PubMed · 9309832
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F Mammano. 1997. Auditory periphery: cochlear processing.. https://pubmed.ncbi.nlm.nih.gov/9309832/
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Though the organ of Corti (OC) has been an object of experimental and theoretical hearing research, open questions remain concerning the processing of acoustic signals by the cochlea where the OC is located. Today there is extensive knowledge about single parts of the organ but a lack of understanding as to how these elements act together. One of the reasons for this is the missing analysis of the mechanics of the OC in three dimensions. In order to fill this gap, we have analyzed a short section (0.06 mm) of the basilar membrane including the OC and evaluated its nonlinear finite element model numerically. The Deiters cells are idealized as thin elastic beams with a comparably low modulus of elasticity of actin. Therefore, they show nonlinear mechanical behavior generating additional frequency components with two-tone stimulation.
This paper describes a model for generating the hair cell receptor potential based on a second-order Boltzmann function. The model includes only the resistive elements of the hair cell membranes with batteries across them and the series resistance of the external return path of the transducer current through the tissue of the cochlea. The model provides a qualitative description of signal processing by the hair cell transducer and shows that the nonlinearity of the hair cell transducer can give rise to nonlinear phenomena, such as intermodulation distortion products and two-tone suppression with patterns similar to those which have been recorded from the peripheral auditory system. Particular outcomes of the model are the demonstration that two-tone suppression depends not on the saturation of the receptor current, but on the behaviour of the hair cell transducer function close to the operating point. The model also shows that there is non-monotonic growth and phase change for any spectral component, but not for the fundamental of the receptor potential.
Computational models of the peripheral auditory system have largely modeled basilar membrane (BM) mechanics as a linear filter-bank-like entity. Recent mathematical work on the nature of auditory system noise suppression allows us to analyze and argue for the incorporation of BM nonlinearities into these models. This analysis shows that vowel perception improves with increasing presence of BM nonlinearities whereas consonant perception degrades with increasing influence of BM nonlinearities. Experimental results on tones and real speech corrupted by noise corroborate the analysis as well as suggest a novel approach to speech processing.