Age, the eye, and the visual channels: contrast sensitivity and response speed.

Age differences in spatial vision were examined by establishing contrast sensitivity functions for young and old adults. In addition, differences in the speed of operation of the different visual channels and their contribution to age differences in reaction time were assessed in a comparison of response speed to sinusoidal gratings of varied spatial frequency. An age-related loss in contrast sensitivity was observed primarily for stimuli of intermediate and high spatial frequency, an effect apparently due mostly to age-related optical differences. Reaction time varied markedly as a function of spatial frequency for the older participants, an outcome only partly attributable to age differences in target visibility. These data indicate a slowing in the speed of operations of individual visual channels and/or a change in the relationship between visual channel classes. These findings also raise a question in regard to the meaning and comparability of any studies that have used measures of response latency to the figural aspects of stimuli.