Aftereffect of contrast adaptation to a chromatic notched-noise stimulus

One of the most challenging topics in the study of human color vision is the investigation of the number of hue-selective channels that are necessary for the representation of color appearance at the post-opponent level and the bandwidth of their sensitivity. The present study aims to elucidate this issue by using a chromatic version of the notch-filtered noise (herein, notched-noise) stimulus for contrast adaptation. After adaptation to this stimulus, some color-sensitive mechanisms that selectively respond to missing hues in the notched-noise stimulus may remain sensitive, while the other mechanisms may be desensitized. The shifts in the color appearance of a gray test field after the adaptation to such a notched noise were measured using the method of adjustment. The results showed systematic shifts in the hue and saturation. They showed neither point nor line symmetric profiles with respect to the achromatic point in an isoluminant plane. The fittings of the results, obtained by using a tiny numerical model for assessing the hue-selective mechanisms, suggested that there are at least two narrowly tuned and at least three broadly tuned mechanisms. The narrowly tuned mechanisms are the most sensitive along the blue and yellow directions. The present study confirmed the variation of multiple channels at the post-opponent level and suggested that this variation may be responsible for the processing of color appearance.