Post-receptor chromatic mechanisms revealed by flickering vs fused adaptation.

For both normals and dichromats, adaptation to certain pairs of alternating monochromatic caused reduced sensitivity for detection of some test wavelengths when compared to sensitivity losses caused by adaptation to the fused (supra-CFF) sums of the same lights. Since the two adaptation conditions caused equivalent photopigment depletion, and since sensitivities to some wavelengths did not differ between conditions, the effects are ascribed to post-receptor adaptation. Such post-receptor effects were not obtained when adapting wavelengths did not straddle the presumed "crosspoints" of opponent-colors mechanisms, and, when only one opponent mechanism was adapted, effects were absent for test wavelengths at the crosspoint of that mechanism. For the red vs green system, increasing the intensities of adapting wavelengths from 2.2 to 5.5 log td did not appreciably increase the magnitudes of postreceptor effects. Quantitative accounts for the results are derived from a vector model for color vision. The results provide general support for opponent-colors interpretations of normal and dichromatic vision and suggest that the flicker/fused adaptation paradigm is a useful tool for probing postreceptor mechanisms of vision.