Otoacoustic Emissions Simulated in the Time-domain by a Hydroynamic Model of the Human Cochlea

Time-domain simulations of the response to click of a human ear show that, if the cochlear amplifier gain (CAG) is a smooth function of basilar-membrane (BM) position, the filtering performed by a middle ear with an irregular (non-smooth) transfer function suffices to produce irregular and long-lasting residual BM oscillations at selected frequencies. Feeding back to the middle ear through hydrodynamic coupling, these oscillations are detected as otoacoustic emissions (OAEs) in the ear canal. If, in addition, also the CAG profile is irregular, residual BM oscillations are even more irregular, often ensuing to self-sustaining oscillations at CAG irregularity loci. Correspondingly, transient evoked OAE spectra exhibit sharp peaks. If both the CAG and the middle-ear transfer function are smooth, residual BM oscillations are characterized by regular waveform, extinguish rapidly and do not generate appreciable emission. Simulating localized damage to the cochlear amplifier results in spontaneous emissions and stimulus-frequency OAEs, with typical modulation patterns, for inputs near hearing threshold.