Nonlinear Distortions and Parametric Amplification Generate Otoacoustic Emissions and Increased Hearing Sensitivity (original) (raw)
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Biophysics of the cochlea II: Stationary nonlinear phenomenology
The Journal of the Acoustical Society of America, 1996
Nonlinearities affecting cochlear mechanics produce appreciable compression in the basilar membrane ͑BM͒ input/output ͑I/O͒ functions at the characteristic frequency for sound-pressure levels ͑SPLs͒ as low as 20 dB ͑re: 20 Pa͒. This is thought to depend upon saturation of the outer hair cell ͑OHC͒ mechanoelectrical transducer ͑MET͒. This hypothesis was tested by solving a nonlinear integrodifferential equation that describes the BM vibration in an active cochlea. The equation extends a previously developed linear approach ͓Mammano and Nobili, J. Acoust. Soc. Am. 93, 3320-3332 ͑1993͔͒, here modified to include saturating MET, with a few corrections mainly concerning tectorial membrane resonance and OHC coupling to the BM. Stationary solutions were computed by iteration in the frequency domain for a wide range of input SPLs, generating BM I/O functions, frequency response envelopes, and two-tone distortion products. Traveling-wave amplitude envelopes were also computed for a fixed suppressor and several suppressed tones in order to evidence the phenomenon of two-tone suppression ͑frequency masking͒ at the mechanical level. All results accord nicely with experimental data.
The Journal of the Acoustical Society of America, 2010
A model of cochlear mechanics is described in which force-producing outer hair cells ͑OHC͒ are embedded in a passive cochlear partition. The OHC mechanoelectrical transduction current is nonlinearly modulated by reticular-lamina ͑RL͒ motion, and the resulting change in OHC membrane voltage produces contraction between the RL and the basilar membrane ͑BM͒. Model parameters were chosen to produce a tonotopic map typical of a human cochlea. Time-domain simulations showed compressive BM displacement responses typical of mammalian cochleae. Distortion product ͑DP͒ otoacoustic emissions at 2f 1 − f 2 are plotted as isolevel contours against primary levels ͑L 1 , L 2 ͒ for various primary frequencies f 1 and f 2 ͑f 1 Ͻ f 2 ͒. The L 1 at which the DP reaches its maximum level increases as L 2 increases, and the slope of the "optimal" linear path decreases as f 2 / f 1 increases. When primary levels and f 2 are fixed, DP level is band passed against f 1. In the presence of a suppressor, DP level generally decreases as suppressor level increases and as suppressor frequency gets closer to f 2 ; however, there are exceptions. These results, being similar to data from human ears, suggest that the model could be used for testing hypotheses regarding DP generation and propagation in human cochleae.
Experimental results in a physical model of the cochlea
Journal of Fluid Mechanics, 1985
Previous contributions made by physical models to the understanding of cochlear mechanics suggested that a new cochlear model should be constructed. This paper illustrates the results obtained with a rectilinear, three-chamber model. The model was geometrically scaled 50: 1 and contained the constituent elements of the cochlear cross-section including the basilar membrane, Reissner's membrane, the tectorial membrane and the organ of Corti. The basilar membrane was stretched crosswise in order to simulate real basilar membrane anisotropy. Two kinds (rigid and elastic) of tectorial membranes were used. The ductus and the sulcus were made visible and the model was also provided with displacement transducers to measure the axial and cross components of the oscillating fluid motion in the scala media. The adoption of a highly flexible membrane, simulating Reissner's membrane, made it possible to vary the viscosity of the scala media compared to that of the other two scalae. The reasons why the simplifications of the previous models were partially rejected and the criteria adopted to assure dynamic similitude between the model and the real cochlea are described in the paper. The results of tests carried out to determine the partial distribution of the amplitude maximum, the phase velocity along the axis of the model and the dispersion curves are shown. The same tests were repeated with partially filled scala vestibuli. Lastly a typical nonlinear feature, that is a continuous flow in the scala media, is described. 362 C. Cancelli, S . D'Angelo, M. Masili and R. Malvano distortions of the acoustic signal (Tonndorf 1970) and to a continuous motion of the fluid from the sulcus to the scala media (Helle 1974b). In addition, the experimental results which Cannel (1969) and Helle (1974a) obtained with physical models have been used by Steele & to prove that the asymptotic method, named WKB, is applicable to fully three-dimensional fluid motion.
A mechano-electro-acoustical model for the cochlea: Response to acoustic stimuli
The Journal of the Acoustical Society of America, 2007
A linear, physiologically based, three-dimensional finite element model of the cochlea is developed. The model integrates the electrical, acoustic, and mechanical elements of the cochlea. In particular, the model includes interactions between structures in the organ of Corti ͑OoC͒, piezoelectric relations for outer hair cell ͑OHC͒ motility, hair bundle ͑HB͒ conductance that changes with HB deflection, current flow in the cross section and along the different scalae, and the feed-forward effect. The parameters in the model are based on guinea-pig data as far as possible. The model is vetted using a variety of experimental data on basilar membrane motion and data on voltages and currents in the OoC. Model predictions compare well, qualitatively and quantitatively, with experimental data on basilar membrane frequency response, impulse response, frequency glides, and scala tympani voltage. The close match of the model predictions with experimental data demonstrates the validity of the model for simulating cochlear response to acoustic input and for testing hypotheses of cochlear function. Analysis of the model and its results indicates that OHC somatic motility is capable of powering active amplification in the cochlea. At the same time, the model supports a possible synergistic role for HB motility in cochlear amplification.
