Effects of Stimulus Phase on the Normal Auditory Brainstem Response

Abstract

The purpose of this investigation was to determine the effects of stimulus phase on the latencies and morphology of the auditory brainstem response (ABR) of normal-hearing subjects. Although click stimuli produced equivalent ABR latencies for the rarefaction and condensation phases, the subtraction of the waveforms from the two phases yielded a difference potential. Tone pip stimuli produced polarity differences that were inversely related to stimulus frequency: the higher the frequency, the smaller the ABR latency differences between responses to rarefaction and condensation stimuli, and the smaller the difference potentials. Thus, whereas the latency of click-evoked ABR is dominated by high-frequency responses with equivalent latencies regardless of stimulus phase, low-frequency responses contribute to the overall morphology of the ABR that yields the phasic difference potential. The implications of these findings are discussed with reference to subjects with high-frequency hearing losses.