Basilar Membrane Displacement Research Articles

3D Computational Modeling of Blast Wave Transmission in Human Ear From External Ear to Cochlear Hair Cells: A Preliminary Study.

Auditory disabilities like tinnitus and hearing loss caused by exposure to blast overpressures are prevalent among military service members and veterans. The high-pressure fluctuations of blast waves induce hearing loss by injuring the tympanic membrane, ossicular chain, or sensory hair cells in the cochlea. The basilar membrane (BM) and organ of Corti (OC) behavior inside the cochlea during blast remain understudied. A computational finite element (FE) model of the full human ear was used by Bradshaw etal. (2023) to predict the motion of middle and inner ear tissues during blast exposure using a 3-chambered cochlea with Reissner's membrane and the BM. The inclusion of the OC in a blast transmission model would improve the model's anatomy and provide valuable insight into the inner ear response to blast exposure. This study developed a microscale FE model of the OC, including the OC sensory hair cells, membranes, and structural cells, connected to a macroscale model of the ear to form a comprehensive multiscale model of the human peripheral auditory system. There are 5 rows of hair cells in the model, each row containing 3 outer hair cells (OHCs) and the corresponding Deiters' cells and stereociliary hair bundles. BM displacement 16.75 mm from the base induced by a 31 kPa blast overpressure waveform was derived from the macroscale human ear model reported by Bradshaw etal. (2023) and applied as input to the center of the BM in the OC. The simulation was run for 2 ms as a structural analysis in ANSYS Mechanical. The FE model results reported the displacement and principal strain of the OHCs, reticular lamina, and stereociliary hair bundles during blast transmission. The movement of the BM caused the rest of the OC to deform significantly. The reticular lamina displacement and strain amplitudes were highest where it connected to the OHCs, indicating that injury to this part of the OC may be likely due to blast exposure. This microscale model is the first FE model of the OC to be connected to a macroscale model of the ear, forming a full multiscale ear model, and used to predict the OC's behavior under blast. Future work with this model will incorporate cochlear endolymphatic fluid, increase the number of OHC rows to 19 in total, and use the results of the model to reliably predict the sensorineural hearing loss resulting from blast exposure.

Intracochlear overdrive: Characterizing nonlinear wave amplification in the mouse apex.

In this study, we explore nonlinear cochlear amplification by analyzing basilar membrane (BM) motion in the mouse apex. Through in vivo, postmortem, and mechanical suppression recordings, we estimate how the cochlear amplifier nonlinearly shapes the wavenumber of the BM traveling wave, specifically within a frequency range where the short-wave approximation holds. Our findings demonstrate that a straightforward mathematical model, depicting the cochlear amplifier as a wavenumber modifier with strength diminishing monotonically as BM displacement increases, effectively accounts for the various experimental observations. This empirically derived model is subsequently incorporated into a physics-based "overturned" framework of cochlear amplification [see Altoè, Dewey, Charaziak, Oghalai, and Shera (2022), J. Acoust. Soc. Am. 152, 2227-2239] and tested against additional experimental data. Our results demonstrate that the relationships established within the short-wave region remain valid over a much broader frequency range. Furthermore, the model, now exclusively calibrated to BM data, predicts the behavior of the opposing side of the cochlear partition, aligning well with recent experimental observations. The success in reproducing key features of the experimental data and the mathematical simplicity of the resulting model provide strong support for the "overturned" theory of cochlear amplification.

3D Finite Element Model of Human Ear with 3-Chamber Spiral Cochlea for Blast Wave Transmission from the Ear Canal to Cochlea

