Space Perception and Color Vision
On the matter of space perception, we have seen that Helmholtz believed that it slowly develops from experience as physiological and psychological events are correlated. Hering, however, believed that, when stimulated, each point on the retina automat- ically provides three types of information about the stimulus: height, left-right position, and depth. Fol- lowing Kant, Hering believed that space perception exists a priori. For Kant, space perception was an innate category of the mind; for Hering, it was an innate characteristic of the eye. This controversy about perception became the Helmholtz-Hering debate, and in various guises continues even today.
After working on the problem of space percep- tion for about 10 years, Hering turned to color vision. Hering observed a number of phenomena that he believed either were incompatible with the Young–Helmholtz theory or could not be explained by it. He noted that certain pairs of col- ors, when mixed together, give the sensation of gray. This was true for red and green, blue and yellow, and black and white. He also observed that a person who stares at red and then looks away experiences a green afterimage; similarly, blue gives a yellow after- image. Hering also noted that individuals who have difficulty distinguishing red from green could still see yellow; also, it is typical for a color-blind per- son to lose the sensation of both red and green, not just one or the other. All these observations at least posed problems for the Young–Helmholtz theory, if they did not contradict it.
