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There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924029087173 AN EXPERIMENTAL STUDY OF VISUAL MOVEMENT AND THE PHI PHENOMENON BY FORREST LEE DIMMICK Thesis presented to the Faculty of the Graduate School of Cornell University in partial fulfillment of the requirements for the d^ree of doctor of philosophy Reprinted from The American Journal of Pstcboloot October 1920, Vol. XXXI, pp. 317-332 AN EXPERIMENTAL STUDY OF VISUAL MOVEMENT AND THE PHI PHENOMENON BY FORREST LEE DIMMICK Thesis presented to the Faculty of the Graduate School of Cornell University in partial fulfillment of the requirements for the degree of doctor of philosophy Reprinted from The American Joubnal op Psychology October 1920, Vol. XXXI, pp. 317-332 %*■ Ktvi uan Y ^ ff^ JJ3Ki$;0 Y "I I 2 2.S 2H 10 17 2 3 60 6b 30 33 7 2 3 Tu 77 69 22 21 2 9 1 80 69 20 29 1 1 W HO .53 21 22 19 25 68 77 19 15 13 8 Average MeanVar 70 6:h 20 20 « 1.5 2 2 74 68 19 25 6 6 2 1 . 6 7 4 4 6 5 2 1 13 10 11 11 4 4 2 1 Uni-, Bi-,^ experiences of unimembral and of bimembral movement. P= Process configuration; M = meaning characterization. TABLE II Optimal Movement with Different Backgrounds (Percent, of 25 Reports for Every O) Horizontal Lines Oblique Line and Horizontal Obs. A B C D A B C D P M P M P M P M P M P M P M P M C 100 76 .53 76 73 80 87 76 53 56 59 52 40 24 40 8 D 60 40 76 48 72 60 60 96 64 68 68 64 80 88 96 72 H .56 ,56 7?, 80 72 68 64 ,52 72 48 72 92 64 68 60 b6 M 76 67 56 ,53 68 67 88 73 100 100 100 100 lOU 40 100 52 S 84 87 72 93 72 40 88 53 96 60 92 60 80 93 92 73 Ta 67 40 53 48 .53 ,56 80 64 67 60 60 76 67 60 47 64 Tu 73 68 93 68 67 68 73 72 80 68 87 84 Y3 i>2 80 72 W 68 60 60 53 52 ,53 60 47 64 80 60 67 76 67 72 93 73 62 67 65 66 62 75 67 78 68 75 74 73 62 73 62 M.V. 10 11 11 13 7 8 11 13 15 12 14 14 11 17 19 17 TABLE III Optimal Movement with Different Temporal Intervals (Percent, of 20 Reports for Every 0) Horizontal Line's Oblique Line and Horizontal Ob3 . 30 60 90 120 150. 30 60 90 120 150 P M P M P M P M P M P M P M P M P M P M c 67 55 92 95 92 90 83 80 58 65 25 62 50 75 70 50 35 25 20 D 50 75 90 65 80 85 80 45 30 35 70 45 95 go 95 95 70 70 45 65 H 55 50 SO 65 80 75 65 60 50 30 50 65 90 95 90 90 55 75 50 30 M 50 75 75 92 90 75 75 75 70 8 100 83 100 100 100 100 100 100 100 58 S 60 83 90 92 95 92 95 42 45 33 100 92 85 100 95 92 100 42 70 33 Ta 50 70 83 55 92 65 42 35 50 35 50 50 83 60 92 100 50 75 25 40 Tu 75 70 100 95 100 85 50 55 58 40 75 75 83 90 100 80 90 60 50 40 W 15 25 70 75 90 83 75 42 50 42 60 67 70 92 100 100 80 67 30 58 Av. 53 64 85 79 90 81 71 54 51 36 66 72 84 85 93 91 74 66 49 43 M.V.12 14 7 14 5 7 14 13 8 10 20 21 9 15 6 8 18 15 18 13 In Tables II and III the results have been arranged to indicate the influence of the pre- and intra-exposure field and of the temporal interval between members. Individual varia- tions appear with the various fields, but they show no uniform tendency, and their nature is indicated in some cases in the introspections. C often objected that the fixation-point on pre-exposure field B interfered with her reports of process; S complained of the dark backgrounds. It is significant, how- ever, that the process-reports and the perceptive characteriza- tions parallel each other. This agreement is very evident when the averages for the group are taken, and it is further supported by the fact that the mean variations are not ex- cessive. We may conclude, then, that the kind of pre-expos- ure field employed had no general and constant effect on the perception or its process-configuration. Table III, on the other hand, brings out a very definite in- fluence of the temporal interval. The O's vary among them- selves, but they agree in that they have curves of percentages which are high for the middle values of the temporal interval and low for the extreme values. Process-reports and per- ceptive characterizations run parallel. The averages, of course, show the conformity even more prettily. Time-interval 90a- has the highest average percent, of optimal movement and of total configurations; 30 f and ISOcrhave the lowest. Just as significant is the fact that the mean variations are smallest at the middle value. The larger variations among O's occur with the longer or shorter times. The evidence of the values, in the above tables, of the various perceptive characterizations indicates unquestionably that we have reproduced the essential factors of Wertheimer's condi- tions. Table I shows that our temporal intervals lie between those which give succession and simultaneity. The two forms of partial movement appear frequently, but optimal movement STUDY OF VISUALfMOVEMENT AND PHI PHENOMENON 323 predominates. The ineffectiveness of variations of the pre- exposure field does not contradict Wertheimer's observation that the color of the stimulus did not affect the perception. Finally, the behavior of the perception with the different time- intervals is exactly that which Wertheimer suggests, though he makes no precise statement. On the other hand, in the column in which Wertheimer would write ' nothing,' under the heading ' process,' we have found a closely parallel set of values which represent the con- figurations of visual process present in the movement-field when the O's were set to describe the experience. The nature of the