Forward and reverse waves in the one-dimensional model of the cochlea

Consideration of a source of oto-acoustic emission in a cochlear model implies consideration of the types of waves that such a source can emit. One wave travels in the normal, forward, direction. As any other forward wave it undergoes little or no reflection and it eventually disappears completely because of dissipation. The other wave travels in the reverse direction and it appears to undergo appreciable reflection. In the present paper this phenomenon is studied via the use of two appropriately simplified long-wave models of the cochlea. One model, the exponential model, puts emphasis on the variation of the stiffness along the length of the basilar membrane. The second model concentrates on what happens in the region of resonance. The latter model turns out to have the largest predictive power for the problem at hand. Consideration of the flow of energy in the cochlear fluid brings forth the explanation why in the used model of the cochlea reflection conditions at the stapes have such a surprisingly small influence on the operating conditions of a potential source of emission.