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Title: Modelling nonlinear interactions within the cochlea
Author: Vignali, Dario
ISNI:       0000 0004 6347 8677
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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The auditory system has a wide dynamic range and remarkable selectivity, due partly to the nonlinear processing within the cochlea. Modelling the performance of the cochlea is a way to gain insight into how it operates and to better understand its mechanical structure, whose arrangement generates nonlinear phenomena. A box model with nonlinear micromechanics was simulated using the state space method and the quasi-linear method to understand nonlinear dynamic interactions within the cochlea. The results from the quasi-linear model were essential for obtaining cochlear compression curves, which were used to tune the saturation parameters of the nonlinear function incorporated into the state space model. The nonlinear state space model allows time domain simulations to be performed that can replicate spontaneous otoacoustic emissions (SOAEs); sounds that can be measured in the ear canal, which are generated inside the cochlea and are by-products of the nonlinear process of the cochlear amplifier. The time domain model was mathematically formulated to reduce the computational load, which has previously limited the number of results that could be obtained. A novel method of incorporating initial conditions into the state space model has also been developed. Time domain simulations illustrate how SOAEs are due to limit cycle oscillations, whose amplitude is controlled by the saturation of the cochlea's amplification process. The results support the standing wave theory, whereby the emissions are produced by the reflection from random perturbations along the length of the cochlear partition at one end and the stapes at the other. Simulations of the interaction between a SOAE and low frequency bias tones give results that are comparable with those produced experimentally, but allow a greater physical interpretation. Simulations are also performed of the interaction between a SOAE and other stimuli, such as a swept tone that sweeps through the frequency of the emission and a high-level, low-frequency tone.
Supervisor: Elliott, Stephen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available