The orientation selectivity of color-responsive neurons in macaque V1

Form has a strong influence on color perception. We investigated the neural basis of the form - color link in macaque primary visual cortex ( V1) by studying orientation selectivity of single V1 cells for pure color patterns. Neurons that responded to color were classified, based on cone inputs and spatial selectivity, into chromatically single- opponent and double- opponent groups. Single- opponent cells responded well to color but weakly to luminance contrast; they were not orientation selective for color patterns. Most double- opponent cells were orientation selective to pure color stimuli as well as to achromatic patterns. We also found non- opponent cells that responded weakly or not at all to pure color; most were orientation selective for luminance patterns. Double- opponent and non- opponent cells' orientation selectivities were not contrast invariant; selectivity usually increased with contrast. Double- opponent cells were approximately equally orientation selective for luminance and equiluminant color stimuli when stimuli were matched in average cone contrast. V1 double- opponent cells could be the neural basis of the influence of form on color perception. The combined activities of single- and double- opponent cells in V1 are needed for the full repertoire of color perception.