Scotopic contrast sensitivity functions (CSFs) were measured for 50 observers between the ages of 20 and 88 years. Using a maximum-likelihood, 2-alternative, temporal forced-choice threshold-estimation algorithm, scotopic CSFs were measured at 7 spatial frequencies ranging from 0.2 to 3.0 cpd, with mean retinal illuminance equated for observers at -0.85 log scotopic Trolands. For each stimulus condition, eight cycles of a horizontal sinusoidal grating were presented within +/- 1 S.D. of a 2-D Gaussian-spatial envelope and within a 1-s Gaussian-temporal envelope. Stimuli were centered on the nasal retina along the horizontal meridian 6 degrees from the fovea. Scotopic CSFs were found to be low-pass. Statistically significant age-related declines in contrast sensitivities were found for spatial frequencies at or below 1.2 cpd. There was also a statistically significant decrease in the high frequency cut-off with age (P < 0.01). An explanation of these results in terms of optical factors is rejected, while the results are consistent with age-related changes in the magnocellular pathway.

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.

Spectral unique hues (blue, green, and yellow) were determined for 50 observers ranging in age from 13 to 74 years. Each unique hue was measured at three luminance levels (0.5-log-unit steps). There were no significant changes in the spectral locations of red-green equilibrium hues (unique blue and yellow) as a function of luminance level or age. In contrast, significant shifts in unique green loci occurred as a function of both age and luminance. Unique green loci shifted toward shorter wavelengths with age. These results are consistent with the hypothesis that with advancing age there is a parallel decline in the input of all three cone types to the red-green chromatic channel and either a selective decline in short-wave-sensitive cone input to the yellow-blue chromatic channel or a change in the way in which cone signals are combined within the yellow-blue channel.

Foveal and parafoveal increment thresholds were measured for 50 observers (12-88 years of age) under conditions that isolated retinal mechanisms dominated by short-(S-), middle-(M-), or long-(L-) wave-sensitive cones. Thresholds were obtained on the plateau of the threshold-versus-intensity function of each isolated mechanism and were referred to the retina by using individual measurements of ocular media and macular pigment density. Age-related increases in foveal thresholds, specified at the retina, were found for all three cone mechanisms. Parallel sensitivity losses for each cone mechanism were also observed at 4°and 8°in the temporal retina. A significant positive correlation was found between foveal macular pigment density and the S-cone, but not the M-and L-cone, log sensitivity difference (0°-8°) specified at the retina. This relation is expected from the hypothesis that the macular pigment protects the photoreceptors from senescent losses in sensitivity. However, because this result is independent of age, it is interpreted as being due to local gain changes resulting from differential filtering of incident light by the macular pigment between the fovea and the parafovea.

The maximum area of complete spatial summation (i.e., Ricco's area) for human short-wavelength-sensitive-(S-) and long-wavelength-sensitive- (L-) cone mechanisms was measured psychophysically at the fovea and at 1.5 degrees , 4 degrees , 8 degrees , and 20 degrees along the vertical meridian in the superior retina. Increment thresholds were measured for three observers by a temporal two-alternative forced-choice procedure. Test stimuli ranging from -0.36 to 4.61 log area (min2) were presented on concentric 12.3 degrees adapting and auxiliary fields, which isolated either an S- or an L-cone mechanism on the plateau of its respective threshold versus intensity function. Test flash durations were 50 and 10 ms for the S- and L-cone mechanisms, respectively. The data indicate that, from 0 degrees to 20 degrees, Ricco's area increases monotonically for the L-cone mechanism, is variable for the S-cone mechanism, and is larger for the S-cone mechanism than for the L-cone mechanism for essentially all retinal locations. This pattern of results most likely reflects differences in ganglion cell density and changes in neural convergence with retinal eccentricity.