Thresholds for the perception of red and green or for blue and yellow, presented in two-color mixtures, were measured at exposure durations of 20, 50, 100, and 300 msec at the fovea and 6° above the fovea, at a constant luminance of 0.12 ft-L. Median foveal thresholds for red and green were constant from 300 to 50 msec and decreased slightly at 20 msec; at 6°, sensitivity to both red and green declined with decreasing exposure time. Median thresholds for blue deteriorated as exposure time decreased from 300 to 100 msec, but improved with further reductions in stimulus duration. The median yellow thresholds declined as exposure time was reduced below 100 msec. The results are compared with previous data obtained as a function of retinal position and luminance and with similar thresholds measured under conditions of constant brightness. The results are also discussed in relation to various estimates of the “risetimes” of different colors.
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