In ongoing vision, the statistical structure of visual inputs plays a central role in perceptual processing. Though natural scenes typically have smoothly varying spatial structure, ongoing saccadic behavior may lead to abrupt change in spatial and temporal contextual statistics. Several past studies, including from our lab, have shown that spatial and temporal context have profound influences on receptive field (RF) properties of single neurons in V1 and provide insights into mechanisms underlying perceptual effects. Placing tilted oriented gratings within and outside the RF such that the two overlap in time but not in space leads to a perceptual tilt-effect (TE), whereas presenting gratings of two different orientations such that they overlap in space but not in time leads to an adaptation induced tilt-after-effect (TAE) whose magnitude depends on the relative orientation of the two stimuli. At the single neuron level TE and TAE lead to marked changes in orientation tuning properties of V1 neurons; however not much is known about contextual interactions when neither stimuli overlap in space or in time. In this study done in awake, fixating monkeys, we recorded from V1 neurons using an adaptation protocol consisting of oriented sinusoidal gratings placed in the RF surround. We used two orientations for surround adaptation: one same as the preferred orientation (iso-oriented surround) of the neuron and the other oriented orthogonally (ortho-surround), and studied the effect of adaptation on gratings of 8 different orientations presented in pseudorandom order within the RF center or RF center+surround. The time course of center responses with and without surround adaptation followed significantly different trajectories: there was an early facilitation of responses that lasted for >200ms when the center stimulus was presented after surround adaptation, whereas this period of facilitation lasted for just 100 ms when surround adaptation was followed by presentation of both center and surround stimuli. In the latter case, the initial facilitation was followed by profound suppression at all orientations. In addition, surround adaptation unmasked center responses to all orientations, revealing significantly greater variability in responses compared to the unadapted center alone responses. In the case of surround adaptation followed by center and surround stimuli, the response variability was confined to nearby orientations and the far flank orientations were minimally affected by adapting context. Our results demonstrate profound and divergent influences of spatial and temporal context on tuning properties and time courses of V1 responses.

Society for Neuroscience Abstract, 2011.