LIBRARY 
 
 ANNEX 
 
 ^X^4.;f 
 
 '^m 
 
 .^"^ 
 
 ■%f: 
 
 s^:- 
 
 
(ll0cneU HttiuBraitjj Blibtarjj 
 
 Sttfata, S^ent gotk 
 
QP 451.W58'"l92r"' '■'""' 
 '"""SiiliiiSi^iiiSffi?...!?? '"ovement on the s 
 
 3 1924 024 829 479 
 
w, 
 
 Cornell University 
 Library 
 
 The original of tinis 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/cu31924024829479 
 
THE ILLUSORY PERCEPTION OF 
 MOVEMENT ON THE SKIN 
 
 BY 
 ANNA KELLMAN WHITCHURCH 
 
 A thesis presented to the Faculty of the Graduate School 
 of Cornell University in partial fulfilment of the require- 
 ments for the Degree of Doctor of Philosophy 
 
 Reprinted from The American Journal of Psychology 
 October, 1921, Vol. XXXII, pp. 472-489 
 
THE ILLUSORY PERCEPTION OF MOVEMENT ON 
 THE SKIN^ 
 
 By Anna Keixman Whitchukch 
 
 CONTENTS 
 
 PAGE 
 
 Introduction 472 
 
 I. Experimental Procedure 473 
 
 II. Manual Experiments 474 
 
 Results of Manual Experiments 474 
 
 III. Mechanical Stimulations: Series 1 475 
 
 Results of Series 1 477 
 
 Series II 478 
 
 IV. Types of Perception 479 
 
 V. Distance of Movement 485 
 
 VI. Rate of Movement 485 
 
 VII. Stimulations of Long and Short Duration 486 
 
 VIII. Experiments upon Non-adjacent Spots 486 
 
 IX. Cutaneous versus Visual Movement 486 
 
 Conclusions 488 
 
 The object of the present investigation was to determine 
 the elementary conditions of the perception of cutaneous move- 
 ment. Wertheimer^ and his successors have found such con- 
 ditions for the perception of movement in the field of vision ; 
 and Dimmick^ has shown a specific existential correlate of 
 the perception of visual movement, namely, the grey flash. 
 Our problem, then, is to find out whether the perception of 
 cutaneous movement can be aroused by successive stimulation, 
 and in that case what is its existential correlate. 
 
 Benussi and others* have already dqne much work upon 
 the arousal of cutaneous movement by successive stimuli 
 operating at long distances apart. Benussi stimulated at dis- 
 tances ranging from 4 cm. to the distance between the fingers 
 
 1 From the Psychological Laboratory of Cornell University. 
 
 2 M. Wertheimer, Ueber das Sehen von Bewegung, Zeit. f. Psych., 
 61, 1912, 161ff. 
 
 3 F. L. Dimmick, An Experimental Study of Visual Movement and 
 the Phi Phenomenon, this Journal, 31, 1920, 317flf. 
 
 * V. Benussi, Kinematohaptische Erscheinungen, Arch. f. d. ges. 
 Psych., 29, 1913, 385 ; Kinematohaptische Scheinbewegung und Auf- 
 fassungsumformung, Ber. u. d. VI Kong. f. exp. Psych., 1914, 31 ; 
 Versuche zur Analyse taktil erweckter Scheinbewegungen, Arch. f. d. 
 ges. Psych., 36, 1916, 59. Cf. also H. E. Burtt, Tactual Illusions of 
 Movement, Jour. Exp. Psych., 2, 1917, 371. 
 
473 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 on the two outstretched arms. Burtt gives reports from stimu- 
 lations 8 to 16 cm. apart, and his apparatus allowed distances 
 from 2 to 18 cm. These distances, however, favor the arousal 
 of visual associations; and minimal distances are for that 
 and for other reasons to be preferred. Incidental reports by 
 von Frey and Metzner,^ apparently overlooked by later experi- 
 menters, prove that such distances may be employed. 
 
 Von Frey and Metzner have given the only reports of 
 work on the skin directly comparable with that of Wertheimer 
 in vision. They were trying to find the best interval in which 
 to distinguish as different the responses of two adjacent 
 pressure spots successively stimulated. They used as stimuli 
 hairs or blunt needles which rested on the skin for 1/9 sec. 
 The intervals between stimulations were 1/9, 1/6, 1/3, 1, 
 4/3, and 2 sec. Near the end of their paper this statement 
 appears : " When two points are stimulated, the difference of 
 the two stimuli is either recognized as such, or (especially 
 with the shorter intervals) is interpreted as a shift (Ver- 
 schiebung) of the stimulus, as a brushing (Streichen) of it 
 over the skin." The only numerical data given show that, with 
 an interval of 4/3 second, 13 out of 29 stimulations aroused, 
 in some form, the perception of movement. 
 
 Experimental Procedure 
 
 The present work was begun in the summer of 1920. The 
 four O's who served were: Miss C. Braddock (B), graduate 
 scholar in psychology; Dr. K. M. Dallenbach (D), assistant 
 professor of psychology; Dr. L. B. Hoisington (H), assistant 
 professor of psychology; Mrs. A. K. Whitchurch (W), gradu- 
 ate scholar in psychology." 
 
 The skin on the left fore-arm of the O's was tested with 
 von Frey hairs of various tension-values until a hair was found 
 which could be felt upon the normal skin, but was too weak 
 to arouse subcutaneous sensations when the skin was lightly 
 etherized. The tension-value of the hair finally selected was 
 7.9 gr./mm. Two hairs were cut to this standard. They 
 measured in length 40 and 42 mm. respectively. 
 
 Five groups of pressure-spots, ranging from 6 to 9 in num- 
 ber, on every O's arm were isolated and stained, so that the 
 same spots could be tested every day. During this preliminary 
 testing one spot was stimulated only once in an hour. The 
 stimulating hair was held 1 mm. above the pressure-spot, and 
 
 ' M. von Frey and R. Metzner, Die Raumschwelle der Haul bei 
 Successivreizung, Zeit. f. Psych., 29 1902, 161ff. 
 ' When W observed, B acted as experimenter. 
 
WHITCHURCH 474 
 
 after the " Ready, now " signal was touched to the spot. The 
 O's were asked to report on the intensity, quahty, and extensity 
 of the sensation. Two reports were taken when the spots 
 were stimulated singly, and two when one spot was compared 
 with another. The introspections were worked over, and the 
 spots most alike were selected and again reported upon, until 
 the first numbers chosen narrowed down to .3 or 4 in a group. 
 Finally we were able to select two adjacent spots in every 
 group which the O's reported as like the spots in every other 
 group. The selected spots were then permanently tattooed 
 with a tiny glass tube just under the hair. The mark was 
 distinct and lasting. The distances between the spots in the 
 various groups were as follows (in mm.) : B (1) 2.5, (2) 
 3, (3) 2.5, (4) 3, (5) 4; D (1) 5, (2) 3.6, (3) 3.2, (4) 
 3.8, (5) 3; H (1) 4.7, (2) 3.4, (3) 4.7, (4) 3.1, (5) 2.4; 
 and W (1) 2.8, (2) 5.5, (3) 3.2, (4) 2.1, (5) 3.8. 
 
