Abstract
Abstract: :
Purpose: To investigate the relative contribution the primary visual cortex and extrastriate visual areas make to instantaneous colour constancy (ICC) in human vision. To establish whether the conscious perception of surround colour changes caused by changes of illuminant in the same eye is a necessary condition for the normal functioning of ICC mechanisms. Methods: We investigated changes in the perceived colour of a central test patch in response to surround illuminant changes in a variety of monocular, binocular and dichoptic experiments. The test patch served both as "reference", when the surround was illuminated with one illuminant, and as matching stimulus, when the surround was illuminated with a different illuminant. A modified version of this technique was also used to assess how the visual system combines the colour of dichoptically fused Mondrians when each is illuminated with different illuminants. In addition, we investigated how monocular ICC measurements in one eye (the test eye) are affected by the presence of a spatially identical surround Mondrian in the other eye (the conditioning eye), for two types of surround illuminant conditions: a. a constant, steady illuminant in the conditioning eye, and b. sequential changes of illuminant in the conditioning eye designed to null out any perceived colour changes in the Mondrian surround as a result of sequential illuminant changes in the test eye. Results:The results reveal no statistically significant difference in ICC between monocular and binocular conditions. The ICC index is however much reduced when the test patch and the Mondrian surround are viewed dichoptically. Measurement of the perceived colour of dichoptically fused Mondrians, each illuminated with a different illuminant, corresponds to that seen under monocular or binocular viewing when the illuminant is approximately half way between the two illuminants (on the mired scale). The perceived colour of the surround illuminant in the test eye can therefore be strongly influenced by the presence of a steady illuminant or illuminant changes in the conditioning eye, without affecting the ICC index. Conclusions:The strength of ICC achieved is completely independent of perceived changes of illuminant colour in the Mondrian surround. Moreover the same ICC index can be elicited in the absence of perceived changes of illuminant in dichoptically fused surround Mondrians, by manipulating appropriately the changes of illuminant in the conditioning eye. These findings point to neural substrates in V1 that are rich in monocularly driven neurons as the principal ICC locus in human vision.
Keywords: color appearance/constancy • color vision