of the objects that give rise to them. The difficulty is increased by the fact that tactual and taste qualities mix with the olfactory. The sweet odour of chloroform is really a taste. The odour of ammonia is largely pain, and the resulting holding of the breath adds a feeling of suffocation. Zwaarde- maker classes as nauseating certain odours that receive their peculiar quality from the incipient retching re- flexes excited in the throat. Of smell we know only that the organ is simple and has its seat in the upper nasal passages, that there are distinguishable qualities, but that their number is uncertain, and that smell com- bines with taste and tactual impressions to produce very complex fusions. Hearing. — The first of the so-called higher senses is hearing. It is higher in its importance for the mental life, in the degree of complexity of the organ, and in the richness of its qualities. In each of the higher senses we must consider the sense excitation at three different stages: (a) the physical stimulus, (6) the change excited in the sense-organ, and (c) the resulting con- scious qualities. The stimulus for hearing, physics teaches, is vibration in the air. The wave-lengths vary in three ways: in the rate of their vibration, in the distance through which the particles vibrate or the amplitude of vibration, and in the form or complexity of the wave. The rate of vibration corresponds to the 8o THE ESSENTIALS OF PSYCHOLOGY pitch of the tone, the amplitude corresponds to the intensity of the tone, and the form to the timbre or tone colour. The form of the wave gives the tone of each instrument its character, e.g. [ the C of the vioHn differs from the C of the piano only in its wave form. Structure of the Ear. — The organ of hearing is the ear. The ear is for convenience of description divided into three parts, — the external ear, the middle ear or drum, and the inner ear or labyrinth. The outer ear is the triunpet of cartilage, popularly called the ear, together with the tube that extends into the skull. Its only fimction is to gather the sound-waves and bring them to the drum. The middle ear extends from the membrane of the drum backward to the bony inner ear. In es- sentials the middle ear is an irregularly shaped hollow in the skull separated from the outer world by the drum membrane, and connected with the throat by the Eustachian tube. So far as it concerns us, it is a cavity across which extends a chain of three bones, the hammer, anvil, and stirrup, from the membrane of the driun to the oval window of the labyrinth. The drum head is a membrane stretched obliquely across the opening of the ear. On its umer surface is the handle of the ham- mer. The head of the hammer fits into the anvil, and this is attached to the head of the stirrup. Each bone receives its name from its shape. When a sound-wave strikes against the membrane of the drum, the mem- brane is forced inward shghtly, and this inward motion carries the handle of the hammer with it. The hammer and the other bones revolve about a ligament attached STRUCTURE OF THE EAR 8i to the top of the middle ear. The pressure of the air wave upon the drum membrane turns the bones about this as a pivot, and the stirrup commimicates the motion to the liquid of the inner ear. When the pressure of the air is relaxed, the membrane of the drum returns Fig. 17. — Diagram of ear, showing relation of parts. {M) and (G) external ear; (P) middle ear with small bones ; (5) cochlea; (.4) auditory nerve ; {R) Eustachian tube. (From Professor Calkins, Fig. 15, after Martin-Czermak.) In this cut the cochlea is turned 90° from its true position for convenience of representation. The top of the cochlea should be turned toward the observer. to its original position or a little beyond and carries with it the chain of bones and the foot of the stirrup. The foot of the stirrup fits closely into the oval window of the inner ear, and the joint is closed by a delicate mem- brane that makes the whole water-tight. WhUe this 82 THE ESSENTIALS OF PSYCHOLOGY ^1 _ Fig. i8. — Section of tube of cochlea. (Lom. j^.) lamina spiralis, through which the nerve passes ; (m.b.) basilar membrane ; (Org. C) organ of Corti ; {m.t.) tectorial membrane. (From Professor Calkins, Fig. 17, after Foster.) is the ordinary course of stimulation, high tones appar- ently pass through the bones of the head. In some cases, too, hearing is normal when the bones have been destroyed by disease. SENSATIONS OF HEARING 83 The Mechanics of the Cochlear Vibration. — The movement of the stirrup transmits the excitation to the inner ear, the point where hearing as a nervous process begins. The auditory portion of the ear is the cochlea. The cochlea, as its name implies, is a tube coiled up like a snail shell for two and a half turns. It is divided down the middle by a ridge of bone and a thin, membrane known as the basilar membrane. Figure 18 shows a cross section of the tube of the cochlea. One of the first questions in connection with the action of the ear is how it is possible for the vibrations of the stirrup and of the oval window to have any effect upon the liquid that fills the cochlea and the imier ear. The vibration of the liquid is rendered possible by the round window, an opening in the bony wall, closed by a delicate mem- brane. It is below the oval window, at the point marked Pt in Figure 17.' Pressure upon the stirrup at the oval window is transmitted through the entire length of the cochlear fluid to the round window. The membrane gives and thus makes possible the vibration of the fluid. The vibrations of the outer air push the membrane of the drum in and out. The drum head starts an oscil- lation of the chain of bones, the stirrup presses against the liquid of the inner ear, and this is permitted to vibrate by the delicate membrane of the round window. The Helmholtz Theory of Hearing. — All of this, is only preparation for the excitation of the nerve of hear- ing. The nerve of hearing ends in connection with the fibres of the basilar membrane. The exact connection between the nerve fibres and the fibres of the basilar membrane has not been altogether made out, but nerve 84 THE ESSENTIALS OF PSYCHOLOGY fibres come through the spiral of bone and end in con- nection with hairs upon the basilar membrane. These hairs are excited in some way by the vibrations of the basilar membrane and they, in turn, excite the auditory nerve. The most generally accepted theory of hearing was suggested by Helmholtz, who regarded the basilar membrane as a series of strings like the strings of a piano. Each string is tuned to some one of the audible tones. Whenever the tone to which a string is tuned is repre- sented in the vibrations of the liquid of the iimer ear, that string is thrown into sympathetic vibration. The vibration of the fibre starts a nervous impulse in the nerve connected with it, and this impulse is transmitted to the brain through a series of neurones. The sensation of sound makes its appearance upon the excitation of cells in the temporal lobes of the cortex. The process of exciting a vibration in the fibre is very similar to that which accompanies speaking into a piano when the keys are held down. When you speak, the strings tuned to your voice are excited sympathetically and can be heard after you finish speaking. In the basilar membrane the fibres are said to mmiber between eighteen and twenty thousand, while the tones that can be distinguished by the ordinary ear have been computed at approximately eleven'thousand. The nmnber of strings is then suffi- cient for the tones that may be heard. The case for the Helmholtz theory is strengthened by the limited number of tones that may be appreciated. The upper and lower limit of hearing may be explained by the limited number of fibres. The lowest tone that may be heard has ap- proximately sixteen vibrations per second ; the highest SENSATIONS OF HEARING 85 varies from about thirty thousand to forty-five thousand per second. Another strong bit of evidence for the theory is that after death there have been found in individuals, who were deaf to certain notes of the scale only, regions of the basilar membrane in which disease had destroyed the fibres. . The objections to the Helm- holtz theory are to be found primarily in the physical improbabiHty that fibres as short as those of the basilar membrane from 0.48 to 0.04 mm. in length, should be able to vibrate in sympathy with the lower tones that are heard. Several authorities have asserted that the fibres are too rigid to vibrate to faint- tones. Whatever the objections, the Helmholtz theory is the one at present generally accepted. Complex Tones and Noises^ — If we may assume that the simple tone corresponds to the excitation of a single fibre of the basilar membrane, it seems probable that the complex tones are due to the excitation of several fibres. A complex tone like a note of the piano would be made up of one tone, the fundamental, and .of others of a rate two, three, four, and other even multiples of that rate. The timbre of the tone varies with the number and char- acter of the overtones. In the violin tone the high over- tones predominate ; in the piano tone the overtones decrease in strength as they increase in pitch. In the ear each of these overtones is taken up by a different fibre and is carried to the cortex separately. In con- sciousness they ordinarily fuse to form a single quality, although by close attention the elements may be dis- tinguished. What then in the air is fused into a single wave of characteristic form is analysed by the basilar 86 THE ESSENTIALS OF PSYCHOLOGY membrane into its separate elements and reunited ia consciousness to form a complex tone. Noises of the contitiuous kind may be regarded as very complex tones made up of many vibration rates that have no simple arithmetical relation to each other. Each is received by a separate fibre and transmitted to the cortex, where the result is a jmnble of sensations. The single crash or crack, the second form of noise, arises from a twitch of the fibre of the membrane that does not persist long enough to give a full tone. Any tone will give a single puff of noise if it is permitted to affect the ear during but two full vibrations. In either case the noise is heard by the same part of the ear that pelrceives the tone/ the fibres of the basilar membrane in the cochlea. Summary. — In short, vibration in the air is received by the membrane of the driun and is transmitted to the oval window through the chain of small bones. At the oval window the oscillations of the bones produce vibra- tions in the liquid of the inner ear. ' The several tones are received by the different fibres of the basilar membrane attuned to them. The vibration of the fibres excites a change in the auditory nerve, and the nervous impulse is carried to the cortex where sensation arises. It is still a question whether we are to assume that each fibre has its own quality of sensation and that there are therefore eleven thousand distinct sensations and eleven thousand distinct sorts of nerve fibre, or whether the different fibres are grouped in some way in larger classes. The objection to the assumption of so many distinct nerve processes and sensations is that it gives hearing a disproportionate number of qualities when compared VISION 87 with the other senses. More cogent is the argument that notes an octave apart seem more alike than notes within the octave. Two C's are more likely to be con- fused than C and G, or C and B. But if we assume that there are fewer simple primary qualities than there are distinguishable tones, there is as yet no agreement as to what these primary qualities are, or how many there are of them. Visual Sensations. — By far the most important sense is sight. We trust vision above the other senses^ in per- ception, and most people think in images. When we recall an object, we remember how it looks rather than any other of its sensory qualities. In discussing sight we have again to consider the three phases of the visual process, — external stimulus, sense-organ, and sensa- tion. There is in vision rather greater dissimilarity be- tween the different phases than in hearing. The physical stimulus is a vibration in the hypothetical ether. The physicist tells us that the ether vibration varies in the same three ways as the sound vibration. Changes in rate or in length of the wave give quality ; changes in the amplitude of vibration give intensity ; while changes in complexity give greys and colours of different degrees of