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{"created":"2022-01-31T13:31:14.023232+00:00","id":"lit28745","links":{},"metadata":{"alternative":"Studies from the Yale Psychological Laboratory","contributors":[{"name":"Ladd, George Trumbull","role":"author"}],"detailsRefDisplay":"Studies from the Yale Psychological Laboratory 6: 1-5","fulltext":[{"file":"p0001.txt","language":"en","ocr_en":"A COLOR ILLUSION,\nBY\nGeorge Trumbull Ladd.\nSome time ago my attention was called by Dr. George T. Stevens, of New York City, to a color illusion which, in spite of its suggestiveness, has not, so far as I am aware, been hitherto discussed or even noticed.\nIn Fick\u2019s Lehrbuch der Augenheilkunde, p. 50, Leipzig, 1897, there is a colored diagram called an \u201cexample of Stilling\u2019s charts\u201d for the purpose of testing color blindness. It consists of a pale-green background, in size 36\u201c*\u201c by 44mm, which is divided into squares of i.8mm by lines of white o.4'nm in width; on this background a red letter E 21\u201c\u201c\u201c by 34mm is constructed out of similar red squares.\nIt was noticed that, when this figure was observed for a few seconds with a fixed gaze, some or all of the red squares disappeared and were replaced by green squares like those of the background. Practice had the usual result of facilitating the speed and completeness of this illusion ; it soon enabled most of those on whom the experiment was tried to get the result in a more or less startling way. I will only add that with me the illusion is invariably connected with a conscious change in fixation of attention, and\u2014if I may be allowed the expression\u2014the internal motor adjustment ; and the red squares always turn dark and become a blackish-green for an instant before they disappear and are replaced by the green of the color o the background.\nThe first suggestion for an explanation of this interesting illusion would connect it with the relations of the retinal images of the two eyes. But such an explanation is at once negatived by the fact that the illusion is obtained equally well, or even better, with one eye. It is thus not an affair peculiar to binocular vision. Neither is it a phenomenon of blurring due to minute rapid movements of the eyes, or to relaxation of the muscle of accommodation. For, although in certain experiments to be described subsequently, the color of the background does frequently seem to throw a film of its own color over the letter, square or strip, which it surrounds, in the original figure as taken from Fick there is no blurring of the red squares, and in all the other experiments the white\ni\ni","page":1},{"file":"p0002.txt","language":"en","ocr_en":"2\tGeorge Trumbull Ladd,\nlines and outlines of the squares and the color of the background remain quite distinct and sharp.\nFurther experiments have been devised to investigate this illusion. Although no final conclusion has been as yet established, enough has been done to show that the phenomenon is more complicated than was at first supposed. A brief description of these experiments will now follow.\nIn the first place, within certain limits, not as yet fixed, changes in the size of the usual objects with which the experiment is conducted do not essentially alter the result. For example, if the diagram in Fick be looked at through a concave lens the diminished letter E will behave in the same way ; although with me it is more difficult to get the illusion, because, as I think, both of the increased clearness of the images and also of the increased tension of the attention and the eyes\u2019 adjustment. On the other hand, as all our experiments show, much larger objects, when viewed from a sufficient distance behave in the same way. The exact limits of size of the retinal images within which this phenomenon is possible have not been calculated, but considerable variation in size is known not to be incompatible with its occurrence.\nIf, now, in order to test the importance of the white lines which divide, in the Fick diagram, both background (or \u201c sul stituting \u201d color) and letter (or \u201c disappearing \u201d color) into squares, we have a strip composed of red squares divided by white lines against an undivided background of lighter or darker green, we get the following result : the red turns dark green or black ; the white lines remain ; and the squares of red become patches of blackish color separated by white outlines on an unchanged color-background. If the background be changed from green to violet or blue the results are substantially the same. But the same change in color takes place with a solid red letter on a background of various colors ; and with a strip of red or orange, not limited in any way by white outlines, on variously colored backgrounds. Indeed, in a number of instances, as I shall soon say, the background substitutes its color and the illusion takes place almost or quite equally well without either being itself divided or having the disappearing color divided into squares. The illusion, then, is not dependent upon the lines that divide the diagram into squares, although such a division seems to have some influence on the speed and completeness of the result.\nA series of experiments was then devised by Dr. Scripture to test the effects of varying the color of the background, or substituting color, while retaining the same red as the disappearing color, without, however, dividing either background or strip into squares.\nA complete set of the Milton Bradley colored papers was obtained ;","page":2},{"file":"p0003.txt","language":"en","ocr_en":"A color illusion.\n3\nin the following experiments the colors will be designated according to the system adopted by the manufacturers. Sheets 2ocm by 30e\u201d1 were cut out for backgrounds ; small strips Tm by 2ocm were cut ready to lay on the backgrounds. In making the experiment a background of a desired color was fastened to a board by tacks and a strip was fixed on it by a pin ; the whole was then observed at a distance of about 3m. It afterwards appeared that the most convenient method of preparing these figures was to place several strips of different colors on a given background ; such a figure with two strips and a white fixation point is shown in the colored plate.\nThe results with Dr. Scripture and myself differed somewhat ; but the interesting thing about these differences seems to be that they remained fairly constant of the same order. That is to say, where I got the illusion of substitution without great difficulty, my colleague got it more readily ; and when I got it not at all, he could obtain it only with increased \u25a0difficulty, or in certain cases (at least on the earlier trials) not at all. This suggests that the detailed differences were due to a constant factor of difference in the two observers.