SUMMARY1. The spatial and temporal frequency selectivity of 148 neurones in the striate cortex, VI, and of 122 neurones in the second 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.2. Neurones in VI and V2 were selective for different but partially overlapping ranges of the spatial frequency spectrum. At retinal eccentricities of 2-5 deg from the fovea, the spatial frequency preferences for neurones ranged from 0 5 to 8-0 cycles/deg in VI and from 0-2 to 2-1 cycles/deg in V2 and were on average almost 2 octaves lower in V2 than in VI. Spatial frequency full band widths in the two cortical areas were in the range 0 8-3 0 octaves, with a mean value of 1-8 octaves, in the parafoveal representation of both VI and V2, and 1-4 and 1-6 octaves respectively in the foveal representation of VI and V2.3. Most neurones in VI 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 VI, 68 % ofthe neurones exhibited low-pass temporal tuning characteristics and 32 % were very broadly tuned, with a mean temporal frequency full band width of 2-9 octaves.However, in V2 only 30 % of the neurones showed low-pass temporal selectivity and 70 % of the cells had bandpass temporal characteristics, with a mean full band width of 2-1 octaves. In V2 the minimal overlap of bandpass tuning curves across the temporal frequency spectrum suggests that there are at least two distinct bandpass temporal frequency mechanisms as well as neurones with low-pass temporal frequency tuning at each spatial frequency. K. H. FOSTER AND OTHERS 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. 5. Neurones 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 neurones which were selective for lower spatial frequencies and higher temporal frequencies.6. These results indicate that neurones in VI and V2 span partially overlapping but essentially different ranges of the spatial frequency spectrum yet have similar spatial frequency band widths, whereas neurones in VI and V2 span similar ranges of the temporal frequency spectrum but have different temporal frequency bandpass characteristics. Taken together, neurones in VI and V2 analyse spatially localized subdomains of the visual scene across an extended range of both the spatial frequency and temporal frequency spectrum.

Recurrent projections comprise a universal feature of cerebral organization. Here, we show that the corticofugal projections from the striate cortex (VI) to the lateral geniculate nucleus (LGN) robustly and multiplicatively enhance the responses of parvocellular neurons, stimulated by gratings restricted to the classical receptive field and modulated in luminance, by over two-fold in a contrast-independent manner at all but the lowest contrasts. In the equiluminant plane, wherein stimuli are modulated in chromaticity with luminance held constant, such enhancement is strongly contrast dependent. These projections also robustly enhance the responses of magnocellular neurons but contrast independently only at high contrasts. Thus, these results have broad functional significance at both network and neuronal levels by providing the experimental basis and quantitative constraints for a wide range of models on recurrent projections and the control of contrast gain.

White noise stimuli were used to estimate second-order kernels for complex cells in cortical area VI of the macaque monkey, and drifting grating stimuli were presented to the same sample of neurons to obtain orientation and spatial-frequency tuning curves. Using these data, we quantified how well second-order kernels predict the normalized tuning of the average response of complex cells to drifting gratings.The estimated second-order kernel of each complex cell was transformed into an interaction function defined over all spatial and temporal lags without regard to absolute position or delay. The Fourier transform of each interaction function was then computed to obtain an interaction spectrum. For a cell that is well modeled by a second-order system, the cell’s interaction spectrum is proportional to the tuning of its average spike rate to drifting gratings. This result was used to obtain spatial-frequency and orientation tuning predictions for each cell based on its second-order kernel. From the spatial-frequency and orientation tuning curves, we computed peaks and bandwidths, and an index for directional selectivity.We found that the predictions derived from second-order kernels provide an accurate description of the change in the average spike rate of complex cells to single drifting sine–wave gratings. These findings are consistent with a model for complex cells that has a quadratic spectral energy operator at its core but are inconsistent with a spectral amplitude model.

Tests of 3D motion perception are the best predictor of EB, while DVA velocity susceptibility is the best predictor of hazard perception. Motion perception training appears to result in faster braking responses.