title: What is the role of the medial olivocochlear system in speech-in-noise processing?
abstract: The medial olivocochlear (MOC) bundle reduces the gain of the cochlear amplifier through reflexive activation by sound. Physiological results indicate that MOC-induced reduction in cochlear gain can enhance the response to signals when presented in masking noise. Some previous studies suggest that this "antimasking" effect of the MOC system plays a role in speech-in-noise perception. The present study set out to reinvestigate this hypothesis by correlating measures of MOC activity and speech-in-noise processing across a group of normal-hearing participants. MOC activity was measured using contralateral suppression of otoacoustic emissions (OAEs), and speech-in-noise processing was measured by measuring the effect of noise masking on performance in a consonant-vowel (CV) discrimination task and on auditory brain stem responses evoked by a CV syllable. Whereas there was a significant correlation between OAE suppression and both measures of speech-in-noise processing, the direction of this correlation was opposite to that predicted by the antimasking hypothesis, in that individuals with stronger OAE suppression tended to show greater noise-masking effects on CV processing. The current results indicate that reflexive MOC activation is not always beneficial to speech-in-noise processing. We propose an alternative to the antimasking hypothesis, whereby the MOC system benefits speech-in-noise processing through dynamic (e.g., attention- and experience-dependent), rather than reflexive, control of cochlear gain.
authors.affiliation: MRC Institute of Hearing Research, Univ. Park, Nottingham, UK. jdb@ihr.mrc.ac.uk
authors.forename: Jessica
authors.initials: J
authors.lastname: de Boer
authors.forename: A Roger D
authors.initials: AR
authors.lastname: Thornton
authors.forename: Katrin
authors.initials: K
authors.lastname: Krumbholz
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods*; D000328:Adult; D003051:Cochlea / Q000502:physiology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009622:Noise; D009847:Olivary Nucleus / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013060:Speech / Q000502:physiology; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult