Retinotopy and color sensitivity in human visual cortical area V8.

Prior studies suggest the presence of a color-selective area in the inferior occipital-temporal region of human visual cortex. It has been proposed that this human area is homologous to macaque area V4, which is arguably color selective, but this has never been tested directly. To test this model, we compared the location of the human color-selective region to the retinotopic area boundaries in the same subjects, using functional magnetic resonance imaging (fMRI), cortical flattening and retinotopic mapping techniques. The human color-selective region did not match the location of area V4 (neither its dorsal nor ventral subdivisions), as extrapolated from macaque maps. Instead this region coincides with a new retinotopic area that we call 'V8', which includes a distinct representation of the fovea and both upper and lower visual fields. We also tested the response to stimuli that produce color afterimages and found that these stimuli, like real colors, caused preferential activation of V8 but not V4.