Evidence against power amplification in the cochlea

Abstract

Sound-induced traveling waves in the mammalian inner ear peak at a frequency-dependent location. Some form of motility is widely believed to boost this peaking by injecting extra power into the wave. We determined the power carried by the wave from two-point recordings of basilar membrane motion in sensitive cochleae. Up to moderate intensities, the peak wave power was slightly less than the acoustic power entering the middle ear. At higher intensities, an increasingly smaller fraction of the acoustic power reached the peak region. Thus, cochlear dynamic compression stems from variable dissipation rather than saturating amplification. Additional measurements revealed that the peaking of the wave envelope is realized by focusing the acoustic power rather than amplifying it.