Dynamics of neuronal sensitivity in primate VI underlying local feature discrimination

Viewing a scene consists of saccades interspersed by brief fixations on image patches of correlated spatial attributes. To understand how image sampling affects the statistics of stimuli at the center of fixation, we recorded the eye positions of two behaving monkeys freely viewing natural scenes. We show that successively viewed patches have large net differences in local orientation structure. This influences the discrimination of local image features and their encoding by visual cortical neurons. We have examined perceptual changes in orientation discrimination induced by brief exposure to oriented image patterns in monkeys and humans, and then used the reverse correlation procedure to investigate dynamic changes in neuronal sensitivity in the primary visual cortex (V1) of behaving monkeys. We find that whereas brief adaptation to an oriented grating impairs perceptual discrimination of nearby orientations by broadening orientation selectivity and changing the preferred orientation of individual V1 neurons, it can actually enhance the discrimination of orthogonal orientations by sharpening neuronal selectivity. Our results indicate that successive fixations on image patches of dissimilar spatial structure enhance both the capacity of the visual system to discriminate local features and neuronal performance in V1.