Early Components of Averaged Evoked Responses to Rapidly Repeated Auditory Stimuli

Abstract

Averaged evoked responses to clicks were elicited from 20 normal-hearing subjects between the ages of 16 and 41. Two thousand clicks were presented to the right ear at the rate of 10 per sec at 60, 30, 10, 5, 0, −5, and −10 dB SL. Sensation levels were varied randomly. In each series two control conditions without stimulation were randomly interspersed. Electroencephalic potentials were recorded from an electrode on the vertex of the skull referred to the left earlobe. The response pattern was relatively consistent with a vertex-negative peak (N a ) at about 20–24 msec, and a vertex-positive peak (P a ) at about 31–35 msec. Another vertex-negative peak (N b ) at about 46–50 msec was seen less frequently. Criteria for response were established on the basis of the occurrence of N a and P a within prescribed latencies as well as the interval between the two peaks of about 12–13 msec. The number of identifiable responses diminished with diminishing sensation levels but responses were observed in about one-half of the subjects as low as −5 dB SL.