Auditory efferents facilitate intensity change detection in humans: evidence from concurrent ear, brain, and behavior measures

Feedback mechanisms in the brain, such as the medial olivocochlear reflex (MOCR), can aid signal detection and discrimination in noise in animals. Extrapolating these findings in elementary perception to speech understanding in noise abilities in humans has been inconclusive. To investigate the functional role of the MOCR in elementary auditory perception in humans, we concurrently measured ear (otoacoustic emissions) and brain (N1-P2 acoustic change complex [ACC]) responses while participants performed a behavioral intensity change detection task. The intensity change was imposed on a triad of deviant clicks that occurred at early-, middle-, or late-temporal positions of a click train commensurate with null-, partial-, and full activation of the MOCR, respectively. We found faster behavioral detection and shorter ACC latencies for the middle- and late-occurring deviants relative to the early deviant. The improved behavioral detection of later-occurring deviants correlated significantly with the degree of MOCR activation and ACC latency. These mutual correlations suggest a direct involvement of the MOCR in human signal detection, underscored by earlier cortical detection. These novel findings advance our understanding of the mechanisms involved in speech perception in noise and aid in developing hearing assistive technologies.