The MOC reflex during active listening to speech

Area of Science:

• Auditory Neuroscience
• Neuroscience
• Otoacoustic Emissions

Background:

• The medial olivocochlear (MOC) efferent system modulates cochlear sensitivity.
• Understanding how cognitive processes like active listening influence MOC activity is crucial for auditory perception research.

Purpose of the Study:

• To investigate whether active listening to speech increases MOC efferent activity.
• To examine potential ear-specific differences in MOC efferent responses during speech perception.

Main Methods:

• Click-evoked otoacoustic emissions (CEOAEs) were measured in 13 adults under four conditions: quiet, contralateral noise, attended speech in noise, and backward speech in noise.
• CEOAEs were used as a measure of MOC efferent activity.
• Stimuli included 60-dB SPL clicks and 60-dB SPL contralateral broadband noise with embedded words at a -3-dB SNR.

Main Results:

• Active listening to speech demonstrated greater suppression of CEOAEs compared to passive listening, specifically between 6-18 ms post-stimulus.
• Right ear CEOAE amplitudes were consistently larger than left ear amplitudes.
• While overall suppression was similar, normalized suppression was greater for right-ear noise and left-ear probe effects.

Conclusions:

• Cortical mechanisms engaged during speech listening modulate cochlear function via the MOC efferent system.
• These findings support a link between cognitive auditory processing and efferent control of the cochlea.