Cochlear Mechanics

Abstract

From an early time frequency analysis has been thought to be mechanical in origin. The first direct measurements, however, showed consistently poor tuning. This led to the concept of a second filter mechanism beyond the basilar membrane. Electrical tuning properties in some species appeared to support this view. With the discovery of otoacoustic emissions, an earlier hypothesis that mechanical amplification might enhance tuning received support. The most recent mechanical measurements demonstrate the extreme vulnerability of basilar membrane tuning and show that under good conditions it can indeed be adequately sharp. Although the outer hair cells are the prime candidates for the cochlear motor, their mode of action is not yet fully worked out. Furthermore there still appears to be room for other mechanisms in some non-mammalians. Some important aspects of psychophysical phenomena such as masking curves, equal loudness curves, recruitment, hearing loss, distortion products, and pich shifts now appear to be explicable at the mechanical level.