Short waves in three-dimensional cochlea models: solution for a 'block' model.

Nonlinearities affecting cochlear mechanics produce appreciable compression in the basilar membrane (BM) input/output (I/O) functions at the characteristic frequency for sound-pressure levels (SPLs) as low as 20 dB (re: 20 microPa). This is thought to depend upon saturation of the outer hair cell (OHC) mechanoelectrical transducer (MET). This hypothesis was tested by solving a nonlinear integrodifferential equation that describes the BM vibration in an active cochlea. The equation extends a previously developed linear approach [Mammano and Nobili, J. Acoust. Soc. Am. 93, 3320-3332 (1993)], here modified to include saturating MET, with a few corrections mainly concerning tectorial membrane resonance and OHC coupling to the BM. Stationary solutions were computed by iteration in the frequency domain for a wide range of input SPLs, generating BM I/O functions, frequency response envelopes, and two-tone distortion products. Traveling-wave amplitude envelopes were also computed for a fixed suppressor and several suppressed tones in order to evidence the phenomenon of two-tone suppression (frequency masking) at the mechanical level. All results accord nicely with experimental data.

Basilar Membrane↗

PubMed1996

Comparing frequency-domain with time-domain solutions for a locally active nonlinear model of the cochlea.

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Basilar Membrane↗

PubMed1995

On equivalence of locally active models of the cochlea.

In the literature on locally active models of the cochlea several forms of the model have been worked out in which elements of the organ of Corti are assumed to produce acoustical energy. In these models use is made of a secondary resonance or a place-dependent delay to achieve activity over a limited part of the length of the basilar membrane, and outer hair cells are postulated as sources of energy production. In the present paper it will be shown that several of these models are formally equivalent. That means that they can be reduced to a standard form, and that the only difference resides in the choice and meaning of the parameters. The results of the analysis serve to facilitate the analysis of function and structure in cochlear models containing sources of local activity. In particular, questions of positive versus negative feedback, and the parts played by resonance and impedance-level differences can be resolved unambiguously. The treatment can be extended to models with higher dimensionality, and can also serve to obtain insight in nonlinear phenomena occurring in cochlear models.

Basilar Membrane↗