 Manual Experiments 
 
 O sat at a low table with his arm in a plaster cast. The 
 adjacent hairs in the five groups were stimulated in turn. 
 The duration of the stimulus was 250 ±25''. The intervals, 
 marked by a silent pendulum, were 750, 1000, and 1250'^. 
 
 worked under two sets of instructions. The ' process ' 
 instruction was : " I shall stimulate the skin on your arm. 
 Describe the cutaneous perception aroused in purely psycho- 
 logical terms. The stimulus will be repeated so that you may 
 complete your description." The ' meaning ' instruction was : 
 " I shall stimulate the skin on your arm. Characterize the 
 cutaneous perception aroused, fully, in any commonsense terms 
 you wish to use. The stimulus will be repeated so that you 
 may complete your report." 
 
 The manual experimenting continued until every had 
 given 50 reports under the ' meaning ' and 50 under the 
 ' process ' instruction with the 750 and the 1250 intervals. 
 With the 1000 interval, every made 100 reports under 
 each set. 
 
 Results of Manual Experiments 
 The reports fell under headings like those which have 
 been obtained in the work on vision: (1) full movement, in 
 which the stimulus moved from the 1st to the 2nd spot stimu- 
 lated; (2) bimembral movement, in which the 1st and 2nd 
 stimulus each moved; (3) unimembral movement, in which 
 either the 1st or the 2nd stimulus moved; (4) intramembral 
 movement, in which the stimulus at one or both spots moved 
 
475 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 within the area of stimulation; (5) pure phi, in which the 
 movement had no quaHtative, intensive, or extensive begin- 
 ning and ending, but was a uniform ' brushing ' over the 
 cutaneous surface. 
 
 Table A sums up the results of this preliminary work. 
 The columns headed M show the percentage of reports under 
 the ' meaning ' instruction ; those headed P the percentage of 
 reports under the ' process ' instruction. The intervals are 
 given in sigma. 
 
 The reports under the two instructions are closely parallel. 
 Long before the completion of the series the O's had settled 
 into a stable manner of reporting. 
 
 The 750 interval is the best of the three for arousing the 
 perception of full movement. Even with this interval, how- 
 ever, the percentages are very low. Since optimal conditions 
 had not been found, and since the lowest interval was the 
 best, we began a new series of experiments with shorter inter- 
 vals. Henceforth we applied the stimuli by means of apparatus. 
 
 Mechanical Stimulation: Series I 
 The apparatus was an adaptation of Benussi's kinohapt.^ 
 The intervals and durations of the stimuli were controlled 
 by a Leipsic time-sense apparatus. 
 
 Both cutaneous and ' subcutaneous '* stimuli were employed. 
 The cutaneous stimuli were two horse-hairs whose tension- 
 value was 4.85 gr./mm., and which measured in length 10 
 and 9.8 mm. respectively. The subcutaneous stimuli were 
 coarser hairs whose tension-value was 10.25 gr./mm. ; they 
 measured 3 and 2.85 cm. respectively. The duration of the 
 stimuli was 150''. The intervals of this series were 100, 250, 
 500, 750, and 1000'^. The adjacent spots in two groups on 
 every O's arm were now stimulated exclusively. 
 
 The cutaneous (C) and subcutaneous (S) stimuli were 
 used alternately as follows : ( 1 ) C 100, 12 M-reports on spots 
 a-b, 12 P-reports on spots a'-b' ; (2) S 250, 12 M-reports on 
 spots a-b, 12 P-reports on spots a'-b'; (3) C 500, 12 M-reports 
 on spots a-b, 12 P-reports on spots a'-b'; and so forth. At 
 the end of the ten groups which this order necessitated, the 
 experiments were continued by reversing the order. Thus 
 after no. 10 came (11) S 100, 12 P-reports on spots Or-b, 12 
 M-reports on spots a'-b'. The practice-effect was thus evenly 
 
 ' For a description of the kinohapt, see V. Benussi, Arch. f. d. ges. 
 Psych., 29, 1913, 385. 
 
 ' We use this shorthand term to designate the stimuli which af- 
 fected both cutaneous and subcutaneous end-organs. 
 
WHITCHURCH 
 
 476 
 
 
 
 
 TABLE. A 
 
 
 
 
 
 Manual Experiments: Percentages 
 
 
 
 
 
 750 
 
 1000 
 
 1250 
 
 
 
 M 
 
 P 
 
 M 
 
 P 
 
 M 
 
 P 
 
 Full 
 
 B 
 
 18 
 
 14 
 
 18 
 
 19 
 
 4 
 
 2 
 
 Movement 
 
 D 
 
 4 
 
 4 
 
 10 
 
 16 
 
 14 
 
 2 
 
 
 H 
 
 48 
 
 30 
 
 27 
 
 34 
 
 
 
 
 
 
 W 
 
 14 
 
 24 
 
 23 
 
 24 
 
 2 
 
 2 
 
 
 Av. 
 
 21 
 
 18 
 
 19.5 
 
 23.3 
 
 5 
 
 1.5 
 
 
 M.V. 
 
 13.5 
 
 9 
 
 5.5 
 
 5.8 
 
 4.5 
 
 .8 
 
 Biraembral 
 
 B 
 
 4 
 
 2 
 
 5 
 
 
 
 2 
 
 2 
 
 Movement 
 
 D 
 
 
 
 
 
 
 
 
 
 
 
 6 
 
 
 H 
 
 4 
 
 
 
 10 
 
 8 
 
 2 
 
 
 
 
 W 
 
 2 
 
 10 
 
 13 
 
 15 
 
 6 
 
 10 
 
 
 Av. 
 
 2.5 
 
 3 
 
 7 
 
 5.8 
 
 2.5 
 
 4.5 
 
 
 M.V. 
 
 1.5 
 
 3.5 
 
 4.5 
 
 5.8 
 
 1.8 
 
 3.5 
 
 Unimembral 
 
 B 
 
 12 
 
 26 
 
 9 
 
 21 
 
 42 
 
 38 
 
 Movement 
 
 D 
 
 12 
 
 8 
 
 26 
 
 11 
 
 30 
 
 20 
 
 
 H 
 
 34 
 
 54 
 
 32 
 
 34 
 
 48 
 
 42 
 
 
 W 
 
 56 
 
 38 
 
 38 
 
 30 
 
 36 
 
 48 
 
 
 Av. 
 
 28.5 
 
 31.5 
 
 26.3 
 
 24 
 
 39 
 
 37 
 
 
 M.V. 
 
