The structure of visual receptive fields of cat's pulvinar neurons.

Receptive fields of 382 neurons in the pulvinar were investigated. The observed receptive fields were classified according to the neurons’ responses to stationary flashing light spots positioned in different parts of the receptive field. New receptive field types with multiple discharge centers were observed. Neurons with these receptive fields generally responded with multimodal discharges to moving visual stimuli. The background illumination resulted in a decrease of the number of on-off and off receptive fields whereas the number of the on receptive fields became higher. In a majority of cases the receptive fields with multiple discharge centers lost their responsivness during background illumination. The changes in the receptive field sizes measured, by light spot in dark and light adapted conditions were attributed mainly to scattered light. The sizes measured by black stimuli under the same conditions remained constant.