Blast-induced auditory trauma is a common injury in military service members and veterans that leads to hearing loss. While the inner ear response to blast exposure is difficult to characterize experimentally, computational models have advanced to predict blast wave transmission from the ear canal to the cochlea; however, published models have either straight or spiral cochlea with fluid-filled two chambers. In this paper, we report the recently developed 3D finite element (FE) model of the human ear mimicking the anatomical structure of the 3-chambered cochlea. The model consists of the ear canal, middle ear, and two and a half turns of the cochlea with three chambers separated by the Reissner's membrane (RM) and the basilar membrane (BM). The blast overpressure measured from human temporal bone experiments was applied at the ear canal entrance and the Fluent/Mechanical coupled fluid-structure interaction analysis was conducted in ANSYS software. The FE model-derived results include the pressure in the canal near the tympanic membrane (TM) and the intracochlear pressure at scala vestibuli, the TM displacement, and the stapes footplate (SFP) displacement, which were compared with experimentally measured data in human temporal bones. The validated model was used to predict the biomechanical response of the ear to blast overpressure: distributions of the maximum strain and stress within the TM, the BM displacement variation from the base to apex, and the energy flux or total energy entering the cochlea. The comparison of intracochlear pressure and BM displacement with those from the FE model of 2-chambered cochlea indicated that the 3-chamber cochlea model with the RM and scala media chamber improved our understanding of cochlea mechanics. This most comprehensive FE model of the human ear has shown its capability to predict the middle ear and cochlea responses to blast overpressure which will advance our understanding of auditory blast injury.

In Vivo Optogenetics Reveals Control of Cochlear Electromechanical Responses by Supporting Cells.

Cochlear sensitivity, essential for communication and exploiting the acoustic environment, results from sensory-motor outer hair cells (OHCs) operating in a structural scaffold of supporting cells and extracellular cortilymph within the organ of Corti (OoC). Cochlear sensitivity control is hypothesized to involve interaction between the OHCs and OoC supporting cells (e.g., Deiters' cells [DCs] and outer pillar cells [OPCs]), but this has never been established in vivo Here, we conditionally expressed channelrhodopsins (ChR2) specifically in male and female mouse DCs and OPCs. Illumination of the OoC activated the nonselective ChR2 cation conductance and depolarized DCs when measured in vivo and in isolated OoC. Measurements of sound-induced cochlear mechanical and electrical responses revealed that OoC illumination suppressed the normal functions of OoC supporting cells transiently and reversibly. OoC illumination blocked normally occurring continuous minor adjustments of tone-evoked basilar membrane displacements over their entire dynamic range and OHC voltage responses to tones at levels and frequencies subject to cochlear amplification. OoC illumination altered the OHC mechanoelectrical transduction conductance operating point, which reversed the asymmetry of OHC voltage responses to high level tones. OoC illumination accelerated recovery from temporary loud sound-induced acoustic desensitization. We concluded that DCs and OPCs are involved in both the control of cochlear responses (which are essential for normal hearing) and the recovery from temporary acoustic desensitization. This is the first direct in vivo evidence for the interdependency of the structural, mechanical, and electrochemical arrangements of OHCs and OoC supporting cells that together provide fine control of cochlear responses.SIGNIFICANCE STATEMENT A striking feature of the mammalian cochlear sensory epithelium, the organ of Corti, is the cellular architecture and supporting cell arrangement that provides a structural scaffold for the sensory-motor outer hair cells. The role of the supporting cell scaffold, however, has never been elucidated in vivo, although in vitro and modeling studies indicate the scaffold is involved in exchange of forces between the outer hair cells and the organ of Corti. We used in vivo techniques, including optogenetics, that do not disrupt arrangements between the outer hair cells and supporting cells, but selectively, transiently, and reversibly interfere with supporting cell normal function. We revealed the supporting cells provide continuous adjustment of cochlear sensitivity, which is instrumental in normal hearing.

The Spectral Extent of Phasic Suppression of Loudness and Distortion-Product Otoacoustic Emissions by Infrasound and Low-Frequency Tones

We investigated the effect of a biasing tone close to 5, 15, or 30 Hz on the response to higher-frequency probe tones, behaviorally, and by measuring distortion-product otoacoustic emissions (DPOAEs). The amplitude of the biasing tone was adjusted for criterion suppression of cubic DPOAE elicited by probe tones presented between 0.7 and 8 kHz, or criterion loudness suppression of a train of tone-pip probes in the range 0.125–8 kHz. For DPOAEs, the biasing-tone level for criterion suppression increased with probe-tone frequency by 8–9 dB/octave, consistent with an apex-to-base gradient of biasing-tone-induced basilar membrane displacement, as we verified by computational simulation. In contrast, the biasing-tone level for criterion loudness suppression increased with probe frequency by only 1–3 dB/octave, reminiscent of previously published data on low-side suppression of auditory nerve responses to characteristic frequency tones. These slopes were independent of biasing-tone frequency, but the biasing-tone sensation level required for criterion suppression was ~ 10 dB lower for the two infrasound biasing tones than for the 30-Hz biasing tone. On average, biasing-tone sensation levels as low as 5 dB were sufficient to modulate the perception of higher frequency sounds. Our results are relevant for recent debates on perceptual effects of environmental noise with very low-frequency content and might offer insight into the mechanism underlying low-side suppression.