 16.5 
 
 14.5 
 
 8.8 
 
 8 
 
 6 
 
 8.5 
 
 Intramembral 
 
 B 
 
 22 
 
 12 
 
 17 
 
 7 
 
 12 
 
 12 
 
 Movement 
 
 D 
 
 14 
 
 
 
 3 
 
 6 
 
 
 
 4 
 
 
 H 
 
 2 
 
 
 
 13 
 
 4 
 
 20 
 
 14 
 
 
 W 
 
 10 
 
 6 
 
 8 
 
 6 
 
 22 
 
 6 
 
 
 Av. 
 
 12 
 
 4.5 
 
 10.3 
 
 5.8 
 
 13.5 
 
 9 
 
 
 M.V. 
 
 6 
 
 4.5 
 
 4.8 
 
 .9 
 
 7.5 
 
 4 
 
 Phi 
 
 B 
 
 
 
 2 
 
 1 
 
 1 
 
 4 
 
 
 
 
 D 
 
 6 
 
 
 
 10 
 
 1 
 
 2 
 
 2 
 
 
 H 
 
 2 
 
 2 
 
 
 
 1 
 
 
 
 
 
 
 W 
 
 12 
 
 10 
 
 3 
 
 6 
 
 
 
 2 
 
 
 Av. 
 
 5 
 
 3.5 
 
 3.5 
 
 2.3 
 
 1.5 
 
 1 
 
 
 M.V. 
 
 4 
 
 3.3 
 
 3.3 
 
 1.9 
 
 1.5 
 
 1 
 
 No 
 
 B 
 
 44 
 
 44 
 
 50 
 
 52 
 
 36 
 
 46 
 
 Movement 
 
 D 
 
 64 
 
 88 
 
 51 
 
 66 
 
 54 
 
 66 
 
 
 H 
 
 10 
 
 14 
 
 18 
 
 19 
 
 30 
 
 44 
 
 
 W 
 
 6 
 
 12 
 
 15 
 
 19 
 
 34 
 
 32 
 
 
 Av. 
 
 31 
 
 39.5 
 
 33.5 
 
 39 
 
 38.5 
 
 47 
 
 
 M.V. 
 
 23 
 
 26.5 
 
 17 
 
 20 
 
 7.8 
 
 9.5 
 
 distributed. Several minutes elapsed betwen the stimulations 
 of the same spot. At the end of every 12 reports O took his 
 arm from the cast for a time, in order that there might be no 
 fatigue. Usually O made reports on one group of experi- 
 
477 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 ments in an hour, and never on more than two. Every O 
 made 24 reports under the ' meaning ' and 24 under the ' pro- 
 cess ' instruction for every one of the intervals employed. 
 
 Results of Series I 
 
 The results of the first series with mechanical stimulation 
 are summarised in Tables B I and B II. The columns M 
 and P show the number of reports of the different types of 
 phenomena given in each group of 24 experiments. 
 
 With both cutaneous and subcutaneous stimuli the 100<^ 
 interval gives the greatest number of full movements. Next 
 to the full movement in frequency comes the unimembral 
 movement. The number of full movements is too small to 
 indicate optimal conditions, and another series was accord- 
 ingly planned. 
 
 The ' process ' and ' meaning ' reports run closely parallel, 
 as is shown by the averages of the groups. 
 
 
 
 
 
 
 TABLE B- 
 
 -I 
 
 
 
 
 
 
 Cutaneous Mechanical Stimulation: 
 
 Series I: Absolute Nuhjb 
 
 ERS 
 
 
 Full 
 Movement 
 
 M 
 B 9 
 D 8 
 H 6 
 WIS 
 
 100 
 P 
 6 
 
 10 
 8 
 
 14 
 
 250 
 M P 
 3 4 
 3 
 7 5 
 
 
 500 
 M P 
 
 
 
 
 1 
 
 
 750 
 M P 
 
 1000 
 M P 
 
 
 Av. 
 M.V. 
 
 9 
 2 
 
 
 9.5 
 2.3 
 
 3.3 
 1.9 
 
 2.3 
 2.3 
 
 .3 
 .4 
 
 
 
 
 
 
 Bimembral 
 Movement 
 
 B 
 D 
 H 7 
 W 8 
 
 
 
 
 5 
 5 
 
 
 
 6 
 5 
 
 1 
 
 6 
 7 
 
 
 
 9 
 8 
 
 3 
 
 7 
 8 
 
 2 
 
 
 2 
 
 
 
 
 
 1 
 
 1 
 2 
 
 
 
 
 2 
 
 
 1 
 
 
 Av. 
 
 M.V. 
 
 3. 
 3. 
 
 8 
 8 
 
 2.5 
 2.5 
 
 2.8 
 2.8 
 
 3.5 
 3 
 
 4.3 
 4.3 
 
 4.5 
 3 
 
 1 
 1 
 
 .3 
 
 .4 
 
 .8 
 .8 
 
 .8 
 .8 
 
 Unimembral 
 Movement 
 
 B 
 D 
 
 H 
 W 
 
 5 
 12 
 10 
 
 3 
 
 
 8 
 12 
 11 
 
 5 
 
 6 
 
 14 
 10 
 13 
 
 4 
 
 9 
 
 11 
 
 15 
 
 10 
 5 
 8 
 
 14 
 
 8 
 1 
 9 
 
 14 
 
 5 
 
 4 
 9 
 7 
 
 6 
 
 3 
 
 10 
 
 8 
 
 4 
 3 
 9 
 
 7 
 
 7 
 
 8 
 7 
 
 
 Av. 
 M.V. 
 
 7 
 3 
 
 .5 
 .5 
 
 9 
 2.5 
 
 10.8 
 2.8 
 
 9.8 
 3,3 
 
 9.3 
 2.8 
 
 8 
 3.5 
 
 6.3 
 1.8 
 
 6.8 
 2.3 
 
 5.8 
 2.2 
 
 5.5 
 2.8 
 
 Intramembral 
 Movement 
 
 B 
 D 
 H 
 
 w 
 
 
 
 
 1 
 5 
 
 2 
 
 
 3 
 
 4 
 
 
 5 
 
 2 
 
 
 13 
 
 5 
 3 
 
 7 
 
 3 
 2 
 
 9 
 
 1 
 5 
 3 
 
 7 
 1 
 5 
 2 
 
 
 Av. 
 M.V. 
 
 
 
 
 2 
 
 1.5 
 
 
 1.8 
 1.8 
 
 1.8 
 1.8 
 
 5.3 
 3.8 
 
 3 
 2 
 
 4.5 
 2.5 
 
 3.8 
 2.3 
 
 No 
 Movement 
 
 B 
 D 
 H 
 
 w 
 
 9 
 3 
 
 1 
 
 
 
 8 
 2 
 
 
 
 14 
 2 
 1 
 4 
 
 15 
 
 15 
 
 2 
 
 2 
 
 11 
 
 19 
 
 2 
 
 2 
 
 8 
 
 23 
 
 6 
 
 2 
 
 4 
 20 
 10 
 12 
 
 11 
 21 
 11 
 13 
 
 10 
 18 
 10 
 14 
 
 10 
 21 
 11 
 14 
 
 
 Av. 
 M.V. 
 
