[Mechanism of directional selectivity of neurons with complex receptive fields in the visual cortex of the cat]

Spatio-temporal interactions within complex receptive fields were investigated in the visual cortex of a cat by means of sequential presentation of two stationary stimuli. When two stimuli were presented in the phase (on-on or off-off) and sequential presentation corresponded to preferred movement direction, the response to second stimulus was enhanced (or less inhibited). When sequential presentation corresponded to opposite movement direction, the response was inhibited. Sequential presentation of two stimuli with opposite phase (on-off or off-on) in preferred direction inhibited the response to the second stimulus, but in nonpreferred direction the response was enhanced (or less inhibited). The strength of interactions depended on distance between stimuli presented in the receptive field and interstimulus time interval. It is concluded that direction selectivity is provided by asymmetry of spatio-temporal interactions between on-inputs and between off-inputs. Interactions between on- and off-inputs, which occur in case of multiedge stimulus movement may be used by the visual system for detecting an object from visual environment, for estimating object size and relative movement velocity.