Effects of lesions of the organ of corti on hearing

Background Lesions causing changes in the microstructure of the organ of Corti may lead to hearing impairment. Aims/objectives The aim of this study was to investigate the effect of various structural lesions on the organ of Corti and the auditory function. Methods A finite element method of the cochlea and the organ of Corti were established based on computed tomography scanning and anatomical data. We evaluated the accuracy of the model by comparing the simulation results to reported experimental data. We simulated and analyzed the impact of the lesions on the sound-sensing function of the cochlea by adjusting the biomaterial parameters of each component of the cochlea. Results In the explored frequency range, the stereocilia and outer hair cells and basilar membrane sclerosis resulted in 23.4%, 47.2%, and 57.8% reduction of basilar membrane displacement, respectively. Lesions of the basilar membrane and stereocilia and outer hair cells in the Corti caused a hearing response curve shift to higher frequencies and a decrease of the amplitude of the basilar membrane. Conclusions and significance Lesions of the internal structure of the Corti cause diminished movement of basement membrane and decreased sensorial function, which ultimately lead to hearing loss.

Inner hair cell stereocilia displacement in response to focal stimulation of the basilar membrane in the ex vivo gerbil cochlea

The inner hair cells in the mammalian cochlea transduce mechanical signals to electrical signals that provide input to the auditory nerve. The spatial-temporal displacement of the inner hair cell stereocilia (IHCsc) relative to basilar membrane (BM) displacement is central to characterizing the transduction process. This study specifically focuses on measuring displacement of the stereocilia hair bundles in the radial dimensions where they are most sensitive. To simplify the mechanical response of the cochlear partition, a mechanical probe was used to drive the BM. Optical imaging was used to measure radial displacement of the inner hair cell stereocilia local to the probe in ex vivo gerbil cochleae. The mechanical probe displaced the BM in the transverse direction using sinusoidal stimuli with frequencies ranging from 10 Hz to 42.5 kHz. IHCsc displacement measurements were made in the radial dimension as a function of their longitudinal location along the length of the BM. The results were used to quantify the frequency response, longitudinal space coupling, traveling wave velocity, and wavelength of the radial displacement of the stereocilia.The measurements were centered at two best frequency locations along the BM: Proximal to the round window (first turn), and in the second turn. At both locations, frequency tuning was seen that was consistent with published place maps. At both locations, traveling waves were observed simultaneously propagating basal and apical from the probe. The velocity of the traveling waves at the center frequency (CF) of the location was higher in the first turn than in the second. As the stimulus frequency increased and approached CF for a location, the traveling wavelength decreased. Differential motion of the BM and IHCsc was observed in the second turn as the stimulus frequency increased toward CF. The longitudinal coupling measured in this study was longer than observed in previous studies. In summary the results suggest that the shape of the wave patterns present on the BM are not sufficient to characterize the displacement of the IHCsc.

Three-Dimensional Finite Element Modeling of Blast Wave Transmission From the External Ear to a Spiral Cochlea.

Blast-induced injuries affect the health of veterans, in which the auditory system is often damaged, and blast-induced auditory damage to the cochlea is difficult to quantify. A recent study modeled blast overpressure (BOP) transmission throughout the ear utilizing a straight, two-chambered cochlea, but the spiral cochlea's response to blast exposure has yet to be investigated. In this study, we utilized a human ear finite element (FE) model with a spiraled, two-chambered cochlea to simulate the response of the anatomical structural cochlea to BOP exposure. The FE model included an ear canal, middle ear, and two and half turns of two-chambered cochlea and simulated a BOP from the ear canal entrance to the spiral cochlea in a transient analysis utilizing fluid-structure interfaces. The model's middle ear was validated with experimental pressure measurements from the outer and middle ear of human temporal bones. The results showed high stapes footplate (SFP) displacements up to 28.5 μm resulting in high intracochlear pressures and basilar membrane (BM) displacements up to 43.2 μm from a BOP input of 30.7 kPa. The cochlea's spiral shape caused asymmetric pressure distributions as high as 4 kPa across the cochlea's width and higher BM transverse motion than that observed in a similar straight cochlea model. The developed spiral cochlea model provides an advancement from the straight cochlea model to increase the understanding of cochlear mechanics during blast and progresses toward a model able to predict potential hearing loss after blast.