 3. 
 2. 
 
 3 
 9 
 
 2.5 
 2.8 
 
 5.3 
 
 4.8 
 
 8.5 
 7.7 
 
 8.5 
 6.6 
 
 9.8 
 6.6 
 
 11.5 
 4.5 
 
 14 
 3.5 
 
 13 
 3 
 
 14 
 3.5 
 
 With the 100 interval, B reported phi in 1 M and 2 P; D in 1 M. 
 
WHITCHURCH 
 
 478 
 
 TABLE B— II 
 Subcutaneous Mechanical Stimulation: Series I: Absolute Numbers 
 
 Full 
 Movement 
 
 M 
 10 
 14 
 
 H 15 
 W 15 
 
 P 
 13 
 10 
 13 
 15 
 
 M 
 
 2 
 18 
 
 7 
 11 
 
 250 
 
 P 
 
 3 
 
 11 
 
 7 
 10 
 
 500 
 M P 
 
 750 
 M P 
 
 Av. 13.5 12.8 
 M.V. 1.8 1.4 
 
 9.5 7.8 
 5 2.8 
 
 No 
 Movement 
 
 B 9 
 
 D 5 
 
 H 1 
 
 W 
 
 10 10 
 
 4 
 
 1 1 
 1 
 
 12 
 8 
 9 
 
 7 
 
 13 
 4 
 6 
 7 
 
 15 
 
 10 
 
 5 
 
 10 
 
 18 
 
 8 
 
 5 
 
 Av. 
 M.V. 
 
 3.8 3.8 2.8 4 
 3.3 2.3 3.6 3 
 
 9 7.5 
 1.5 2.8 
 
 9.5 10.3 
 3 3.9 
 
 With the 100 interval, D reported phi in 1 M. 
 
 1000 
 M P 
 
 Bimembral 
 Movement 
 
 B 
 D 
 H 
 W 
 
 
 2 
 4 
 4 
 
 1 
 3 
 
 6 
 
 
 
 6 
 4 
 3 
 
 
 8 
 5 
 5 
 
 3 
 2 
 
 6 
 
 4 
 
 1 
 9 
 
 2 
 2 
 
 1 
 4 
 
 
 
 
 
 1 
 2 
 
 1 
 
 
 
 
 
 
 
 
 
 
 Av. 
 M.V. 
 
 2.5 
 
 1.5 
 
 2. 
 2 
 
 5 
 
 3.3 
 1.8 
 
 4.5 
 2.3 
 
 2.8 
 1.8 
 
 3.5 
 3 
 
 2. 
 
 3 
 9 
 
 .8 
 .8 
 
 .3 
 
 .4 
 
 
 Unimembral 
 Movement 
 
 B 
 D 
 
 H 
 W 
 
 5 
 2 
 4 
 5 
 
 3 
 4 
 8 
 3 
 
 
 12 
 
 
 
 10 
 
 10 
 
 11 
 1 
 
 10 
 8 
 
 7 
 12 
 10 
 
 9 
 
 4 
 
 20 
 
 9 
 
 7 
 
 8 
 
 7 
 
 8 
 
 13 
 
 
 9 
 
 6 
 
 11 
 
 15 
 
 
 2 
 9 
 7 
 
 4 
 
 8 
 
 4 
 
 
 Av. 
 M.V. 
 
 4 
 1 
 
 4. 
 1. 
 
 5 
 ,8 
 
 8 
 3.3 
 
 7.5 
 3.5 
 
 9.5 
 1.5 
 
 10 
 5 
 
 9 
 2 
 
 
 10.3 
 2.8 
 
 4.5 
 3.5 
 
 4 
 2 
 
 Intramembral 
 Movement 
 
 B 
 D 
 H 
 W 
 
 
 
 
 
 
 
 2 
 
 
 
 
 
 
 2 
 
 
 
 
 
 1 
 
 
 2 
 2 
 5 
 2 
 
 3 
 
 8 
 1 
 
 6 
 
 5 
 2 
 
 
 5 
 
 4 
 2 
 
 3 
 
 1 
 
 4 
 
 12 
 
 4 
 
 5 
 
 5 
 
 13 
 
 
 Av. 
 M.V. 
 
 
 
 5 
 8 
 
 .5 
 .8 
 
 .3 
 .8 
 
 2.8 
 1 
 
 3 
 2.3 
 
 3. 
 2. 
 
 3 
 3 
 
 2.8 
 1.8 
 
 5 
 3.5 
 
 6.8 
 3.2 
 
 20 
 
 21 
 
 11 
 
 5 
 
 16 
 19 
 
 11 
 7 
 
 14.3 13.3 
 6.3 4.3 
 
 Series II 
 
 The intervals chosen for the next series were 25, SO, "^S, 
 and 100''. The arrangement of the groups and the procedure 
 were as before.. 
 
 The results are summarised in Tables C I and C II. The 
 100'' interval gives the greatest number of full movements 
 with cutaneous stimulation, and the 75" interval with sub- 
 cutaneous stimulation. Again the ' process ' and ' meaning ' 
 reports parallel each other. 
 
 A group of 24 experiments with each stimulus in each of 
 the intervals 125 and 150'^ was made as a part of this series 
 with O's H and W. Full movements were reported in the 
 following cases: C 125, H 9M and 8P, W 8M and 6P; C 
 150, H 5M and 4P, W 4M and 4P; S 125, H 6M and 4P, 
 W 5M and 3P; S 150, H 6M and 6P, W 5M and 4P. 
 
479 
 
 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 
 
 
 TABLE C— I 
 
 
 
 
 
 Cutaneous Mechanical Stimulation: Series II; 
 
 Absolute Numbers 
 
 
 Full 
 Movement 
 
 B 
 D 
 H 
 W 
 
 25 
 M P 
 
 5 1 
 2 6 
 
 
 50 
 
 M P 
 19 23 
 
 9 6 
 10 4 
 10 13 
 
 75 
 
 M P 
 17 16 
 
 7 8 
 11 11 
 14 15 
 
 M 
 14 
 11 
 14 
 16 
 
 100 
 
 P 
 
 19 
 
 9 
 
 15 
 
 14 
 
 
 Av. 
 M.V. 
 
 1.8 
 1.8 
 
 1.8 
 2.1 
 
 12 
 3.5 
 
 11.5 
 6.5 
 
 12.3 
 3.3 
 
 12.5 
 3 
 
 13.8 
 1.4 
 
 14,3 
 2.8 
 
 Bimembral 
 Movement 
 
 B 
 D 
 H 
 W 
 
 
 
 
 
 4 
 2 
 
 
 
 4 
 
 
 
 
 2 
 
 4 
 
 
 
 3 
 3 
 
 
 
 4 
 4 
 
 
 
 3 
 5 
 
 
 Av. 
 M.V. 
 
