Contour integration in striate cortex. Classic cell responses or cooperative selection?
Psychophysics has established various rules of contour integration in gestalt perception. We tested the rule of good continuation by stimulating behaving monkeys with simple figures composed of Gabor patches, while recording from upper layer cells in visual cortex (V1). By decomposing these figures into their components and stimulating receptive field centers and surrounds separately with this stimulus set, we tested center-surround interaction for linearity. In pure-fixation tasks, the interaction was negative for the early strong evoked response, i.e., in this phase figural context rather inhibited the cells. However, in the following tonic response phase, a subgroup of neurons showed positive interaction during the whole stimulus presentation period of at least 1,000 ms. Attention to the figure in discrimination tasks only slightly improved this positive interaction between 150 and 300 ms. We interpret these results as selective cooperation and mutual facilitation of cortical V1 cells, thereby supporting the saliency of borders and contours in perception of visual scenes.