Model of cochlear microphonic explores the tuning and magnitude of hair cell transduction current

The mammalian cochlea relies on the active forcing of sensory outer hair cells (OHCs) to amplify traveling wave responses along the basilar membrane. These forces are the result of electromotility, wherein current through the OHCs leads to conformational changes in the cells that provide stresses on surrounding structures. OHC transducer current can be detected via the voltage in the scala tympani (the cochlear microphonic, CM), and the CM can be used as an indicator of healthy cochlear operation. The CM represents a summation of OHC currents (the inner hair cell contribution is known to be small) and to use CM to probe the properties of OHC transduction requires a model that simulates that summation. We developed a finite element model for that purpose. The pattern of current generators (the model input) was initially based on basilar membrane displacement, with the current size based on in vitro data. The model was able to reproduce the amplitude of experimental CM results reasonably well when the input tuning was enhanced slightly (peak increased by ∼6 dB), which can be regarded as additional hair bundle tuning, and with a current/input value of 200–260 pA/nm, which is ∼4 times greater than the largest in vitro measures.

Emotion Recognition in Hindi Language using Gender Information, GMFCC, DMFCC and Deep LSTM

Long Short-Term Memory (LSTM) captures long-term dependencies accurately than other types of neural networks, and it is frequently used in deep learning. In this work, we have explored Deep LSTM with a dropout layer that minimizes the training overfitting. We have considered IITKGP-SEHSC emotional dataset for emotion recognition. We only deal with five types of emotions, namely angry, fear, happy, neutral, and sad emotions recorded from male and female speech. Since the IITKGP-SEHSC dataset is monolingual that means only spectral features are sufficient for emotion recognition. Traditional MFCC deals with low-frequency information. Here, we have explored two features, namely Gammatone Mel Frequency Cepstral Coefficient (GMFCC) and Discrete wavelet Mel Frequency Cepstral Coefficient (DMFCC). GMFCC deals with basilar membrane displacement obtained from the gammatone filter, and it is useful for recognizing gender from emotional speech. DMFCC deals with MFCC analysis on the high-frequency components of speech rather than the low-frequency components. In the proposed work, DMFCC has been explored for recognizing emotions from speech. The average accuracy of gender classification with Deep LSTM and GMFCC is 98.3%. The average emotion recognition rate with Deep LSTM and DMFCC is 92% and 88.7% individually for male speech and female speech, respectively. Our proposed model is built by combining the above sub-models, and it gives emotion recognition accuracy of 91.2% for male speech and 87.6% for female speech, respectively.

Nonlinearity of intracochlear motion and local cochlear microphonic: Comparison between guinea pig and gerbil

Studying the in-vivo mechanical and electrophysiological cochlear responses in several species helps us to have a comprehensive view of the sensitivity and frequency selectivity of the cochlea. Different species might use different mechanisms to achieve the sharp frequency-place map. The outer hair cells (OHC) play an important role in mediating frequency tuning. In the present work, we measured the OHC-generated local cochlear microphonic (LCM) and the motion of different layers in the organ of Corti using optical coherence tomography (OCT) in the first turn of the cochlea in guinea pig. In the best frequency (BF) band, our observations were similar to our previous measurements in gerbil: a nonlinear peak in LCM responses and in the basilar membrane (BM) and OHC-region displacements, and higher motion in the OHC region than the BM. Sub-BF the responses in the two species were different. In both species the sub-BF displacement of the BM was linear and LCM was nonlinear. Sub-BF in the OHC-region, nonlinearity was only observed in a subset of healthy guinea pig cochleae while in gerbil, robust nonlinearity was observed in all healthy cochleae. The differences suggest that gerbils and guinea pigs employ different mechanisms for filtering sub-BF OHC activity from BM responses. However, it cannot be ruled out that the differences are due to technical measurement differences across the species.

