A central mechanism of chromatic contrast.

The color appearance of a light can be altered by introducing a second, surrounding field. This phenomenon, called chromatic induction, is attenuated by chromatic variation within a remote region outside the surround [Shevell & Wei (1998). Vision Research, 38, 1561-1566]. We now consider the locus of the neural mechanism mediating the attenuation caused by the remote chromatic contrast. In the first experiment, the magnitude of chromatic variation within the remote region is changed either: (i) in the same eye that views the patch judged in color; or (ii) in only the opposite eye. The measurements are virtually the same in both cases, which implies attenuation of chromatic induction is mediated by a central, binocular mechanism. In the second experiment, the patch with its immediate inducing surround is changed in binocular disparity relative to the remote region with chromatic variation. The patch and surround, seen together in one depth plane, are perceived to be in front of, behind, or in the same plane as the remote region with chromatic variation. Attenuation of chromatic induction is strongest when the patch and surround are in the same depth plane as the remote region. This change of color appearance with disparity is consistent with a central binocular process. Overall, the color-appearance measurements are explained by monocular encoding of chromatic differences at edges, and a central binocular mechanism of chromatic-contrast gain control.