Date of Degree


Document Type

Capstone Project

Degree Name





John Preece

Subject Categories

Speech and Hearing Science | Speech Pathology and Audiology


otoacoustic emissions, medial olivocochlear, suppression, speech in noise, corticofugal, efferent, MOC


This systematic review analyzed the research concerning the medial olivocochlear reflex (MOCR) and speech-in-noise abilities in normal hearing adult listeners. In an attempt to understand the underlying difficulties in this population, the following research questions were proposed: 1) Does the research indicate that the magnitude of MOC suppression measured via OAEs is related to a normal hearing subject’s ability to recognize speech-in-noise? 2) Are MOC effects measured via OAEs lateralized? Is there a right ear advantage as suggested by Khalfa, Morlet, Micheyl, Morgon & Collet (1997)? Ten studies met the standards for inclusion for this review. Analysis of the research revealed some involvement of the MOCR in speech-in-noise abilities. However, the studies were mixed in their findings. Several studies did not find substantial correlations while others found significant favorable correlations. Interestingly, all of the studies that utilized speech-in-noise tests with words as the target stimuli found better speech recognition performance with increased MOC activity. In regards to laterality, the studies did not all point to a clear right ear advantage. The variability of the findings does not dampen the promise of potential clinical applications. Instead, they lay the groundwork for future controlled experiments that can confirm the involvement of MOCR in the discrimination of speech in the presence of background noise.