 
 
 1.5 
 1.5 
 
 1 
 1.5 
 
 1.5 
 1.5 
 
 1.5 
 1.5 
 
 2 
 2 
 
 2 
 2 
 
 Unimembral 
 Movement 
 
 B 
 D 
 H 
 W 
 
 1 
 
 12 
 5 
 
 1 
 
 
 8 
 5 
 1 
 
 
 
 12 
 
 9 
 
 3 
 
 
 14 
 11 
 
 4 
 
 
 
 11 
 
 7 
 
 6 
 
 3 
 6 
 
 7 
 6 
 
 2 
 
 10 
 
 6 
 
 4 
 
 2 
 
 9 
 6 
 5 
 
 
 Av. 
 M.V. 
 
 4.8 
 3.8 
 
 3.5 
 3 
 
 6 
 
 4.5 
 
 7.3 
 5.3 
 
 6 
 3 
 
 5.5 
 1.3 
 
 5.5 
 2.5 
 
 5,5 
 2 
 
 Intramembral 
 Movement 
 
 B 
 D 
 H 
 W 
 
 3 
 
 
 2 
 
 4 
 
 
 
 
 3 
 
 
 
 
 
 
 
 
 
 2 
 
 
 
 
 
 
 
 1 
 
 
 2 
 
 
 
 
 
 
 
 
 
 
 Av. 
 M.V. 
 
 1.3 
 1.3 
 
 1 
 
 1.5 
 
 .8 
 1.1 
 
 
 .5 
 .8 
 
 .3 
 
 .4 
 
 .5 
 .8 
 
 
 No 
 Movement 
 
 B 
 D 
 H 
 W 
 
 20 
 
 7 
 
 17 
 
 21 
 
 20 
 14 
 13 
 23 
 
 1 
 2 
 1 
 9 
 
 1 
 4 
 5 
 7 
 
 5 
 6 
 
 4 
 
 
 5 
 
 10 
 
 2 
 
 
 
 6 
 3 
 
 
 
 3 
 6 
 
 
 
 
 Av. 
 M.V. 
 
 16.3 
 4.3 
 
 17.5 
 4 
 
 3.3 
 2.9 
 
 4.3 
 1.8 
 
 3.8 
 1.9 
 
 4.3 
 3.3 
 
 2.3 
 2.3 
 
 2.3 
 2.3 
 
 With the 25 interval, D reported phi in 1 P; with the 50 interval, B reported it in 1 M, 
 and D in 1 M. 
 
 Types 'of Perception 
 
 The reports arising from the cutaneous and subcutaneous 
 stimulations are so nearly alike that we shall for the most 
 part confine our discussion to the former and shall mention 
 the ' subcutaneous ' reports only where differences occur. The 
 reports under the ' meaning ' and ' process ' instructions will 
 not be treated separately. They will be grouped together in 
 the following discussions, and throughout ' meaning ' will be 
 dealt with first. 
 
 (1) Full Movement. — In all cases of full movement, the 
 stimuli are felt as two touches with movement between them 
 from a to b. The type appearing most often is that of the 
 dumb-bell pattern. The stimulus touches, lifts, and moves in 
 a narrow line to a new position. In ' process ' the first 
 impression is a round or oval bit of extent. The impression 
 
WHITCHURCH 480 
 
 TABLE C— II 
 Subcutaneous Mechanical Stimulation: Series II: Absolute Numbers 
 25 50 75 100 
 
 Full 
 Movement 
 
 B 
 D 
 H 
 
 W 
 
 M 
 
 1 
 
 7 
 
 
 
 
 
 P 
 5 
 6 
 
 
 
 M 
 
 5 
 
 6 
 
 3 
 
 2 
 
 P 
 2 
 
 1 
 3 
 
 
 M 
 11 
 18 
 16 
 19 
 
 P 
 
 14 
 12 
 15 
 18 
 
 M 
 15 
 11 
 10 
 17 • 
 
 P 
 
 17 
 15 
 10 
 15 
 
 
 Av. 
 M.V. 
 
 2 
 2.5 
 
 2.8 
 2.8 
 
 4 
 1.5 
 
 1.5 
 
 1 
 
 16 
 2.5 
 
 14.8 
 1.8 
 
 13.3 
 2.5 
 
 14.3 
 2.1 
 
 Bimembral 
 Movement 
 
 B 
 D 
 H 
 
 W 
 
 
 
 
 
 
 
 
 
 
 2 
 
 
 
 
 
 1 
 
 
 
 2 
 2 
 
 
 
 3 
 1 
 
 
 
 
 1 
 
 
 
 Av. 
 M.V. 
 
 
 
 
 .5 
 .8 
 
 .3 
 
 .4 
 
 1 
 
 1 
 
 1 
 1 
 
 .3 
 .4 
 
 Unimembral 
 Movement 
 
 B 
 D 
 H 
 
 W 
 
 
 11 
 2 
 
 .4 
 
 
 
 13 
 
 1 
 
 2 
 
 1 
 16 
 9 
 4 
 
 6 
 
 21 
 
 9 
 
 4 
 
 1 
 
 6 
 4 
 
 5 
 
 
 7 
 4 
 
 
 
 9 
 
 11 
 
 6 
 
 
 
 2 
 
 13 
 
 9 
 
 
 Av. 
 M.V. 
 
 4.3 
 3.8 
 
 4 
 4,5 
 
 7.5 
 5 
 
 10 
 5.5 
 
 2.8 
 2.3 
 
 4 
 2 
 
 6.5 
 3.5 
 
 6 
 
 5 
 
 Intramembral 
 Movement 
 
 B 
 D 
 H 
 W 
 
 7 
 
 
 
 
 
 
 
 1 
 
 
 2 
 
 3 
 
 
 3 
 
 1 
 
 
 2 
 
 1 
 
 
 
 1 
 
 
 
 
 1 
 
 
 
 
 2 
 
 
 
 
 
 Av. 
 M.V. 
 
 1.8 
 2.6 
 
 .3 
 
 , .4 
 
 1.3 
 
 1.3 
 
 1 
 
 1 
 
 .8 
 .8 
 
 .3 
 
 .4 
 
 .3 
 
 .4 
 
 .5 
 .8 
 
 No 
 Movement 
 
 B 
 D 
 H 
 
 W 
 
 16 
 
 6 
 
 22 
 
 20 
 
 19 
 
 5 
 
 22 
 
 22 
 
 16 
 2 
 
 9 
 18 
 
 13 
 2 
 9 
 
 20 
 
 10 
 5 
 2 
 
 
 4 
 12 
 
 
 
 8 
 3 
 
 
 
 5 
 7 
 
 
 
 
 Av. 
 M.V. 
 
 16 
 5 
 
 17 
 6 
 
 11.3 
 5.8 
 
 11 
 
 5.5 
 
 4.3 
 3.3 
 
 4 
 4 
 
 2.8 
 3.9 
 
 3 
 3 
 
 With the 100 interval, D reported phi in 1 M. 
 
 extends in time into another oval or circular bit of experience 
 like the first. The following reports are typical: 
 
 ,H (C 100 M) The hair touched lightly and began moving at once. 
 As it moved it pressed more lightly and almost lifted off. Then, as it 
 moved on, it pressed harder, and came down fairly lightly at the end. 
 it moved faster at the beginning than it did in the middle. 
 
