Analysis of visual modulation sensitivity. II. Peripheral retina and the role of photoreceptor dimensions.

Temporal-frequency characteristics were measured as a function of retinal location, with test-field size scaled to provide equivalent sensitivity at each eccentricity. The results showed that the temporal-frequency limits increased uniformly by about a factor of 2 between the fovea and 45 degrees eccentricity, corresponding to a decrease in the response-time constant from 70 to 35 msec. These data were compared with the change in inner- and outer-segment diameters of the cones across the same retinal range. The data conform to the hypothesis that visual time constant varies inversely with cone outer-segment diameter. A second hypothesis that visual sensitivity increases in proportion to come outer-segment length in the central fovea was also supported.