Dissertation Defense - Asheesh Momi - Yale University

The Physics of Cochlear Dynamics and Tuning

The human ear is a remarkably active mechanical system, capable of detecting faint sounds, sharply resolving frequency, and operating over an enormous dynamic range. These abilities arise from sound-induced surface waves on the cochlea’s basilar membrane, whose response is classically understood in terms of localized modes that peak sharply at frequency-dependent positions. However, my work shows that the cochlea also supports a distinct set of collective low-frequency extended modes, whose motion resembles global standing waves. This new mode structure raises several questions: how can active forces tune localized modes to high sensitivity without destabilizing extended modes, why do two qualitatively different classes of modes arise, and what role might extended modes play in hearing? Through computational and analytic modeling, this work investigates how active feedback, cochlear geometry, and mode structure together shape the sensitivity and stability of hearing.

Thesis Committee: Benjamin Machta (advisor), Thierry Emonet, Christopher Lynn, Joe Howard, Pascal Martin (Institut Curie)