Abstract
Vision that is served by the S cones alone is poor in both spatial and temporal resolution (e.g., Humanski & Wilson, 1992; Kelly, 1961; Stockman, MacLeod, & DePriest, 1991; Wisowaty & Boynton, 1980). However, few studies have directly compared S cone and achromatic vision measured under comparable conditions and in meaningful units. In this experiment, we measured contrast sensitivity functions using Gabor patches with carrier frequencies from 1 to 16 cpd, with a two-temporal alternative forced-choice method. Stimuli contrast-reversed at 2 or 10 Hz, and had color directions that were achromatic or that isolated the S cones using silent substitution. All stimuli had constant spatial and temporal bandwidth (1.2 octaves) and the adaptation conditions were kept constant (grey background at 59 cd/m2). Sensitivities are expressed in terms of cone contrast vector length. All CSFs were low-pass (down to 1 cpd). At 2 Hz, S cone and achromatic sensitivities were similar for low spatial frequency patterns, but, unsurprisingly, achromatic sensitivity was higher at higher spatial frequencies. Increasing the temporal frequency to 10 Hz had relatively little effect at low spatial frequencies but it caused a decrease in sensitivity at higher spatial frequencies in both conditions. The