Middle-latency and 40-Hz auditory evoked responses in normal-hearing subjects: click and 500-Hz thresholds.

Click and 500-Hz tone-burst thresholds were determined by four independent judges from sequentially recorded auditory brain stem responses--middle-latency responses (ABR-MLR)--and from 40-Hz event-related potentials (ERP) in 10 normal-hearing subjects. The thresholds determined from the two electrophysiologic methods were compared to each other and to behavioral pure-tone thresholds by means of matched-pair t tests (alpha less than or equal to .016 for each comparison). Thresholds estimated from both techniques closely approximated behavioral audiometric thresholds. The general trend was for the 40-Hz ERP thresholds to be lower than the MLR thresholds. However, the statistical analysis indicated that the differences between the two electrophysiologic thresholds and pure-tone audiometric thresholds were not significant. At threshold, the amplitudes of the 40-Hz ERPs were almost twice as large as the MLR amplitudes for clicks and only slightly larger than the MLR amplitudes for the 500-Hz tone-bursts. It was concluded that the MLR and the 40-Hz ERP techniques are equally viable procedures for threshold estimation in adults.