Cochlear waves: interaction between theory and experiments

Abstract

Review of past experimental and theoretical research leads to a statement of the mechanism producing the vibration maximum in the cochlea. It is shown that theoretically calculated propagation times of cochlear waves agree with the empirical data. The waves have a frequency-independent propagation velocity between the stapes and the vicinity of the vibration maximum. This means that they must be considered as “long waves” in this part of the cochlea. On the basis of the theoretically derived and experimentally confirmed resistive input impedance of the cochlea, a sound pattern is devised for an analytical investigation of auditory nerve responses. Application of the pattern reveals that single units of the nerve respond to both velocity and displacement of the basilar membrane. Motion or displacement toward scala tympani produces excitation, motion, or displacement toward scala vestibuli, inhibition. These results indicate that both inner and outer hair cells excite the same nerve fibers.