On the use of click-evoked electric brainstem responses in audiological diagnosis. I. The variability of the normal response.

The normal click-evoked BSER was studied in a total of 28 young (aged 12 to 40) normally hearing subjects in regard to wave latencies and amplitude ratios, considered to be (besides wave replicability) the characteristics of major interest from a clinical point of view. Latency means and standard deviations (S.D.), and peak-to-peak amplitude ratios between wave V on the one hand and wave I and III, respectively, on the other were determined in a sample of 20 subjects using unfiltered clicks at 20 to 90 dB SL. The latency averages were compared with those of other reports. Latency S.D.s were found to be generally less than 0.25 ms at levels above 50 dB SL. Medians of amplitude ratios (AV/AI and AV/AIII) were found to be significantly greater than unity. No significant latency differences concerning waves I, III, and V could be established on stimulation with condensation, rarefaction, and alternating clicks in 10 subjects at 80 and 60 dB SL, nor did the peak-to-peak amplitude predominance of wave V change with click polarity. With half-octave filtered clicks (2 and 4 kHz), latencies were found to increase significantly (and the responses to become less precise) at 80 and 60 dB SL in a sample of 12 subjects. Changing the interstimulus interval (ISI) from 80 to 60 to 40 ms (at 80 and 60 dB SL) hardly made any difference in regard to I, III, and V latencies, or wave V amplitude supremacy. Finally, a satisfactory test-retest reliability was established in a sample of 6 subjects, the intersession interval being 6 months.