A role for tectorial membrane mechanics in activating the cochlear amplifier

The mechanical and electrical responses of the mammalian cochlea to acoustic stimuli are nonlinear and highly tuned in frequency. This is due to the electromechanical properties of cochlear outer hair cells (OHCs). At each location along the cochlear spiral, the OHCs mediate an active process in which the sensory tissue motion is enhanced at frequencies close to the most sensitive frequency (called the characteristic frequency, CF). Previous experimental results showed an approximate 0.3 cycle phase shift in the OHC-generated extracellular voltage relative the basilar membrane displacement, which was initiated at a frequency approximately one-half octave lower than the CF. Findings in the present paper reinforce that result. This shift is significant because it brings the phase of the OHC-derived electromotile force near to that of the basilar membrane velocity at frequencies above the shift, thereby enabling the transfer of electrical to mechanical power at the basilar membrane. In order to seek a candidate physical mechanism for this phenomenon, we used a comprehensive electromechanical mathematical model of the cochlear response to sound. The model predicts the phase shift in the extracellular voltage referenced to the basilar membrane at a frequency approximately one-half octave below CF, in accordance with the experimental data. In the model, this feature arises from a minimum in the radial impedance of the tectorial membrane and its limbal attachment. These experimental and theoretical results are consistent with the hypothesis that a tectorial membrane resonance introduces the correct phasing between mechanical and electrical responses for power generation, effectively turning on the cochlear amplifier.

3D Finite Element Modeling of Blast Wave Transmission from the External Ear to Cochlea.

As an organ that is sensitive to pressure changes, the ear is often damaged when a person is subjected to blast exposures resulting in hearing loss due to tissue damage in the middle ear and cochlea. While observation of middle ear damage is non-invasive, examining the damage to the cochlea is difficult to quantify. Previous works have modeled the cochlear response often when subjected to an acoustic pressure input, but the inner ear mechanics have rarely been studied when the ear is exposed to a blast wave. In this study we aim to develop a finite element (FE) model of the entire ear, particularly the cochlea, for predicting the blast wave transmission from the ear canal to cochlea. We utilized a FE model of the ear, which includes the ear canal, middle ear, and uncoiled two-chambered cochlea, to simulate the cochlear response to blast overpressure (BOP) at the entrance of the ear canal with ANSYS Mechanical and Fluent in a fluid-structure interface coupled analysis in the time domain. This model was developed based on previous middle and inner ear models, and the cochlea was remeshed to improve BOP simulation performance. The FE model was validated using experimentally measured blast pressure transduction from the ear canal to the middle ear and cochlea in human cadaveric temporal bones. Results from the FE model showed significant displacements of the tympanic membrane, middle ear ossicles, and basilar membrane (BM). The stapes footplate displacement was observed to be as high as 60µm, far exceeding the displacement during normal acoustic stimulation, when the 30kPa (4.35 psi, 183dB (SPL), Sound Pressure Level) of BOP was applied at the ear canal entrance. The large stapes movement caused pressures in the cochlea to exceed the physiological pressure level [< 10Pa, 120dB (SPL)] at a peak of 49.9kPa, and the BM displacement was on the order of microns with a maximum displacement of 26.4µm. The FE model of the entire human ear developed in this study provides a computational tool for prediction of blast wave transmission from the ear canal to cochlea and the future applications for assisting the prevention, diagnosis, and treatment of blast-induced hearing loss.

Objective sound quality evaluation for the vehicle interior noise based on responses of the basilar membrane in the human ear

The paper proposes a new method for objective sound quality evaluation for the vehicle interior noise based on the displacement of the basilar membrane in the human ear. The method was mainly carried out in four steps. Firstly, the noise samples in different seats of a car under different working conditions were collected through the vehicle interior noise test. Secondly, the subjective evaluation values (SEVs) of the noise samples were obtained by the adaptive grouped paired comparison method. In the third step, the statistical mean values of the basilar membrane displacement responses (SMVBMDR) were calculated in a lumped-parameter model of the human ear, and thereby a SMVBMDR-based feature matrix was established. Finally, taking the traditional psychoacoustic metrics and the extracted feature matrix as input, two BP neural network models for sound quality evaluation for the vehicle interior noise were established, respectively. To verify effectiveness of the new metric SMVBMDR, the correlations between this metric and the SEVs, as well as between the traditional psychoacoustic metrics and the SEVs were respectively analyzed. The results show that the SMVBDMDR has a higher correlation with the SEVs. Besides, the sound quality prediction of the model based on the SMVBMDR is more accurate than that of the model based on the traditional psychoacoustic metrics. The above results indicate that the new metric SMVBMDR can be used as an effective physiological acoustic metric for objective sound quality evaluation for the vehicle interior noise.

