Auditory brainstem response (ABR) peak amplitude variability reflects individual differences in cochlear response times.

Previously, it was shown [Don et al., J. Acoust. Soc. Am. 94, 2135-2148 (1993)] that cochlear response times are gender specific and about 13% shorter in females than in males. It is also suggested that one of the possible reasons click-evoked auditory brainstem response (ABR) waveforms recorded from females are better defined and have larger amplitudes than those of males is due to a sex difference in cochlear response times leading to better synchronization of the cochlear output across the frequency regions. Variability in cochlear response times would also lead to variability in click evoked ABR amplitudes. The high-pass noise masking derived ABR technique was used to investigate the effect of normalizing the individual temporal variability at the neural and cochlear levels. This involved adjusting for differences in neural conduction time (I-V delay) by a compression or expansion of the derived ABR waveforms and by adjusting for differences in cochlear response times by a shift of the derived ABR waveforms. A summation of the compressed and shifted ABRs results in a normalized unmasked ABR waveform that can then be compared for amplitude variability with the unprocessed unmasked ABRs. Compensation for the neutral I-V variability had little effect while compensation for cochlear response times, particularly the delay between the 5.7- and 2.8-kHz regions, greatly affected the amplitude of wave V of the compounded ABR. This work provides a better understanding of the significant relationship between cochlear response times and variability of the ABR peak amplitudes.