Cone opponency: An efficient way of transmitting chromatic information.

Cone or color opponency provides visual neurons with a spectral selectivity more sharply tuned than the absorption spectra of the cone photoreceptors. It is achieved by subtractive interaction of inputs from different cones. In different species, there are different varieties of cone and color opponency, but in human and primates, there are two cone-opponent pathways, one with subtractive input from the middle- and long-wavelength cones and the other with subtractive inputs from the short-wavelength (S) cone and some combination of the other two. These pathways are distinctive anatomically as well as physiologically, and the S-cone pathway is phylogenetically the older. We review these pathways. This way of coding for color is thought to be efficient from an informational standpoint; we argue that these pathways are specialized for transmitting the surface characteristics of objects.