Abstract

Unique hues were measured at the fovea and at 10° and 20° temporal eccentricities with stimuli of varying sizes to investigate the spatial limitations of the yellow-blue and red-green opponent processes. All stimuli were presented for 500 ms and eccentric measurements were made under conditions that eliminated rod contributions. For all three observers, compared to the fovea, unique green loci shifted to shorter wavelengths at 20°, with a greater shift for smaller stimuli. This is consistent with the eccentricity-dependent decline in S-cone density. For two observers, unique yellow showed no change with large test stimuli at 20°, as compared to the fovea, but it shifted to shorter wavelengths when test size was reduced. The third observer's unique yellow shifted to longer wavelengths relative to the fovea and shifted to shorter wavelengths with smaller test size. Preliminary data suggest that at 20° the minimum test size for unique yellow determinations is smaller than the minimum test size for unique green, thus indicating a difference in the spatial requirements of the two color-opponent systems. Measurements made in the nasal retina will also be reported.

© 1992 Optical Society of America