THE NEUROPHYSIOLOGY OF FIGURE GROUND SEGREGATION IN PRIMARY VISUAL-CORTEX

The activity of neurons in the primary visual cortex of the awake maca que monkey was recorded while the animals were viewing full screen arr ays of either oriented line segments or moving random dots. A square p atch of the screen was made to perceptually pop out as a circumscribed figure by virtue of differences between the orientation or the direct ion of motion of the texture elements within that patch and the surrou nd. The animals were trained to identify the figure patches by making saccadic eye movements towards their positions. Almost every cell gave a significantly larger response to elements belonging to the figure t han to similar elements belonging to the background. The figure-ground response enhancement was present along the entire extent of the patch and was absent as soon as the receptive field was outside the patch. The strength of the effect had no relation with classical receptive fi eld properties like orientation or direction selectivity or receptive field size. The response enhancement had a latency of 30-40 msec relat ive to the onset of the neuronal response itself. The results show tha t context modulation within primary visual cortex has a highly sophist icated nature, putting the image features the cells are responding to into their fully evaluated perceptual context.