Abstract
Recent in vivo recordings from the mammalian cochlea indicate that although the motion of the basilar membrane appears actively amplified and nonlinear only at frequencies relatively close to the peak of the response, the internal motions of the organ of Corti display these same features over a much wider range of frequencies. These experimental findings are not easily explained by the textbook view of cochlear mechanics, in which cochlear amplification is controlled by the motion of the basilar membrane (BM) in a tight, closed-loop feedback configuration. This study shows that a simple phenomenological model of the cochlea inspired by the work of Zweig [J. Acoust. Soc. Am. 138, 1102 (2015)] can account for recent data in mouse and gerbil. In this model, the active forces are regulated indirectly, through the effect of BM motion on the pressure field across the cochlear partition, rather than via direct coupling between active-force generation and BM vibration. The absence of strong vibration-amplification feedback in the cochlea also provides a compelling explanation for the observed intensity invariance of fine time structure in the BM response to acoustic clicks.
Highlights
The peripheral auditory system transforms air-borne pressure waves into neural impulses that are interpreted by the brain as sound and speech
We compare the predictions of the 3D chimeric and 2D box models with basilar membrane (BM) transfer functions measured under conditions where the cochlea behaves almost linearly: in vivo at low sound levels and post-mortem
Because in vivo responses evoked by lowlevel tones at frequencies in the low-frequency tail region are too small to be measured, we compare model responses in this region, where BM responses are approximately linear, with data obtained at slightly higher levels
Summary
The peripheral auditory system transforms air-borne pressure waves into neural impulses that are interpreted by the brain as sound and speech. The cochlea of the mammalian inner ear is a snail-shaped electrohydromechanical signal amplifier, frequency analyzer, and transducer with an astounding constellation of performance characteristics These include sensitivity to subatomic displacements with microsecond mechanical response times; wide-band operation spanning ten or more octaves in frequency; an input dynamic range corresponding to a million-million-fold change in signal energy (120 dB); and the ability to rapidly vary the response gain over 2–3 orders of magnitude while keeping the phase nearly invariant [1,2,3]. During normal hearing, soundinduced vibrations of the stapes launch hydromechanical
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