Stimulus Frequency Otoacoustic Emissions Provide No Evidence for the Role of Efferents in the Enhancement Effect

Abstract

Auditory enhancement refers to the perceptual phenomenon that a target sound is heard out more readily from a background sound if the background is presented alone first. Here we used stimulus-frequency otoacoustic emissions (SFOAEs) to test the hypothesis that activation of the medial olivocochlear efferent system contributes to auditory enhancement effects. The SFOAEs were used as a tool to measure changes in cochlear responses to a target component and the neighboring components of a multitone background between conditions producing enhancement and conditions producing no enhancement. In the "enhancement" condition, the target and multitone background were preceded by a precursor stimulus with a spectral notch around the signal frequency; in the control (no-enhancement) condition, the target and multitone background were presented without the precursor. In an experiment using a wideband multitone stimulus known to produce significant psychophysical enhancement effects, SFOAEs showed no changes consistent with enhancement, but some aspects of the results indicated possible contamination of the SFOAE magnitudes by the activation of the middle-ear-muscle reflex. The same SFOAE measurements performed using narrower-band stimuli at lower sound levels also showed no SFOAE changes consistent with either absolute or relative enhancement despite robust psychophysical enhancement effects observed in the same listeners with the same stimuli. The results suggest that cochlear efferent control does not play a significant role in auditory enhancement effects.

Olivocochlear Efferents in Animals and Humans: From Anatomy to Clinical Relevance

“…The most recent studies, however, provide compelling evidence that overshoot is unrelated with an MOC-related reduction in cochlear gain and undermine the link between overshoot and MOC efferents [( 137 , 147 , 148 ); see also Ref. ( 149 )].…”

Auditory Enhancement in Cochlear-Implant Users Under Simultaneous and Forward Masking

“…Such a mechanism could potentially produce inhibition that adapts over time. However, direct tests of the role of the efferent system or other low-level contributors have not provided strong evidence so far (Carcagno et al 2014;Beim et al 2015).…”

Auditory enhancement under simultaneous masking in normal-hearing and hearing-impaired listeners

“…On the other hand, efferent effects (Guinan, 2006) could potentially contribute to changing cochlear responses with the appropriate time constants. Evidence against a peripheral locus for enhancement effects comes from a study in humans that failed to find correlates of enhancement in the human cochlea via otoacoustic emissions (Beim et al, 2015) and from a study in the cat auditory nerve (Palmer et al, 1995) that found evidence for adaptation but not absolute enhancement. However, neither study can be said to unequivocally rule out cochlear or auditorynerve contributions to enhancement.…”

“…However, neither study can be said to unequivocally rule out cochlear or auditorynerve contributions to enhancement. In the human study (Beim et al, 2015), otoacoustic emissions were measured under passive conditions; it is possible that different results might have been obtained if the participants had been simultaneously performing an active detection task, if one assumes that attention-based efferent activation plays a role. In the case of the auditory-nerve study of Palmer et al (1995), the cats were anethsetized, again potentially limiting any role of the efferent system.…”