saturation, — varying mixtures of greys with colours. The rate or length corresponds to colour. Red has a wave-length of some 800-833 ^ ytt (thousandths of thou- sandths of a millimetre), violet a wave-length of less than half, or 380-400 fi jx. The colours between have intermediate wave-lengths. Change in amplitude pro- duces varying brightnesses, from black through the colours (what colour depends upon the wave-length of the light) 88 TEIE ESSENTIALS OF PSYCHOLOGY to white. Mixtures of certain light-waves give white or grey, and of others give different spectral colours according to the wave-lengths that are mixed. In any case it is evident that the qualities of the things as we see them are not at all like the vibrations which cause them. There is nothing in the colours to indicate that violet is a more rapid vibration than red. There are many disparities even in relations. Red and violet are more unlike physically, but the sensations are more alike than those of red and yellow, or of red and any intermediate colour nearer red in vibration rate. The Structure of the Eye. — The key to the difference between the physical stimulus and the qualities of colour must lie in the eye. That vibrations of different lengths give similar sensations must be due to the sunilarity of the physiological processes which they arouse in the retina. The eye can be best understood if it is compared to a camera. Three parts are essential to a camera : the box or container, the lens, and the sensitive plate. The box or frame of the eye is to be foimd in the sclerotic coat, the tough membrane that holds the parts together, and is kept distended into a sphere by the pressure of the liquid within. The organ is mounted in its socket, a conical hollow in the skull. It is held in its socket by threads of coimective tissue and is turned by three pairs of muscles. Within the sclerotic coat is first the choroid coat which nourishes the eye and has some nerves and muscular fibres ; within that is the retina which cor- responds to the sensitive plate. The lens system of the eye is made up of two parts, the cornea and the crystal- line lens. The cornea is really only a part of the sclerotic THE EYE 89 Fig. 19. — Section of eye. (Scler.) sclerotic coat ; {Chor.) choroid ; {Ret.) retina; {Ppt.) optic nerve; {Fov. c.) fovea; (Pr. cil.) ciliary process, imder it is the ciHary muscle which adjusts the lens for different distances ; (Conj.) conjunctiva. {Cam. ant.) is the anterior chamber, filled with the aqueous humour ; {Corpus mtreum) is the vitreous humour that fills the main body of the eye. (From Angell's 'Psychology,' Fig. 47.) coat which projects slightly and forms in consequence a stronger lens. It is transparent instead of white and opaque as is the sclerotic coat. The lens is just back of go THE ESSENTIALS OF PSYCHOLOGY 'the iris, the membrane which by its pigment gives the characteristic colour to the eye. It is attached to the choroid coat by a ligament, the suspensory ligament. That in turn is connected with the ciliary muscle which forms part of the choroid coat. In front of the lens lies the anterior chamber filled with a liquid much like water, as its name, aqueous himiour, implies. Back of the lens is a large chamber, filled with the jellylike vitreous humour. The Eye as an Optical Instrument. — The rays of light are bent at the front surface of the cornea, and at the two surfaces of the lens. The whole system has the same effect as if the light came through a single pinhole 15 mm. in front of the retina or 7 mm. hack of the cornea. The size of the image of any object thrown upon the retina will be found by drawing a line from the sides of the object to the retina through this nodal point where the pinhole might be. One extremely im- portant function of the lens is the accommodation or focussing of the eye. A camera that cannot be adjusted for different distances is of little value since pictures could be taken at one distance only. An eye with a fixed system of lenses could see objects at but one dis- tance. The eye is accommodated for different distances by changing the shape of the lens. The lens is relatively flat when one is looking at a distant object, but becomes thick and well rounded when one looks at a near object. This thickening of the lens may be seen if one will look across another's eye as he looks at objects at different distances. When the eye is adjusted for distance, the iris is flat; when it is focussed on a finger held close, THE EYE gi the iris is pushed forward by the lens. The shape of the lens is changed by the contraction of the ciliary muscle. When looking at a near object the muscle contracts and permits the lens to take on its normal, rather round shape. When the muscle is relaxed, the lens is tightly stretched by the suspensory ligament and so becomes flatter and thinner. (See diagram.) Another adjustment of the eye that may be mentioned is the change in the size of the pupil. The iris is really a part of the choroid coat that might have been drawn away from the attachment to the cornea. The pupil is the hole in the iris. When the eye is in the dark, the muscles that hold the pupil open are contracted ; when the light is bright, the sphincter of the iris contracts, the other muscles relax, and the pupil becomes small. The dilation permits a larger amount of Hght to enter the eye, the contraction protects the eye against too bright light. The real seeing portion of the eye is the retina. * The retina is a part of the brain that has come to the surface in the course of development. It is made up of three layers of neurones. The structures that receive the light are the rods and cones. These are farthest away from the light, nearest the choroid coat. There is an intermediate and an inner neurone layer. The axones of the inner layer of so-called large ganglion celft com- bine to form the optic nerve. In exciting the eye a ray of light traverses the outer neurones as a physical im- pulse (vibration in the ether), strikes upon the rods and cones, is there transformed into a nervous impulse and transferred, first to the intermediate bipolar cells, then 92 THE ESSENTIALS OF PSYCHOLOGY Fig. 20. — Schematic diagram of the nervous structure of the retina. (/) the layerof pigment cells; (//) the rods and cones; (7/) the bipolar cells; {IX) the large ganglion cells ; and (X) the axones that later unite to constitute the optic nerve. (From Professor Calkins, Fig. 14, after Howell.) • THE EYE 93 to the outermost large gangKon cells, and finally is carried back to the brain. Thus the nervous impulse goes back over part of the course that was traversed originally by the light-wave. Fovea and Blind Spot. — At the centre of the retina is a small depression or pit known as the fovea. In and about this the retina has a yellow pigment which gives the name, yellow spot, to the general region. Owing to the pit the light suffers less absorption than at other portions of the retina in reaching the sensitive struc- tures. In the fovea there are only cones, and they are more closely set than elsewhere. The lack of absorp- tion and the slight distance that separates the cones make the fovea the point of clearest vision. From the fovea outward the cones decrease in number until on the periphery they practically disappear. The en- trance of the optic nerve is not provided with rods and cones and in consequence is not sensitive to light. It is what is known as the blind spot. We know, theij, that the vibrations in the ether come to the rods and cones in the deepest coat of the retina. There in some way they are transformed into nerve impulses, pass from one to another of the three neurones in the eye, and then to the basal ganglia and cortex. Vision a Photo-chemical Process. — The first ques- tion of function is how ether vibrations are changed to nerve impulses. An analogy for this is found in the action of light in producing chemical changes in the photographic plate. It is possible to observe directly changes of this kind in the visual purple found in the outer portions of the rods. This bleaches when exposed 94 THE ESSENTIALS OF PSYCHOLOGY to light and becomes purple when the eye is kept in the dark. The bleaching of the visual purple has, however, only an indirect relation to seeing. The increased sensi- tiveness that comes after a long period in the dark is due to the effect of the visual purple^ but ordinary day- light vision is practically unaffected by it. Primary Colours and Their Combinations. — For an explanation of the action of the retina we are compelled to rely upon indirect evidence obtained by experiment and observation. We may be guided again by the doc- trine of specific energies. There are apparently six specific qualities from which -all visual processes must be derived. These are the two brightnesses, white and black, and four colours, red, yellow, green, and blue. The spectral quahties and purple are obtained from the four primary colours. Orange is a combination of red and yellow and may be produced by combining red and yellow lights in the right proportions. When a spec- trally pure ray of orange Ught falls upon the retina, it excites the two responses red and yellow in different degrees, and the results of the two physiological pro- cesses combine in the brain or in consciousness to pro- duce the single sensation of prange. Similarly, yellow and green combine to produce canary yellow, green and blue to give robin's egg blue and other shades. Finally the circle is completed by the fact that red combines with blue to give first indigo, then violet and the whole series of purples that fiU the gap be- tween the ends of the spectrum. It is interesting to note that, while all the other mixed colours may be produced either by having a single pure light-wave fall SENSATIONS OF SIGHT 95 upon the retina or by combining two lights in proper proportions, the purples can be induced, only by com- bining lights. There is no single ether-wave that gives a purple colour. Nevertheless, purple is quite as uni- tary in sensation as any of the colours due to a single wave-length. The relation of the spectral colours to the simple colours may be illustrated by a square. (See diagram, Fig. 21.) The corners represent the simple colours, the sides the combina- tions that may be produced from them. With each of these colours a brightness is com- bined. These series of bright- nesses extend from black to white. All wave-lengths excite the brightnesses, and the qual- ity of the brightness depends upon the amplitude of the wave, not at all upon the length. Each of the waves at a certain moderate intensity excites brightness in very slight degree, colour in larger amount. This is the pure spectral colour. A faint red light appears black because it affects the brightness organ only ; as it grows brighter it becomes first dark brown, then dark red, then red, then bright red and pink, and with very great intensities approaches white. Where Ijie colour is present in greatest propor- FiG. 21. — Colour pyramid. (]5rom Titchener: 'Textbook of Psychology,' Fig. 15.) 