The human auditory brainstem response to high click rates: aging effects.

In 1999 J. Walton, M. Orlando, & R. Burkard (Hearing Research, 127, 86-94) investigated aging effects on auditory brainstem response (ABR) wave V latency using a tone-on-toneburst forward-masking paradigm. They found that at short forward-masking intervals, wave V latency shift was greater in normal-hearing older adults than in normal-hearing young adults for moderate level, high-frequency toneburst maskers and probes. It was not possible to evaluate wave I latency because stimulation and recording procedures did not produce a consistently observable wave I. In order to optimize the recording of wave I, the present study used a high-level (115 dB pSPL) click stimulus, combined with a tympanic membrane inverting electrode, and investigated the latencies and amplitudes of waves I and V across click rate. Young adults had hearing thresholds within normal limits, whereas older adults had normal hearing or mild threshold elevation. All data were collected and analyzed with a Nicolet Bravo. Using conventional recording procedures, ABRs were obtained at click rates of 11, 25, 50, and 75 Hz. Using maximum length sequences (MLSs), ABRs were obtained at 100, 200, 300, 400, and 500 Hz. Results across age groups were very similar. With increasing click rate, peak latencies increased, the I-V interval increased and peak amplitudes decreased. The most notable difference between age groups was that wave I amplitude was substantially smaller in the older subjects. It appears that changes in the ABR with increasing rate are remarkably similar in young and older adults when audiometric thresholds are normal or near-normal in both age groups.