The Effect of Test Conditions on the Early Components of the Averaged Electroencephalic Response

Abstract

The effect of test conditions on the early components of the averaged electroencephalic response was examined in 12 normal hearing subjects between the ages of 21 and 43. Clicks at 50 dB SL were presented to the right ear at the rate of 9.6/sec while the subject was (1) sitting in the dark with eyes closed, (2) sitting quietly in the light with eyes open, and (3) reading. Order of presentation was counter-balanced with each condition repeated three times. 1024 clicks were used in obtaining each of the nine averaged responses. Electroencephalic activity was recorded from an electrode on the vertex referred to the left earlobe. The polyphasic response pattern was relatively consistent, characterized by a configuration with mean peak latencies of (N _o ) 7.6 msec, (P _o ) 16.5 msec, (N _a ) 26.9 msec, (P _a ) 40.6 msec, and (N _b ) 54.0 msec. No significant differences occurred in either latency or amplitude of the response with the different test conditions. Latency and amplitude of the response did not differ as a function of order, although the first response was usually larger than the mean of the remaining eight.