Interaction of Direction and Speed Selectivity in Cat Primary Visual Cortex

Abstract

We have studied the selectivity for speed and direction of directionally selective (DS) cells in the primary visual cortex of the cat. Most of the 37 DS neurons tested were velocity tuned. From a set of velocities in the range from 2 to 80 deg s⁻¹, each velocity was optimal for a certain proportion of these cells. The distribution was as follows: 2 deg s⁻¹ was optimal for 16% of all tested neurons, 5 deg s⁻¹ for 14%, 10 deg s⁻¹ for 27%, 20 deg s⁻¹ for 30%, 40 deg s⁻¹ for 8%, and 80 deg s⁻¹ for 5%. The preferred direction determined with a single light spot was compared with that obtained with a pair of spots moving at a mutual angle of 60° over the receptive field. For 40% of the neurons tested the preferred direction to the single moving spot coincided with that obtained with the two-spot stimulus. The responses to the latter could be successfully computed as a combination of responses to single spots moving in the given directions. This result indicates a high capacity for motion processing in the primary visual cortex of the cat.