The detection of movement direction and effects of contrast reversal in the cat's striate cortex

Abstract

Single cell responses to moving visual stimuli have been recorded in the striate cortex of anaesthetized and immobilized cats, and the effects of the reversal of stimulus contrast have been tested. The detection of the direction of movement of a light stimulus in the cat's striate cortex depends to a certain extent on the receptive field type and—in cells having simple receptive fields—also somewhat on the eccentricity in receptive field location. In a high proportion of striate cells a reversal in stimulus contrast either changes the degree of the direction sensitivity or even reverses the preferred direction. The effects of the contrast reversal are much stronger in simple than in complex cells. Susceptibility to contrast reversal is observed mainly in directional asymmetric and bidirectional cells; the responses of the majority of unidirectional cells remain stable under contrast reversals. These latter cells are therefore the directional selective cells and they comprise about 25% of the total striate cell population.