Non-cardinal color mechanism strength differs across color planes but not across subjects.

This study tested two hypotheses: (1) that non-cardinal color mechanisms may be due to individual differences: some subjects have them (or have stronger ones), while other subjects do not; and (2) that non-cardinal mechanisms may be stronger in the isoluminant plane of color space than in the two planes with luminance. Five to six subjects per color plane were tested on three psychophysical paradigms: adaptation, noise masking, and plaid coherence. There were no consistent individual differences in non-cardinal mechanism strength across the three paradigms. In group-averaged data, non-cardinal mechanisms appear to be weaker in the two planes with luminance than in the isoluminant plane.