Model Of Middle Ear Research Articles

Significance of middle ear model for prediction of metabolic exhaustion of the auditory system

Modern day military noise is complex, involving irregular impulses riding on top of moderate continuous background noise. An accurate prediction of injury from complex noise exposure requires both a cochlear metabolic exhaustion (ME) model and an accurate middle ear model (MEM), accounting for acoustic reflex (AR) and annular ligament (AL) nonlinearities. An end-to-end biomechanical model including a ME model was developed that established a good correlation between the outer hair cell energy deficit (OHC-D) outcomes and the temporary threshold shift (TTS) data from chinchilla complex noise exposure, explained the data collected, and provided insights on the effect of complex noise exposure on outcomes, including the effect of inter-pulse Interval (IPI), shot sequence, and background noise. Literature data were used to derive the open ear and middle ear transfer functions (TF). In this paper, the model results are discussed with an emphasis on the MEM component. The differences in the end-to-end model results are compared between the new MEM and a MEM adopted from the improved AHAAH-ICE model that includes the AR and AL nonlinearities, with model parameters adjusted for chinchilla. The results show that the TFs from the two MEMs cannot be matched using mere parametric optimization, due mainly to the fact that the chinchilla middle ear is rather tuned to the higher frequencies compared to that of human. There is a need for an improved MEM for the chinchilla middle ear TF including AR effects.

Development of a non-parametric probabilistic model of the human middle ear

The middle ear is the part of peripheral auditory system that works to transmit the sound energy from the outer to the inner ear, matching their highly different impedances. Due to its importance for the human hearing, the middle ear has been studied through mathematical models over the past 70 years. The use of deterministic approaches has been the mainstream on the development of these models despite it is well recognized that middle ear has a natural variability with respect to its mechanical and dynamical properties, kwon as random uncertainties. In this work a lumped-element model of the middle ear is used as a baseline deterministic model for the development of a probabilistic model using a non-parametric approach. This probabilistic approach is characterized by adding the uncertainties directly into the global matrices of the modeled system. Furthermore, an optimization process using a single objective function was used for fitting both probabilistic and baseline deterministic models. The probabilistic model developed presents promising results, showing statistical responses in agreement with experimental evidences. In addition, advantages were identified in comparison to a model previously developed with a parametric probabilistic approach.

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.

Phase variation with altering phosphorylcholine expression of nontypeable Haemophilus influenzae affects bacteria clearance and mucosal immune response in the middle ear and nasopharynx

Nontypeable Haemophilus influenzae (NTHi) is a chief pathogen in both acute otitis media and otitis media with effusion. Phosphorylcholine (ChoP) is expressed on lipooligosaccharides, and ChoP has phase variation, which is related to its adhesion to and invasion of epithelial cells in the upper airway. However, little is known about the role of ChoP expression. We examined the kinetics of the mucosal clearance of NTHi from the nose and middle ear and the mucosal immune response to NTHi infection by comparing ChoP(+) and ChoP(-) strains in a mouse model of middle ear and nasal challenge. Six-week-old male BALB/c mice were subjected to bacterial challenge in the middle ear and nasopharynx. Mice were inoculated with a suspension of a ChoP(+) strain or ChoP(-) strain of NTHi. On days 1, 3, and 7 after inoculation, the middle ear wash (MEW) and nasal wash (NW) were harvested from each group. The samples were used for bacterial counts and the supernatant was used to measure the level of cytokines and C-reactive protein (CRP). MEWs in the ChoP(+) strain group had significantly higher bacterial counts than those in the ChoP(-) strain group on day 1. However, bacteria were eradicated in the ChoP(+) strain group on day 7. NWs in the ChoP(+) strain group had higher bacterial counts than those in the ChoP(-) strain group during the experiment, however, there was no significant difference between the two strains. The levels of cytokines were significantly higher in the ChoP(-) strain group than in the ChoP(+) strain group in MEWs, but these cytokine levels were low in NWs. The CRP concentration in the ChoP(-) group was high on day 7 in the MEWs. In NWs, the CRP concentration was low in all groups during the experiment. ChoP expression of NTHi changes the organism susceptible to killing by CRP, and the ChoP(+) strain might be gradually eradicated from the middle ear via the CRP-complement cascade, but not from nasopharynx. Based on our findings, phase variation by altering Phosphorylcholine expression of nontypeable Haemophilus influenzae affects bacteria clearance and mucosal immune response in the middle ear and nasopharynx.

