REVERSALS OF THE COLOR-DEPTH ILLUSION EXPLAINED BY OCULAR CHROMATIC ABERRATION

Although many colour-depth phenomena are predictable from the interocu lar difference in monocular chromatic diplopia caused by the eye's tra nsverse chromatic aberration (TCA), several reports in the literature suggest that other factors may also be involved. To test the adequacy of the optical model under a variety of conditions, we have determined experimentally the effects of background colour on perceived monocula r chromatic diplopia and perceived depth (chromostereopsis). A Macinto sh colour monitor was used to present red, blue, and green test stimul i which were viewed monocularly or binocularly (haploscopically) throu gh 1.78 mm artificial pupils. These apertures were displaced nasally a nd temporally from the visual axis under controlled conditions to indu ce a variable degree of TCA, Monocular chromatic diplopia and binocula r chromostereopsis were measured for red and blue targets, and also fo r red and green targets, presented on either a black background or on a background which was composed of the sum of the targets' spectral co mposition (e.g. red and blue presented on magenta; red and green prese nted on yellow). In all cases, chromatic diplopia and chromostereopsis were found experimentally to reverse in sign with this change in back ground. Furthermore, we found that a given coloured target could be lo cated in different depth planes within the same display when located o n different background colours. These seemingly paradoxical results co uld nevertheless be explained by a simple model of optical TCA without the need to postulate additional factors or mechanisms.