Effect of stimulation sites on the performance of electromagnetic middle ear implant: A finite element analysis

Electromagnetic middle ear implants (MEIs), which use the mechanical vibration of their implanted transducers to treat hearing loss, have emerged to overcome the limitations of conventional hearing aids. Several reports have indicated that the electromagnetic MEI's performance changed with different stimulation sites of the transducer. The aim of this study was to analyze the influence of the transducers' stimulation sites on the electromagnetic MEIs' performance. To aid this investigation, a human ear finite-element model was developed from micro-CT images of an adult's right ear. The validity of the model was confirmed by comparing the model-derived results with experimental data. Then, stimulation forces, which simulate ideal electromagnetic transducers, were respectively applied at five typical coupling sites: the umbo, incus body, incus long process, the round window, and the stapes. The stimulation sites' influence on the electromagnetic MEI's performance was studied by analyzing their corresponding basilar membrane displacements. The results show that stimulation of the round window with a force produces more cochlear stimulation than equal force stimulation of the umbo, incus body, incus long process and the stapes, though the superiority of the round window depends on its smaller area compared to the stapes footplate. Among the forward stimulation, the stapes is the optimal stimulation site for the electromagnetic transducer regarding its hearing compensation's efficiency. The performance of the umbo stimulation is comparable to that of the incus-long-process stimulation. Driving the incus body is less efficient than stimulating the other forward driving sites. Additional, using the stapes response to evaluate the forward stimulation gives results similar to those deduced by the basilar membrane response; in contrast, for the round-window stimulation, the evaluation result based on the stapes response is prominently less than the one calculated by the basilar membrane response, especially in the mid-high frequency range.

The Influence of Piezoelectric Transducer Stimulating Sites on the Performance of Implantable Middle Ear Hearing Devices: A Numerical Analysis.

To overcome the inherent deficiencies of hearing aids, implantable middle ear hearing devices (IMEHDs) have emerged as a new treatment for hearing loss. However, clinical results show that the IMEHD performance varies with its transducer’s stimulating site. To numerically analyze the influence of the piezoelectric transducer’s stimulating sites on its hearing compensation performance, we constructed a human ear finite element model and confirmed its validity. Based on this finite element model, the displacement stimulation, which simulates the piezoelectric transducer’s stimulation, was applied to the umbo, the incus long process, the incus body, the stapes, and the round window membrane, respectively. Then, the stimulating site’s effect of the piezoelectric transducer was analyzed by comparing the corresponding displacements of the basilar membrane. Besides, the stimulating site’s sensitivity to the direction of excitation was also studied. The result of the finite element analysis shows that stimulating the incus body is least efficient for the piezoelectric transducer. Meanwhile, stimulating the round window membrane or the stapes generates a higher basilar membrane displacement than stimulating the eardrum or the incus long process. However, the performance of these two ideal sites’ stimulation is sensitive to the changes in the excitation’s direction. Thus, the round window membrane and the stapes is the ideal stimulating sites for the piezoelectric transducer regarding the driving efficiency. The direction of the excitation should be guaranteed for these ideal sites.

Numerical analysis of the influence of otitis media on the hearing compensation performance of round-window stimulation

In order to study the influence of tympanic membrane lesion and ossicular erosion caused by otitis media on the hearing compensation performance of round-window stimulation, a human ear finite element model including cochlear asymmetric structure was established by computed tomography (CT) technique and reverse engineering technique. The reliability of the model was verified by comparing with the published experimental data. Based on this model, the tympanic membrane lesion and ossicular erosion caused by otitis media were simulated by changing the corresponding tissue structure. Besides, these simulated diseases' effects on the round-window stimulation were studied by comparing the corresponding basilar-membrane's displacement at the frequency-dependent characteristic position. The results show that the thickening and the hardening of the tympanic membrane mainly deteriorated the hearing compensation performance of round-window stimulation in the low frequency; tympanic membrane perforation and the minor erosion of ossicle with ossicular chain connected slightly effected the hearing compensation performance of round-window stimulation. Whereas, different from the influence of the aforementioned lesions, the ossicular erosion involving the ossicular chain detachment increased its influence on performance of round-window stimulation at the low frequency. Therefore, the effect of otitis media on the hearing compensation performance of round-window stimulation should be considered comprehensively when designing its actuator, especially the low-frequency deterioration caused by the thickening and the hardening of the tympanic membrane; the actuator's low-frequency output should be enhanced accordingly to ensure its postoperative hearing compensation performance.