Effect of transducer fixation in the human middle ear on sound transfer

An ear is one of the smallest and the most important organs in a human body. Hearing loss becomes a significant problem for modern societies. Therefore, a non-linear model of the human middle ear is used to study effectiveness of a middle era implant. Special care is focused on the effect of floating mass transducer fixation on the ear system dynamics and sound transfer to the inner ear. A transducer fixation is realized by means of a coupler. Its characteristic plays the key role in stapes excitation. A numerical analysis for two variants of damping properties is performed, representing the intact and pathological ear stimulated by a low and strong external signal. A stiffness characteristic of the coupler can shift a main resonance region of the middle ear structure and cause polyharmonic and even chaotic motion of the stapes and the transducer. As a result, the conditions of regular and irregular vibrations of the stapes, near the primary resonance, are defined. Finally, practical remarks about how to avoid polyharmonic and irregular oscillations are proposed.

Analysis of the Human Middle Ear Dynamics Through Multibody Modeling.

The dynamics of the human middle ear (ME) has been studied in the past using several computational and experimental approaches in order to observe the effect on hearing of different conditions, such as conductive disease, corrective surgery, or implantation of a middle ear prosthesis. Multibody (MB) models combine the analysis of flexible structures with rigid body dynamics, involving fewer degrees-of-freedom (DOF) than finite element (FE) models, but a more detailed description than traditional 1D lumped parameter (LP) models. This study describes the reduction of a reference FE model of the human middle ear to a MB model and compares the results obtained considering different levels of model simplification. All models are compared by means of the frequency response of the stapes velocity versus sound pressure at the tympanic membrane (TM), as well as the system natural frequencies and mode shapes. It can be seen that the flexibility of the ossicles has a limited impact on the system frequency response function (FRF) and modes, and the stiffness of the tendons and ligaments only plays a role when above certain levels. On the other hand, the restriction of the stapes footplate movement to a piston-like behavior can considerably affect the vibrational modes, while constraints to the incudomalleolar joint (IMJ) and incudostapedial joint (ISJ) can have a strong impact on the system FRF.

The role of third windows on human sound transmission of forward and reverse stimulations: A lumped-parameter approach.

The vestibular and cochlear aqueducts serve as additional sound transmission paths and produce different degrees of volume velocity shunt flow in cochlear sound transmission. To investigate its effect on forward and reverse stimulations, a lumped-parameter model of the human ear, which incorporates the third windows, was developed. The model combines a transmission-line ear-canal model, a middle-ear model, and an inner-ear model, which were developed previously by different investigators. The model is verified by comparison with experiments. The intracochlear differential-pressure transfer functions, which reflect the input force to the organ of Corti, were calculated. The results show that middle-ear gain for forward sound transmission is greater than the gain for reverse sound transmission. Changes in the cochlear aqueduct impedance have little effect on forward and reverse stimulations. The vestibular aqueduct has little effect on forward stimulation, but increasing its impedance causes deterioration on reverse stimulation below 300 Hz. Decreasing its impedance increases the excitation effect during reverse stimulation over the entire frequency, especially below 1000 Hz. Moreover, compared with the case without the third windows, the presence of the third windows has little effect on forward stimulation. Whereas, it boosts the reverse stimulation's performance below 300 Hz.

Sound Transmission in the First Nonlinear Model of Middle Ear with an Active Implant

This paper shows an influence of a transducer of a middle ear implant on ear dynamics on the basis of the multi-degree-of-freedom biomechanical system. Results of numerical simulations of an ear model with implant are compared with those of the healthy middle ear. Two variants of damping are analysed. The first one typical for a normal healthy middle ear structure and the second one describes pathological properties of the human ear. Moreover, the behaviour of the transducer under various external excitations is investigated. For some set of parameters, the middle ear with the implant behaves regularly but sometimes even chaotically in case of strong excitation.

Pilot study of pressure-flow properties in a numerical model of the middle ear.