Phase of Shear Vibrations within Cochlear Partition Leads to Activation of the Cochlear Amplifier
PLoS ONE, 2014
Since Georg von Bekesy laid out the place theory of the hearing, researchers have been working to understand the remarkable properties of mammalian hearing. Because access to the cochlea is restricted in live animals, and important aspects of hearing are destroyed in dead ones, models play a key role in interpreting local measurements. Wentzel-Kramers-Brillouin (WKB) models are attractive because they are analytically tractable, appropriate to the oblong geometry of the cochlea, and can predict wave behavior over a large span of the cochlea. Interest in the role the tectorial membrane (TM) plays in cochlear tuning led us to develop models that directly interface the TM with the cochlear fluid. In this work we add an angled shear between the TM and reticular lamina (RL), which serves as an input to a nonlinear active force. This feature plus a novel combination of previous work gives us a model with TM-fluid interaction, TM-RL shear, a nonlinear active force and a second wave mode. The behavior we get leads to the conclusion the phase between the shear and basilar membrane (BM) vibration is critical for amplification. We show there is a transition in this phase that occurs at a frequency below the cutoff, which is strongly influenced by TM stiffness. We describe this mechanism of sharpened BM velocity profile, which demonstrates the importance of the TM in overall cochlear tuning and offers an explanation for the response characteristics of the Tectb mutant mouse.
BioMed Research International, 2014
The cochlea plays a crucial role in mammal hearing. The basic function of the cochlea is to map sounds of different frequencies onto corresponding characteristic positions on the basilar membrane (BM). Sounds enter the fluid-filled cochlea and cause deflection of the BM due to pressure differences between the cochlear fluid chambers. These deflections travel along the cochlea, increasing in amplitude, until a frequency-dependent characteristic position and then decay away rapidly. The hair cells can detect these deflections and encode them as neural signals. Modelling the mechanics of the cochlea is of help in interpreting experimental observations and also can provide predictions of the results of experiments that cannot currently be performed due to technical limitations. This paper focuses on reviewing the numerical modelling of the mechanical and electrical processes in the cochlea, which include fluid coupling, micromechanics, the cochlear amplifier, nonlinearity, and electrical coupling.
Hydromechanical Structure of the Cochlea Supports the Backward Traveling Wave in the Cochlea In Vivo
Neural Plasticity
The discovery that an apparent forward-propagating otoacoustic emission (OAE) induced basilar membrane vibration has created a serious debate in the field of cochlear mechanics. The traditional theory predicts that OAE will propagate to the ear canal via a backward traveling wave on the basilar membrane, while the opponent theory proposed that the OAE will reach the ear canal via a compression wave. Although accepted by most people, the basic phenomenon of the backward traveling wave theory has not been experimentally demonstrated. In this study, for the first time, we showed the backward traveling wave by measuring the phase spectra of the basilar membrane vibration at multiple longitudinal locations of the basal turn of the cochlea. A local vibration source with a unique and precise location on the cochlear partition was created to avoid the ambiguity of the vibration source in most previous studies. We also measured the vibration pattern at different places of a mechanical cochle...
Hydromechanical Structure of the Cochlea Supports the Backward Traveling Wave in the Cochlea In Vivo
Neural Plasticity, 2018
The discovery that an apparent forward-propagating otoacoustic emission (OAE) induced basilar membrane vibration has created a serious debate in the field of cochlear mechanics. The traditional theory predicts that OAE will propagate to the ear canal via a backward traveling wave on the basilar membrane, while the opponent theory proposed that the OAE will reach the ear canal via a compression wave. Although accepted by most people, the basic phenomenon of the backward traveling wave theory has not been experimentally demonstrated. In this study, for the first time, we showed the backward traveling wave by measuring the phase spectra of the basilar membrane vibration at multiple longitudinal locations of the basal turn of the cochlea. A local vibration source with a unique and precise location on the cochlear partition was created to avoid the ambiguity of the vibration source in most previous studies. We also measured the vibration pattern at different places of a mechanical cochlear model. A slow backward traveling wave pattern was demonstrated by the time-domain sequence of the measured data. In addition to the wave propagation study, a transmission line mathematical model was used to interpret why no tonotopicity was observed in the backward traveling wave.
Acoustic input-admittance of the alligator-lizard ear: Nonlinear features
Hearing Research, 1984
The acoustic input-admittance at the alligator lizard's tympanic membrane varies with stimulus level: the magnitude of the variation can he as much as a factor of three. At 1.6 kHz. the frequency of maximum admittance magnitude. the admittance varies when the stimulus level exceeds 65 dB SPL. At frequencies above or below 1.6 kHz, larger SPLa are needed to produce admittance changes. With stimulus frequencies below 0.3 kHz or above 4.0 kHz the admittance is virtually constant for stimulus Icvelh up to at leaat 100 dB SPL. The nonlinear behavior (a) is greatly reduced when the cochlear partition is destroyed, (h) does not return when the mechanical load of the partition IS replaced, (c) is decreased by the introduction of proteolytic enzymes into the inner ear. and (d) ia not affected by some manipulations that greatly reduce cochlear potentials. The results suggest that the mechanical properties of the cochlear partition are the source of the nonlinear admittance. Parallels hetween this phenomenon and two-tone distortion products in the ear canal (Rosowski et al. (1984): Hearing Res. 13. 141-158) suggest that the same nonlinear mechanical source that generates the level-dependent admittance also produces two-tone distortion products in the lizard ear canal. Pubhahed demonstrations ol level-dependent admittance In mammalian ears. although rather different from thehe results. do not rule out the presence of a similar mechamsm in the mammalian cochlea. Illard. cochlear mechanics. middle-ear mechanics, cochlear nonlinearit)
Some observations on cochlear mechanics
Journal of The Acoustical Society of America, 1978
A set of experiments was conducted using the MSssbauer effect to determine the vibratory characteristics of the basilar membrane, Reissner's membrane, the malleus, incus, and oval window in squirrel monkey.