Abstract

Central mechanisms of color are defined to be the central neural processes that are equated in asymmetric color matching. For normal trichromats, asymmetric color matches are nonsingular: given any match, all sufficiently small perturbations of one of the matched colors can be matched by perturbations of the other. This fact, together with the other laws of color matching, yields a rigorous representation of normal color percepts as a 3-D manifold, and also allows the deduction that all effects of adaptation and contrast can be understood as effects on exactly three independent central mechanisms. Thus, for normal color vision, the 3-D bottleneck imposed at the receptor level by cone pigments is matched to a 3-D bottleneck at the level of central mechanisms. An experiment that I conducted with M. Alpern and D. Kirk suggests that nonsingularity holds also for the asymmetric matches of protanopes and deuteranopes. If so, the 2-D receptor space of these color defectives is accompanied by restriction to two central dimensions. This is consistent with theories in which dichromacy involves loss of an opponent mechanism but conflicts with various findings suggesting that dichromats have at least three independent central color mechanisms.

© 1985 Optical Society of America