A visual evoked potential study of metacontrast masking

In a comparison of the subjective appearance of, and the scalp-recorded potentials evoked by, the first of two successively presented patterns of spatially adjacent elements, we recorded typical U-shaped metacontrast masking functions but found no discernible modification of either of the two initial VEP components, C1 and C2. These results, together with the previously established properties of C1 and C2, suggest that the early stages of contour-specific processing in the visual cortex have relatively short response latencies and durations and are uninfluenced by the subsequent presentation of metacontrast masking stimuli. The VEP data would thus appear to conflict with the basic assumptions of inhibition theories of metacontrast.