Effect of efferent neural activity on cochlear mechanics

The literature relevant to efferent-induced mechanical change in the cochlea is reviewed. New data are presented on efferent-induced change in ear-canal sound pressure using a single-tone sound stimulus. Efferent-induced changes in sound pressure are largest relative to the baseline sound pressure at low sound levels and for frequencies between 2 and 20 kHz. Group delays calculated from phase vs. frequency slopes were 0.5 to 7 ms and may represent sound travel times into and back out of the cochlea. Three hypotheses are given which qualitatively explain much of the extant data on the action of cochlear efferents.