Abstract
Mechanisms of color vision in cortex have not been as well characterized as those in sub-cortical areas, particularly in humans. We used fMRI to investigate the initial transformation of sub-cortical inputs by human visual cortex. From V1 onwards we found a stronger response to patterns modulating in color between lime and magenta than between orange and cyan even though the stimuli were matched for cone contrast and the response they would elicit in the postulated L−M and S−(L + M) sub-cortical opponent channels. This result implies that sub-cortical chromatic channels are recombined early in cortical processing to form novel representations of color. The bias for lime-magenta over orange-cyan will be discussed with reference to single-unit data from macaque V1 and human psychophysics to explore the idea that visual cortex efficiently deploys chromatic mechanisms in anticipation of a diet of images characteristic of the natural environment.