The effects of broadband elicitor duration on transient-evoked otoacoustic emissions and a psychoacoustic measure of gain reduction.

PURPOSE

Measures of the human medial olivocochlear reflex (MOCR) typically rely on long duration (>100 ms) or continuously presented broadband elicitors. MOCR gain reduction measured by otoacoustic emissions (OAE) exhibits multiple time constants, including in the hundreds of milliseconds, when elicited by broadband noise. Psychoacoustic studies of gain reduction have largely adopted these elicitor characteristics, but less is known about how broadband elicitor duration affects auditory perception. Additionally, the literature on the relationship between psychoacoustic and OAE measures of gain reduction has yielded mixed results, which is counterintuitive if both measures reflect the same mechanism. In this study, the effects of ipsilateral broadband elicitor duration were evaluated using forward masking psychoacoustic and transient-evoked OAE (TEOAE) paradigms in individuals with normal hearing.

METHODS

Ipsilateral pink broadband noise was used as the elicitor in both experiments, presented at 50 dB SPL (50-800 ms) for the psychoacoustic measures and 50 dB FPL (50-400 ms) for the TEOAE measures. Gain reduction was quantified as the change in signal threshold (2 kHz) and the change in TEOAE level (1/3-octave band centered at 2 kHz) with and without the presence of the elicitor.

RESULTS

The average time constants for psychoacoustic and TEOAE gain reduction were similarly short (<100 ms), with near-maximal effects observed for elicitor durations of 200 ms. However, individual comparisons of TEOAE and psychoacoustic gain reduction revealed mixed results. Potential factors contributing to this discrepancy are discussed.

CONCLUSION

The human MOCR reduces cochlear gain on relatively short time scales (<100 ms) with ipsilateral broadband elicitors.