Failure of direction discrimination at detection threshold for both fast and slow chromatic motion

Abstract

Separate pathways have recently been proposed for “fast” and “slow” motion, whose properties differ in the way that color contrast is processed [see Nature (London) 367, 268 (1994); Trends Neurosci. 19, 394 (1966); and Vision Res. 36, 1281 (1996) and 35, 1547 (1995)]. One reported difference is that for slow motion the direction of chromatic stimuli cannot be determined at detection threshold, whereas at higher temporal rates detection and direction discrimination threshold coincide. Using a carefully designed psychophysical procedure, we measured simultaneously the thresholds for detection, direction discrimination, and color identification for isoluminant red–green and achromatic Gabor pat..