 H (C 100 P) The process began limited in extent. It increased in 
 one direction to fairly extended, with slight contraction ending in a 
 little spread of extent. It began as neutral pressure, becoming in- 
 creasingly like contact until it was almost pure contact, with a rapid 
 shift to pure neutral pressure. It was fairly weak, diminishing in 
 intensity, during the extent of the process, and becoming more intense 
 at the end. The whole was very short. 
 
 The next type is much like the dumb-bell pattern, save that 
 the movement does not start from the center of the first 
 touch, but rather begins at the edge. In ' process ' the first 
 impression is described as static. Then there follows a growth 
 from the edge. 
 
481 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 H (C 100 M) A hair touched and rested; and then something 
 started to move from the edge of the first touch and moved a little 
 way, rested, and lifted off. 
 
 H (C 100 P) The process was limited and static for a bit; then 
 growth began from the edge and became fairly extended. At first it 
 was a dull neutral pressure, quickly shifting to a brighter pressure, 
 and becoming neutral at the end. It was fairly weak, and dropped to 
 weak. It was of short duration. 
 
 D (C 100 P) The process began as a contact fused with a wiry 
 prick, immediately followed by a vague, diffuse, large pressure sensa- 
 tion localized differently. 
 
 In a third type the touches at beginning and end are of 
 the same size as the moving touch between. There is no nar- 
 rowing during the movement. In ' process ' the terminals are 
 marked by diiferences in quaHty and intensity, but not by a 
 spread of extent. The first may be a pressure rather intense, 
 merging into a spreading that is less intense, but of continuous 
 extent, and ending in another intense pressure of the same 
 extent. 
 
 W (C 100 M) A touch moved smoothly across my arm. It pressed 
 harder at the beginning and ending than it pressed in the middle of 
 its course. It was the same breadth all the way. 
 
 W (C 100 P) The process began, limited in extent, and spread in 
 time, becoming weak during the spread but not contracting, and in- 
 creasing in intensity as it became more extended. It began as good 
 contact, and remained contact throughout. There was no change in 
 extent at the terminals. The whole was short. 
 
 D (C 100 P) The process was neutral pressure, the area' of which 
 seemed to expand to another neutral pressure. 
 
 B (C 100 P) The process was a contact changing in intensity along 
 a line. 
 
 The O's describe the extension of the process in various 
 other ways. It is called a ' flowing,' an ' extending in time,' 
 a ' diffusing in time.' At first the word ' flow ' was frequently 
 used, but during the later reports it does not appear. Two 
 O's have said that ' flow ' does not describe truly the depth of 
 the sensation. Even when the intensity is weak, the growth 
 seems to have the feel of something deeper than ' flow.' 
 'Ooze ' has sometimes been used. H usually described the 
 process as ' growth ;' B and W used the term ' spread ' most 
 frequently ; D spoke of ' extension and diffusion,' ' sensory 
 continuum in time,' ' progression in time.' 
 
 With cutaneous stimuli the terminals, with few exceptions, 
 are contact or neutral pressure. The same terms usually 
 describe the subcutaneous experience; occasionally this is 
 called ' drag ' in the reports of H and W. In a few cases 
 the subcutaneous stimuH produced a ' thicker ' feel in the 
 spread than did the cutaneous. In nearly all cases, except 
 
WHITCHURCH 482 
 
 those just mentioned, the reports for the two stimuli are 
 exactly alike. 
 
 (2) Full Movement in an Arc. — Occasionally the O's re- 
 ported a full movement in the shape of an arc. The first touch 
 became larger in some one direction, and at the coming of 
 the second it seemed to be pulled round to that position. In 
 ' process ' this type is described as a pressure becoming ex- 
 tended irregularly, and spreading around one side to another 
 impression. 
 
 D (C 75 M) A touch went around in an arc to a new position. 
 
 B (C 100 M) The hair moved on my arm in the form of an arc, 
 and rested in another place. 
 
 H (C 100 P) The process began limited and spread in extent out 
 around one side, becoming narrower and ending in a slightly greater 
 extent. It was neutral pressure, then contact with a shift to neutral 
 pressure. It was fairly .weak, decreasing in intensity during the ex- 
 tent, and increasing to fairly weak at the end. It was of short duration. 
 
 B (C 100 P) A contact diffused in a half circle and fused with 
 another contact. 
 
 No reported the arc movement more than five times in 
 all the experiments performed. It occurred only when full 
 movements were reported. Unimembral and bimembral move- 
 ments did not take the arc form. 
 
 (3) Bimembral Movement. — In the bimembral movement 
 the stimuli are felt as two touches which move, but which have 
 a spatial and temporal interval between them. In nearly all 
 cases a moves toward b, and b moves away from a to a resting 
 place. Occasionally b touches and then moves on and off 
 without resting. In ' process ' the experience is described as 
 two pressures or contacts, separated spatially and temporally, 
 both diffusing in time. 
 
 B (C SCO M) A hair touched me and moved a bit. It lifted off, 
 and came down moving into a new place. 
 
 H (C 100 P) The first process began very limited and grew in 
 extent to slightly extended. It was a neutral pressure quality fading 
 out, and it was very short. The second process was limited and shrank 
 in time to very limited. It was neutral pressure with a hint of contact 
 at the beginning, and it was weak and short. 
 
 D (C 100 P) Two neutral pressures occurred successively in time 
 and were localized differently in space. The first became diffused in 
 time, and the second likewise. 
 
 (4) Unim,embral Movem,ent. — In the unimembral move- 
 ment, sometimes the first stimulus moved and the second was 
 stationary, but more often the second was the moving mem- 
 ber. Stimulus a touched and was gone ; b touched while mov- 
 ing away from o to a new position. In ' process ' one of the 
 impressions was said to spread or extend in time. 
 
483 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 H (C 100 M) A hair touched me fairly lightly and lifted off. It 
 touched again in another place, moving a short distance. It rested 
 and lifted off. 
 
 W (C 100 P) First there was a contact limited and very weak. 
 Near it in space was a contact spreading in time to a larger extent and 
 becoming more intense during the spread. 
 
 H (C 100 P) The process began limited, and grew slightly in ex- 
 tent; it was dull neutral pressure becoming pure pressure in the ex- 
 tent. It was fairly weak, with the intensity dropping off. It was very 
 short. The second process was very hmited neutral pressure, and was 
 fairly weak and short. 
 
 There were other reports more rarely given. Sometimes 
 only one stimulus was felt, and it moved to a stopping place, 
 or began as static and moved off. In ' process ' such experi- 
 ences were called " a spreading contact growing more extended 
 and more intense as it spread," or " a contact which spread 
 and faded out." 
 
