The effects of direct sequential masking on evoked potentials in the auditory area of the cortex in guinea pigs.

Thresholds for the appearance of evoked potentials to clicks in test series were determined in the quiet and in conditions of sequential masking of one stationary and four moving sound images. Differences in the thresholds for the appearance of evoked responses to signals in the quiet and in the presence of the marker were taken as a measure of the extent of masking. The overall responses of the auditory area of the guinea pig cortex showed direct masking as a clear reduction in the magnitude of the response to the first click in the series as compared with the response in the quiet. The extent of masking decreased with increases in the time delay and was independent of the position of the sound image corresponding to this click in different test signals. This observation may provide indirect support for the hypothesis that the initial part of the signal is subject to greater masking than the final part. The magnitude of responses to subsequent clicks in series were determined by a combination of two factors--the action of the sequential masker in the "masker-signal" system and the interaction between the responses to individual clicks in the series making up the test signal.