Effect of Human Auditory Efferent Feedback on Cochlear Gain and Compression

Abstract

The mammalianauditorysystemincludesabrainstem-mediatedefferentpathwayfromthesuperiorolivarycomplexbywayofthemedialolivocochlear system,whichreducesthecochlearresponsetosound (WarrandGuinan,1979;Libermanetal.,1996).Thehumanmedialolivocochlearresponsehasan onsetdelayofbetween25and40msandriseanddecayconstantsintheregionof280and160ms,respectively(BackusandGuinan,2006).Physiological studies with nonhuman mammals indicate that onset and decay characteristics of efferent activation are dependent on the temporal and level characteristics of the auditory stimulus (Bacon and Smith, 1991; Guinan and Stankovic, 1996). This study uses a novel psychoacoustical masking technique usingaprecursorsoundtoobtainameasureoftheefferenteffectinhumans.Thistechniqueavoidsconfoundscurrentlyassociatedwithotherpsychoacousticalmeasures.Bothtemporalandleveldependencyoftheefferenteffectwasmeasured,providingacomprehensivemeasureoftheeffectofhuman auditoryefferentsoncochleargainandcompression.Resultsindicatethataprecursor(Ͼ20dBSPL)inducedefferentactivation,resultinginadecrease in both maximum gain and maximum compression, with linearization of the compressive function for input sound levels between 50 and 70 dB SPL. Estimatedgaindecreasedasprecursorlevelincreased,andincreasedasthesilentintervalbetweentheprecursorandcombinedmasker-signalstimulus increased, consistent with a decay of the efferent effect. Human auditory efferent activation linearizes the cochlear response for mid-level sounds while reducing maximum gain.

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…Estimates of cochlear gain were calculated as the difference in masker threshold between the 2-kHz and 1.2-kHz short maskers (Yasin et al 2014). Gain was determined separately for each signal level.…”

“…The 2.4-kHz masker frequency was chosen because it has produced substantial suppression of a 2-kHz masker in previous studies with young adults (Shannon 1976;Sommers and Gehr 2010). Gain was estimated as the difference in threshold between the on-frequency masker and the 1.2-kHz masker (Yasin et al 2014). For experiment 2, suppression was measured by presenting a short or long, 1.2-or 2.4-kHz suppressor simultaneously with the on-frequency masker and just …”

Aging Effects on Behavioural Estimates of Suppression with Short Suppressors

“…In Experiment 1, older adults were found to have less gain than younger adults, measured as the difference in on-frequency and off-frequency masker threshold for a fixed signal level (Yasin et al 2014). The off-frequency, 1.2-kHz masker is understood to have a linear BM response at the signal frequency place, and the on-frequency, 2-kHz masker and signal have a compressive BM response at the signal frequency place (Oxenham and Plack 2000).…”

“…The 2.4-kHz masker frequency was chosen because it has produced substantial suppression of a 2-kHz masker in previous studies with young adults (Shannon 1976;Sommers and Gehr 2010). Gain was estimated as the difference in threshold between the on-frequency masker and the 1.2-kHz masker (Yasin et al 2014). For experiment 2, suppression was measured by presenting a short or long, 1.2-or 2.4-kHz suppressor simultaneously with the on-frequency masker and just prior to presentation of the 10-ms, 2-kHz signal.…”

Frequency Tuning of the Efferent Effect on Cochlear Gain in Humans

“…The experiment consisted of two phases (Yasin et al 2014). In phase 1, for each listener, signal level at threshold was measured per precursor frequency in the presence of a precursor and absence of any tonal masker, to take the forward masking of the precursor into account.…”