Christopher Shera
Professor of Otolaryngology and Physics & Astronomy
Research Topics
- Mechanics of hearing
- Cochlear amplification and nonlinearity
- Mechanisms and applications of otoacoustic emission
- Comparative hearing
Research Overview
The peripheral auditory system transforms air-borne pressure waves into neural impulses that are interpreted by the brain as sound and speech. The cochlea of the inner ear is a snail-shaped electro-hydromechanical signal amplifier, frequency analyzer, and transducer with an astounding constellation of performance characteristics, including sensitivity to sub-atomic displacements with microsecond mechanical response times; wideband operation spanning three orders-of-magnitude in frequency; an input dynamic range of 120 dB, corresponding to a million-million-fold change in signal energy; useful operation even at signal powers 100 times smaller than the background noise; and ultra-low power consumption (15 μW). All of this is achieved not with the latest silicon technology or by exploiting the power of quantum computers — neither has yet approached the performance of the ear — but by self-maintaining biological tissue, most of which is salty water. How does the ear do it?The Auditory Physics Group studies how the ear amplifies, analyzes, and creates sound. The goal is not only to understand how the cochlea achieves its astounding sensitivity and dynamic range but to use that knowledge to enhance the power of noninvasive probes of peripheral auditory function (e.g., otoacoustic emissions). Our approach involves a strong, quantitative interplay between theoretical modeling studies and physiological measurements. Ongoing work in the lab focuses on models of cochlear amplification, mechanisms of OAE generation, middle-ear transmission, and comparative studies of cochlear mechanics.
Selected Publications
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Shera CA (2015) The spiral staircase: Tonotopic microstructure and cochlear tuning. J Neurosci 35:4683–4690
Joris PX, Bergevin C, Kalluri R, Mc Laughlin M, Michelet P, van der Heijden M, Shera CA (2011) Frequency selectivity in Old-World monkeys corroborates sharp cochlear tuning in humans. Proc Natl Acad Sci USA 108:17516–17520
Shera CA, Guinan JJ, Oxenham AJ (2010) Otoacoustic estimation of cochlear tuning: Validation in the chinchilla. J Assoc Res Otolaryngol 11:343–365
Shera CA (2007) Laser amplification with a twist: Traveling-wave propagation and gain functions from throughout the cochlea. J Acoust Soc Am 122:2738–2758
Shera CA, Guinan JJ (2007) Cochlear traveling-wave amplification, suppression, and beamforming probed using noninvasive calibration of intracochlear distortion sources. J Acoust Soc Am 121:1003–1016
Shera CA, Tubis A, Talmadge CL (2005) Coherent reflection in a two-dimensional cochlea: Shortwave versus long-wave scattering in the generation of reflection-source otoacoustic emissions. J Acoust Soc Am 118:287–313
Shera CA (2003) Mammalian spontaneous otoacoustic emissions are amplitude-stabilized cochlear standing waves. J Acoust Soc Am 114:244–262
Shera CA, Guinan JJ, Oxenham AJ (2002) Revised estimates of human cochlear tuning from otoacoustic and behavioral measurements. Proc Nat Acad Sci USA 99:3318–3323
Shera CA (2001) Intensity-invariance of fine time structure in basilar-membrane click responses: Implications for cochlear mechanics. J Acoust Soc Am 110:332–348
Kalluri R, Shera CA (2001) Distortion-product source unmixing: A test of the two-mechanism model for DPOAE generation. J Acoust Soc Am 109:622–637
Shera CA, Guinan JJ (1999) Evoked otoacoustic emissions arise by two fundamentally different mechanisms: A taxonomy for mammalian otoacoustic emissions. J Acoust Soc Am 105:782–798
Zweig G, Shera CA (1995) The origin of periodicity in the spectrum of evoked otoacoustic emissions. J Acoust Soc Am 98:2018–2047