Binocular Rivalry of Achromatic Colors

Abstract

In an earlier paper one of the present authors reported experiments which strongly suggest that achromatic surface-colors (white, gray, black) are the result of a process of interaction. This is certainly true of the surface-colors that are perceived in a dark room when adjacent areas of the retina are stimulated by two different intensities of neutral light. Not only are the achromatic colors seen under these circumstances dependent on the relation of the two light-intensities rather than on the absolute intensities, but stimulation by two light-intensities also represents the simplest condition under which surface-colors are seen; a single bright area in a dark field does not look white or gray but has a luminous appearance. Only upon the introduction of a second bright area of different intensity (adjacent with the first and preferably surrounding it) will the luminous appearance change into that of a surface-color, which will be white, gray, or black, depending on the relation of the light-intensities in the two areas. If the intensity of the surrounding area is one-half the intensity of the inner area, the inner area will look white; if the intensity of the outer area is twice that of the inner area, the inner area will look light gray; as the intensity of the outer area is further raised, the gray of the inner area becomes darker and darker, with a good black appearing at a ratio of approximately 20:1. In the light of these results it is interesting to examine the retinal rivalry which occurs when different achromatic colors are presented to corresponding regions of the two eyes. Does rivalry depend on the difference in stimulation or on the result of interaction, i.e. on the difference in the achromatic colors that would be seen if the left-eye-arrangement or the right-eye-arrangement were presented alone? The usual procedure of demonstrating retinal rivalry is compatible with either interpretation. When, in a stereoscope, a white figure is presented to one eye and a congruent black figure to the other eye, both on a gray ground and so arranged that their images fall on corresponding retinal regions, strong rivalry is experienced. In the retinal images of the two figures, the intensity of stimulation under these conditions differs by a factor of twenty, and, by viewing monocularly, O would see a black figure with one eye and a white figure with the other. It is possible, however, to present neutral light stimuli in such a way that achromatic surface-colors will not be perceived. It also is possible to make O see different achromatic colors in each monocular view when the intensities of stimulation in the corresponding areas are the same. The usual coincidence of difference in color with difference in stimulation can thus be avoided. Method. The experiments were done with an arrangement similar to that described in the previous paper. Of two identical lanterns placed side by side in a dark room, one projected a circular area of light (disk) on a screen and the other projected a