Relationship between auditory intensity discrimination in noise and olivocochlear efferent system activity in humans.

Recent physiological data in animals suggest a role of the medial olivocochlear system (MOCS) in auditory intensity discrimination in noise. In this study, the existence of statistical relationships between intensity difference limens (IDLs) and MOCS functioning was tested in humans. IDLs were measured in conditions of quiet and of ipsilateral, contralateral, and dichotic noise. MOCS functioning was assessed through the contralateral evoked otoacoustic emission (EOAE) amplitude attenuation effect. A first finding was that IDLs measured in the presence of ipsilateral noise were reduced when contralateral noise was added. Furthermore, the observed shift in IDL appeared to be significantly correlated to the contralateral EOAE amplitude attenuation effect. These results support the hypothesis that MOCS functioning plays a role in intensity discrimination in dichotic noise in humans.