Background: Constructing a three-dimensional (3D) model through non-invasive techniques will greatly benefit the diagnosis and treatment of otitis media. However, such a model should reflect the physiological characteristics of the middle ear; in particular, the pressure-flow responses determine the validity of the model. Objectives: A 3D model of the middle ear was constructed by digital scanning and simulation. The pressure-flow properties in the model were measured to evaluate whether the model could reflect the real middle ear under physiological and pathological conditions. Materials and methods: Computed tomography (CT) scanning data from a healthy woman were input into Mimics 20.0 to construct 3D images of the middle ear. The 3D images were treated with Ansys 15.0 for finite element mesh generation. Msc Nastran 2014 were used for the fluid-solid coupling calculations. Results: The pressure-flow rate in the model resembled a Venturi tube, namely, the pressure decreased with increasing flow velocity, especially in the Eustachian tube. In the absence of the right mastoid process, the differences in air pressure and the maximal velocity in the model were reduced. Conclusions: This numerical model based on CT images of the middle ear recapitulates the biomechanical characteristics of the real middle ear. Significance: This study provides an easy and rapid approach to constructing a middle ear model for diagnosis and treatment of otitis media.

Assessment of hearing loss induced by tympanic membrane perforations under blast environment.

This study provides an approach to estimating tympanic membrane perforation-induced hearing loss (HL) using a human middle ear model. Sixty-one cases of tympanic membrane perforation originating from fireworks were reported from the Ear-Nose-Throat Department. The otoscope, audiometry data and diagnosis records were organized, and gender, age, etiology, perforation size and diseased ear side were classified as independent variables. A multinomial regression model was used to analyze the potential effects of the variables on HL. Meanwhile, a human middle ear model was implemented to calculate the ensued HL resulting from different perforation areas and sites. In addition, linear regression models were used to establish functions between perforation size and HL. The audiometry data indicate that HL at high frequencies (f > 2kHz) is much more profound than that at the speech frequency band (f < 1kHz). Compared with mild HL (<15dB), mediate HL (15-30dB) was correlated with the perforation area (p < 0.05, 95% CI), while severe HL (>30dB) was affected by both perforation size and age (p < 0.05, 95% CI). However, other factors, including gender and diseased ear side, do not show a statistically significant effect on HL. Furthermore, the Kruskal-Wallis test result reveals that HL at frequencies of 0.25 kHz ≤ f ≤ 8kHz is strongly associated with the perforation size (p < 0.05, 95% CI). It is conclusive that HL is positively proportional to the perforation size. However, HL is not correlated with the perforation site for small perforation areas of < 10% (p > 0.05, 95% CI).

How flexibility and eardrum cone shape affect sound conduction in single-ossicle ears: a dynamic model study of the chicken middle ear.

It is believed that non-mammals have poor hearing at high frequencies because the sound-conduction performance of their single-ossicle middle ears declines above a certain frequency. To better understand this behavior, a dynamic three-dimensional finite-element model of the chicken middle ear was constructed. The effect of changing the flexibility of the cartilaginous extracolumella on middle-ear sound conduction was simulated from 0.125 to 8kHz, and the influence of the outward-bulging cone shape of the eardrum was studied by altering the depth and orientation of the eardrum cone in the model. It was found that extracolumella flexibility increases the middle-ear pressure gain at low frequencies due to an enhancement of eardrum motion, but it decreases the pressure gain at high frequencies as the bony columella becomes more resistant to extracolumella movement. Similar to the inward-pointing cone shape of the mammalian eardrum, it was shown that the outward-pointing cone shape of the chicken eardrum enhances the middle-ear pressure gain compared to a flat eardrum shape. When the outward-pointing eardrum was replaced by an inward-pointing eardrum, the pressure gain decreased slightly over the entire frequency range. This decrease was assigned to an increase in bending behavior of the extracolumella and a reduction in piston-like columella motion in the model with an inward-pointing eardrum. Possibly, the single-ossicle middle ear of birds favors an outward-pointing eardrum over an inward-pointing one as it preserves a straight angle between the columella and extrastapedius and a right angle between the columella and suprastapedius, which provides the optimal transmission.

How Stapes Ankylosis and Fracture Affect Middle Ear Dynamics: A Numerical Study.

