THE INFLUENCE OF CONTRAST ADAPTATION ON COLOR APPEARANCE

Most models of color vision assume that signals from the three classes of cone receptor are recoded into only three independent post-recepto ral channels: one that encodes luminance and two that encode color. St imuli that are equated for their effects on two of the channels should be discriminable only to the remaining channel, and are thus assumed to isolate the responses of single channels. We used an asymmetric mat ching task to examine whether such models can account for changes in c olor appearance following adaptation to contrast-to temporal variation s in luminance and chromaticity around a fixed mean luminance and chro maticity. The experiments extend to suprathreshold color appearance th e threshold adaptation paradigm of Krauskopf, Williams and Heeley [(19 82) Vision Research, 32, 1123-1131]. Adaptation changes the perceived color of chromatic test stimuli both by reducing their saturation (con trast) and by changing their hue (direction within the equiluminant pl ane). The saturation losses are largest for test stimuli that lie alon g the chromatic axis defining the adapting modulation, while the hue c hanges are rotations away from the adapting direction and toward an or thogonal direction within the S and L-M plane. Similar selective chang es in both perceived color and perceived lightness occur following ada ptation to stimuli that covary in luminance and chromaticity. The sele ctivity of the aftereffects for multiple directions within color-lumin ance space is inconsistent with sensitivity changes in only three inde pendent channels. These aftereffects suggest instead that color appear ance depends on channels that can be selectively tuned to any color-lu minance direction, and that there are no directions that invariably is olate responses in only a single channel. We use the perceived color c hanges to examine the spectral sensitivities of the chromatic channels and to estimate the distribution of channels. We also examine how ada ptation alters the contrast-response function, how it affects reaction times for luminance and chromatic contrast, the extent to which the a ftereffects exhibit interocular transfer, and the way in which the per ceived color changes differ from those induced by conventional light a daptation.