Color adaptation is a process in which, following extended exposure to a certain color (i.e., adaptation color), the perceived color shifts to the color direction opposing the adaptation color. Color adaptation is closely linked to photoreceptor sensitivity changes, such as von Kries adaptation and cone-opponent processes. Color perceptual contrast, on the other hand, reduces following adaptation to a stimulus with spatial and/or temporal color modulation along the color direction (e.g., perceptual saturation of the red-green direction).
Color contrast adaptation refers to this phenomenon. Color contrast adaptation has been used to study how colors are represented in the visual system. For a study, researchers investigated color perception following color contrast adaptation to stimuli with temporal color modulations along difficult color loci on a luminance-chromaticity plane in the current study. The chromaticity corresponding to perceptual achromaticity (the achromatic point) shifted to the same color direction as the adaptation chromaticity in each test stimulus luminance after the observers adapted to color modulations with different chromaticities at higher, medium, and lower luminance (e.g., temporal alternations among red, green, and red, each at a different luminance level). In contrast, after adaptation to color modulations with more complicated luminance-chromaticity correspondences, the luminance reliance of the achromatic point shift was not detected (e.g., alternating red, green, red, green, and red, at five luminance levels, respectively).
A noncardinal model built of channels favoring intermediate color orientations between the cardinal chromaticity and luminance axes was also used to predict the occurrence or nonoccurrence of the luminance-dependent achromatic point shift. The findings implied that noncardinal channels have a role in the luminance-dependent perceived colour shift following adaptation.