visual experience which filled the interval can be pointed out most clearly by direct reference to the introspections. Optimal Movement ; Meaning Reports ; Stimulus I C. A horizontal line appeared in the upper part of the field, moved down to a lower position, and stopped ; the movement was slow, smooth, and continuous. D. I saw a h6rizontal line move quickly from a position above the fixation point to one below, and disappear. It seemed to come in, move down, and go out, as if that were only a part of some larger movement. The movement was rapid but smooth. H. A black horizontal line appeared and moved down very rapidly, and then came to rest in a lower position for a short time. The move- ment was uniform but very fast. M. A line moved from an upper horizontal position to a lower one; it slowed up just before it reached the final position; the movement was continuous all the way from one to the other. S. A rectangle moved down smoothly and stopped for an instant. The speed of the line increased as it moved, and was very rapid just before it stopped. Ta. A horizontal line appeared in the center of the field and moved down * smoothly ; it became shorter as it moved, and stopped in a position lower down. Tu. A line dropped downward very smoothly and rapidly, until it reached the lower position, and then disappeared. W. I saw a line drop smoothly and quickly from one position to another. Stimulus II C. I saw an oblique line which moved down across the field to the horizontal with a smooth and continuous movement. D. A dark grey rectangle moved smoothly and rapidly from an oblique position to a horizontal. H. An oblique line fell down into a horizontal position. The move- ment was continuous, but faster just before it reached the final position. M. An oblique line moved down through an arc to the horizontal. S. An object in the oblique position fell to the horizontal. The movement was rapid, and stopped short at the end. Ta. An oblique line appeared, turned downward, and took the hori- zontal position. The movement was smooth. Tu. I saw an oblique line first, and it moved steadily down into a horizontal position. W. The oblique fell rapidly into the horizontal; I saw movement all the way. 324 DIMMICK Process Reports ; Stimulus I C. At the upper part was a black horizontal extent which immediately gave place to a grey patch below and joining it. The bottom of the grey was darker and at that place appeared later a black extent similar to the first. The grey changed in quality; it was one continuous ex- tent, but it was different at different places. D. A black line appeared just above the middle of the field. It dis- appeared, and extending down from where it had been was a grey band, light at the top and dark at the bottom, and at the lower side was a very dark strip of grey. The grey patch did not change in extent, but the patterning of brightnesses changed. H. The upper line was not definite at the lower edge, but fused into a filmy grey that was a little darker at the right and left extremes, and terminated in a black process lower down. M. There was a line of very dark grey at the top, and immediately below a darkening of the field in the general form of a rhombus, the edges of which were fuzzy but fairly definite. At the bottom of this figure was a definite line, and in the middle a darker streak which could hardly be called a line. S. At the top was a black rectangle, clear and intense. Below was a grey patch, longer in the horizontal dimension, but not clear. At the bottom was a definite line. Ta. At first an irregular rectangle, black and sharp at the top, ap- peared. Its lower side was grey and blurred. Below was a wide grey line, sharp at the bottom but indefinite above. The lower and upper sides of the upper and lower lines respectively shaded off and joined each other. Tu. First, there was a line above the middle of the field; below it, a dark grey which faded out farther down until it reached a lower horizontal line, the upper part of which was grey and indefinite, the lower part black and sharp. W. A horizontal line appeared and disappeared, and below where it had been there was a wide grey rectangle of light tint at the top, medium in the middle, and dark at the bottom. Below appeared a second line. Stimulus II C. First there was a black oblique at the top, which immediately became greyer, and then was replaced by a grey patch, which extended down to the horizontal, where a line appeared. D. The oblique came in first; then below it there was a grey which extended down to a horizontal line below; this grey was not uniform but light and dark in streaks. H. An oblique line appeared and then a horizontal, and between them the field was grey in a solid fan-shape. M. An oblique appeared; then below it there came a sector of pale grey which was darker near the bottom, where it became a more defi- nite line. The first line had faded out before the last one came. S. A black oblique line appeared; then something grey came below it which was rather indefinite, and extended down to the horizontal line. Ta. I saw an oblique line which was blurred downward. The upper part was black and clear-cut. The lower part shaded off into a grey, at the bottom of which came a horizontal line. Tu. I saw an oblique line and a horizontal, and the space between them was grey. The oblique was