96 THE ESSENTIALS OF PSYCHOLOGY tion, it is said to be saturated. As the grey becomes more and more prominent, the colour is said to be less and less saturated. These degrees of saturation are represented by the radiating lines on the square of the colour pyramid. Complementary Colours. — One result of mixing colours, the phenomenon of complementary colours, is particularly important for theory. When colours at opposite comers of our colour square are mixed in suitable proportions, they give, not an intermediate colour, but brightness. Apparently the complementary colours produce exactly opposite effects upon the sub- stance sensitive to them : each destroys the effect of the other. When they thus neutrahse each other, the only effect is to excite the organ of brightness, and the result is white, grey, or black, according to the intensity of the colours. When any two colours are mixed, there is always partial cancellation, and the resulting colours are always less saturated than the components would be. If all the colours of the sun's rays are mixed, the com- ponents all cancel each other and the result is the white or slightly yellowish daylight. We may represent the greys upon our diagram by a line BW through the centre of the square extending above and below. The fact that each light ray at a sUght intensity excites only grey or black may be indicated by connecting each comer of the square with the ends of the line. It seems prob- able, too, that the Hghts in maximum intensity excite only the brightness organ. This is represented by con- necting each comer of the square with the top of the brightness line as well. Thus drawn, every point on SENSATIONS OF SIGHT 97 the pyramid inside and out represents some colour or shade, and all visual qualities are represented. After-images. — The fact of complementariness makes it probable that the colour qualities of each pair have their seat in a single organ. This assumption is fur- thered by other facts of vision. Thus if one looks at any colour or any brightness for a few seconds and then looks at another surface, the complementatry colour will be seen. Red gives an after-image of green, yellow an after-image of blue, and vice versa. It is assumed that the after-image is due to the fact that when the organ is excited in one way, recovery from the excitation gives the complementary colour. Colour-Blindness. — Even stronger evidence for as- signing each pair to a single organ is derived from the phenomenon of colour-blindness and the distribution of the colours upon the retina. . Individuals are found who lack altogether the red and green components of colour, but none who can be shown to be altogether lacking in one alone. If one is colour-bhnd, it is either to red and to green or to all colours, never to red or to green alone. Approximately three per cent of the male population is colour-blind in sufficient degree to be uncertain in the discrimination of red from green. Since for some reason the railway and navigation authorities hit upon these two colours for their signals, it is essential that all colour-blind men be excluded from their employ, hence the careful examination to which they subject apphcants for work. The phenomena of colour-bhndness are pres- ent in every normal eye. In a band about the centre red and green cannot be seen. Beyond this band the gS THE ESSENTIALS OF PSYCHOLOGY eye is totally colour-blind; only black and white are appreciated there. This outer colour-bHndness may be demonstrated by moving a small bit of paper of some colour out toward the periphery of the field of vision while the eye is kept fixed upon a point. If the colour be primary, it will turn to grey when it changes at all in quality. If it be a composite colour like orange, it will change first to yellow and then, when it gets beyond the blue-yellow zone, to grey. The Colour Pairs Seen with a Single Organ. — These phenomena taken together indicate that colour qualities are connected in pairs with their organs. Red and green have a single organ as have blue and yellow, black and white. The process that gives red is in some way op- posed to the process that gives green. Yellow is opposed to blue in the same way. There is less evidence that black and white are opposed, but that is still the usual assumption. When opposed processes are excited, they destroy each other ; when one is excited and the stimulus withdrawn, the other colour makes its appearance. When one colour disappears or is not found, the other also is not present. No altogether satisfactory explana- tion of what the change is, or of what the nature of the opposition may be, has been found, but that the process is a chemical one, and that the two directions are op- posed is generally accepted. Colour Contrast. — One other phenomenon related to complementariness and after-images is contrast. If two complementary colours are placed side by side, each becomes brighter because of the presence of the other. If a colour is seen against a grey background, it will be SENSATIONS OF SIGHT 9Q surrounded by a fringe of the complementary colour. Red will give a green, blue a yellow, and so on. The contrast effect may be observed if a small patch of grey paper be placed upon a coloured surface. The effect will be increased if a bit of translucent paper be put over the colour and the square of grey. Contrast colours are also very clearly seen when a shadow is thrown upon a coloured field, as when two shadows of the same object are cast by different coloured lights. The ex- planation of contrast is probably to be found in the opposition between the chemical processes excited by complementary colours. When a surface is stimulated by one light, the opposite process is induced in the surrounding areas of the retina. The Colourless Visual Sensations. — Whenever light which does not affect the colour processes stimulates the retina, brightness or black-white sensations result. All light affects the black-white organ, but when the colour processes are also stimulated they are appreciated only as they make the colour brighter or darker or re- duce its saturation. Brightness alone ■ is appreciated, as has been seen, when complementary colours cancel each other ; in the eyes of the totally colour-blind and on the periphery of the normal eye ; when the lights are too faint to excite the colour processes ; and when the coloured objects are very small or the stimulus has a very short duration. In the dark all colours become greys of different shades. Very small patches of colour are also grey. A coloured object at a great distance becomes a grey of a brightness that corresponds to the intensity of the light. It is for this reason that very lOO THE ESSENTIALS OF PSYCHOLOGY brilliant colours may be used in the uniforms of troops. When seen from a distance these stimulate a very small patch on the retina, and if they are of the brightness of the surrounding natural objects will not be observed. The light blue of the French uniforms, the khaki of the British and American troops, and the light grey of the German are equally difficult to detect at a distance. When different colours of slight extent are interspersed or larger patches side by side are seen from a great distance, they combine just as they do when mixed by rotation. Thus the small bits in a mosaic, or the differ- ent coloured threads in worsted combine to prodtu;e uniform shades. At present all agree that there are two organs for brightness, one for faint and another for bright or moderate lights. The faint Hghts affect the rods alone, and the brighter lights, the cones. The light that is noticed at night after one has been long in the open excites the rods. The greater sensitiveness of the eye after long adaptation to the dark comes from the in- crease in the amount of visual purple which sensitises the rods, as sensitive plates may be increased in sensi- tiveness by the application of proper chemicals. Summary of the Facts of Vision. — In brief we may assume that there are six processes in the retina from which all of the visual qualities are compounded. These six qualities are grouped in pairs, red and green, blue and yellow, and black and white, and each pair finds physio- logical explanation in opposed processes in the same substance. When the two processes are equally ex- cited simultaneously, there is no effect upon the colour SENSATIONS OF MOVEMENT lOI organ, but only the resulting effect upon the brightness organ. When one process has been aroused, its opposite succeeds it after a brief persistence of the first. In colour-blindness the red-green organ is most often lack- ing. Next most frequently wanting is the yellow-blue organ, while the black-white organ is always present unless the eye be totally blind. It is interesting to note that the manifold wave-lengths in ether affect the retina in but six different ways. However, what is lost in complexity in the retina is got back with interest in consciousness. The six processes by their combina- tions give rise to from thirty to fifty thousand distin- guishable qualities. It is interesting to note that the physiologically complex colours are little if any less simple as conscious qualities than the simple physio- logical colours. So true is this that just what are the simple physiological qualities is still a matter of dispute. Each colour theory has a different set of primary colours and the only hope of agreement depends, not upon intro- spective analysis, but upon physiological experiment. Einaesthetic Sensations. — In addition to the tradi- tional five senses of man, many new sense qualities and sense-organs have been discovered relatively recently. Most important of these is the sensation complex that tells us of the movement of the body, of weight, and re- sistance. When one moves the hand, one knows at once the amount and direction of the movement even with the eyes closed. Pathological cases are found, however, in which the patient is unconscious of move- ment and of weight. When he moves, he has no idea that he has moved, and he has no idea of the position I02 THE ESSENTIALS OF PSYCHOLOGY of his members when they are at rest. These cases emphasise the fact that the normal man must have some special sense-organ for the detection of move- ments. Investigation has shown that the sensations come from organs in the muscles and tendons. In the tissue of muscles and tendons are sense-organs not unlike some of the organs found in the skin. When the muscle is contracted, the cells of the muscle become shorter and thicker. This change exerts pressure upon and stimu- lates the sensory ends between the muscle ceUs. For example, whenever the arm is moved, there is a con- traction in one set of muscles and a relaxation in the opposing set. In one set of muscles the sense-organs will be compressed, in the other set the pressure will be relaxed. Each movement and each position has a complex of increasing and decreasing stimulations which is characteristic for that movement in quality and in- tensity. Strains and weights when the arm is not moved reveal themselves in similar pressure exerted upon the sense-organs of the tendons in addition to that upon the muscle-organs. It is by these organs that we become aware of the fundamental physical properties of the world, — of motion, of energy, and of mass. The Static Sense. — One of the most interesting of the recently discovered sense-organs is the organ of the static sense found in the semicircular canals and neigh- bouring organs of the ear. Hairs project into the liquid of the semicircular canals. When the Uquid is disturbed by the motion of the body, the hairs are moved and they in turn excite the nerves connected with them. These impulses are transmitted to the motor neurones that THE STATIC SENSE IO3 control the movement of the body, and movements are made which adjust the members to the new position or bring the body back to the upright. When the organs of the labyrinth are injured, proper motor adjustments are difficult or impossible. An animal with injured semi- circular canals will not be able to stand, or at least to stand steady. When the organs are lacking in man, reflex eye-movements are wanting. It is, perhaps, a question whether the static sense is a real sense, for we become aware of its action only indirectly through the movements it induces or, when the excitation is more intense, by the disturbances of the alimentary tract that give rise to the sensation of giddiness. When stiU more intense, the stimuli from these organs call out the more active phenomenon of vomiting involved in sea- sickness. What the immediate quality of the sensation from the static sense may be, is not known. Organic Sensations. — Many other sense-organs and sense qualities are known less definitely. The sensations from them have not been satisfactorily analysed, and their organs are not well known from physiological ex- periments. We ordinarily group them into a single mass of organic sensation. Of these hunger has been shown recently to be due to the reflex contraction of the walls of the stomach. Thirst has its seat in the upper throat or back of the mouth. It is probable that there are special organs that inform us of circulatory disturbances, of the respiratory processes, and of many others less weU distinguished. . One is aware of feeling well or feeling ill, and if one will examine the experience more closely, vague sensory qualities may be analysed I04 THE ESSENTIALS OF PSYCHOLOGY from the mass. It is to be hoped that these complexes of organic sensation may some day be analysed and their sense-organs determined. Until that time we can merely refer to the mass and say nothing more. Summary of Sense Qualities. — If we sum up the re- sults of this discussion of the qualities of sensation, we find that there are relatively few simple qualities re- ceived from sense-organs and, regarded from the physio- logical side, relatively few sorts of sense endings. A table will show the number of qualities from each sense. Qualities from the