Eye Movements and Spatial Pattern Vision

Models of human lightness and color perception must take account of color constancy, a tendancy for apparent surface color to be relatively independent of the color and intensity of the illuminating light source. Our observers matched the lightnesses apparent reflectances and brightnesses apparent luminances of regions in simple and complex achromatic spatial patterns. The data showed that the observers knowledge of the surface reflectances was unaffected by brightness changes due to varying illuminance. A third perceptual dimension, local brightness contrast, was different from both lightness and brightness. In further experiments we found that moving a patch from a black background to a white background could produce an error of apparent surface color of about 1.5 Munsell Value steps. Similar experiments at mesopic mean luminances revealed that the brightness contrast produced by a fixed luminance contrast declines with mean luminance.