Forward and reverse waves in nonclassical models of the cochlea

In "classical" models of the cochlea the mechanical properties of the cochlear partition (in which the basilar membrane plays a dominant role) depend only on the local longitudinal coordinate. Wave propagation in such models is the same for both propagation directions, towards the apex and towards the base. "Nonclassical" models contain mechanical properties that depend on variables at more than one location. In such models the properties of wave propagation may well be asymmetrical. This note presents an analysis of feed-forward and feed-backward models, with the emphasis on the properties of forward and reverse waves. In both of these classes of model, wave amplification for forward waves turns into wave attenuation for reverse waves. The slope of the phase pattern is nearly the same for the two types of waves, it is increased in feed-forward models and decreased in feed-backward models-with respect to a model without feedback. (C) 2007 Acoustical Society of America.