title: The MOC reflex during active listening to speech.
abstract: OBJECTIVE
  The purpose of this study was to test the hypothesis that active listening to speech would increase medial olivocochlear (MOC) efferent activity for the right vs. the left ear.
  
  
  METHODS
  Click-evoked otoacoustic emissions (CEOAEs) were evoked by 60-dB p.e. SPL clicks in 13 normally hearing adults in 4 test conditions for each ear: (a) in quiet; (b) with 60-dB SPL contralateral broadband noise; (c) with words embedded (at -3-dB signal-to-noise ratio [SNR]) in 60-dB SPL contralateral noise during which listeners directed attention to the words; and (d) for the same SNR as in the 3rd condition, with words played backwards.
  
  
  RESULTS
  There was greater suppression during active listening compared with passive listening that was apparent in the latency range of 6- to 18-ms poststimulus onset. Ear differences in CEOAE amplitude were observed in all conditions, with right-ear amplitudes larger than those for the left. The absolute difference between CEOAE amplitude in quiet and with contralateral noise, a metric of suppression, was equivalent for right and left ears. When the amplitude differences were normalized, suppression was greater for noise presented to the right and the effect measured for a probe in the left ear.
  
  
  CONCLUSIONS
  The findings support the theory that cortical mechanisms involved in listening to speech affect cochlear function through the MOC efferent system.
authors.affiliation: University of Arizona, Tucson, AZ, USA. agarinis@u.washington.edu
authors.forename: Angela C
authors.initials: AC
authors.lastname: Garinis
authors.forename: Theodore
authors.initials: T
authors.lastname: Glattke
authors.forename: Barbara K
authors.initials: BK
authors.lastname: Cone
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology; D001306:Auditory Pathways / Q000502:physiology; D003051:Cochlea / Q000502:physiology*; D004525:Efferent Pathways / Q000502:physiology; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D006801:Humans; D009847:Olivary Nucleus / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D012018:Reflex; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult