Fri, 01/17/2014 - 11:00am - 12:30pm
CCRMA Seminar Room
Few aspects of the hearing process are free from controversy and/or contradiction. However, there is a consensus on several basic features. Nerves are restricted in transferring frequency information to the brain. Consequently, mechanical devices are used in the inner ear for useful neural excitation. The semicircular canals provide very low frequency information associated with body motion, while the mammalian cochlea provides high frequency hearing. The cochlea acts as a real-time Fourier analyzer with a mapping of each frequency of the sound to a place along the cochlea. This mapping can be explained by a simplified "box model", containing only water and an elastic partition, whose stiffness is consistent with the geometric and material properties of the basilar membrane in the cochlea. The analysis of the three-dimensional motion has been prohibitive by direct numerical methods, but is easily treated by the 'WKB' asymptotic method. Recent improvements in modeling and computer power promise a convergence between numerical and asymptotic results. The "passive" fluid-elastic response is close to the actual response for high intensity of sound. However, for low intensity in the living mammal, the response is amplified by around two orders of magnitude, due to some "active" process. Recent results seem to confirm that this is due to piezoelectric behavior of the mammalian outer hair cell. The organ of Corti contains all the receptor cells and is an integral part of the basilar membrane. Consideration of the geometry of this organ leads to a "feed-forward/negative feed backward" model for the active process. This requires no tuning of the active process, i.e., an "open loop" system, which produces remarkable agreement with in vivo measurements. Very recent measurements of the mechanical response (Fred Nuttal, Oregon and John Oghalai and colleagues at Stanford) and electrical field (Elizabeth Olsen, Columbia) appear to confirm the model.
ABOUT Charles Steele
Charles joined the Stanford Faculty in 1966, in the department of Aeronautics and Astronautics. Motivated by a paper by von Bekesy in Mathematical Problems in Biology, he took an interest in the fluid-elastic response of the cochlea - the aero/astro of an inner space. He has some 120 archival publications and 58 Ph.D. students. About one-third of those worked on middle and inner ear mechanics. From NIH, Claude Pepper Award, 1988; From Germany, Humboldt Senior Fellowship Award, 1994; Honorary Ph.D. Zaporozhye State University, Ukraine, 1997; From ASME, Warner T. Koiter Medal, 1999. He was elected to the American Academy of Engineering in 1995. Editor-in-Chief, International Journal of Solids and Structures, 1985 - 2005 (Elsevier). Founder, Journal of Mechanics of Materials and Structures, 2005 (a nonprofit operation). Professor Emeritus 2003, but continuing research on auditory mechanics with colleague Sunil Puria and Ph.D. students, in collaboration with Tony Ricci, John Oghalai, and Gerry Popelka in the Department of Otolaryngology, Head and Neck Surgery.