Loci of achromatic points throughout the life span

Mixtures of monochromatic lights that appear achromatic were measured for 50 normal, trichromatic observers ranging in age from 11 to 78 years. Stimuli were presented to one eye as a 1 degree-diameter, 1-s flash (10-s interstimulus interval) in Maxwellian view. We found the achromatic locus by varying the intensity ratio of each observer's spectral unique blue and unique yellow while maintaining constant overall retinal illuminance. Measurements were made for three levels of retinal illuminance (10, 100, 1000 trolands). Additional verification of the position of the achromatic locus in color space was obtained for 23 subjects with the use of a mixture composed of 600-nm light and its spectral complement. There were no significant changes in the achromatic loci as a function of age. The mean achromatic locus in CIE chromaticity space was x, y = 0.31, 0.31 or u',v' = 0.21, 0.46. These results suggest that partial compensation for age-related changes in visual mechanisms occurs in a way that preserves constancy of the achromatic locus across the life span.