wide and had no definite outline on the lower side. STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 325 W. An oblique line appeared and disappeared, and then a horizontal came below. Between the two was a triangular light grey patch, which was darker near the bottom line. Unimembral Movement ; Meaning Reports ; Stimulus I C. A horizontal line moved down smoothly but not continuously. It moved part-way, then disappeared, then reappeared lower down and stationary. D. The first line appeared and remained stationary. Below it another line came in, moving downward. The movement was over most of the space between the two positions, but was of the lower line. H. A line appeared in the upper part of the field for an instant; then a little lower down something moved into the field, and stopped as a black line at the bottom. M. A horizontal line came into the part of the field moving, then another appeared lower down and stationary. S. A line moved down smoothly, getting faster as it went, and then the end-position stood out, sharp and stationary. Ta. A line moved down, and as it moved another appeared lower down and remained stationary. Tu. First I saw a line which wavered but did not change position, and at the same time there was something moving down into a position below. W. A line dropped into a lower position. The motion was best near the bottom, and there was a blank space just below the top position. Stimulus II C. An oblique and horizontal appeared, and the first moved down toward the second but never reached it. D. I saw two lines, one oblique and one horizontal. The latter re- mained stationary, and the oblique moved down toward it, but was gone before reaching it. H. An oblique line came in and moved downward, and below it stood a horizontal line. M. An oblique line moved down toward the horizontal. The move- ment was jerky and definitely of the oblique, not of the horizontal. S. I saw a line move down very rapidly through an arc. The first part of the movement was not clear, i.e., it seemed to be part way down before I saw it; above was a blank. Ta. An oblique line appeared, then a horizontal, and the oblique moved down to the horizontal. Tu. An oblique line appeared in the upper part of the field and moved down faster and faster until I could not see the movement. Then the horizontal came in. W. An oblique line moved rapidly to the horizontal. The movement was best at the beginning, and just at the bottom there was a space of no movement at all. Process Reports; Stimulus I C. I saw a black line; and below it was a grey band which was not uniform in quality, but which had no definite lines in it. Below was a second sharp black line. D. Two lines came successively. The upper was clear-cut and sta- tionary; the lower was at first a band of greys, the upper edge of which was indefinite and concave. 326 DIMMICK H. A black line appeared in the upper part of the field. Below and detached from it by a bright streak was a rather indefinite grey, which fused into a black line lower in the field. M. First came a line in the upper part, then a grey, and another line below. The grey joined the lower line but was separated from the upper by a bright streak. S. I saw a horizontal line, then lower down another with a grey patch above it. Ta. The first line was wide ; the upper part black, the lower part grey and blurred. There was a bit of white background between this and the lower line. Tu. There was a sharp definite line, Just below it was white, and all the rest below was grey, darkening downward until it joined the lower line. W. I saw two horizontal lines, one below and after the other. A band of greys extended up from the lower toward but not to the upper. Stimulus II C. There was a wide patch of grey in the shape of a sector. It was dark at the top and shaded off into light grey downward. The grey did not reach to the horizontal line which came in at the bottom. D. A sharply defined oblique line appeared and then a horizontal. When the horizontal came, the field just above it was greyish. H. First there was an oblique line with a patch of bright field just below it; then at the bottom a narrow sector of light grey, which was later replaced by a horizontal. S. A black oblique appeared first; below it was white. Then came a horizontal line, with an oblique grey on its upper edge. Ta. The oblique was grey on its lower side and blurred downward. There was a white space between it and the horizontal line. Tu. I saw an oblique line clearly; then the background below it be- came dark at the top and light lower down. At the bottom there was a horizontal line with a white streak above it. W. A distinct oblique line appeared at the top, then a horizontal, and between them a series of grey triangles, light at the top and dark at the bottom and joined on to the lower line. BiMEMBRAL MOVEMENT; MEANING REPORTS; STIMULUS I C. A horizontal line moved down and stopped. The movement was not continuous; there was a place in the middle where it disappeared entirely. Farther down it came back again. D. A horizontal line appeared and started to move, then disappeared, but reappeared lower down, and moved into the lower position. H. A heavy black line appeared and started to move, but disappeared. Part way down it reappeared, and moved into the lower position and stopped. M. Two black