Neural Mechanisms of Color Vision Double-Opponent Cells in the Visual Cortex

From the Foreword by Nobel Laureate David Hubel:
"We now have the first clear demonstration of double opponent cells in the primate visual system. Given the temperament of those who work in the field of color vision there seems little doubt that heated debates will continue, but for the present at least, the subject seems to be as close to settled as such things can be in science."

How the brain represents color remains one of the most controversial topics in neurophysiology. We know that color is represented through an opponent mechanism, demonstrated by the fact that some colors are exclusive of others. Yet how these antagonistic chromatic axes are represented in the cortex has been a mystery.

Dr. Conway mapped the spatial and temporal structure of the cone inputs to single neurons in the primary visual cortex of the alert macaque. Color cells had receptive fields that were often Double-Opponent, an organization of spatial and chromatic opponency sufficient to form the basis for color constancy and spatial color contrast. Almost all color cells gave a bigger response to color when preceded by an opposite color, suggesting that these cells also encode temporal color contrast. In sum, color perception is likely subserved by a subset of specialized neurons in the primary visual cortex. These cells are distinct from those that likely underlie form and motion perception. Color cells establish three color axes sufficient to describe all colors; moreover these cells are capable of computing spatial and temporal color contrast - and probably contribute to color constancy computations - because the receptive fields of these cells show spatial and temporal chromatic opponency.