Spatial and temporal contrast sensitivity of neurones in areas 17 and 18 of the cat's visual cortex.

Abstract

The spatial and temporal tuning properties of 238 cortical neurons were examined and recorded using conventional techniques from acutely prepared anesthetized cats. Spatial and temporal frequency tuning curves using sinusoidal grating stimuli presented to each neuron''s receptive field by a digital computer on a cathode ray tube was determined. Tuning curves were measured either by determining response amplitude as a function of spatial or temporal frequency, or by measuring contrast sensitivity (the inverse of the contrast of the grating that just elicited a detectable response). The 2 measures give very similar tuning curves in all cases. In area 17, 184 neurons were recorded; of these 156 had receptive fields within 5.degree. of the area centralis. In area 18, 54 neurons were recorded, and several experiments performed in which corresponding portions of both area 17 and area 18 were recorded in the same electrode penentration. Neurons in area 18 preferred spatial frequencies that were, on average 1/3 as high as those preferred by area 17 neurons at the same retinal eccentricity. Temporal frequency tuning characteristics were determined for some neurons from each area, using gratings that moved steadily across the screen. Neurons from area 17 all responded well to low temporal frequencies, and less well to higher frequencies (in excess of, usually, 2 or 4 Hz). In contrast, neurons recorded from area 18 sometimes had similar tuning properties, but more commonly showed a pronounced reduction in response as the temporal frequency was moved either above or below some optimum value (usually 2-8 Hz). Areas 17 and 18 act in parallel to process different aspects of the visual information relayed from the retina via the lateral geniculate complex. Some or all of the differences between the areas may be attributalbe to the predominance of Y cell input to area 18 and the predominance of X cell input to area 17. The 2 areas seem reasonable candidates for the pattern (area 17) and movement (area 18) detecting mechanisms whose existence was inferred from psychophysical experiments in both humans and cats.