HOW AN ARRAY OF DISCRETE RESONATORS, COUPLED BY FLUID, CAN REPRODUCE THE DYNAMICS OF CLICK-EVOKED OTOACOUSTIC EMISSIONS

This paper describes a basic representation of cochlear mechanics. To represent the cochlear partition, we begin with an array of discrete tuned resonators, immersed in fluid. The resonators are stimulated by an impulse from another resonator, which is taken to be the middle ear. A “state space” representation of the classic transmission line model is used to describe the multiple fluid-borne interactions which take place between all the resonators. The overall response seen at the middle ear looks remarkably similar to a click-evoked otoacoustic emission (CEOAE), if the place–frequency map of the cochlea contains tuning irregularities.The paper describes, step by step, how the CEOAEs are generated. We show that impulse responses from each oscillator are transported back to the ear canal, and that these responses add up to create a standing wave pattern in the fluid pressure. This standing wave is the sum of waves repeatedly travelling back and forth between an irregularity and oscillator 1. If only one irregularity is present, the impulse response of oscillator 1 (the “stimulus”) is followed by a weak single oscillation, with the characteristics of a “gammachirp”. If irregularities are present all along the cochlear partition, many gammachirps add up to produce a signal with similar characteristics as a CEOAE measured in a normal hearing ear.