skin 4 Qualities of taste 4 Qualities of smell uncertain (9?) Qualities of hearing imcertain (11,000?) Qualities of sight 6 Qualities of kinaesthetic sensations . . . . i or 2 Qualities of organic sensations ioori2(?) In all there are but forty or fifty different sorts of nerve ends from which all the varieties of our conscious qualities are derived. We might obtain a much larger total if we considered the number of qualities that could be recog- nised by unaided observation as distinct in consciousness. Then we should have 11,000 tones, some 40,000 colour qualities, unlimited tactual qualities, the different com- plexes of taste and smell, one for each distinguishable substance, — to say nothing of the vast number of organic complexes that change with each of our moods, and with our condition of health. Emmieration on this basis has never been attempted except for sight and soimd, but it is probable that the other senses give similar large numbers of sensations or complexes of sensations. WEBER S LAW I05 Intensities of Sensation. — One other aspect or attri- bute of sensation importaijt in practice is intensity. The intensity of sensation is dependent upon the intensity of the stimulus. The more energy acts upon the sense- organ, the greater the intensity. While intensities play a very large part in our life, they are not easily described or even thought of in absolute terms. They cannot be easily remembered. We have no accurate names for the degrees of intensity in our non-scientific vocabulary. Pounds and kilograms, ergs and horse-power, are ob- viously artificial units and correspond to nothing that we can picture easily. For everyday usage slight, moderate, and intense are the only terms available to designate intensities. The difficulty in description and discussion is all the more marked because experiments show that there is no direct relation between the in- tensity of the physical stimulus and the resulting con- sciousness. As nearly as one can make out a thousand ounces do not give a thousand times as much weight sensation as one ounce. Sensations seem to increase in amount very much more slowly than stimuli increase in intensity, — if one may speak of the amount of sensation at all. Intensities of sensation cannot be described by words as we describe qualities of sensation, and they can- not be measured by measuring the intensity of the physical stimulus and assuming that the sensation will harmonise with that. Both the simple methods of approach fail us. Weber's Law. — The attempt to discover some means of dealing with the intensities of sensation led indirectly to the establishment of a law of relation between stimulus and sensation which is known from the name of the man Io6 THE ESSENTIALS OF PSYCHOLOGY who first noticed the relation as Weber's law. This asserts that the least noticeable difference between two stimuli is not constant for all intensities, but varies with the intensity of the stimuli compared. Thus in lifting weights one can distinguish between an ounce and an ounce and a fortieth. But if a pound be the standard, one cannot notice the addition of a fortieth of an ounce ; a fortieth of a pound must be added. In any sense-department it has been found that an addi- tion to be just noticed must be some fraction of the stimulus present, rather than an absolute amount. The fraction that must be added is different for each sense. It varies from about one one-hundredth for sight to about one-third or one-fourth for smell. Several different formulae have been used to express the relation. Per- haps the best known and the simplest is that sensations increase in arithmetical ratio, as stimuli increase in geo- metrical ratio. The stimulus must always be multiplied by some fraction, — for passive pressure, e.g. by four- thirds (f) to obtain the next unit of sensation. Deviations from Weber's Law. — The most obvious outcome of the law in everyday life is that only relative differences can be appreciated. One is aware of the relative difference in brightness between the black of the print and the white of the page, but is not aware of the absolute change in the brightness of each between noon and evening. Were the law to hold absolutely, the light might fade and we be unaware of it. The fraction that can be noticed is not absolutely constant, however, but holds only for the middle ranges of in- tensity. As the light grows dim, the just distinguishable WEBER S LAW 107 differences must increase, until at twilight white must be more than sixty times as bright as the black of the print to be readily noticed as different from it. Simi- larly, as the absolute brightness is increased, the frac- tion increases or, put the other way, the relative sensi- tivity decreases. Slight differences are not so easily noticed in the full glare of the sun as in diffuse daylight. One cannot read ordinary print at night or with ease in the glare of the noonday sun. The Sensation Threshold. — Not on^ may differences between intensities be too slight to be noticed, but stimuli may be too faint to give rise to any sensation whatever. As one moves a watch away from the ear, the sound becomes fainter and fainter until it finally disappears. One may touch a pressure spot on the skin with a hair so soft that it gives no sensation. The intensity that can be barely noticed, that first gives rise to a sensation, is called theliminal or threshold stimulus. At the other extreme it is probable that a stimulus may be too in- tense to be felt. Probably, however, intensities that do not destroy the sense-organ merely tend to be lost in the accompanying pain ; they do not actually dis- appear. The upper Umen is of relatively little im- portance, and there is Httle known about it because of the injury which work upon it might do to the sense-organ. QUESTIONS 1. M'hat is a sensation? Is it a physiological or psychological process f 2. What determines the quality of a sensation? Does it depend more upon the stimulus or upon the organ stimulated? Is there sound when there is no ear to hear? I08 THE ESSENTIALS OF PSYCHOLOGY 3. -What is the physiological zero point? Is it always the same? Is it the same for the exposed hand and for the elbow which has just been uncovered ? 4. What elementary sensations are excited when the hand is put into water at 48° C? at 10° C? What is the paradoxical cold sensation? 5. Name the components of the 'taste' of ice cream; of hot coffee ; of pepper. 6. Describe the action of the three small bones of the ear during hearing. 7. Is the basilar membrane broader near the oval window or near the apex of theacochlea ? 8. What is a noise : (o) physically? (6) physiologically? 9. What is an octave ? an overtone? How aretheC of the violin and of the piano different ? 10. State the Helmholtz theory of hearing. What facts tend to prove it ; what to disprove it ? 11. Are the gangUon cells or the rods and cones nearer the vitreous himiour ? nearer the pupU ? 12. Why is vision clearest at the fovea? 13. Describe the different forms of colour-blindness. What sensation does the colour-blind man receive from a primary red? from orange ? 14. Under what circumstances does the normal eye see grey? What different organs are excited when we see grey ? 15. What is the visual purple? Where is it and what is its function? 16. How does seeing the stars at night and not during the day illustrate Weber's law ? 17. What is meant by the sensation or absolute limen? the difference limen? EXERCISES I. Mark off an area on the skin a centimetre square. Touch each point of the area with a pointed metal rod warmed to about 40° C. Mark the spots where warmth is felt. Repeat with the SENSATION 109 rod cooled by immersion in ice-water. Mark the points where cold is felt. Compare with the warm spots. Are they the same ? Stimulate a definite cold spot with a rod heated to about 55° C. What stimulus do you receive ? Why? 2. Press gently upon the different regions of the area above with a pointed toothpick or human hair. Mark the points where press- ure is felt. Go over the same area with a sharpened horsehair fastened by wax to a handle. Note the points where pain is felt. Compare with pressure and with the temperature spots. Can you make out any law of arrangement ? 3. Observe in a glass the red openings of the papillae on the end of the tongue. Mark five papillae on a drawing of the tongue. With a brush stimulate each papUla successively with a solution of salt, sugar, vinegar, and quinine. Are all of the spots sensitive to each substance? How can you explain the results by the doctrine of specific energies? 4. Fatigue the nostril for camphor by smelling a lump of the gum until it is no longer perceived. Try the nose for iodine. Fatigue again for camphor and try for vanilla. Test in the same way for rubber, asafcetida and other substances. What do the results prove of the nature of olfactory qualities? 5. Draw the ear to demonstrate the relations of the bones of the middle ear to the cochlea and the auditory nerve. 6. Demonstrate the presence of overtones in a note of the piano. Strike the lowest C while the key that gives' the octave is held down. As the first key is dropped you will hear the octave still resounding by sjrmpathetic action induced by the first overtone of the fundamental. Proceed in the same way to determine what other overtones are present in the note first struck. How do these overtones affect the ear? 7. Mix blue and yellow in different combinations on a rotating colour-mixer. If this be not at hand, a substitute may be prepared as follows : Place a square of yellow paper and a square of blue paper of the same size a fbot apart upon a black cloth on a table. Hold a pane of clear glass vertical midway between them and look through the glass at one, and adjust the second square so that its no THE ESSENTIALS OF PSYCHOLOGY reflected image covers the first. When the two colours are brought to coincide the apparatus makes a simple colour mixer. The intensities of the colours may be varied by turning the glass plate about the line of contact with the table. What colour does the mixture of blue and yellow give rise to when the apparatus is adjusted to give equal amounts of each? Try mixtures of other primary colours to give the list of spectral colours. 8. Place a bit of green paper over a dot on a sheet of grey paper. Look intently at the green paper for ten seconds. Blow the green bit away and look for three seconds or so at the dot. What colour replaces the green? Repeat with the other colours and record results. 9. Place a centimetre square of grey paper on a large square of red. Cover both with tissue or other translucent paper. Note the colour of the small square as seen through the tissue paper. What gives it a colour? Test on surfaces of other colours. What is the general law ? 10. Look steadUy at a point on a wall, preferably a grey wall. Have an assistant move centimetre squares of coloured paper away from the fixation point. Note the point where the different colours disappear or change. Measure the distance from the fixation point in different directions. Compare the distances for different colours. Can you interpret the results by the phenomena of colour-blindness mentioned in the text ? 1 1 . Draw the eye showing the lens system and its relation to the iris, retina, and various coats. On a larger scale draw a portion of the retina that shall indicate the nervous connections between the rods and cones and the fibres of the optic nerve. 