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.

Psychophysical auditory filter estimates reveal sharper cochlear tuning in musicians

“…24 These studies provide evidence for music-induced plasticity at initial stages of auditory sensory processing mediated by strengthened "top-down" feedback from the caudal brainstem to the cochlea. While the functional role of the MOC in human hearing is still debated, 22 it is speculated that it may provide an "antimasking" effect, helping to improve signal detection in noise 25 and/or discrimination sensitivity. 22 Musicians excel at both of these skills.…”

Loudness Context Effects in Normal-Hearing Listeners and Cochlear-Implant Users

“…As a result, investigating LCE in CI users may provide us with important information about the potential underlying mechanisms. Some researchers have suggested that the cochlear gain changes induced by the MOC efferent system may be important for speech perception in noise (e.g., Guinan 2010;Garinis et al 2011;Clark et al 2012;de Boer et al 2012;Mishra and Lutman 2014). Therefore, any differences in the results between normal-hearing listeners and CI users may provide guidance for future CI signal processing systems to restore normal context effects for auditory and speech perception.…”

Acoustic Stapedius Reflex Function in Man Revisited

“…Nevertheless, these methodological differences cannot account for all of the disparate findings. de Boer and Thornton (2008) found correlations between perceptual learning in a speech discrimination task and MOC inhibition, regardless of whether contralateral noise was present, but failed to find a similar correlation for a slightly different speech discrimination task in a later study (de Boer et al 2012), and Kumar and Vanaja (2004) found a benefit of MOC inhibition at an SNR of +10 dB and +15 dB, but an MOC-related deficit at SNRs of 0 dB and +20 dB. Therefore, benefits associated with MOC inhibition may be specific to particular tasks and spectral distributions of signals and maskers (Micheyl et al 1995;Micheyl & Collet 1996).…”

“…However, some studies have not found a relationship between MOC activity and speech-innoise perception (Harkrider & Smith 2005;Mukari & Mamat 2008;Wagner et al 2008), and negative effects of MOC activity have been reported for syllable discrimination in noise (de Boer et al 2012). Some of these differences might be attributable to differences in methodology.…”