Investigation of the human tympanic membrane oscillation ex vivo by Doppler optical coherence tomography

Investigations of the tympanic membrane (TM) can have an important impact on understanding the sound conduction in the ear and can therefore support the diagnosis and treatment of diseases in the middle ear. High‐speed Doppler optical coherence tomography (OCT) has the potential to describe the oscillatory behaviour of the TM surface in a phase‐sensitive manner and additionally allows acquiring a three‐dimensional image of the underlying structure. With repeated sound stimuli from 0.4 kHz to 6.4 kHz, the whole TM can be set in vibration and the spatially resolved frequency response functions (FRFs) of the tympanic membrane can be recorded. Typical points, such as the umbo or the manubrium of malleus, can be studied separately as well as the TM surface with all stationary and wave‐like vibrations. Thus, the OCT methodology can be a promising technique to distinguish between normal and pathological TMs and support the differentiation between ossicular and membrane diseases. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In vivo dynamic characterization of the human tympanic membrane using pneumatic optical coherence tomography

Decreased mobility of the human eardrum, the tympanic membrane (TM), is an essential indicator of a prevalent middle ear infection. The current diagnostic method to assess TM mobility is via pneumatic otoscopy, which provides subjective and qualitative information of subtle motion. In this study, a handheld spectral-domain pneumatic optical coherence tomography system was developed to simultaneously measure the displacement of the TM, air pressure inputs applied to a sealed ear canal, and to perform digital pneumatic otoscopy. A novel approach based on quantitative parameters is presented to characterize spatial and temporal variations of the dynamic TM motion. Furthermore, the TM motions of normal middle ears are compared with those of ears with middle ear infections. The capability of noninvasively measuring the rapid motion of the TM is beneficial to understand the complex dynamics of the human TM, and can ultimately lead to improved diagnosis and management of middle ear infections.     

Infrasonic hearing in birds: a review of audiometry and hypothesized structure–function relationships

The perception of airborne infrasound (sounds below 20 Hz, inaudible to humans except at very high levels) has been documented in a handful of mammals and birds. While animals that produce vocalizations with infrasonic components (e.g. elephants) present conspicuous examples of potential use of infrasound in the context of communication, the extent to which airborne infrasound perception exists among terrestrial animals is unclear. Given that most infrasound in the environment arises from geophysical sources, many of which could be ecologically relevant, communication might not be the only use of infrasound by animals. Therefore, infrasound perception could be more common than currently realized. At least three bird species, each of which do not communicate using infrasound, are capable of detecting infrasound, but the associated auditory mechanisms are not well understood. Here we combine an evaluation of hearing measurements with anatomical observations to propose and evaluate hypotheses supporting avian infrasound detection. Environmental infrasound is mixed with non‐acoustic pressure fluctuations that also occur at infrasonic frequencies. The ear can detect such non‐acoustic pressure perturbations and therefore, distinguishing responses to infrasound from responses to non‐acoustic perturbations presents a great challenge. Our review shows that infrasound could stimulate the ear through the middle ear (tympanic) route and by extratympanic routes bypassing the middle ear. While vibration velocities of the middle ear decline towards infrasonic frequencies, whole‐body vibrations – which are normally much lower amplitude than that those of the middle ear in the ‘audible’ range (i.e. >20 Hz) – do not exhibit a similar decline and therefore may reach vibration magnitudes comparable to the middle ear at infrasonic frequencies. Low stiffness in the middle and inner ear is expected to aid infrasound transmission. In the middle ear, this could be achieved by large air cavities in the skull connected to the middle ear and low stiffness of middle ear structures; in the inner ear, the stiffness of round windows and cochlear partitions are key factors. Within the inner ear, the sizes of the helicotrema and cochlear aqueduct are expected to play important roles in shunting low‐frequency vibrations away from low‐frequency hair‐cell sensors in the cochlea. The basilar papilla, the auditory organ in birds, responds to infrasound in some species, and in pigeons, infrasonic‐sensitive neurons were traced back to the apical, abneural end of the basilar papilla. Vestibular organs and the paratympanic organ, a hair cell organ outside of the inner ear, are additional untested candidates for infrasound detection in birds. In summary, this review brings together evidence to create a hypothetical framework for infrasonic hearing mechanisms in birds and other animals.     

