Visual response properties of neurons in the middle and lateral suprasylvian cortices of the behaving cat.

The visual response properties of cells in the middle (MS) and lateral (LS) suprasylvian cortices were studied in alert cats, which were trained to fixate a spot of light and maintain fixation when a second test light was introduced in the midst of fixation. This second light served to test for visual sensitivity, and it could be moved at different speeds in any direction under computer control. Over half of the cells exhibited a visual response. With a small spot of light, most cells were directionally selective and responded better to a moving spot than to a stationary one. In some cases movements of the spot in the non-preferred direction revealed an inhibitory process. The visual receptive fields were large and often extended into the ipsilateral hemifield, though the centers of the receptive fields were usually in the contralateral field. We used Fourier analysis to quantify directional selectivity and compared these results to other commonly used measures of directional selectivity. Compared to cells in MS, there was a higher incidence of visual cells in LS and the visual cells were more directional. We also made comparisons between our results and those found in anesthetized cats and awake monkeys.