Numerical models of the human middle ear have been developed throughout the last 30 years, for different purposes. While several types of pathologies have been studied, stapedial disorders were seldomly explored. This papers aims to clarify how stapes fracture and some forms of stapes ankylosis, such as stapedial tendon (ST) ossification, augmented pyramidal eminence (PE) and bony bar presence, affect the sound transmission through the middle ear. In addition, the stapes dynamics is also analyzed by means of total displacement and first principal strain. For the purpose of the study, first, a three-dimensional finite element model of the human middle ear is detailed and validated under normal (healthy) conditions. The model is then modified to represent the stapedial disorders of interest. A measure is established for evaluating how the disorders reduce sound transmission through the middle ear. Results of the reduction of sound transmission showed that the different forms of stapes ankylosis affect primarily low frequencies, while the stapes fracture mostly affects high frequency sound transmission. According to the results, an augmented PE does not restrict stapes movement unless followed by some ossification of the ST. In addition, the question whether the fracture is in the anterior or posterior crus and the distance of the fractured part from the stapes footplate have a relevant role in the reduction of the sound transmission. Finally, the analysis of total displacement and first principal strain of the stapes helped to highlight some differences among the stapedial disorders.

A study on the effect of ligament and tendon detachment on human middle ear sound transfer using mathematic model.

The objective of this study is to investigate the effects of ligament and tendon detachment on human middle ear sound transfer. For this purpose, a geometric human middle ear model was reconstructed based on the computed tomography scanning data of the temporal bones from healthy adult volunteers. For the ear model, pars tensa was assumed to be fit for a 5-parameter Maxwell model and inverse method was used to obtain the necessary coefficients. Furthermore, frequency response method was implemented to investigate the vibration behaviors of tympanic membrane umbo and stapes footplate under an acoustic stimulus of 90 dB within 0.2-8 kHz. Meanwhile, nine patterns of fractured ligaments and tendons, whose effects on the middle ear sound transfer function were simulated by setting free the nodes of the ligaments and tendons of interest. The results indicate that the displacement of tympanic membrane umbo and stapes footplate as well as the velocity transfer function lies within the bounds of the published experimental data. The detachments of ligaments or tendons except for lateral mallear ligament may incur both gains as much as 15 dB and losses of -8 dB in the velocity of stapes footplate at low frequencies (f≤ 1 kHz), while no significant changes were observed at high frequencies (f > 1 kHz). However, detachment of the ligaments or tendons induces tiny changes in the displacement of stapes footplate at the frequencies of 0.2-8 kHz.

Assessment methodology for pressure-related aural discomfort in high-speed trains using airtightness experiments and mathematical models

This study aimed at establishing an evaluation methodology for aural discomfort induced by the interior pressure changes in high-speed trains running in tunnels. Experiments in pressure cabin, which can reveal the relationship between aural discomfort and pressure change, were discussed. Furthermore, a human middle ear model was used to simulate the vibration. The experimental conditions were considered as pressure loads, which were exerted on the tympanic membrane. Furthermore, the aural discomfort was hierarchically divided into four levels: ideal, good, bad, and worse. Four indicators, such as the tympanic membrane displacement and stress and the stapes footplate displacement and velocity, were used to establish the discomfort criteria. Logistic regression analysis was used to investigate the incidences of each level as well as to obtain the thresholds between levels. The outcomes have a p-value of less than 0.05; hence, the response results of the indicators are statistically significant. Additionally, the thresholds of the indicators were obtained and used to differentiate the aural discomfort levels. The intervals of the four indicators are (0,T1), (T1,Tc), (Tc,T3), and (T3,&gt;T3) for the discomfort levels of ideal, good, bad, and worse, respectively. Moreover, the onset mechanism of aural sensations was revealed using the four indicators. It can be implied that large tympanic membrane and stapes footplate displacements tend to elicit ear complaints, such as fullness, otalgia, and vertigo, whereas the large stapes footplate velocity affects the onset of tinnitus and hearing loss.

The Effect of Virtual Three‐Dimensional Stereoscopic Middle and Inner Ear Models on First‐Year Dental Students' Short‐Term Retention

