Five decades of research on cochlear mechanics.

A review of Békésy's experiments on postmortem preparations shows the fundamental features of cochlear macromechanics. Early mathematical theory was able to explain Békésy's observations in terms of the hydrodynamics of surface waves and to account for some experimental artifacts. More recent experiments in vivo have shown that the cochlear frequency analysis is sharper than observed by Békésy and may occur in two interacting stages. It is suggested that the second stage may result in part from a resonance of hair-cell stereocilia loaded by the mass of the tectorial membrane, and it is calculated that the damping is small enough to allow such a resonance. The resonance would make the basilar membrane with the organ of Corti appear as a fourth- rather than a second-order system.