12. Bend the finger at the second joint. Can you detect deeper lying sensations? Can you distinguish them in quality from the pressure sensations ? What is the sense-organ that gives rise to them ? REFERENCES TiTCHENER : Textbook of Psychology, pp. 59-224. Angell : Psychology, pp. 109-1 50. SENSATION III Howell : Text-book of Physiology, ch. xviii. MvERS: Experimental Psychology, vol. I, chs. ii-ix. Seashore : Elementary Experiments in Psychology, chs. i-ii', vii, viii (for further experiments and fuller description of the experiments described in the exercises). CHAPTER V SELECTION AND CONTROL— ATTENTION Omnipresence of Selection. — One of the most strik- ing facts of consciousness is selection or control. A man is not absolutely under the domination of habit, of external stimulation, or of the habitual elements in the thinking processes, but can decide for himself, within limits, what he shall hear or see, what he shall think or what he shall do. He may admit faint stimuli to consciousness while stronger ones are acting upon the sense-organs ; he may repress a strong habit and permit a weaker one to run its course; or he may choose a faint memory when several that are ordinarily more insistent are pressing for return. Evidently, selec- tion is of fundamental importance in perception, in action, and in memory. Since selection affects so many different processes and has so many different phases, it becomes necessary to distinguish between the ques- tions that may be answered in the same way everywhere and those that must be treated differently in each field. Three questions must be answered in connection with each kind of selection : (i) what is the effect of selec- tion upon the process affected? (2) what determines the course of selection ? (3) what are the concomitants of the selective activity? Of these the first takes differ- ent forms in each field ; the second and third are gen- PHENOMENA OF ATTENTION IIJ eral : an answer in one connection will hold with little change for both of the others. The conditions of selec- tion and the means of knowing that selection is being made are the same for perception, for memory, and for will. In this chapter we shall discuss primarily atten- tion or the selection of sensations but we shall also point out the similarities between the attention processes and the control processes in thought and action. Effects of Attention on Sensation. — The general effects of selection are the same for perception, for thought, and for action. We read on a railroad train in spite of the noise and other distractions; we hear the faint sounds of a conversation in a storm or in a boiler shop and are for the moment not aware of the din. When studying attentively, one may be spoken to several times without being disturbed. Similarly, one can continue a train of thought even when other very pleasant mem- ories suggest themselves or in the midst of external dis- turbances. A stimulus that has given rise on different occasions to a number of different responses and might now be the means of exciting several different movements will arouse but one of these, — that one will be selected from the other possible ones. Each of these selections is of the same kind. One process is given free rein ; all others are checked. More frequently in attention, the processes not selected are not absolutely excluded from consciousness, but are given a subordinate place. As one attends, certain sen- sations are clearly appreciated ; the others axe less clear. One of the much discussed problems of attention concerns the difference between the sensation directly attended 114 THE ESSENTIALS OF PSYCHOLOGY to and the others that constitute the background of consciousness. Two conflicting theories have been held : one, that attention increases the intensity of the sensa- tion, the other, that the change is peculiar and must be given a different name, clearness. All agree that the effect of attention is similar to increased intensity. Both make the sensation easier to describe, make all judgments about it more accurate, and give it a more important place in consciousness. But the two effects must be different in some way for one seldom mistakes a change in attention for a change in the intensity of the stimulus. It is not assumed that the violin has increased in in- tensity when its tones are picked out from the mass of an orchestra, nor is it assumed that the tactual sensations grow weak when they are not attended to. It is certain that attention and intensity are sufficiently different in their effect upon consciousness to prevent them from being mistaken for each other. It is generally asserted that attention increases the clearness of a mental state. The state becomes clearer, its details are more promi- nent, it can be more easily used and understood. This quality of clearness is, however, different from intensity in spite of the fact that both make a mental state more important. Analysis and Synthesis. — Analysis and synthesis may both be referred to the effect of selecting different states. In analysis some one part of a total process is made prominent, and this makes possible the recognition of its constituents. As one attends to one of the notes of a chord, that note becomes prominent in the complex. Analysis of the chord consists in making each of its CONDITIONS OF ATTENTION 1 15 components prominent one after another. Synthesis is also a result of increasing the clearness of mental states. It differs from analysis only in that the total effect of the mass is attended to rather than some one component. With the chord one may attend to deter- mine the closeness of fusion of the components or the pleasantness of the compound. This serves to unite the elements into a single whole. The results of atten- tion may be either to analyse or to synthesise, but in either case the primary effect is to increase the promi- nence of part or of whole. This change in clearness with the resulting analysis or synthesis may affect memory or thought processes as well as sensations. One may analyse either the memory or the sensational elements from a perception, or one may turn from a perception to study mental imagery, or may attend to one part after another of an idea. The effect upon ideas is the same as upon sensations. In action, selection is more likely to be of wholes than of parts, although on occa- sion one element of a complex act may be emphasised without changing the others. The Conditions of Attention. — Why one selects or attends is not so easy to determine. Usually the con- ditions are hidden. Attention comes without antece- dent desire or warning. One often finds one's self at- tending without any preliminary intention and even against one's will. When one desires to attend, in ad- vance of attention, it is a problem why one desires, and this usually escapes notice even when the question is raised. Nearly always one is concerned to know only that one desires to attend and does not care to know Il6 THE ESSENTIALS OF PSYCHOLOGY why. Indirect methods, however, have thrown con- siderable light upon the conditions of attention. These methods consist in studying the circumstances in the individual and the outside world that precede attention, and in generalising the results of the observation in laws. In the Ught of these observations two sets of conditions may be distinguished, the subjective and the objective. The one is a series of circumstances in the outside world that precedes attention, the other the earlier experiences of the individual. These conditions may be first deter- mined for attention to external stimuli, although the results hold for all selection. Objective Conditions of Attention. — The circum- stances in the outer world that favour the entrance of a sensation are to be found in the amount of energy exerted by the stimulus upon the sense-organ. The amount of energy expended ma,y be due to the intensity of the stimulus, to its duration, or to the area of the sense-organ affected, (i) An intense sound such as an explosion, a bright light, a strong odour, will force them- selves upon attention, however much one may desire to attend to something else. (2) Similarly a large object will be seen where a small one might escape notice. (3) Up to a certain point, too, the greater the duration of a stimulus, the more Ukely it is to enter consciousness. Beyond that, greater duration leads to neglect; one attends and passes on to something else, and the stimulus is no longer appreciated. This is but another way of stating that change is more important than absolute intensity or extent in determining the course of attention. One notices a whistle of changing pitch or intensity where CONDITIONS OF ATTENTION I17 a constant one would escape notice. One even appre- ciates the ticking of a watch as it stops, although the preceding continuous ticking has not been noticed at all. Similarly, objects that move towards or away from us are noticed, although the same objects would escape notice if stationary, and our only way of knowing that they move away or approach is from the changing size. Change, whether in size or intensity, whether it be in- crease or decrease, attracts attention. These char- acteristics of the outside world that tend to compel us to receive a sensation may be said to be opposed to attention. They express, not the selective activity of consciousness, but the forces in the outside world that oppose voluntary selection. If they alone acted, consciousness would be but a plaything of external forces. It is usual to extend the meaning of the term attention to cover all the factors that explain the entrance of sensations, and one cannot understand the subjective factors without a knowledge of these objective con- ditions, whether one calls them conditions of atten- tion or not. One might add in this connection, in anticipation of the later discussions, that there are similar objective conditions which oppose subjective control, both in memory and in action. In both, these are found in the closeness of connection between sensa- tion or idea and other ideas or movements. The develop- ment of the laws must be left to the later chapters. The Subjective Conditions of Attention. — The sub- jective conditions give the individual spontaneity and self-expression in the selection of sensations. They reflect the earUer life of the individual in very much Il8 THE ESSENTIALS OF PSYCHOLOGY the same way that the objective conditions reflect the outer world at the moment. It is possible to enumerate five factors of greater or less generality that determine the nature of attention. Enumerated in the order of nearness in time to the particular act of attending, these are: (i) the idea in mind, (2) the purpose or attitude at the moment, (3) the earlier education, (4) duty (as the expression of social or individual ideals), and (s) heredity. The first can be seen either in the infiuence of an immediately preceding sensation or of an immediately preceding idea. If one has heard or seen or is thinking of some object and that object pre- sents itself, it will be noticed where otherwise it might escape attention. It is easier to hear an overtone if a tone of the same pitch has been heard at full strength just before. Similarly, in listening to an orchestra, re- calling the tones of a violin or looking at the violin will be certain to make the tones of that instrument promi- nent, when otherwise they might not be noticed. If when looking for an object one wiU hold its picture in mind, one wiU see it at once. When a bird in a tree has been seen once through a glass, it will con- tinue to be seen easily, although it may have been looked for in vain a long time, before it was first discovered. Mental Attitude a Condition of Attention. — The second of the subjective conditions of attention takes three forms. Each is an expression of a mental attitude and is a little more general than the idea or sensation prominent at the moment. The most usual and most definite way of arousing the attitude is to ask a ques- CONDITIONS OF ATTENTION II9 tion. This may be illustrated by a simple experiment. Cut a number of bits of paper of different shapes and colours. Cover them with a piece of cardboard and expose them for an instant as you ask, ' What colours do you see? ' After exposure the observer can tell pretty accurately what colours were shown. If then you ask him what the forms were or how many bits were shown, it will be found that he can give no correct answer. One sees what corresponds to the question; all else is excluded from consciousness. Sometimes the question arises spontaneously or is suggested by a sen- sation. You wonder if it is raining, and as you look out of the window with this question in mind, you notice a drizzle or see spots upon the roof that would other- wise have escaped you. Very many observations grow in this way out of specific questions, and it is surprising to note how certain the question is to bring to mind any object that may contain the answer to, or correspond to, the question, and how little one sees that does not correspond to some question. Most people cannot say whether the four on the watch is IIII or rV, because they look for the time, not the characters. Purpose as Mental Attitude. — Next in order of explidtness of conscious anticipation is the purpose. This differs from the formulated question only in that the end to be attained is less definite or less definitely formulated. Often one first has a vague general problem and this suggests one definite question after another and these in turn control the specific acts of attention. Usu- ally one