Cochlear Mechanics, Otoacoustic Emissions, and Medial Olivocochlear Efferents: Twenty Years of Advances and Controversies Along with Areas Ripe for New Work

Abstract

Reviewed are progress, exciting new developments, and areas that need work. Topics considered are: Cochlear amplification is from energy injected into the traveling wave by outer-hair-cell somatic motility. Calcium-activated stereocilia motility does not work at high frequencies because of the slowness of calcium binding and unbinding. Cochlear mechanics and micromechanics in the apical half of the cochlea are different from in the base. Cochlear micromechanics and the multiple fluid drives to inner hair cell (IHC) stereocilia. Interaction of the multiple IHC fluid drives can explain phase reversals in auditory nerve fiber responses without phase reversals in basilar membrane responses. The mechanisms by which medial olivocochlear (MOC) efferents change cochlear mechanics and micromechanics. The generation mechanisms for otoacoustic emissions (OAEs). Distortion product OAEs (DPOAEs) travel backward by slow traveling waves. Stimulus frequency OAEs (SFOAEs) arise mainly from near the peak of the traveling wave. Using OAEs to reveal cochlear properties. Cochlear tuning is sharper in humans than in cats, guinea pigs, and chinchillas. Measuring MOC effects using changes in OAEs and the need for high OAE signal-to-noise ratios. MOC effects in humans. The role of MOC efferents in hearing. MOC activity makes it easier to hear signals in noise. MOC activity and selective attention. MOC activity reduces acoustic trauma.