horizontal lines appeared and both moved down a little. S. An object appeared and moved downward. A little way below another line appeared, and moved down and stopped. Ta. A line appeared, moved down and disappeared; after a short space another appeared, and moved down and stopped. Tu. A horizontal line moved down very rapidly, disappeared for an instant, then moved down again into the lower position. The upper part of the movement was the more rapid. W. The line moved down quickly but with a flicker, i.e., it started to move, there, was a break, then the last part of the movement came out distinctly. STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 327 Stimulus II C. An oblique line moved down to the horizontal. The movement was not smooth ; it disappeared in the middle so that there was a blank space. D. An oblique appeared and began to move, but very soon disap- peared. Then a horizontal appeared, which seemed just at the end of a movement down. H. The oblique started moving, then for a bit I saw nothing, then the line moved from just above into its horizontal position. S. An oblique line moved down to the horizontal, but there was a pause in the movement part-way down. Ta. An oblique line came in and started to move, but soon faded out; then something below jumped in, and moved down to the horizontal. Tu. An oblique line moved down to the horizontal but not smoothly; there was a flash of good movement at the beginning and end. W. An oblique line dropped to the horizontal, but I did not see move- ment all the way. There was a blank in the middle. Process Reports ; Stimulus I C. I saw a line in the field above the middle. Its edges were not sharp, and it shaded off at the lower side. Below appeared another line, which was surrounded with grey at first and then became quite distinct. D. A horizontal line came in with a grey blur on the lower side. The grey extended farther down from the extremities of the line than from the middle, so that its lower side was concave though not sharply outlined. The second line had a similar grey above it. A roundish patch of white background was left between the two. H. I saw a black line a little above the middle of the field, then an- other below the middle and equal in extent to the first. Between was a grey, with a slight gap of bright field in it. M. There appeared two lines of grey. Both were indistinct on the edges that were toward each other. S. I saw a line that was clear and black at the upper edge but indis- tinct below. Then came a space in which there was nothing, and then I saw a hazy line at the bottom. Ta. The first line was grey all over and a little wider at the ends ; the middle part had no definite outlines. The second line had black and clear outlines at the ends but the middle part was indefinite at the top, and the grey margin of it was a little concave. Tu. First an upper and then a lower horizontal appeared, and the space between was grey except at the center, where it was the same as the background. W. I saw a horizontal line, then another below it. Between them was a blur of grey, darker at the top and bottom and white in the middle. Stimulus II C. I saw an oblique line. It disappeared and the field was only white, then a horizontal appeared. Both lines were indistinct and blurred toward the interior of the angle. D. I saw an oblique line. It disappeared and I saw a horizontal. The oblique was at first a sharp line, then it shaded off into the back- ground below it. The horizontal was indefinite along its upper edge when it came. 328 DIMMICK H. An oblique line appeared which was not sharply outlined. Just below it was a very light grey. Then a horizontal appeared, which was indefinite on its upper edge at first but soon became sharply out- lined. S. First there appeared an oblique line, which was not clear at the lower edge but shaded off into grey. Below there was an interval of white, and at the bottom a horizontal which also lacked definition. Ta. The upper side and end of the oblique had clear-cut outlines, but the lower side was greyish and blurred down. The upper side of the horizontal had no definite outline. For the demonstration of bimembral movement, Wertheimer recommends a stimulus consisting of two squares for the first member and a horizontal line for the second. This stimulus aroused bimembral movement in 94% of the times it was pre- sented to our O's and corresponding process-configurations in 84% of the times it was given under the process-instructions. The typical reports are as follows : Meaning Report; Special Stimulus C. I saw a horizontal line and above it two squares. All three moved down a little and then disappeared. Pkocess Report C. Two squares appeared in the upper part of the field. They were grey and indefinite at the bottom. Below them came a black horizontal line, which shaded off into grey at the top. The parallel values for the percentage of the three forms of movement are sufficient evidence that every perception of movement of these sorts has a corresponding process-config- uration. The conclusion is further substantiated by the fact that in a number of reports the O's have stated that a certain movement had a particular process-aspect and conversely that when, for instance, the grey was spread over the whole field, the movement was best. Wertheimer's fourth movement