Constraints imposed by zero-crossing invariance on cochlear models with two mechanical degrees of freedom.

The zero crossings of basilar-membrane (BM) responses to clicks are nearly independent of stimulus intensity. This work explores the constraints that this invariance imposes on one-dimensional nonlinear cochlear models with two degrees of freedom (2DoF). The locations of the poles and zeros of the BM admittance, calculated for a set of linear models in which the strength of the active force is progressively decreased, provides a playground for evaluating the behavior of a corresponding nonlinear model at increasing stimulus levels. Mathematical constraints on the model parameters are derived by requiring that the poles of the admittance move horizontally in the s-plane as the active force is varied. These constraints ensure approximate zero-crossing invariance over a wide stimulus level range in a nonlinear model in which the active force varies as a function of the local instantaneous BM displacement and velocity. Two different 2DoF models are explored, each capable of reproducing the main qualitative characteristics of the BM response to tones (i.e., the tall and broad activity pattern at low stimulus levels, the large gain dynamics, and the partial decoupling between gain and phase). In each model, the motions of the two masses are compared with response data from animal experiments.

Influence of ossicular chain malformation on the performance of round-window stimulation: A finite element approach.

As a novel application of implantable middle ear hearing device, round-window stimulation is widely used to treat hearing loss with middle ear disease, such as ossicular chain malformation. To evaluate the influence of ossicular chain malformations on the efficiency of the round-window stimulation, a human ear finite element model, which incorporates cochlear asymmetric structure, was constructed. Five groups of comparison with experimental data confirmed the model's validity. Based on this model, we investigated the influence of three categories of ossicular chain malformations, that is, incudostapedial disconnection, incus and malleus fixation, and fixation of the stapes. These malformations' effects were evaluated by comparing the equivalent sound pressures derived from the basilar membrane displacement. Results show that the studied ossicular chain malformations mainly affected the round-window simulation's performance at low frequencies. In contrast to the fixation of the ossicles, which mainly deteriorates round-window simulation's low-frequency performance, incudostapedial disconnection increases this performance, especially in the absence of incus process and stapes superstructure. Among the studied ossicular chain malformations, the stapes fixation has a much more severe impact on the round-window stimulation's efficiency. Thus, the influence of the patients' ossicular chain malformations should be considered in the design of the round-window stimulation's actuator. The low-frequency output of the round-window simulation's actuator should be enhanced, especially for treating the patients with stapes fixation.

A comparative finite-element analysis of acoustic transmission in human cochlea during forward and reverse stimulations

Acoustic energy can be transmitted into the cochlea by two modes: one mode is the forward stimulation where acoustic waves are normally transmitted from the tympanic membrane (TM) to the cochlea via the ossicular chain, another mode is the reverse stimulation where a transducer is coupled to the round window (RW) and it provides a direct mechanical stimulation to the cochlea via the RW membrane. Due to the difference of the energy transmission pathway, the acoustic waves encounter different impedances and the basilar membrane (BM) vibrates with different forms during the acoustic transmission processes. To understand the dynamic characteristics of human cochlea during forward and reverse stimulations, a finite element model of human ear is developed in this study. And the cochlear input impedance, the cochlear reverse impedance, and the BM displacement responses are derived. The results show that the cochlea input impedance keeps stable in a certain frequency range, while the RW impedance and middle ear impedance vary obviously with frequency. And the middle ear impedance is higher than the cochlear input impedance at lower frequencies. Furthermore, the BM motions in response to two stimulations not only have the phase difference, but also have the efficiency difference. The vibration efficiency of the BM in response to forward stimulation is about 13 dB higher than that to reverse stimulation. But under the impulsive stimulus, the maximum displacement of the BM occurs in the middle cochlea for both of stimulations.