Chromatic information processing

The investigation of visual processing mediated solely by chromatic information requires conditions preventing an S's use of the luminance differences normally accompanying a chromatic change. In Exp I, which involved a discriminative reaction time (RT) task, chromatic and white stimuli of the same luminance were presented on a dimmer achromatic background. The 3 Ss were instructed to respond only to the chromatic stimuli. RT was slowest at 570 nm and somewhat faster to short wavelengths than to long wavelengths. In Exp II, which compared 2 discriminative RT tasks, RT was faster when 3 Ss responded to color than when they responded to white. Exps III and IV, with 3 Ss each, demonstrated that a brighter white surround decreased the perceived brightness of chromatic stimuli as well as their perceptual similarity to white, but did not affect RT. The response strength of the chromatic processing channel is discussed. (47 ref)