Abstract
In the primary visual cortex (V1), a neuronal response to stimulation of the classical receptive field (CRF) is suppressively modulated by the stimulus presented at the receptive field surround (SRF). This surround suppression is considered as a neuronal basis of perceptual figure-ground segregation. Using stationary flashes of sinusoidal grating as stimuli, we examined the dependency of surround suppression on the stimulus size (Exp. 1) and that on the orientation-contrast between CRF and SRF stimuli (Exp.2) in V1 neurons of anesthetized cats. In Exp.1, CRF was stimulated with a flash (500 ms) of the grating patch with optimal parameters and varying diameters. Temporal analysis of SRF effect demonstrated followings; 1) there were two groups of cells exhibiting different types of suppression in early component (0-80 ms) of response (fast suppression), that is, SRF diameter-independent (type I) and SRF diameter-dependent (type II) suppression, and 2) late component (100 ms <) of response was progressively suppressed with an increment of stimulus size (late suppression) in both type I and II cells. In Exp.2, CRF was stimulated with a flash (500 ms) of circular grating and SRF was stimulated with a flash (50 ms) of annular grating that was either iso- or cross-oriented to the CRF orientation. In type I cells, fast suppression is less orientation-specific, but both fast and late suppressions were orientation-specific in type II cells. There seems to be an interaction of functionally distinct pathways with different spatiotemporal properties for underlying mechanism of surround suppression. [J Physiol Sci. 2007;57 Suppl:S38]
