Color appearance in the peripheral retina: effects of stimulus size.

Hue and saturation scaling were used to measure the appearance of spectral lights as a function of stimulus size for nine loci across the horizontal retinal meridian. At a given locus, each hue (R, Y, G, and B) grew as a function of stimulus size up to some asymptotic value. The parameter values of Michaelis-Menten growth functions fitted to the hue data were used to derive the sizes of the so-called perceptive fields of the hue mechanisms. The fields for all mechanisms increased with eccentricity, and this increase was greater on the temporal than on the nasal retina. By increasing stimulus size it was possible to achieve fovealike color vision to eccentricities of 20 deg. However, even the largest stimuli failed to produce fully saturated hues at 40 deg. The retinal size scales of the four hue mechanisms were not the same; those for R and B were similar, and these mechanisms had the smallest perceptive fields everywhere. The perceptive fields of the hue mechanisms at all loci were larger than anatomical estimates of the sizes of retinal receptive fields.