phenomenon, intra-mera- bral movement, appears according to his statement in the stage of simultaneity. Our O's, likewise, reported a number of cases, when the temporal interval was shortest, in which the lines stood still, but in which there was a quick " jerking back and forth " or an " unsteadiness " as if the line moved inside itself. Under similar conditions, with the instruction to report process, the lines were sometimes of a multiform grey, variously patterned. Further analysis of intramembral movement, with the stimuli which Wertheimer says are espe- cially favorable for its arousal, confirms what we have already said. Typical reports are as follows: STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 329 Intramembral Movement; Meaning Reports; Stimulus III^ C. The line seemed to double over on itself at the middle; that is, there seemed to be a smooth gliding movement from left to right within the line which did not, however, change position. W. I saw a horizontal line in which there seemed to be movement across, left to right. It was not movement from one position to an- other, for there was only one line and the movement was within it. Stimulus IV^ S. There was a square which contracted and expanded as if it were elastic. Ta. A square appeared and stretched to right and left. Stimulus V M. An oblique line appeared and shrank towards its upper end until it became almost a square. Tu. There appeared a line in the oblique position which seemed to move toward its upper end, but did not change its general position. Process Reports ; Stimulus III C. I saw a horizontal line which was black at the right end, dark grey at the left, and light in the middle. The left-hand part was not evenly outlined, and there was no definite line where it joined the black part. Stimulus IV S. First a black square appeared; then in its place was a greyish rectangle longer in the horizontal, then one darker and longer, then one black and slightly shorter. Ta. I saw a black square which was fairly clearly outlined at first. Then it became greyish, and to the right of it was a horizontal line of dark grey. Then the whole figure was a horizontal line black at the left end and lighter toward the right. Stimulus V M. An oblique line appeared. Then it was lighter at the lower end, and shaded into a dark grey upward. At the top was a sharp black square. Tu. First I saw a dark grey oblique line; its upper end was darker, with a light place just below it. The lower part of the figure faded out into a light grey. Movement within an object without change of position of that object thus presents nothing new. Under the char- acterization-attitude, it is movement on a par with the change of position of a form or object ; descriptively, it is reflected in consciousness as the visual quality grey. ^ Stimulus III consisted of two horizontal lines, the second of which was in a line with but to the left of the first. * Stimulus IV consisted of a square and a horizontal line of the same width. The centers of the two forms came at the same point. B Stimulus V consisted of an oblique line and a square of the same width. The square came at the upper end of the position of the line. 330 DIMMICK The Pure Phi Phenomenon Finally, a number of cases of Wertheimer's pure Phi were reported by our O's. Frequently the line was not seen during the movement ; there was simply " something moving " or just " movement." Sometimes neither of the lines was clearly per- ceived ; just a bit of movement downward. The cases in which both lines were perceived with only movement between are entered in Table I as optimal movement, and are paralleled by total process-configurations. The appearance of movement detached from its object occurred, as Wertheimer notes, when the stimulus was new or for some other reason was incom- pletely perceived. Under exactly these same conditions, but with the instructions to report process, our O's noted a flash of grey without the usual limiting lines above and below. Object-Stimuli The remaining stimuli which were given by Wertheimer and which we repeated yield results agreeing with those al- ready reported, but add nothing new to our analysis of the perception of movement. The six object-pictures which we added to Wertheimer's list showed the effect of central asso- ciations by giving- optimal movement over the whole range of our conditions, and total configurations of process in all but a very few cases. Colored Stimuli In the description of the stimuli used in his experiments, Wertheimer tells us that he varied the color of the members. In another place he remarks that partial movement results when the two members are not of the same color. Aside from this, the implication is that one color gives movement as well as another. After our main series had been completed, we presented stimuli of various colors to our O's. The stimuli were shown in series of ten exposures at the optimal time (90 0-) and with a pre-exposure field of the same quality as the background. The colors of these stimuli were red, green, and blue on white backgrounds, white and yellow on black backgrounds, red on a green background, and blue on a yellow background. Movement, optimal in all but a few cases, was reported by all O's for all colors and backgrounds when the instructions were to ' characterize.' Under the descriptive attitude