has some definite purpose in observation as in action, and this serves to control attention even when I20 THE ESSENTIALS OF PSYCHOLOGY there is no definite question in mind. In a laboratory one may be seeking for the solution of some problem with no definite question formulated. Under those circmnstances one is very likely to notice anything that harmonises with the purpose. Similarly one notices animal Hfe in the field of a microscope more easily in the zoological laboratory, and plant structures more easily in the botanical laboratory. The purpose is not very insistent in these cases but is none the less opera- tive. In everyday life what is appreciated corresponds very closely to the purpose, whether that purpose be serious and permanent or trivial and transitory. On a hunting trip one is set for the perception of game, as in a classroom one is set to understand a lecture or hear a question. This ' set ' constitutes the purpose, and is effective even when not kept in mind. One often has still less definitely conscious ' sets.' In these one is not aware of a purpose and has no definite question. The bias arises from some previous experience and is not preceded by a desire to see one thing or group of tilings rather than another. Nevertheless any object that corresponds to the attitude will be noticed at the expense of other objects. After one has detected escap- ing gas, other odours often will be noticed, even after all thought of detecting an odour has vanished. All three of these factors serve to quicken attention for one group of things rather than for another, and together they constitute its most important condition. What does not correspond to the attitude; purpose, or question of the moment is not admitted to consciousness, and all that does correspond to it will be noticed, no matter CONDITIONS OF ATTENTION 121 how unfavourable the circumstances in other respects. Practically the only difference in the three sorts of attitudes is to be found in the degree of anticipation of the object attended to. The question very definitely foreshadows the object to be seen; the purpose gives only a general idea of the class of objects to be expected ; while the attitude is not at all conscious and gives no expectation. The attitudes change from hour to hour, and even from moment to moment. They are practi- cally the only occasions for the shifting of attention. Education as a Condition of Attention. — The influ- ence of the earUer Hfe in determining the general charac- ter of attention is as marked as the influence of the atti- tude in the changes of its temporary character. Two influences of education may be distinguished. First it makes certain forms of attention more effective. The skill of tea and wine tasters, the keeimess of the savage for following a trail, are due, not to any improve- ment in the sense-organ through practice, but to train- ing in attention. In every sense department and in every sort of observation one comes with practice to appreciate differences that at first cannot be detected. One important result of any sort of education is the increased capacity for observation. A second influence of education upon attention is the more usual one of determining the stimulus to be effective. What is seen or heard is usually an indication of the character of earlier experiences. If a man enters a strange room, he wiU notice first some object which his education has prepared him to see. A fisherman will notice the rod on the wall, the athlete, the mask and foil or the lacrosse 122 THE ESSENTIALS OF PSYCHOLOGY stick, the scholar will see the books, and the artisan the implements of his trade. It is possible to determine what a man's occupation or training is by studying the objects he observes and the order in which he sees them. Even more generally one will hear one's own name when spoken in a conversation of which nothing else is heard. Sometimes education acts indirectly by preparing ques- tions and purposes; often education acts directly — one is not aware of any preliminary purpose. In brief, education gives capacity for discrimination and also determines the order in which presented objects shall enter consciousness, and whether they shall enter at all. Social Determinants of Attention. — One effect of education upon attention is important enough for sepa- rate mention. This is the effect of social training which serves to hold attention to the momentarily unpleasant for the attainment of future benefits. One is con- stantly being taught that certain things must be attended to in spite of the fact that others are more in harmony with the momentary mood. It is of course not possible to analyse, in their completeness, the forces that make for this sort of attention, but so far as they can be ana- lysed they may be referred to social influences and be brought together imder the term social pressure. One ordinarily works for the object at present less pleasant to gain some greater remote good. The value of the remote good is learned from and usually enforced by society, and enforced as a duty, not as a good. The impulse to work for it is given through ideals, and the ideals can be traced to the society of the individual. The boy of to-day seeks to avoid manual labour and to CONDITIONS OF ATTENTION 123 enter the professions, even when they are relatively un- remunerative, because of .the small esteem in which working with the hands is held by society. Each ideal demands for its attainment holding attention for a long time to matter that is not pleasant. When you turn from reading a novel to this chapter, you are governed by social pressure. First is the pressure exerted by teacher and class to stand well, and then the desire to attain the end for which this knowledge is a preparation. Both ends are desirable in the last analy- sis because of the social approval they receive. The punishment of failing to attend is social contempt ; the reward of persistent attention is social approval. Society sets the end, social pressure compels one to attend for its attainment. The attention that comes from social pressure is distinguished from the other forms of atten- tion due to education in that the end and the process are unpleasant, and attending seems the result of effort, while in the others the end and process are pleasant and are interesting. Heredity and Attention. — To understand certain characteristics of attention we must go back of the experience of the individual to his original nature. This is determined first by the evolution of the race and second by the immediate heredity of the individual. The first explains the fact that all are attracted by move- ment and by individuals of the opposite sex, and that love stories and stories of fighting universally hold us. Under the second fall the differences in taste shown by individuals. Liking for music or art goes back in part to a tendency to observe certain stimuli rather than 124 THE ESSENTIALS OF PSYCHOLOGY others. Many similar characteristics and capacities must be explained in large .part by innate differences in attention. It is still impossible to say how far any particular act of attention is due to an hereditary influ- ence and how far to education and other acquired tend- encies. Certain it is, however, that each plays an important part. The more fundamental ways of attend- ing are hereditary. The Nervous Basis of Attention. — In harmony with our preliminary statement that all mental action has a corresponding activity in the cortical cells, it is neces- sary to relate the conditions of attention to nervous processes. The nervous basis of attention is undoubt- edly the selective preparation of certain cortical cells that makes excitation easy. This preparation is a state of partial activity that needs but to be increased by the stimulus to give full consciousness. In conse- quence a stimulus too weak to affect cells not thus prepared will arouse these to full activity. Each of the conditions discussed above may be traced to some prepa- ration of this sort. The influence of the immediately preceding stimulus is to leave the cells it excites in a state of partial activity ; they are still quivering from the earlier stimulation, and so respond easily to the new stimulus. The influence of the question or purpose is to arouse in some slight degree a whole group of connected cells. When a question is asked, the nervous impulse spreads from the cells excited by the question to others that have previously been excited in the same connec- tion. An object appealing to any one of these cells will find entrance to consciousness made easy for it. INTEREST 125 Part of the work has already been done. The influence of education is, first, to connect the nerve-cells into large groups, and so to prepare for questions and pur- poses, and secondly, to make possible the spread of preparation from group to group, and thus to determine the course of the spread of preparation. It probably also makes certain paths permanently more permeable, and so more open to excitation than they were in advance of training. The hereditary bias has a similar explana- tion, except that the selective permeability is present in advance of training. Preliminary preparation in the nervous system is correlated with selection of sen- sations in consciousness, and each of the conditions of selection induces in the nervous system a state of partial activity which prepares for full activity. Interest and Non-voluntary Attention. — The condi- tions of attention can be reduced to certain peculiarities in the outside world and to different events in the life of the individual. But if one should ask the average non- scientific individual why he attends, he would answer in practically every case that he attended because he was interested or because he made an effort. If we examine our own consciousness, it is evident that atten- tion from interest and attention from effort are nat- ural divisions. It is desirable to refer this popular ex- planation and classification to the conditions already discussed. A list of the things that are interesting includes those that are attended to naturally and uni- versally, such as stories of conflict. Attention to these we have seen to be due to heredity, to education, or to passing attitude or purpose. Some interests are general 126 THE ESSENTIALS OF PSYCHOLOGY and innate, some are acquired by education, and some are temporary and seem to come and go without cause. To say that attention is due to interest is merely to say that it is due to some one of the subjective conditions other than social pressure. Attention from these conditions is pleasant and spontaneous. It has some- times been called non-voluntary attention. Effort and Voluntary Attention. — Attention due to effort falls almost universally under the socially condi- tioned. When one is said to strive to attend, the incen- tive is ordinarily some ideal of social origin. The real occasion for attending is the social approval that is •expected or the blame that is feared if one fails to attend. The social incentive is generally given the name duty. This sort of attention is also marked off from the others by the accompan3dng diffuse contractions in different parts of the body that give sensations of strain. These constitute the feeling of effort. Attention induced by ideals of social origin and accompanied by effort is called volxmtary attention. Involuntary Attention. — Attention conditioned by the nature of the stimuli from the external world com- pletes the list. This is called involuntary attention, since it may be opposed to the purpose and to the domi- nant ideals of the moment. It is always effortless, but may or may not be interesting. To exclude these stimuli is the usual object of effort. We may say that there are three sorts of attention : voluntary, non-volim- tary, and involuntary. Voluntary attention is condi- tioned by social pressure and is accompanied by effort ; non-voluntary attention is conditioned by the idea in ATTENTION AND MOVEMENT 1 27 mind, the mental attitude of the moment, education, or heredity, and is accompanied by interest; involun- tary attention is conditioned by the character of the stimuli that are presented, and either is accompanied by interest or is attention to the distraction that should be resisted and so through conflict gives occasion for effort. The different forms cannot always be distinguished, but they serve the practical purposes of classification. The Motor Phenomena of Attention. — Movements are among the most striking characteristics