What is the role of the medial olivocochlear system in speech-in-noise processing?

J Neurophysiol. 2012 Mar;107(5):1301-12. doi: 10.1152/jn.00222.2011. Epub 2011 Dec 7.

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustic Stimulation / methods*
  • Adult
  • Cochlea / physiology*
  • Evoked Potentials, Auditory, Brain Stem / physiology
  • Female
  • Humans
  • Male
  • Noise*
  • Olivary Nucleus / physiology*
  • Reaction Time / physiology
  • Speech / physiology
  • Speech Perception / physiology*
  • Young Adult