Contralateral suppression of evoked otoacoustic emissions and detection of a multi-tone complex in noise.

Although some findings suggest that auditory efferent fibers are involved in perception in noise, their function remains controversial. The contralateral suppression of evoked otoacoustic emissions (EOAEs) has recently provided a means of exploring the medial olivocochlear system (MOCS) in humans. In an experiment based on this paradigm, the present study examined the relationships between variations of both EOAEs and detection-in-noise thresholds, induced in the same subjects by a contralateral 50-dB-SPL broad-band noise masker. EOAEs were recorded in response to a burst of a multitone complex composed of 1, 1.5 and 2-kHz components. The detection thresholds of this 3-component complex were measured at 2 ipsilateral noise levels: 50 and 70 dB SPL. The main finding was a significant correlation between EOAE suppression and threshold variations under contralateral masking. A relationship was also found between the contralateral suppression of EOAEs and threshold variation induced by the increase in ipsilateral noise level. These findings support the notion that the MOCS is involved in the detection of multicomponent stimuli in noise.