Time-course of the human medial olivocochlear reflex

The time-course of the human medial olivocochlear reflex (MOCR) was measured via its suppression of stimulus-frequency otoacoustic emissions (SFOAEs) in nine ears. MOCR effects were elicited by contralateral, ipsilateral or bilateral wideband acoustic stimulation. As a first approximation. MOCR effects increased like a saturating exponential with a time constant of 277 +/- 62 ms, and decayed exponentially with a time constant of 159 +/- 54 ms. However, in ears with the highest signal-to-noise ratios (4/9), onset time constants Could be separated into "fast," tau = similar to 70 ms. "medium," tau = similar to 330 ms, and "slow," tau = similar to 25 s components, and there was an overshoot in the decay like all under-damped sinusoid. Both the buildup and decay Could be modeled as a second order differential equation and the differences between the buildup and decay could be accounted for by decreasing one coefficient by a factor of 2. The reflex onset and offset delays were both similar to 25 ms. Although changing elicitor level over a 20 dB SPL range produced a consistent systematic change in response amplitude, the time course did not show a consistent dependence oil elictor level. nor did the time-courses of ipsilaterally, contralaterally, and bilaterally activated MOCR responses differ significantly. Given the MOCR's time-course, it is best suited to operate oil acoustic changes that persist for 100's of milliseconds. (c) 2006 Acoustical Society of America.