Adaptation of the auditory brainstem response: effects of click intensity, polarity, and position.

The aim of this research was to study the effects of several stimulus parameters on adaptation characteristics of the auditory brainstem response (ABR). Recordings were obtained from normal hearing adults to separate trains of 5 rarefaction and 5 condensation clicks with interclick intervals of 10 msec and intertrain intervals of 500 msec at three intensities. Absolute latencies for waves I, III, and V were essentially unchanged by polarity; latency shifts, however, were induced by parametric manipulations of click intensity, polarity, and position in the train. Furthermore, variations in ABR wave morphology appeared with changes in intensity and polarity. Adaptation, as measured by amplitude, was considerable; the measures of adaptation, however, were not related in a simple manner to the latency shifts. The findings indicate that adaptation of the ABR is a consequence of an interplay of central and peripheral processes to click polarity, sequence, and intensity. Finally, the results provide evidence that when fast stimulus presentation rates are used to estimate thresholds rapidly, one must be aware that certain stimulus parameters can alter the ABR waveforms.