Effects of rise-fall time and repetition rate on the auditory brainstem response to 0.5 and 1 kHz tone bursts using normal-hearing and hearing-impaired subjects.

This study was designed to compare normal-hearing and hearing-impaired auditory brainstem response (ABR) thresholds using 1 msec rise-plateau-fall times with ABR thresholds using two-cycle rise-fall times and a one-cycle plateau. Because tone bursts of 500 Hz and 1000 Hz were selected for study, the respective two-cycle rise-fall times were 4 msec and 2 msec. This study also compared ABRs using repetition rates of 25.6/sec and 40/sec to determine if these two rates yield different ABR thresholds. Sixteen normal-hearing subjects and 13 subjects with mild-to-moderate sensorineural hearing loss participated in this study. The results revealed that increasing rise-fall time from 1 msec to 4 msec at 500 Hz, and from 1 msec to 2 msec at 1000 Hz, had little or no effect on the ABR threshold. Moreover, no differences in ABR thresholds were observed for the two repetition rates. Thus, these data suggest that differences in repetition rate do not account for the discrepancies in thresholds among studies. The predication of pure-tone thresholds in dB HL from ABR thresholds in dB nHL was assessed using correction factor and regression procedures. Both methods yielded a reasonable approximation of the degree and configuration of hearing loss. Approximately 85% of pure-tone thresholds were predicted within +/- 10 dB at 500 Hz and 1000 Hz. The present investigation suggests that either the 1 msec or 2-cycle-rise-fall times may be used for clinical purposes.