Ipsilateral suppression of transient evoked otoacoustic emission: role of the medial olivocochlear system.

Contralateral sound stimulation produces suppression of transient evoked otoacoustic emission (TEOAE), which is attributed to a reflex activation of the medial olivocochlear system. More pronounced suppression of TEOAE produced by ipsilateral masking could involve efferent-mediated effects along with effects of cochlear origin. However, this has not been investigated so far. Therefore, changes of click-evoked OAE under ipsi- and contralateral forward masking by clicks and noise-bursts were investigated in an extremely long-lasting experiment in one normal-hearing volunteer. The reduction of TEOAE under ipsilateral click-to-click forward masking was maximal during the first milliseconds after masker delivery implying that predominant role of the cochlear processes in TEOAE ipsilateral suppression. Ipsilateral forward masking by noise burst revealed additional TEOAE suppression with longer latency. Its time course was similar to that of the contralateral masking effect. The latter data suggest the involvement of the medial olivocochlear system in TEOAE ipsilateral suppression.