Study of instantaneous color constancy mechanisms in human vision

We have extended the experiments of McCann et al. by incorporating their Mondrian stimulus into a dynamic color matching (DCM) technique that allows the subject to match accurately the color of any test patch under sequential changes of illuminant. Changes in the perceived color of a central test stimulus as a result of surround illuminant changes are investigated in a number of successful binocular and dichoptic experiments. The contribution made by distant patches to instantaneous color constancy (ICC) is found to be small, with the immediate surround (i.e., $<1.5-deg$ separation) contributing most of the constancy effect. A modified DCM technique was developed to study ICC in patients with unilateral damage to the primary visual cortex. The results of this part of the study suggest that retinal mechanisms do not contribute to ICC. Experiments carried out in subjects with cerebral achromatopsia reveal the existence of hidden constancy, even when the subjects are unable to see the result of functioning ICC mechanisms. Dichoptic implementation of the DCM technique yields reduced but significant ICC index values with more equal contribution from distant surrounds. Our findings suggest that early stage processing of chromatic information in the primary visual cortex contributes significantly to ICC, with only small contributions from extrastriate areas of the cortex. © 2004 SPIE and IS&T.