Towards a model for the origin of cochlear echoes

A preliminary model is developed which quantitatively accounts for many features of stimulus-frequency acoustic emissions as observed in the ear canal, including multiple echoes and resonance. The model is based on a conventional middle-ear model and an elementary cochlear model with the addition of a new element feeding a signal, based on the cochlear travelling wave, back to the stapes. Parameters of the new element in the model are shown to be determinable from external acoustic observations and experimental examples are given. The physical nature and location of the new element in relation to the cochlea has not yet been experimentally determined, but means of testing various hypotheses are discussed. Clues concerning the physiological basis of the primary source of the emissions are reviewed but it is concluded that modelling of this aspect must proceed in parallel with investigations into the basis of cochlear frequency selectivity.