 (5) Intramembral Movement. — The intramembral move- 
 ment is " the feeling of movement as if the hair were held 
 in an unsteady hand," or " a wiggling of the hair against the 
 skin." In ' process ' the experience is described as " a slight 
 shift of the intensive pattern in time." 
 
 D (C 250 M) There were two touches successive in time and local- 
 ized differently in space. The first quivered as if held in an unsteady 
 hand. 
 
 B (C SOO P) There were two contacts differently localized and suc- 
 cessive in time. The second had changes of intensity in time; other- 
 wise it was just two. 
 
 W (C 1000 P) The first process was a contact which fluctuated in 
 intensity in the touched area-. The second process was pure contact, 
 very limited and short. 
 
 H (C 100 P) The first process was very limited and rather a bright- 
 ish pressure of moderate intensity and very short. The second proc- 
 ess was a fairly limited neutral pressure quality. There was a shift 
 in time of the intensive patterns from moderate to fairly weak. The 
 whole was short. 
 
 (6) Intramembral plus Unimembral Movements — In the 
 manual experiments and the first series of the mechanical 
 stimulations there were reported some cases of combined per- 
 ceptions of intramembral and unimembral movement. Some- 
 times one stimulus gave the perception of intramembral move- 
 ment, and the other that of unimembral movement. Occa- 
 sionally one stimulus would begin its movement as intramem- 
 bral, and then extend into unimembral movement. These 
 reports do not appear in the last series, in which the reports 
 of unimembral and intramembral movements became uniform 
 and clear-cut, with no hint of confusion or addition. 
 
 (7) Phi Movement. — The phi movement occurs infrequently. 
 A typical ' meaning ' report is : " It felt as if a moving some- 
 
WHITCHURCH 484 
 
 thing flicked against my arm." In this perception we do not 
 have the feeHng of two touches, or of one touch moving to 
 a new position. In ' process ' there were no distinct terminal 
 experiences ; the pressure is called " a weak, spreading contact, 
 a bit more intense in its middle portion." Most of the pure 
 phi-reports occurred in the manual experiments, and came 
 early in the series. 
 
 (8) Backward Movement. — In the manual experiments and 
 in the first series with the mechanical stimulations there were 
 a few reports of unimembral and bimembral movement in 
 which the stimulus seemed to move backward. That is, one 
 impression was felt; and the second, instead of moving away 
 from it to a new position, would be felt some distance away 
 moving toward the first. H and W reported this perception 
 three or four times in the manual experiments, but not after- 
 wards. B reported it twice in the manual experiments ; four 
 times in Series I with the mechanical stimulations, and not at all 
 in Series II. D reported backward movement three times in the 
 manual experiments; in Series I of the mechanical stimula- 
 tions he gave no' such reports ; in Series II he reported it 24 
 times (6.25% of all the reports in that series)." 
 
 (9) No Movement: Two Points Distinct. — In nearly all 
 cases in which no-movement was reported, the perception was 
 of two points touched successively in time and having spatial 
 separation. Sometimes the one impression was more diffuse 
 than the other, or differed from it slightly in quality; usually 
 the two were reported as alike. This type of perception oc- 
 curred in all experiments with intervals above 50"^. 
 
 (10) No Movement: Conjunctive. — A report made fre- 
 quently with the 25" intervals belongs to the no-movement 
 group, though it indicates something more than merely two 
 touches which did not move. The second stimulation was 
 added to the first, or placed beside it. Sometimes the second 
 grew larger after it had appeared, and again it came as a 
 diffuse,' ill-defined touch. In ' process ' one contact or pressure 
 had added to it another, and there was little separation of 
 the two in space and time. 
 
 D (C 25 M) There were two light touches which came separately, 
 but whose areas overlapped. 
 
 H (C 25 P) The first process was very limited. It was a weak 
 contact and very short. Beside it catne another process of pressure 
 
 8 D's observation of backward movement evidently became a matter 
 of habituation. Very occasionally in this series he reported triple 
 pressure; as, for instance, pressure at a followed by a pressure at 6 
 which moved back toward a and then ended with increased intensity. 
 
485 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 quality, with a fringe having in it a hint of contact. It was of very 
 weak intensity and very short. 
 
 H (C 25 P) The process was very limited and was added to. It 
 became fairly limited in one dimension. It was of neutral pressure 
 quality with a fringe of contacty pressure. It was fairly weak. The 
 whole process was fairly extended and fairly weak. 
 
 (11) No M'ovement: Superpositive. — Occasionally the two 
 stimulations seemed to be successive in time but to fall upon 
 the same spot. 
 
 W (C 25 M) There were two touches, first one and then another 
 beside it covering it. The two were almost successive in time. 
 
 H (C 25 P) The first process was very limited, and while it was 
 still present another limited process covered it. The second was more 
 extended, but there was perfect fusion of the two. Both were good 
 neutral pressure quality, of weak intensity. The first was very, very 
 short. The second was slightly longer. 
 
 D (C 25 P) The first process seemed obscured by the second. I 
 was conscious of the first, but it was absorbed by the second, which 
 was big and which gradually became bigger. 
 
 It will be noted that whereas B, H and W have a large 
 number of reports falling into the no-movement group in the 
 25" interval, D has but few.^" 
 
 Distance of Movement 
 Under the ' process ' instruction the O's never reported how 
 far the stimulus moved in full movement, or how far apart 
 were the members in part movement. In ' meaning ' the per- 
 ceptive distance in the larger intervals, as occasionally reported, 
 was always greater than it was in reality, and varied accord- 
 ing to the interval. With the 1000'^ interval it was reported 
 as 1.5 to 2 cm. As the intervals shortened, the distance de- 
 creased to 4 or 5 mm. at the 100"' interval, and at the 25" 
 interval the stimulations were side by side. 
 
 Rate of Movement 
 Rate of movement, like distance, was reported only under 
 the ' meaning ' set. Sometimes during the manual experi- 
 ments the O's said that the movement went " quick as a 
 flash " or " rapidly." Sometimes in the full movement reports 
 one part of the movement was said to move more quickly 
 than another. In bimembral movements, the O's occasionally 
 said that " the second went quicker than the first." Aside 
 from instances where one part of a movement could be com- 
 pared with another in the same perception, the was uncertain 
 of the rate, and hesitated to report it. During the mechanical 
 
 lo See footnote 9. 
 
WHITCHURCH 486 
 
 stimulations the reports of rate dropped out. If questioned 
 about it, the O's said: "I am not sure," or "I can't report 
 on it." 
 
 Stimulations of Long and Short Duration 
 After the series with the duration of the stimulus at 150'', 
 four other series (2C and 2S) of 24 experiments each were 
 performed with H and W. In these series the 75 and 100 
 intervals were used, and the durations were 75 and 200°'. No 
 full movements were reported by W with duration at 200'^; 
 H gave such reports in 6M and 4P at C 100. With duration 
 at 75'^ with C 100, H reported full movement in 14M and 17P, 
 and W in 14M and 15P. These reports are almost the same 
 in number and content as those with the duration at 150'^. 
 With C 75, H had no full movements and W had 5M and 
 8P. With S 75 neither H nor W reported full movement. 
 With S 100, H had 8M and 2P full movements, and W had 
 8M and 8P. Since the intervals longer and shorter than 150 
 proved to be not so good as 150, and in only one case com- 
 pared favorably with it, no farther experiments were per- 
 formed with them. 
 
