Color Optical Illusions, Retiring and Advancing Colors

For years the artist and the decorator have felt that certain colors seem to advance nearer than others or that the latter seem to retire more than the former. The author [Retiring and Advancing Colors, M. Luckiesh, Amer. Jour. Psych. 1918, 29, p. 182.] obtained actual measurements of this phenomenon, but the evidence also indicated that the effects were not the same for all persons. The phenomenon is very noticeable in the case of the image of a colored lantern-slide projected upon a screen and is readily observed when the image consists of letters of various colors. In the case of red and green letters, for example, the former appear (to most persons) to be considerably nearer the observer than the green letters. It has appeared to the writer that the optical illusion is apparent even for white letters upon a dark background. In general, the colors whose dominant hues are of the shorter wave-lengths (violet, blue, blue- green, green) are retiring and those whose dominant hues are of the longer wave-lengths (yellow, orange, red) are advancing.

In order to obtain experimental measurements two light-tight boxes, each containing a light-source, were arranged to run independently upon tracks. Over the front end of each a diaphragm was placed so that the observer saw two characters as in Fig. 68. A saturated red filter was placed over one and a saturated blue filter over the other.

Fig. 68. - For demonstrating retiring and advancing colors.

In a dark room the observer saw a blue E and a red H standing out in the darkness. One of these boxes was fastened so as to be immovable and the observer moved the other to and fro by means of a cord over pulleys until the two characters appeared equidistant from him. This was done for a series of distances of the stationary box from the observer's eye. Nearly all the observers (without being acquainted with the positions) were obliged to set the red H further behind the blue E in order that both appeared at the same distance. This added distance for the red H was as much as 2.4 feet when the blue E was at a distance of 24 feet. In other words the difference in the positions of the two was as much as 10 per cent of the total distance in this case.

Many other interesting data were obtained but most of these are not particularly of interest here. Some of the experiments tended to show the effect of certain optical defects in the eye and the variations and even reversal of the effect for some persons were accounted for by differences in the curvatures, etc., of certain eye-media for the observers. These details do not fit in this discussion but it may be interesting to be aware that the phenomenon can be explained by the chromatic aberration in the eye. This may not be the true explanation, or it may be only partially correct. Perhaps some of the optical illusion is purely psychological in origin. Certainly the illusion is very apparent to most careful observers.