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Abstract:
Human functional neuroimaging experiments have identified a colour area on the ventral surface of occipital cortex. However, the precise function, location, and extent of this area are disputed as is its possible homology with macaque V4. The discovery of this area has also diverted attention from measurements in other parts of the colour pathways. We present two results from our humans and macaque neuroimaging work. (i) Measurements in V1 show that changes in the background cone absorption rate influence the response gain to a constant-amplitude probe stimulus. The response gain appears to be controlled separately within each of the cone classes. These gain changes are significant for colour constancy and appear to be localised in the retina. (ii) Macaque cortex shows strong responses to isoluminant colour both dorsally and ventrally in V2 and V4. In humans, the largest responses to the same stimuli are confined to the ventral surface anterior to V3v. These data indicate that colour signals are processed in a pathway beginning at the retina and extending well into extrastriate cortex. Colour constancy is refined at several stages along this pathway. Finally, there appear to be differences between the humans and macaque colour pathways.
