Inhibition and disinhibition of direction-specific mechanisms in human vision

Abstract

MOTION-SENSITIVE mechanisms in human vision are selective for direction of stimulus movement. Psychophysical experiments reveal direction-specific channels which can be selectively desensitised or adapted^1,2. At threshold these direction-specific mechanisms operate independently; they have little or no sensitivity for the opposite direction of motion^3–6. Independence at threshold does not, of course, preclude interaction at suprathreshold stimulus levels. Indeed, inhibition has been found above threshold between otherwise independent spatial frequency-specific mechanisms^7,8, orientation-selective mechanisms^9,10, and binocular disparity-specific mechanisms¹¹. We report here comparable measurements of inhibition between direction-specific channels. We also show that in appropriate conditions the inhibition can itself be reduced or eliminated, a disinhibition effect.