Effects of click-polarity on ABR parameters in the older population.

This study was designed to evaluate the effects of stimulus polarity on the auditory brainstem responses (ABRs) in the older population. Nine men between the ages of 40 and 69 years participated in the study. Rarefaction and condensation clicks were delivered at 70 and 80 dB nHL to elicit the ABRs. The latencies were significantly earlier for rarefaction clicks for components II and V. The inter-peak interval I-II was significantly shorter for rarefaction clicks than for condensation clicks. The amplitudes of the IV-V complex did not change with stimulus polarity at 80 dB nHL, but at 70 dB nHL larger amplitudes were observed with rarefaction clicks yielding a significant polarity-intensity interaction. The IV-V/I ratio elicited by rarefaction clicks was larger than that produced by condensation clicks at 80 dB nHL, but it was much larger for rarefaction clicks at 70 dB nHL resulting in a significant polarity-intensity interaction. The waveform morphology also changed with click polarity, with the most prominent effects apparent on components II and IV. A new hypothesis suggesting separate generators for ABRs recorded in response to the two click polarities is proposed. Use of both condensation and rarefaction clicks is recommended in recording ABRs for clinical use.