Spatial and temporal frequency selectivity of neurones in visual cortical areas V1 and V2 of the macaque monkey.

Abstract

The spatial and temporal frequency selectivity of 148 neurons in the striate cortex, V1, and of 122 neurons in the 2nd visual cortical area, V2, of the macaque monkey were studied using sine-wave gratings of suprathreshold contrast drifting over the receptive field at the preferred orientation and direction. Neurons in V1 and V2 were selective for different but partially overlapping ranges of the spatial frequency spectrum. Most neurons in V1 and some in V2 responded well at temporal frequencies up to 5.6-8.0 Hz before their responses dropped off at still higher frequencies. In V2 the minimal overlap of bandpass tuning curves across the temporal frequency spectrum suggests that there are at least 2 distinct bandpass temporal frequency mechanisms as well as neurons with low-pass temporal frequency tuning at each spatial frequency. A matrix of spatial and temporal frequency combinations was employed as stimuli for neurons with bandpass temporal frequency selectivity in both V1 and V2. The resultant spatio-temporal surfaces provided evidence that a neuron''s preference for spatial frequency is essentially independent of the test temporal frequency; however, in V2 there was some tendency for temporal frequency peaks to shift slightly towards lower frequencies when non-optimum values of spatial frequency either above or below the preferred value were tested. Neurons with pronounced directional selectivity were encountered over a wide range of spatial frequencies, although in both cortical areas there was a tendency for an increased incidence of directional selectivity among neurons which were selective for lower spatial frequencies and higher temporal frequencies. Neurons in V1 and V2 span partially overlapping but essentially different ranges of the spatial frequency spectrum yet have similar spatial frequency band widths, whereas neurons in V1 and V2 span similar ranges of the temporal frequency spectrum but have different temporal frequency bandpass characteristics. Neurons in V1 and V2 analyse partially localized subdomains of the visual scene across an extended range of both the spatial frequency and temporal frequency spectrum.