Spatio-temporal interaction in the parallel pathways of visual system

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In the primary visual cortex (V1), a response to a stimulus in the classical receptive field (CRF) is suppressively modulated by a stimulus presented in the CRF surround (SRF). We examined the temporal dynamics of the response to CRF stimulation and the surround suppression in terms of spatial-frequency (SF) tuning of cat V1 neurons using stationary flashes of a circular sinusoidal grating patch (duration, 500ms) and an annulus (50ms) as CRF and SRF stimuli. In Experiment 1 (N=39), we stimulated CRF with grating patch of optimal orientation and varying SFs. The preferred SF shifted from low to high along time course of response. In Experiment 2 (N=48), CRF was stimulated with grating of optimal orientation and SF, while SRF was stimulated with grating of optimal orientation and varying SF sandstimulus-onset-asynchrony (SOA). SF tuning of surround suppression changed along time course of response, and effective SF of surround suppression shifted from the SF lower than that of CRF stimulus (CRF-SF) to that near CRF-SF. By changing SOA, we examined surround suppression on different temporal phases of CRF response. SRF stimulus only with low SF (<0.2c/deg) suppressed the initial phase of CRF response. These results suggest that multiple mechanisms with different SF- and temporal characteristics are involved in the surround suppression.