Spindle-shaped oscillations of the basilar membrane elicited
by a sequence of clicks (red bar = stapes).
The
currently believed explanation of otoacoustic emissions (OAEs) is that they
arise from reflected waves in the cochlear duct. The model presented here
provides a different explanation that ascribes the phenomenon to long-lasting
post-stimulus oscillations of the basilar membrane (BM) feeding
back instantly to the stapes by hydrodynamic coupling.
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.
CONTENT OF SIMOAE.ZIP
- 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.
Abstract of the paper that introduces the novel view.
Otoacoustic Emissions from Residual
Oscillations of the Cochlear Basilar Membrane in a Human Ear Model.
Authors: Renato Nobili, Aleš Vetešník,
LorenzoTuricchia and Fabio Mammano
JARO, 2003, in press.
Abstract
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
|
