Effect of prolonged contralateral acoustic stimulation on transient evoked otoacoustic emissions

Although the suppressive effect of the medial olivocochlear system (MOCS) on peripheral auditory active mechanisms is well documented in humans, the effect of efferent inhibition over prolonged periods of acoustic stimulation is less well documented, especially as observed by transient evoked otoacoustic emission (TEOAE) suppression. The present study evaluated the relationship between the duration of contralateral acoustic stimulation and the suppression of TEOAE in 10 normal-hearing adults. TEOAE recordings with linear clicks (60 dB SPL) were measured at four intervals during 15 min of continuous contralateral white noise (45 dB SL), followed by two post-noise recordings. An identical within-subject control condition was recorded without contralateral noise. Experimental and control measurements were repeated three times, on separate days. Results revealed significant and sustained TEOAE amplitude reduction for the entire duration of contralateral stimulation. Suppression increased gradually for the duration of contralateral noise presented, but not sufficiently to be statistically significant. Three minutes after noise termination, TEOAE amplitudes increased to values significantly above control recordings. The MOCS is able to sustain suppression over a prolonged duration of contralateral stimulation, supporting its role as an active modulator of outer hair cell mechanics during ongoing stimuli.