The Effect of Spatial and Temporal Interactions on the Responses of Single Units in the Cat's Visual Cortex

Abstract

Single unit recordings from the striate cortex of the cat were used to study information processing in the visual cortex. This was done in two steps: First, the proportions of units in the cortex responding to stimulus-on only, stimulus-off only, or both, were compared to the theoretical probability of similarly distributed responses, given a random selection of TV on-center and/or off-center fibers. It was shown that afferent input onto a cortical pyramidal neuron probably comes from only a few (three to six) individual fibers, forming parallel and relatively independent input/output (I/O) pathways. Second, by comparing the responses of cortical units to single and two-point stimulation, it was shown that interactions occur between neighboring neurons receiving nearby projections of the visual world. These interactions modulate the responses in the I/O pathways, effectively “tuning” the cells to respond selectively to a more specific stimulus configuration than would otherwise be required. The results of this experiment are consistent with a model of cortical function expressing asymmetric and anisotropic lateral inhibitory interactions between cortical neurons which receive their inputs from a very few input fibers.

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Notes on contributors

Robert W. Phelps

Joyce Laing works in the Department of Child and Family Psychiatry, Playfield House, Cupar, Fife, and is a Consultant Art Therapist to Psychiatric Hospitals and Prisons and Chairwoman of the Scottish Society of Art and Psychology