Dynamics of relaxation processes of spontaneous otoacoustic emissions
Abstract
The dynamical response of spontaneous otoacoustic emissions (SOAEs) to suppression by ipsilateral pulsed external tones of different frequencies and levels is investigated in nine female subjects under normal conditions and in four female subjects during periods when aspirin is being administered. A simple Van der Pol limit-cycle oscillator driven by an external tone is used as an interpretive model. Typical results for both the onset of, and recovery from suppression yield 1/$r\sb1$ (where $-r\sb1$ is the negative linear component of the damping function) in the range of 2-25 msec. In accordance with the predictions of the model: (a) the relaxation time for the onset of suppression increases with the amount of suppression induced by the external tone, (b) the values of $r\sb1$ and the amplitudes of the unsuppressed emissions exhibit an inverse correlation, (c) the values inferred for $r\sb1$ are not significantly dependent on the frequency of the pulsed suppressor tone and (d) the inferred $r\sb1$ values are not significantly dependent upon the amount of suppression. In investigations involving subjects under aspirin administration, the changes in the relaxation time constants indicate that the main effect of aspirin administration is to reduce the negative damping parameter $r\sb1.$ The salicylate is apparently not metabolized in some subjects whose emissions are negligibly affected by aspirin administration. A modification of the single-oscillator model is used to describe pulsed suppression data obtained from a primary SOAE (2545 Hz) which is suppressed by a neighboring secondary emission (2895 Hz). The response of the SOAE amplitude during pulsed suppression is modeled by a pair of Van der Pol limit-cycle oscillators with the primary oscillator linearly coupled to the displacement of the secondary higher-frequency one. The relaxation time constants for the onset of, and recovery from, suppression are 4.5 and 4.8 msec, respectively, for the primary SOAE and 7.5 and 10.5 msec for the secondary one. Aspirin administration reduces the magnitude of the overshoot by reducing the level of the higher frequency SOAE and thereby eliminating the suppression of the lower frequency one.
Degree
Ph.D.
Advisors
Tubis, Purdue University.
Subject Area
Acoustics|Audiology|Biophysics
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