Chromostereopsis - Theory

Theory

In 1885, Einthoven proposed a theory which states: “The phenomenon (chromostereopsis) is due to chromatic difference of magnification, for since, for example, blue rays are refracted more than red rays by the ocular media, their foci not only lie at different levels (chromatic aberration) but make different angles with the optic axis, and will thus stimulate disparate points. It follows that individuals with temporally eccentric pupils see red in front of blue, while with nasally eccentric pupils the relief is reversed.” Einthoven first explained chromatic aberration in the eye, which means that the eyes will not focus all the colors at the same time. Depending on the wavelength, the focal point in the eyes varies. He concluded that the reason why people see red in front of blue is due to the fact that light with different wavelengths project onto different parts of the retina. When the vision is binocular, a disparity is created, which causes depth perception. Since red is focused temporally, it appears to be in front. However, under monocular vision, this phenomenon is not observed.

However, Bruecke objected Einthoven’s theory based on the grounds that not all people see red as closer than blue. Einthoven explained that this negative chromostereopsis is probably due to eccentrically positioned pupils because shifting the pupil can change the position of where light wavelengths focus in the eye. Negative chromostereopsis was further studied by Allen and Rubin who suggested that changing the angle between the pupillary center and visual axis can change the direction of chromostereopsis. If the pupillary center is located temporal to the visual axis, red will appear closer. The reverse effect is observed when the pupillary center is nasal to the visual axis.