of the attentive consciousness. They serve as the only sign of attention to the onlooker, and are prominent in the experience of the individual attending. As one attends, the various sense-organs are adjusted to receive the impression most effectively. When one attends to an object in the field of vision, the eyes spontaneously turn toward it, the two eyes converge that it may be seen with the fovea in each eye, and the lens is adjusted to give the clearest possible image. The turning and converging of the eyes can be seen by the observer. One knows when talking to a person whether one is being looked at or whether the gaze is directed beyond and infers from that the degree of attention one is receiv- ing. This is the most common indication of the nature of the thing attended to. Not only is there a charac- teristic position of the eye^ for attention in the field of vision, but for hearing also and even for touch and taste. Attention to objects perceived by the other senses is usually followed by visual attention to the same object. When one hears a soimd, one turns the eyes toward it, and when touched, one looks to see what 128 THE ESSENTIALS OF PSYCHOLOGY is against the skin. There are definite adjustments of the other senses to give the best condition for observa- tion. In addition to the adjustment of the sense-organs essential to perception, many more general muscular contractions accompany attending. One of the most important is the inhibition of all movement. When one is listening, all movements cease ; even those that have started are stopped in mid course. Any sort of strong attention causes an unintentional cessation of activity. At the same time the breath is held mo- mentarily, the heart beats faster, and other changes in circulation may be noticed. Quite as obvious and more important from the conscious side are numerous general contractions in voluntary muscles. In any attending the muscles everywhere are slightly tense. In marked degrees of voluntary attention the brow is wrinkled, the muscles of the jaws are set, and the fists may be clenched. All of these are to the observer signs of attention, and at the same time they indicate to the man who attends that he is attending. The diffuse contractions give rise to the strain sensations which constitute the feeling of effort in voluntary attention. The motor processes serve to adjust the sense-organs to the most adequate reception of stimuli, — holding the breath and inhibiting general movements prevent the interference of distracting sensations, while the cir- culation is adjusted to the increased demands of the organism. On the other side they indicate to the observer that the man is attending, and to himself they give some idea of the degree of attention or at least of the amount of conflict in attention. ATTENTION AND MOVEMENT 1 29 Is Attention or Movement Primary? — Much con- troversy has arisen in the last few years as to whether attention or movement is primary. One theory is that attention is due to the motor response ; the other that attention is first and the response a mere accompani- ment or result. The truth seems to lie between them. The essential fact in attention is. the selective prepara- tion. Movements of accommodation and clearness of conscious states are both results of this preparation. The preparation, as has been seen, is the .outcome of the preceding activities of the individual, near and remote, and of the effects that these activities have had upon the nervous organism. The effect of this preparation as expressed in the attitude toward any stimulus is what we call attention. As seen by the in- dividual, this is marked by selection of stimuli and by clearness of certain conscious states. As seen by an- other, attention is a series of movements, a visual fixa- tion, a bodily attitude, or general strain. Of the effects of the preparation, we can never be sure whether clear- ness or movement comes first. In many cases it can be observed that the stimulus presents itself in some vague way and the sense-organs gradually adjust themselves to give greater definiteness of impression. This is the usual order in involuntary attention. When the stimu- lus is expected, the sense-organs are prepared in advance. In that case preparation is usually determined by some memory process which precedes and initiates movement. This is true of voluntary and of certain forms of non- voluntary attention. Attention Means Preparedness. — Attention, then, 130 THE ESSENTIALS OF PSYCHOLOGY means neither the clearness of consciousness nor the movements that accompany the clearing up of a con- scious state, but fundamentally the condition of pre- paredness of the individual and the organism that gives rise both to the, change in consciousness and to the movements. This preparedness makes for selection, not merely of sensations, but of ideas and of movements. These have the same conditions and the same accom- panying states of effort and interest. One is interested in mental states and actions as one is interested in objects, and one feels effort in holding to a train of thought or in selecting a course of action as in carrying out a diffi- cult bit of reading or observation. The same charac- teristics that are prominent in attention are prominent in the selection of thought and action. The fundamental phase of attention is the preparedness that determines selection. It is the same in essence as the factors to be discussed later which control thinking and action. This, not any conscious change in sensation or move- ment, is what must be emphasised in attention. This preparedness is not, however, itself conscious. One does not know that one is likely to see one thing rather than another until one sees it, and one does not know that certain movements of accommodation are coming until they are made. The only sign of the change that has been wrought by earlier activities is the effect in modify- ing selection and in inducing the accompanying actions. The Duration of Attention. — Two practical questions arise with reference to attention. The first is, how long any single stimulus may occupy the dominant place, the second, how many things may be attended to at DUUATION OF ATTENTION 13I once. To the question how long one may attend, various answers have been given. The ordinary opinion is that one may attend indefinitely. One seems to pay atten- tion to the book one is reading for hours at a stretch, and one listens to a lecture for an hour with slight dis- traction. In all such cases, however, the material is con- stantly changing, one is not attending to the same stimulus, nor to the same sensation during the whole period. If one attends to any faint stimulus, the ticking of a watch or a faint grey ring on a revolving disk, it will be seen that one does not hear the sound nor see the ring all the time. It will be seen for a second or two, will vanish for four or five seconds, and then appear again. The total length of the cycles wUl be about six to ten seconds. These alternations are often called attention waves. More recently -they have been referred to some periodical change in the sense-organ or in the nervous system, so are not to be regarded as changes in atten- tion in the narrowest sense. We must find some other answer to the question how long one may attend. While watching the faint ring to see when it comes and goes, one is aware of a constant shifting of attention. One drifts away from the ring to wonder whether one is attending or is attracted by some extraneous matter or thing, and often the change in the sensation comes while thus distracted. A record that has been made recently of the maximum time that attention can be held to any single stimulus indicates that the pulsations are very short indeed. If one attempts to keep attention fixed upon a single point in a picture, it will be found that at least once a second something about the point will 132 THE ESSENTIALS OF PSYCHOLOGY come in to crowd it out of consciousness. If the stimu-,. lus be absolutely simple and one is careful to record each appearance of something else, it seems that one can hold attention strictly to a single thing for less than a second. When in the popular sense attention is given to a thing for an hour at a time, attention is constantly shifting from part to part, or is turning to other objects or thoughts for longer or shorter periods. Attention for more than a second or so to absolutely the same stimulus is either impossible or results in the pathological condition of hypnotism. The Range of Attention. — The question how many things may be attended to at once has also been variously answered at different periods in the history of psychology. The first statement, on purely a priori grounds, was that a imitary mind could have not more than one conscious process at one time. More recently experiments dem- onstrated that if a number of objects were shown for one-fifth of a second or less, four or five objects might be seen.. More recently still, however, careful observation of the process of determining the number of objects shows that even with short exposures the objects are not attended to at once, but are impressed upon con- sciousness and persist for a time in the memory after- image, where they may be attended to separately and counted. It is as if one took an instantaneous photo- graph of a group of objects and counted them on the film after development. The memory after-image per- sists only a second or two, however, and the number of objects that may be seen with a short exposure depends upon the niunber that can be attended to and counted RANGE OF ATTENTION I33 before the image disappears. It seems probable from all the experiments that only a single object may be attended to at once. Very much the same conclusion has been reached about the related problem of the number of things that may be done at once. Often two or more operations are apparently carried on at the same time. Careful in- vestigation, however, shows that two things can be done at once only if one has become so habitual as to require no attention. One may easily carry on a conversation while walking, but in this case walking has become so automatic that it requires no conscious guidance. Should the way become very rough, conversation will cease or will suffer long and frequent interruptions. Ex- periments have been made to show that one can read a selection and add a series of figures at the same time more quickly than one could do both in succession, but if either task is difficult enough to require full attention, the two will take more time when carried on together than when done successively. When easy and familiar, one task will be carried on automatically while attention is given to the other, but when both require full atten- tion, only one can be carried on at a time to advantage. Attention and Inattention. — A natural question arises as to what the opposite of attention may be, or whether there is ever a time when one does not attend. Com- plete inattention is noticed only during sleep or periods of unconsciousness.* Even in sleep there is apparently some selective adaptation to stimuli. A sleeping man will be aroused by his name even if spoken in a tone so low that he has heard nothing else of the conversation. 