Several studies in virtual three‐dimensional (3D) anatomy have shown either no difference in traditional and 3D learning among dental students or disadvantages in 3D learning over traditional learning. There are few studies in the literature that explore the effectiveness of virtual stereoscopic 3D anatomy models on dental students' learning. This study aimed to determine if virtual 3D stereoscopic anatomical models of the middle and inner ear could improve first‐year dental students' short‐term retention. This study also aimed to determine if there was a correlation between first‐year dental students' spatial abilities and their learning gains from virtual 3D anatomy exposure. During the fall 2018 semester, the first‐year dental students were invited to participate in 3D learning sessions pertaining to the middle and inner ear. Students (n=18) attended to a 3D learning session featuring virtual stereoscopic middle and inner ear models. During the learning session, the student participants completed a pre‐test before and a post‐test after the virtual 3D learning experience. At the end of the 3D learning sessions, students completed a mental rotation test (MRT) for measuring their spatial abilities and a survey for assessing their perceptions of 3D learning. The average scores on all of the students' performance measures, pre‐tests, post‐tests, and MRT's, will be analyzed using a repeated measures ANOVA. In addition, the pre‐ and post‐ knowledge test performances, respectively, of the students with high and low spatial ability will be compared using a one‐way ANOVA. The results of the statistical analyses will determine whether there is a significant difference between the pre‐ and post‐3D test scores of the first‐year dental students and whether there is a significant relationship between first‐year dental students' spatial abilities and learning. Overall, the first‐year dental students perceived the 3D learning sessions of middle and inner ear anatomy to be a positive learning experience. The use of virtual stereoscopic 3D anatomy has the potential to improve first‐year dental students' learning of the anatomy of regions as complex as the middle and inner ear when used as a supplement to traditional instruction.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A lumped-element model of the chinchilla middle ear.

An air-conduction circuit model was developed for the chinchilla middle ear and cochlea. The lumped-element model is based on the classic Zwislocki model of the same structures in human. Model parameters were fit to various measurements of chinchilla middle-ear transfer functions and impedances, using a combination of error-minimization-driven computer-automated and manual fitting methods. The measurements used to fit the model comprise a newer, more-extensive data set than previously used, and include measurements of stapes velocity and inner-ear sound pressure within the vestibule and the scala tympani near the round window. The model is in agreement with studies of the effects of middle-ear cavity holes in experiments that require access to the middle-ear air space. The structure of the model allows easy addition of other sources of auditory stimulation, e.g., the multiple sources of bone-conducted sound-the long-term goal for the model's development-and mechanical stimulation of the ossicles and round window.

Human ear finite element model study of the effects of ear canal and middle ear cavity on air conduction and bone conduction

Objective:To study the influence of the ear canal and middle ear cavity on air conduction and bone conduction. Method:A finite element model of the human middle ear was established. By establishing the external ear canal and the middle ear cavity, we evaluated the effects of the external canal and the middle ear cavity on air conduction and bone conduction. Result:In air conduction, the external canal improved the stapes response at the frequency range of 0.5 kHz to 6 kHz, and the maximum increase was 11 dB at 3 kHz. The middle ear cavity mainly reduced the response of stapes at mid-low frequency, with the drops of 2-4 dB under 2 kHz; in bone conduction, ear canal slightly reduced the low-frequency response, but increased the response of the stapes at the mid-high frequency, with a maximum increase of 1.9 dB at 1.5 kHz. The middle ear cavity mainly increased the stapes response at mid-frequency near 1.5 kHz, with a maximum increase of 2.5 dB. Conclusion:Our results show that, in air conduction, the ear canal significantly increases the middle-frequency response, while the middle ear cavity decreases the low-mid frequency response. Whereas, the ear canal and the middle ear cavity have slightly effect on bone conduction.

Determination of Resonant Frequencies of an Acoustical System of the Human by Means of Objective Methods of a Research of Hearing