there was always noted a grey patch covering the space between the two members. When the backgrounds were white or a light color, the grey was a little darker than medium. On the black field it appeared whitish. We may state, then, with assurance STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 331 that the grey which is the psychological equivalent of the per- ceived movement is under our conditions independent, for its quality, of the quality of the members of the stimulus, but shows an influence of the background which has the appear- ance of a brightness-contrast effect. Korte's Reverse Movement Korte,!" in a later investigation, studied the perception of movement backward from the second member to the first, which, he said, resulted from making the second member more " intense " and by directing the attention to it. He varied " intensity " either by making the second member wider than the first, or by putting short perpendiculars across its ends. With an increase in " intensity " merely, only a slight back- vvard jerk appeared. Neither was attention to the second line suffi- cient alone ; but with an increase of " intensity " and a direction of the attention to the second member, the backward movement was plainly evident. We attempted to repeat Korte's conditions. Our stimuli with mem- bers of different " intensities " were a grey line on white followed by a black line of the same width; a grey line on black followed by a white line of the same widtii ; a black line of 1 mm. width on a white background followed by a black line of 4 mm. width ; and a white line on black followed by a line of the same size with short pei-pendiculars across the ends. At first the O's were given the usual meaning- instructions, and a series of ten exposures was presented. Then they were instructed to attend to the more " intense " line, and ten more exposures were made ; and finally they were asked to try to get the line to move from the more " intense " position to the other. The perception was always from the member presented first to the second, save for a very few ihstajices with the third instruction when O re- ported that perhaps there might be a hint of a jerk backwards; but even then no positive movement, such as they had seen with the other stimuli, vvas perceived, We have repeated Korte's conditions as nearly as his description of them permits; and to his stimuli, which give spatial and form insist- ence, we have added intensive insistence. Since we never get a posi- tive movement-perception as we do under Wertheimer's conditions, it seems evident that we are not in the presence of compulsory condi- tions, and that the two perceptions are not of the same order.^'^ The Nature of the Process-Configuration Now that we have pointed out the quality of the psycho- logical correlate of Wertheimer's Phi, we must emphasize that this is but one of its attributive aspects. It must not for a moment be assumed that it is a simple text-book grey, the grey that lies at the center of the color-pyramid, or the grey of a piece of grey paper. The temporal attribute is beaten up with ^'' A. Korte, Kinematoskopische Untersuchungen, Zeit. f. Psych, u. Physiol, d. Sinnes., 72, 1915, 193. ^^ We are engaged in further experiments of this kind, the results of which will be reported later. We are also repeating certain ex- periments of F. Kenkel and V. Benussi. 332 DIMMICK the quality into an integration of the first order. All O's describe the experience as a " flashing," " flickering," " un- steady," "shimmery," "flame-like," "liquid," "live" grey. It is further reported as a " curtain " or " film " which is not superficial but hardly bulky. The background seems at times to shine through the interstices of the grey, giving it a sort of transparency. In texture it resembles the Flachenfa/rbe described by Katz^^ and the adaptation-film of Sheppard.^' Conclusions We have, in this investigation, been concerned primarily with a critically descriptive analysis of the reflection in con- sciousness of a stimulus-complex which is compulsory for the visual perception of movement. We have found that this reflection in consciousness takes the form of a primary in- tegration of a visual quality (grey) with a duration which is characteristically brief. The integration is a multiform grey flash which is independent of the quality of the stimulus but is directly determined by the temporal interval between the exposures of the two stimulus-members. The spatial attri- bute is a constant factor for any one exposure, but may vary from exposure to exposure (as the perception of movement also varies between optimal and partial). There is, then, no movement in the multiform grey flash;, the space is constant; the integration is of time and quality. Wertheimer, finding that there " is no visual fiUing-in of the field of movement," argues that the perception of move- ment must have as its physiological correlate a short-circuit in the cortex. The grey flash which we have found to be the psychological correlate of the perception of movement obvi- ates the necessity of such recourse to novel and speculative conditions. 12 D. Katz, Die Erscheinungsweisen der Farben, 1911, 6flf. 1' H. Sheppard, Foveal Adaption of Color, Amer. Jour. Psy., xxxi 1920, 58. •'V^5V -* iy» / '^■' ./.^!- >ii^ ^'^:^ ' --.-^ K fc: [ i -f ^ ^■^^"1 1