Theory of cochlear mechanics.

This paper attempts to define the current state of the theory of cochlear mechanics on the basis of past and current experimental and theoretical work. It begins with von Békésy's discovery of traveling transversal waves in the cochlea and with related early mathematical theory and ends with insights engendered by Russell and Sellick's demonstration that inner hair cells are as sharply tuned as the auditory-nerve fibers and by the finding of the M.I.T. groups of Weiss and Peake that sharp tuning of hair cells can exist in the absence of basilar-membrane tuning. Evidence for a sharpening of tuning beyond basilar-membrane vibration is reviewed and two mechanisms for such sharpening are considered--one arising from an interaction between basilar-membrane wavelength and longitudinal coupling within the tectorial membrane and one from the radial-mode resonance of the tectorial membrane and its viscoelastic coupling to the organ of Corti. Simple calculation reveals that damping of the radial-mode vibration should be small enough to allow such a resonance.