Different pathological processes lead to changes of human auditory system characteristics. Nowadays, hearing diagnosis is not surprising and does not cause unnecessary questions, because most people understand the importance of health care and know about problems that can arise if they are not warned in advance. In the world there are many methods and programs for objective diagnosis of human hearing. Today, among hearing diagnosing objective methods, multifrequency acoustic impedancemetry and otoacoustic emission are most widely used in clinical practice. Comparison of the obtained characteristics in normal and pathological conditions allows us to judge the degree of changes in the auditory organ and diagnose some of its diseases. However, a large discrepancy between intersubject data may overlap deviations from norms. This is the main problem in diagnosis of hearing system. Determination the resonant frequency of human auditory system structural elements in a comprehensive study, using objective methods gives us a possibility to detect changes in ear conductive system more accurately. Significant changes in the resonance frequency of human middle ear make it possible to detect an existing pathology at a functional level. Resonant frequency shift (to one or the other side) may indicate the presence of otosclerosis, auditory ossicles chain break, etc. In this work, the parameters of the human middle ear were obtained theoretically, based on a two-circuit model of the human middle ear, and confirmed experimentally, using tympanometry and otoacoustic emission, which eliminate the main problem of hearing diagnostics and offer new diagnostic parameters for sound-conducting ear system diseases diagnosing, namely, value of resonant frequencies. Determining the resonant frequency of human auditory system structures in a comprehensive study using objective methods, allows us to identify changes in ear sound-conducting system. To study human auditory system resonant frequency, an electromechanical model of human middle ear was selected and its main parameters were determined: eardrum and tympanic cavity flexibility, acoustic impedance of air in the tympanic cavity and auditory tube, resonant frequency of first and second circuits of middle ear vibrating system, auditory ossicles weight. Purpose of the study - to search and identify effective ways to improve objective acoustic diagnostic methods and substantiate the choice of tympanometry and otoacoustic emission as the main methods for studying the state of the human auditory system, which allow a detailed assessment of pathological processes. Ref. 10, fig. 2, tabl. 1.`

Model-based hearing diagnostics based on wideband tympanometry measurements utilizing fuzzy arithmetic

Today's audiometric methods for the diagnosis of middle ear disease are often based on a comparison of measurements with standard curves, that represent the statistical range of normal hearing responses. Because of large inter-individual variances in the middle ear, especially in wideband tympanometry (WBT), specificity and quantitative evaluation are greatly restricted. A new model-based approach could transform today's predominantly qualitative hearing diagnostics into a quantitative and tailored, patient-specific diagnosis, by evaluating WBT measurements with the aid of a middle-ear model. For this particular investigation, a finite element model of a human ear was used. It consisted of an acoustic ear canal and a tympanic cavity model, a middle-ear with detailed nonlinear models of the tympanic membrane and annular ligament, and a simplified inner-ear model. This model has made it possible for us to simulate pathologies like the stiffening of ligaments or joints, because we can simply change the corresponding mechanical parameters of the model. On the other hand, it is also possible to identify pathologies from measurements, by analyzing the parameters obtained by a system identification procedure. This reduces the number of required model parameters through sensitivity studies and parameter clustering. Uncertainties due to the lack of knowledge, subjectivity in numerical implementation and model simplification are taken into account by the application of fuzzy arithmetic. The most confident parameter set can be determined by applying an inverse fuzzy method on the measurement data. The principle and the benefits of this model-based approach are illustrated by the example of a two-mass oscillator, and also by the simulation of the energy absorbance of an ear with malleus fixation, where the parameter changes that are introduced can be determined quantitatively through the system identification.

Sound localization in the lizard using internally coupled ears: A finite-element approach

A number of interesting differences become apparent when comparing the hearing systems of terrestrial vertebrates, especially between mammals and non-mammals. Almost all non-mammals possess only a single ossicle, enabling impedance matching and hearing below 10 kHz. The middle ear (ME) evolved as a chain of three ossicles in mammals, enabling sound transmission up to higher frequencies than in similar-sized non-mammals. The relatively low-frequency hearing in non-mammals is associated with audible wavelengths that are significantly larger than the head. Therefore, it is unlikely that localization of the sound source can be obtained by using external cues between the ears (intensity and time difference between both sides), especially when compared to similarly sized mammals. The heads of many non-mammals contain large air-filled cavities, which acoustically couple both MEs. This article studies acoustic responses and sound-source localization capabilities of the coupled MEs of the brown anole (Anolis sagrei), using finite-element modeling. Based on high-resolution μCT data, 3D finite-element models of the ME and interaural cavity were constructed. The parameter values in the ME model were determined such that the response of the isolated ME matches experimental data of literature and the velocity ratio between the tympanic membrane (apex) and footplate reflects the anatomical arrangement of the columellar lever in the anole. It was found from simulation of the coupled ME model that the interaural connection amplifies intensity differences between both sides and thus enhances the capability of sound-source localization. In addition, the interaural canal doubles the phase differences of the incident external sound waves between the eardrums. In isolated ears, generating such phase differences would require head sizes twice as large. Effects of the inner-ear loading on the sound-source localization of the coupled MEs were investigated as well. The inner-ear load lowered the peak velocity ratios between the ears, but created broader plateaus of useful directionality, indicating that inner-ear loading not only influences sound perception but also sound localization in internally connected ears.