\nThe results obtained by viewing a standard red strip at a convenient distance, and with the proper fixation of the eye, while the color of the background is changed, may be divided into two general classes. With certain backgrounds the illusion of disappearance and substitution takes place with no great difficulty but with surprising ease and suddenness, after a little practice has given the requisite knowledge of how to experiment. With certain other backgrounds the substitution takes place only with increased difficulty or not'at all, with me as a rule not at all. To the first class of backgrounds belong the two greens used, namely, standard green and bluish-green, violet, blue and black. To the second class belong the backgrounds, yellow, orange, light gray, white, light blue, light green and a light reddish violet. That is to say, this standard red strip, if viewed with a proper amount and kind of fixation on a background of two kinds of green, or of dark violet, dark blue, or black, will itself darken, disappear, and be placed for a longer or shorter interval by the color of the background. But the same strip, if placed upon a background of yellow, orange, gray, white, or light blue, light green, light violet, will maintain its place, although growing darker ; or if it disappears at all, does so with great difficulty and only for an instant. As I have already said, I could not myself get the illusion in these cases at all.\nSuppose now that a strip of orange be viewed upon the same backgrounds as in the foregoing experiments, then somewhat similar phenom-","page":3},{"file":"p0004.txt","language":"en","ocr_en":"4\nGeorge Trutnbull Ladd,\ny\nena result, but with interesting differences. With the backgrounds of green, dark violet, dark blue or black I get the illusion ; but only by persistent trying, and for a briefest instant' of time. On the backgrounds of yellow, gray, white, light blue, light green, violet of tint No. i Dr. Scripture obtains the illusion only with great difficulty, if at all, and then for a brief instant of time. But on the other class of backgrounds the illusion is rather more easily obtained by him with the orange than with the red strip. With me, however, on both classes of backgrounds, the red strip and the orange strip behave in markedly different ways. Whereas, in the case of the red strip fhe color darkens\u2014and this whether substitution ultimately takes place or nbt, and whatever the color of the background\u2014in the case of the orange strip, the color grows lighter, the color of the background seems to encroach from both sides on the color of the strip, until (where\u2014as in all cases of the second class of backgrounds\u2014the illusion does not become perfect) the orange strip becomes a narrow line of sunlight on a unicolored background.\nIf now the orange and the red strips be hung not far apart on the same background of color, each of them behaves, for both observers, in the same way as when viewed apart on a similarly colored background. And if orange and red strips be placed side by side, with one half over a background of the first class (see the colored plate) and the other half over a background of the second class, each half of each strip will seem to follow, for each observer, the course similar to that already described in the separate experiments.\nThis color phenomenon is probably.a general one. It was observed by most persons at a meeting of the American Psychological Association at which these figures were exhibited. It was quite evident at the first trial to a girl fourteen years of age who was asked to observe the strips. I am not yet able to satisfy myself as to the most probable explanation of this somewhat startling color illusion. In the well-known case of a dark spot on a colored background Blix 1 has suggested that with long fixation the retina becomes less sensitive on the parts on which the colored rays fall, and more sensitive on the part corresponding to the dark spot, and that this latter portion, being sensitive to the colored light arriving after general dispersion in the eye, finally gives as intense a color sensation as the other portion. Any one, however, who has seen the red stripe suddenly turn to a bright green knows that the intensity of the green is far beyond any light that might arrive through dispersion.\nDr. Scripture has suggested that the fatigue of the eye for the color of\n1 Blix, Ueber gleichfarbige Induktion, Skand. Arch. f. Physiol., 1893 V 13 (reviewed in Zt. Psych. Phys. Sinn., 1894 VII 411).","page":4},{"file":"p0005.txt","language":"en","ocr_en":"A color illusion.\n5\nthe disappearing strip or letter creates a temporary blind-spot or succession of blind-spots, which is then filled in by the color of the background as the permanent blind-spot of the eye is constantly filled in by the surrounding colors in all our normal vision. This suggestion explains some of the phenomena which I have been describing. It explains the dependence of the result on the character of the fixation, the customary preliminary darkening of the disappearing color, and the character of the substitute color, when substitution takes place. But I am not able to reconcile this suggestion with the fact that the illusion takes place only with such great difficulty, or not at all, when the disappearing color is dark and the background is light. Would not one expect rather the opposite result, namely, that the darker background would more speedily and completely fill in the eye fatigued by the lighter color. Moreover, I cannot see why the orange strip under the principle of fatigue, should grow brighter and of a lighter shade, as it certainly does for my eye ; and, in fine, why in the case of the second class of backgrounds, I am quite unable to fatigue my eye for either orange or red so as to obtain the illusion by substitution of the color of these backgrounds.\nFinally, as far as I can determine in my own case, and by questioning several others with whom the experiment has been tried, the illusion is somehow dependent upon the rhythm of attention, and, in a limited way, it is under the control of will exerted through some obscure modification of the point and manner of .regard. But whatever the prima facie explanations may be, the illusion seems to me unusually interesting and complicated, and in its suggestiveness quite worthy of further investigation.","page":5}],"identifier":"lit28745","issued":"1898","language":"en","pages":"1-5","startpages":"1","title":"A color illusion","type":"Journal Article","volume":"6"},"revision":0,"updated":"2022-01-31T13:31:14.023238+00:00"}