Color appearance across the retina: effects of a white surround.

Hue and saturation scaling was used to measure the appearance of spectral lights as a function of stimulus size at loci spaced across the horizontal meridian. At a given locus, each hue (red, yellow, green, and blue) grew as a function of stimulus size to some asymptotic value. Growth functions fitted to the hue data were used to derive the sizes of perceptive fields of the hue mechanisms. We had previously investigated the size scales of these fields by using stimuli presented on a dark background: Field sizes for all mechanisms increased with eccentricity, this increase was greater on the temporal than on the nasal retina, and the retinal size scales of the different hue mechanisms were not the same. We now report the results of repeating the study with stimuli embedded in a white surround rather than in darkness. The main effects of the white surround were as follows: Sizes of perceptive fields of all mechanisms were smaller everywhere than with the dark surround. For small fields, stimuli appeared everywhere more saturated with the white surround, but larger stimuli appeared less saturated.