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= approximately 70 ms, "medium," tau = approximately 330 ms, and "slow," tau = approximately 25 s components, and there was an overshoot in the decay like an 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 approximately 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 on 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 on acoustic changes that persist for 100's of milliseconds.
Backus
Bradford C
BC
Eaton Peabody Laboratory of Auditory Physiology, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA. bradford.c.backus.95@alum.dartmouth.org
Guinan
John J
JJ
D000161:Acoustic Stimulation; D000328:Adult; D001307:Auditory Perception / Q000502:physiology*; D003056:Cochlear Nerve / Q000502:physiology; D017626:Cochlear Nucleus / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009847:Olivary Nucleus / Q000502:physiology*; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D011930:Reaction Time; D012018:Reflex / Q000502:physiology*; D013997:Time Factors