 Experiments Upon Non-Adjacent Spots 
 A short series of 24 experiments with each stimulus was 
 performed upon non-adjacent spots. The spots a-c and a'-c' 
 were used. H and W again served as O's. The stimulations 
 were made with the 75 and 100'' intervals. The duration was 
 150'^. H reported no movement during any of the experi- 
 ments. W in S 75 had 8M and 12P unimembral movements. 
 The movement always occurred with the second member. 
 With C 100, W reported 12M and 14P unimembral move- 
 ments, also at the second member. The movements were 
 very short. There was just a hint that the second stimulus 
 slid a very short distance into place. In ' process ' the second 
 stimulus had a very slight diffusion in time. 
 
 Cutaneous Versus Visual Movement 
 Dimmick under his best conditions obtained full movement 
 with ' process ' instructions in 90 to 93% of his reports, and 
 with 'meaning' instructions in 81 to 91%. We under the 
 most favorable conditions obtained on the average with C 
 only 13.75 (57%) M-reports and 14.25 (59%) P-reports out 
 of a possible 24; and with S, 16 (67%) M and 14.75 (61%) 
 P. It seems from a comparison of these figures that the 
 cutaneous perception of movement is less fundamental and 
 
487 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 compulsory than the visual. There was, it is true, a diflference 
 in the plan of the two investigations, since Diramick's stimulus 
 a in his regular series always bore a fixed spatial relation to 
 his stimulus b; whereas the spatial relations of the spots 
 stimulated by us varied from group to group. Our stimulus b 
 might lie above or below a, to right or to left of a. It is 
 difficult to say how far this difference influenced the results; 
 but it seems from what indications we have that the influ- 
 ence was slight. (1) A special C-series made with H, in 
 which the same two spots a-b were stimulated in the same 
 order in successive observations to the point of exhaustion, 
 yielded no increased percentage of full movements. (2) The 
 conditions of our mechanical stimulation approximated those 
 of Dimmick's experiments. After the first two or three 
 stimulations of two spots at the beginning of a group of 
 twelve experiments, O knew when the second stimulation 
 came that it was in the same place as before, and so learned 
 to expect it at that place. H, who observed in Dimmick's 
 work, said : " I was not conscious of expecting the second 
 stimulation in the place where it came, but when it did come 
 I had the feeling that it was where it ought to be and where 
 it had been before." H further remarked that the expect- 
 ancy was " the same sort of thing as in Dimmick's experi- 
 ments." W, who also observed with Dimmick, verifies these 
 reports. 
 
 Only one 0, B, reported associated visual images, and she 
 only in the early stages of practice. H and W declared that 
 visual images did not appear; and D when questioned said 
 that he had them occasionally, but that they were never a 
 determining factor in his perceptions. 
 
 The aberrant types of perception, the arc-movement and 
 the backward movement, seem to be conditioned upon some 
 directional emphasis within the tactual spread. Ordinarily 
 the spread of sensation is roughly circular or oval. If, how- 
 ever, some lateral segment of a's spread is unusually inten- 
 sive, the arc movement necessarily follows ; and if a's spread 
 is uniformly weak, and b's is strongest over a segment that 
 points toward a, the perception of backward movement fol- 
 lows. We have no means of knowing how these local emphases 
 arise, but the O's reports show that they appeared and formed 
 the basis of judgment. There is, of course, nothing parallel 
 in Dimmick's results .^^ 
 
 I'- Dimmick tried to get backward movement by artificial emphasis 
 and failed : op. cit., 331. 
 
WHITCHURCH 488 
 
 Conclusions 
 
 (1) We have succeeded in synthetizing the perception of 
 cutaneous movement, from two separate and successive stimu- 
 lations, under conditions that parallel Wertheimer's synthesis 
 of visual movement. 
 
 (2) The optimal conditions for the arousal of the perception 
 are: with cutaneous stimuli, a duration of ISO and an 
 interval of 100'' ; with stimuli that also affect the subcutaneous 
 organs, a duration of ISO"' and an interval of 75". 
 
 (3) (a) The most important conditions of the perception, 
 under our conditions, are the interval elapsing between the 
 successive stimuli and the adjacency of the spots stimulated. 
 (b) The duration of ISO'' is best for arousing the perception 
 of full movement ; the number of full movements aroused with 
 longer times is much lower. The same thing is true also of 
 the duration of 75°' except in one instance, namely C 100, 
 where the number of full movements aroused compared favor- 
 ably with those reported when the duration was 150°'. (c) 
 The stronger of our two intensities, the ' subcutaneous ' stimu- 
 lus, yields a slightly larger percentage of full movements with 
 its best interval, 75", than does the cutaneous stimulus at its 
 best interval, lOO''. 
 
 (4) Whereas Dimmick was able to secure the perception 
 of visual movement, under optimal conditions, in practically 
 100% of his trials, we found that the perception of cutaneous 
 movement appeared, under the same conditions, in only 57 to 
 67% of our observations. Since, so far as we can discover, 
 there is nothing in the arrangement of the two experiments 
 that accounts for this difference of result, we are forced to 
 the conclusion that the cutaneous perception is less funda- 
 mental and compulsory (in Dimmick's sense) than the corre- 
 sponding visual perception. 
 
 (5) Support for this view is found in a comparison of 
 the existential correlates of the two perceptions. Dimmick's 
 grey flash is an integration of quality with time ; space is not 
 involved. The existential correlate of the cutaneous per- 
 ception appears, on the other hand, to be an integration of 
 quality, time and cutaneous extent. While Dimmick's O's 
 reported a curtain or film of shimmering, liquid, live grey, our 
 O's (in part the same as Dimmick's) report a pressure dif- 
 fusing, growing, extending, in time. The integration appears 
 to be of a higher order, and therefore less stable and inevitable 
 
489 PERCEPTION OF MOVEMENT ON THE SKIN 
 
 (6) We regard it as entirely premature to theorise from the 
 results of Wertheimer and Dimmick in vision and from our 
 own results in touch to ' the ' perception of visual or cutaneous 
 movement. It may very well be that the singular number 
 must be replaced in this and similar connections by the plural. 
 ' Movement ' is, after all, a gross meaning that may be carried 
 by several existential correlates; or, to put the same thing in 
 other words, an organism whose outfit of sense-organs is as 
 complex as our own may be adequate to the 'perception of 
 movement ' by way of several different primary integrations. 
 
^'I^i- 
 
 
 .M;ES, 
 
 
 ,.«>--:.r''->sfi-%.a 
 
 "^'ci^MS-^^-M 
 
 ^*^^' l¥