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SHBT PhD Thesis Defense

An analytic model of the cochlea, functional interpretations and implications of using alternate forms of longitudinal coupling


Samiya Alkhairy

Tuesday, May 30, 2017 – 1:00 PM
MIT 4-231


In this talk, we develop a model of the mammalian cochlea and apply it to help us understand how the cochlea works given measurable observations. Specifically, we illustrate the model application by determining the wavenumber and impedance (which encode how the cochlea works) from measurable response characteristics such as bandwidth. We develop the model based on a mixed physical-phenomenological approach. The physical component is from classical work and provides us with the relationship between the wavenumber, impedance, pressure and velocity. The phenomenological component centers around constructing a suitable expression for the wavenumber. Using our constructed wavenumber and classical physics allows us to derive the expressions for the remaining variables. The expressions for the wavenumber, impedance, pressure and velocity are closed form expressions in space and frequency, and are all in terms of the same three model constants. After developing the model, we test it qualitatively and quantitatively. We then determine closed form expressions for the model constants in terms of reported response characteristics such as peak normalized frequency, maximum group delay, bandwidth, and phase accumulation. We apply this to the human cochlea and determine the wavenumber and impedance from reported sharpness of tuning from psychoacoustic studies and the empirically found species-independent relationship between sharpness of tuning and maximum group delay. We determine how the wavenumber and impedance vary with location in the cochlea, and make functional interpretations regarding wavelength, gain, damping and stiffness, which is particularly of interest in humans where mechanical measurements cannot be made.

Thesis Supervisor:
Christopher A. Shera, PhD
Professor of Otolaryngology, HMS


Thesis Committee Chair:
John J. Guinan, Jr., PhD
Professor of Otolaryngology, HMS


Thesis Readers:
Dennis M. Freeman, PhD
Professor of Electrical Engineering, MIT


Alan J. Grodzinsky, ScD
Professor of Biological, Electrical, and Mechanical Engineering, MIT


John J. Rosowski, PhD
Gudrun Larsen Eliasen and Nels Kristian Eliasen Professor of Otology and Laryngology, HMS