Orientation-contingent color aftereffects are determined by real color, not induced color.

Abstract

Three experiments were concerned with whether orientation-contingent color aftereffects (McCollough effects) occur when the perceived colors of differently oriented gratings derive from colored shadows, a compelling instance of simultaneous color contrast. Whereas strong orientation-contingent aftereffects occurred with pink light reflected from vertical gratings viewed in alternation with green light reflected from horizontal gratings, none occurred when pink and green colored shadows were presented with the same physically achromatic gratings (Experiment 1). No aftereffects were evident even after an extended (15-min) period of alternating presentation (Experiment 2). In Experiment 3, colored bars matched in chromaticity to the colored shadows produced strong aftereffects. These outcomes agree with those of Thompson and Latchford (1986), who showed that the McCollough effect is a function of the real color of reflected light, rather than of the apparently constant color of gratings in different illuminants. The implications of the present findings for the neural basis of simultaneous color contrast and the McCollough effect, and for Thompson and Latchford’s explanation of the latter, are considered.