134 THE ESSENTIALS OF PSYCHOLOGY In profound slumber a mother is ' set ' for the move- ments of her child, the nurse for the patient. In the insane, too, attention is present although in a reduced or distorted form. The so-called states of inattention of the normal man are really states of attention, but of attention to something at the moment undesired. They divide into two forms, — scattered or diffuse attention, and absent-mindedness. In the one, attention is con- stantly shifting to a new object, and no one is kept before consciousness long enough to be fully appreciated. IS the other, attention is so absorbed in some one thing or course of thought that other sensations have little chance to enter. The first form is more frequent in childhood and in certain pathological states, the other is more usual in maturity and is frequently found in men of more than usual training and ability. Both forms of inattention are desirable if not in excess ; in fact they are extremes of the two desirable characteristics of attention. Attention is most effective when all useful objects are attended to, and attention is kept upon them long enough to appreciate them fully. Dispersed attention insures entrance of all important objects, the abstracted state protects against distraction that might prevent full understanding. It is only excessive in- stability or too great and inappropriate immersion in anything that should be guarded against. Attention and Distraction. — It is generally thought that any distraction, any stimulus, that may present itself at the time one is endeavouring to attend to any- thing else will diminish the amount of attention and so render observation less accurate. Experiments show ATTENTION AND DISTRACTION I35 that this is not always true. If one is comparing two intensities, e.g. first undisturbed and again when a phonograph is playing near by, it is found that at times the judgment made during the distraction may be more accurate. * Certain individuals and all individuals under certain conditions seem to do better work when the room is not too quiet. Much depends upon the strength of the distraction and the health and attitude of the in- dividual. Acts that require a very short time are less affected than those that occupy more time. Recent experiments by Dr. Morgan offer a suggestion that may explain the apparent contradiction. He asked a number of students to press a certain key when one of a number of colours appeared upon a disk and to press another key when another colour appeared, etc. Other complications were introduced which demanded very close attention. The quickness of mental processes was measured by the time required to make the re- sponse. Simultaneous records were taken of the pres- sure exerted upon the key, and of the depth of breath- ing. The task was performed first without, then with, distraction. In most subjects the distraction at first caused a decrease in the quickness and accuracy of work, but this soon changed to an increase in effectiveness. Study of the records of breathing and of the pressure exerted upon the key showed that while the distraction acted, the key was pressed harder, the breathing was deeper, and that slight vocal movements were used to aid in thinking of the movement to be made. The apparent explanation of the effect of distraction in the light of the results is that the individual exerts himself 136 THE ESSENTIALS OF ' PSYCHOLOGY to overcome the distraction and puts forth more than enough extra effort to overcome it and in consequence does more than before, but at the expense of extra fatigue. The Genesis of Attention. — Attention* must be present in the child in some form from the very earliest months ; the change with years is primarily in the con- ditions that control selection and the constancy with which attention is kept upon one object. At first, se- lection must be controlled by the external stimuli and heredity. The infant is attracted by intense stimuU of any sort and by moving objects. Very early, experience shows its effect and the child begins to notice, in the chaos of the new and unfamiliar, objects that have been seen frequently. From this time on, each experience prepares the way for a new experience. The effect of these experiences is determined by the closeness of the relation of the experience to inherited tendencies. When they oppose heredity the effect is slighter than when they aid it. At this stage the development of interests be- gins. These are to grow with all learning and all ex- perience and must change and develop with each new experience. With the school years or earlier comes the appreciation of duty and other rudimentary social de- mands. At this stage the child makes a beginning in keeping attention fixed upon the more unpleasant thing which is approved by society in the face of the more pleasant. Training in attention of this sort comes at first through seeing the advantages of attending in harmony with social ideals as enforced through dis- cipline. Later, obedience to the calls of duty becomes SELECTION AND CONTROL I37 more or less habitual and the habit constantly grows and changes through application in new fields. In terms of our classification, attention begins with the involuntary and the hereditary sort of non-voluntary attention ; soon the other non- voluntary forms develop ; and last of all the voluntary. Summary. — As sensations constitute the primary structures of consciousness, so attention or selection is the primary function. It is possible to select sensations, memories, and actions. The conditions that lead to the selection are the same in each case. They are to be found in the intensity of the stimuli, the strength of the memory or the habit on the one side, and in the mo- mentary attitude, education and heredity, and social 'pressure on the other. Selection in any one of these fields is accompanied by interest if conditioned by edu- . cation or heredity, and is accompanied by diffuse strain sensations that give rise to the feeling of effort if the selection is controlled by duty. The act of selection is called attention when applied to sensations; it is called voluntary control of ideas when applied to recall ; and is called will when applied to action. So far we have considered explicitly only the control of sensation, although what has been said here of conditions and ac- companiments holds of the other processes as well, as will be made clear in due time. It should be emphasised that the terms used to describe the fact are less important than the fact. The fact of selection is called will in many of its applications, as it has been called attention in this chapter. There should be no quarrel as to whether will or attention is the more important, as each 138 THE ESSENTIALS OF PSYCHOLOGY is but a word used to designate different applications of this fundamental process with its conditions and ac- companiments. The fact is essential, the name is a matter of usage. We shall make use of the fact in connection with all mental operations. QUESTIONS 1. Give an instance of the way sensations are selected. Do the sensations that are not selected enter consciousness? If so how do they differ from those which are selected? 2. What is the motive for attending to a musical selection? To solving these problems? To a loud noise? Why do you notice your own name whenever it is seen on a page? Trace the acts of attention to the conditions mentioned in the text. 3. Cite instances of attention that are due to each of the subjective conditions. 4. Are the movements which accompany an act of attention its cause or its effect ? Give evidence in favor of your opinion. 5. Is interest cause or effect of attention? What is inter- est? In what sense is it a condition, in what sense a mental state ? 6. Answer the same questions for effort. 7. Outline the changes in the nervous system that explain selection. Are they the same for all conditions ? 8. Is distraction ever favorable to mental work ? EXERCISES I. Paste five bits of paper of different shapes and colours and four letters upon a square of cardboard. Show it to a group with the request to teU what colours they see. Note the answers. After an interval of half an hour ask what the shapes of the coloured papers were ; then what letters were seen. Compare the per- centages of objects seen that corresponded to the questions with those which did not. SELECTION AND CONTROL 139 2. Look closely at a point on an evenly illuminated and coloured wall. Can you distinguish any difference in the intensity or bright- ness of the point looked at as compared with the surrounding areas? Have an assistant strike several notes upon some instru- ment. Attend first to one then to another. Does the attending increase the apparent intensity of the tone or merely increase its clearness ? 3. Recall as definitely as you can some act of attention that in- volved effort. Can you analyse the components of the feeling of effort ? Lift a heavy weight that also requires effort. Is the qual- ity the same as in the effort of attention? Can you trace the feel- ing to any sense-organ ? 4. Watch a small dot so far away that it can just be seen. Can you see it aU the time ? How many times a minute does it come and go ? 5. Try to keep attention upon a dot when near enough to be seen easUy. Can you watch it all the time? Keep a list of the memories or other sensations that come in to crowd it out. How many times will attention wander from it and come back to it in ten seconds ? 6. Have an assistant prepare a set of cards with different num- bers of dots upon them. Let him place the cards face down upon a table and show them one after another for an instant by turning them over and back. What is the largest number of dots that may be seen at a single glance ? Do you count them during the expo- sure or from memory later ? 7. Try counting from 20 downward and at the same time write the digits from i up to 20. Take the time. Take the time required for each separately. Compare. Introspect to explain the difference in time required. ^ 8. Add a column of two-place figures whUe the room is quiet and all is favourable. Add a second column of the same difficulty while an electric beU is ringing continuously. Add while two people are having a conversation near you. Compare times and errors under the three conditions. I40 THE ESSENTIALS OF PSYCHOLOGY REFERENCES PiLLSBtmY : Attention, chs. i-v. Angell : Psychology, ch. v. Titchener: Elementary Psychology of Feeling and Attention, chs. v-vii. James : Principles of Psychology, vol. i, ch. xi. Seashoee : Elementary Experiments in Psychology, ch. xiii. J. B. Morgan : The Overcoming of Distractions. Archives of Psychology, 35. CHAPTER VI RETENTION AND ASSOCIATION The Materials of Memory and Imagination. — Before we can regard our enumeration of the elements of con- sciousness as complete, we must consider those due to the rearousal of earlier experiences. With eyes closed and other senses unstimulated one still has conscious processes, and at all times elements not derived im- mediately from sense-organs mingle with the sensations. You may now recall an event of last year, although the sense-organ is now not excited at all. You can see the landscape in its original colours, can reinstate the tem- perature of a summer day although it is now winter, may in fact renew all of its features at will. These ex- periences in their ultimate qualities are of the same character as the sensations. The colours are the spec- tral colours, the tones are the tones of the scale, the cold is the familiar cutaneous sensation. They come now, however, not from the sense-organs, but are ex- cited by the action of other central parts of the nervous system. To indicate the similarity in quality to sen- sation and the fact that they are due to the stimulation of one part of the cortex by another, these elementary components of memories are sometimes called centrally aroused sensations. A little observation and reflection show that in every case these processes ultimately 141 142 THE ESSENTIALS OF PSYCHOLOGY originate in the senses. The object that you recall is the same object that you saw last year. On occasion you may compare the memory of the object with the object itself and -assure yourself of the similarity. Even when the image represents nothing that has been seen before, the elements of which it is composed are of the same character as the sensations. The elements are merely rearranged in new combinations. The sensory quahties, whether peripherally or centrally aroused, are like the colours upon the painter's palette. They are relatively few, but from their combinations all the con- scious experiences may be obtained, as the artist may paint any scene with his few colours. All the centrally aroused sensations, the elements of memory and imagina- tion, come originally from the senses. They are retained in some way and reinstated on suitable occasion. An understanding of these centrally aroused sensations re- quires an answer to three questions : (i) how are they retained and where are they between the time of en- trance and of their reinstatement? (2) under what cir- cumstances do they return? (3) how do they compare in quality with the original sensations? Theories of Retention. — Theories of the nature of retention have varied, from the metaphor of the ancients that mind was like wax on which impressions might be made by a seal, to the equally crude physiological theory that each idea was kept in a single nerve-cell. The gen- erally accepted theory at present is that retention is a physiological process allied to habit. Aristotle sug- gested that memories were due to the repetition on re- call of the same movements that were made when the THEORIES OF RETENTION I43 original experience was first received. Of course his knowledge of