DISCRIMINATION OF CONE CONTRAST CHANGES AS EVIDENCE FOR COLOR CONSTANCY IN CEREBRAL ACHROMATOPSIA

One proposed mechanism for underpinning colour constancy is computatio n of the relative activity of cones within one class - cone ratios, or cone contrasts - between surfaces in a fixed scene undergoing a chang e in illuminant. Although there is evidence that cone ratios do determ ine colour appearance under many conditions, the site or sites of thei r computation is unknown. Here, we report that a cerebrally achromatop sic observer, MS, displayed evidence of colour constancy in asymmetric colour matching tasks and was able to discriminate changes in cone ra tios for simple, but not complex scenes, We hypothesise that the site of local cone-ratio computation is therefore early in the visual syste m, probably retinal.