Otoacoustic Emission Simulations
Spindle-shaped oscillations of the basilar membrane elicited by a sequence of clicks (red bar = stapes).
Download SIMOAE.ZIP (2,938 KB) - A Matlab routine package providing time domain simulations of transient evoked otoacoustic emissions according to the theory described in the paper quoted at the end of this page.
The Matlab GUI interface used to simulate OAEs from the human cochlea.With the Matlab (versions 5+, 6+) programme presented here, the user may load data files representing acoustic signals of 200 kHz sampling rate as stapes acceleration (top diagram). Otoacoustic emissions (OAEs) are displayed as fluid pressure sensed by the stapes during the time course of basilar membrane (BM) oscillations primed and/or maintained by the signals (middle diagram). The time course of BM acceleration is displayed in the bottom diagram with adjustable scales (slider at right). The popup menu above the bottom diagram is used to select one of the following displayed variables: BM acceleration, BM velocity, BM displacement, stereocilia velocity, stereocilia displacement.
Inputting a signal, whose magnitude is changed by the slider at the right of the top diagram, the user may observe, at different scales (slider at the right of the middle diagram), the time course of the cochlear fluid pressure as would be detected in the scala vestibuli (near stapes).
Transient evoked otoacoustic emissions appear to be related to irregular post-stimulus oscillations of the BM, as those elicited by a click inputted to the ear canal and filtered by a middle ear that presents an irregular transfer function (signal file FILT_CLICK.SIG). Emissions are not observed if the BM residual oscillations evolve as spindles of regular shape and time course, as those elicited by an ideal click directly applied to the stapes (signal file UNFILT_CLICK.SIG).
The acoustic impedance of the model, i.e. scala-vestibuli-pressure/(stapes-footplate-area X stapes-velocity), mimics that of a human ear: It is almost purely resistive and its magnitude is about 20 acoustic GOhm.
- README.RTF - Rich Text Format document with a few notes on the model and its usage.
- SIMOAE.M - The main Matlab routine creating the Graphic User Interface (GUI, see figure above), which allows you to simulate the responses of a human cochlea to acoustic stimuli entered as stapes acceleration. Enter simoae at the Matlab command prompt to start the programme.
- ALLDATA.M - Called by SIMOAE.M to load all data files that are needed to run the routine and prepare undamping parameters.
- BMOPS.MAT, TMOPS.MAT, LAMBDATA.MAT - Data files called by ALLDATA.M.
- SIGMOID.M - Profile of the transduction function of the outer hair cell motor, on which the nonlinear properties of the cochlea model dynamics depend.
- UNFILT_CLICK.SIG - Input signal file representing an ideal click (second time derivative of a Gaussian pulse). Load this to see that no otoacoustic emissions are generated by this sort of stapedial input.
- FILT_CLICK.SIG - Input signal representing a click as filtered by a human middle ear (shown in top diagram of the GUI figure above). Load this to see that evoked otoacoustic emission of realistic magnitude are generated by this sort of stapedial input.
- 05KHZ.SIG, ...,6KHZ.SIG - Input signals representing tone bursts of various frequencies. These can be loaded to test acoustic impedance properties and input-output curves of the model.
- STEPS.SIG - Input signal representing a double-square transient. It can be used to make manifest the resistive characteristic of the acoustic impedance of the model. Indeed, the scala vestibuli pressure response elicited by this acoustic stimulus is shaped about as a triangle, meaning that pressure is about proportional to the time integral of the input signal, i.e. to the stapes velocity.
Otoacoustic Emissions from Residual Oscillations of the Cochlear Basilar Membrane in a Human Ear Model. Abstract
Authors: Renato Nobili, Aleš Vetešník, LorenzoTuricchia and Fabio Mammano
JARO, 2003, in press.
Sounds originating from within the inner ear, known as otoacoustic emissions (OAEs), are widely exploited in clinical practice but the mechanisms underlying their generation are not entirely clear. Here we present simulation results and theoretical considerations based on a hydrodynamic model of the human inner ear. Simulations show that, if the cochlear amplifier (CA) gain is a smooth function of position within the active cochlea, filtering performed by a middle-ear with an irregular, i.e. non-smooth, forward transfer function suffices to produce irregular and long-lasting residual oscillations of cochlear basilar membrane (BM) at selected frequencies. Feeding back to the middle-ear through hydrodynamic coupling afforded by the cochlear fluid, these oscillations are detected as transient evoked OAEs in the ear canal. If also the CA gain profile is affected by irregularities, residual BM oscillations are even more irregular and tend to evolve towards self-sustaining oscillations at the loci of gain irregularities. Correspondingly, the spectrum of transient evoked OAEs exhibits sharp peaks. If both the CA gain and the middle-ear forward transfer function are smooth, residual BM oscillations have regular waveforms and extinguish rapidly. In this case no emissions are produced. Finally, and paradoxically albeit consistent with observations, simulating localized damage to the CA results in self-sustaining BM oscillations at the characteristic frequencies (CFs) of the sites adjacent to the damage region, accompanied by generation of spontaneous OAEs. Under these conditions, stimulus-frequency OAEs, with typical modulation patterns, are also observed for inputs near hearing threshold. This approach can be exploited to provide novel diagnostic tools and a better understanding of key phenomena relevant for hearing science.
For further information please contact: renato.nobili@unipd.it
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