The suppressive influence of moving textured backgrounds on responses of cat striate neurons to moving bars.

The suppressive action of a moving textured background on responses to moving bars was investigated in 118 striate neurons, 19 dorsal lateral geniculate neurons, and 5 perigeniculate neurons in paralyzed and anesthetized cats. In standard conditions the background was a two-dimensional (2D) noise pattern, the bar moved at optimal speed, and its contrast level was adjusted to yield 50% of the maximum response. Neuronal responses to the moving bar were suppressed when the background moved at the same speed or faster than the bar. The direction of motion of the bar had little influence. This suppressive effect was equally strong in all three experimental samples. The suppressive effect of the moving background was uniformly distributed among the cortical population, being equally strong in all layers, in all parts of the visual field representation, and for different categories of cortical cells. The suppressive effect of the moving background depended little on the structure of the background or on the speed of the bar. The suppression increased with decreasing contrast of the bar. Many (80%) cortical cells and all geniculate neurons responded to the movement of the 2D noise on its own. Most of these cells responded to isolated features ("grains") in the pattern rather than to movement of the whole pattern. There was no difference in strength of suppression between cortical neurons responsive and unresponsive to the moving 2D noise. The possible origins of this suppressive influence of moving backgrounds and its significance for the processing of visual scenes, more complicated than a single stimulus, are discussed.