Comparison of latencies of N1 and transient evoked otoacoustic emissions: An evaluation of reverse travel in the cochlea

Savithri Shyamla Narayan, Purdue University

Abstract

Transient evoked otoacoustic emissions (TEOAE) are delayed responses to short-duration frequency-specific stimuli that are measured in the ear canal after stimulus offset. This delay (latency) must stem, in part, from travel along the cochlear partition to the place of best frequency and back to the ear canal. If both the forward and reverse transmission of sound energy are along the cochlear partition, then the TEOAE latencies should be approximately twice that of an independently estimated forward travel time, obtained in this study from the N1 latency at 65 dB pe SPL. TEOAEs consisted of multiple bursts and each individual burst had approximately the same latency at all stimulus levels. Two response bursts were selected based on certain 'identifiable features', similar to those observed by Tanaka et al. (1990). The earlier of the two bursts had an approximately linear amplitude dependence on stimulus level while the later one saturated for levels above 55 pe dB SPL. The latency of the earlier burst was too short to account for travel along the cochlear partition and was, hence, taken as an indication that the first response to the stimulus occurs through the cochlear fluid. While the later burst could be detected in the ear canal signals for all individuals, the first burst was only detected for stimulus frequencies above 2 kHz and at the lower frequencies when the stimulus frequency was close to that of a click-evoked otoacoustic emission (CEOAE) for that individual. TEOAEs and N1 were also measured under aspirin administration. The elevation of N1 detection thresholds paralleled that of the behavioral thresholds. TEOAEs were measured on all three days of the aspirin schedule although the CEOAEs were eliminated within 36 hours. The occurrence of the first burst evoked with stimulus frequencies below 2 kHz reduced progressively with aspirin consumption while those evoked with a 3 kHz stimulus showed only a small elevation in detection threshold. The pattern of the response bursts for low frequency stimuli were more complicated than those observed during the pre- and post-aspirin sessions, and the earlier burst was also more vulnerable to salicylates.

Degree

Ph.D.

Advisors

Long, Purdue University.

Subject Area

Neurology|Acoustics|Psychology|Experiments

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