Abstract
Detection and discrimination of color, as well as luminance contrast sensitivity at high spatial frequencies, declines with age. The effect of aging on sensitivity to purely chromatic stimuli of various spatial frequencies, however, is not known. In this investigation, we explore the effects of age on the chromatic contrast sensitivity function. The stimuli were color-varying Gabor patches at 4 different spatial frequencies (0.5, 1, 2, and 4 cycle/deg) modulated along 2 chromatic axes (S varying or L-M varying.) Each set of stimuli was presented in two ways. First, chromatic contrast sensitivity was measured for stimuli equated at the cornea (i.e., the stimulus had the same mean luminance and chromaticity for all observers). Second, chromatic contrast sensitivity was measured for stimuli adjusted based on each individual's ocular media density to create equal stimulation of each of the three cone types at the retina. Stimuli were adjusted for equal sensation luminance using HFP, and displayed on a CRT viewed through a telescopic optical system with a small exit pupil and an achromatizing lens. A 2AFC procedure was used with a QUEST adaptive staircase. The results demonstrate that when stimuli were equated at the cornea, older subjects (> 65 years) were less sensitive to chromatic contrast than were younger subjects (< 35 years) at all spatial frequencies. This difference appeared to be more dramatic for S-varying stimuli, but did not depend greatly on spatial frequency. When stimuli were equated at the retina, the difference in sensitivity between younger and older subjects persisted; however, under these conditions, the difference for the S-varying stimuli was considerably reduced. These results demonstrate a loss in sensitivity of neural mechanisms mediating human chromatic contrast sensitivity along both S- and L-M chromatic axes.