Modulatory influences of moving textured backgrounds on responsiveness of simple cells in feline striate cortex

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Abstract
The modulatory influences of synchronously moving textured backgrounds on responsiveness to optimally oriented moving bar stimuli were investigated in 107 simple cells, with incidental observations on 4 complex cells, recorded in the lightly anesthetized feline striate cortex. Background motion depressed bar responsiveness in 74% of simple cells, facilitated bar responsiveness in 4% and was without influence in 22%. These results confirm earlier observations. Moving checkerboard patterns typically elicited stronger effects than moving visual noise. Occluding a moving background by a mask of stationary texture of variable width and length indicated that the zone of background influence extended well beyond the excitatory receptive field along its axis but not transverse to it. This was confirmed by a converse experiment using a window of moving texture in an otherwise stationary background. The influence of background motion varied markedly with location relative to the cell''s receptive field. A small stationary rectangular window of moving texture at different locations along the receptive field axis typically suppressed bar response when over the receptive field but facilitated it at either end. Conversely, with the background moving and the masking texture stationary, suppression was minimal when the masking patch was centered over the receptive field. Systematically varying the phase relationship between bar and background motion showed the interaction in simple cells to be greatest for in-phase motion and least for motion in antiphase. The opposite is true for complex cells. All the above effects showed non-linearities and could be enhanced by making texture velocity greater than bar velocity or by selecting the polarity of contrast and length of a bar stimulus of optimal orientation and width so as to elicit relatively weak (submaximal) criterion responses. Since textured backgrounds themselves evoke no response from simple cells, and since all specific afferents are known to be excitatory, it seems likely that textural influences upon simple cells are mediated only through complex cells.