EFFECTS OF CLICK POLARITY ON THE AUDITORY BRAIN-STEM RESPONSES OF OLDER MEN

This study was designed to evaluate the effects of stimulus polarity o n the auditory brainstem responses (ABRs) in the older population. Nin e men between the ages of 40 and 69 years participated in the study. R arefaction and condensation clicks were delivered at 70 and 80 dB nHL to elicit the ABRs. The latencies were significantly earlier for raref action clicks for components II and V. The inter-peak interval I-II wa s significantly shorter for rarefaction clicks than for condensation c licks. 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 observ ed with rarefaction clicks yielding a significant polarity-intensity i nteraction. The IV-V/I ratio elicited by rarefaction clicks was larger than that produced by condensation clicks at 80 dB nHL, but it was mu ch larger for rarefaction clicks at 70 dB nHL resulting in a significa nt polarity-intensity interaction. The waveform morphology also change d with click polarity, with the most prominent effects apparent on com ponents II and IV. A new hypothesis suggesting separate generators for ABRs recorded in response to the two click polarities is proposed. Us e of both condensation and rarefaction clicks is recommended in record ing ABRs for clinical use.