Effects of background illumination of visually evoked responses of neurons in the Clare-Bishop area of the cat.

Functional properties of visually driven neurons were investigated at various levels of background illumination. Roughly 50 percent of the investigated cells inhibited their responses to stationary flash lights after background illumination, about 25 percent did not show any difference and 25 percent were facilitated. The increase of the background illumination influenced the movement evoked responses in various ways. The activity of 42 percent cells of this group was inhibited by an illumination of the background and 19 percent of cells revealed a facilitation of their responses. About half of the cells changed their directionally sensitive responses into direction non-sensitive ones and 35 percent did the opposite. Seventy one percent of multimodal neurons lost their response multimodality, whereas 14 percent of them preserved this property during the background illumination.