Optimal stimulation frequency for vibrational optical coherence elastography

Vibrational optical coherence elastography (OCE) is a promising tool for extracting the mechanical property of soft tissue. Purpose of this study is focusing on settling the optimal frequency range for vibrational OCE with evenly distributed stress filed. A finite element model of 2% agar phantom was built by ANSYS with a vibration stimulation frequency range from 200 to 3000 Hz. Practical experiments were carried out for cross‐validation with the same frequencies and sample. Lateral and horizontal stress filed distributions under different frequencies were mathematically evaluated by coefficient of variance and degree of linearity. Results from simulation and practical experiment cross‐validated each other and 1000 Hz was set as the maximum ideal frequency for vibrational OCE, while the minimum frequency is set by theoretical calculation with a result of 250 Hz. An ex vivo biological sample was utilised to testify performance of vibrational OCE with excitation frequencies in and out of concluded optimal range, which showed that stiffness was better mapped out in optimal frequency range.     

Smartphone‐based spectral imaging otoscope: System development and preliminary study for evaluation of its potential as a mobile diagnostic tool

We develop a novel smartphone‐based spectral imaging otoscope for telemedicine and examine its capability for the mobile diagnosis of middle ear diseases. The device was applied to perform spectral imaging and analysis of an ear‐mimicking phantom and a normal and abnormal tympanic membrane for evaluation of its potential for the mobile diagnosis. Spectral classified images were obtained via online spectral analysis in a remote server. The phantom experimental results showed that it allowed us to distinguish four different fluids located behind a semitransparent membrane. Also, in the spectral classified images of normal ears (n = 3) and an ear with chronic otitis media (n = 1), the normal and abnormal regions in each ear could be quantitatively distinguished with high contrast. These preliminary results thus suggested that it might have the potentials for providing quantitative information for the mobile diagnosis of various middle ear diseases.     

3D finite element model of the chinchilla ear for characterizing middle ear functions

Chinchilla is a commonly used animal model for research of sound transmission through the ear. Experimental measurements of the middle ear transfer function in chinchillas have shown that the middle ear cavity greatly affects the tympanic membrane (TM) and stapes footplate (FP) displacements. However, there is no finite element (FE) model of the chinchilla ear available in the literature to characterize the middle ear functions with the anatomical features of the chinchilla ear. This paper reports a recently completed 3D FE model of the chinchilla ear based on X-ray micro-computed tomography images of a chinchilla bulla. The model consisted of the ear canal, TM, middle ear ossicles and suspensory ligaments, and the middle ear cavity. Two boundary conditions of the middle ear cavity wall were simulated in the model as the rigid structure and the partially flexible surface, and the acoustic-mechanical coupled analysis was conducted with these two conditions to characterize the middle ear function. The model results were compared with experimental measurements reported in the literature including the TM and FP displacements and the middle ear input admittance in chinchilla ear. An application of this model was presented to identify the acoustic role of the middle ear septa—a unique feature of chinchilla middle ear cavity. This study provides the first 3D FE model of the chinchilla ear for characterizing the middle ear functions through the acoustic-mechanical coupled FE analysis.     

In vivo noninvasive measurement of spatially resolved corneal elasticity in human eyes using Lamb wave optical coherence elastography

Current elastography techniques are limited in application to accurately assess spatially resolved corneal elasticity in vivo for human eyes. The air‐puff optical coherence elastography (OCE) with an eye motion artifacts correction algorithm is developed to distinguish the in vivo cornea vibration from the eye motion and visualize the Lamb wave propagation clearly in healthy subjects. Based on the Lamb wave model, the phase velocity dispersion curve in the high‐frequency is calculated to obtain spatially resolved corneal elasticity accurately with high repeatability. It is found that the corneal elasticity has regional variations and is correlated with intraocular pressure, which suggests that the method has the potential to provide noninvasive measurement of spatially resolved corneal elasticity in clinical practice.     

Effects of whole body vibration on outer hair cells’ hearing response to distortion product otoacoustic emissions

Whole body vibration (WBV) is one of the most vexing problems in industries. There is a debate about the effect of WBV exposure on hearing system as vibration-induced hearing loss. The purpose of this study was to investigate outer hair cells' (OHCs') hearing response hearing response to distortion product otoacoustic emissions (DPOAEs) in rabbits exposed to WBV. It was hypothesized that the DPOAE response amplitudes (A(dp)) in rabbits exposed to WBV would be lower than those in control rabbits not exposed to WBV. New Zealand white (NZW) rabbits as vibration group (n = 6, exposed to WBV in the z-axis at 4-8 Hz and 1.0 ms(-2) root mean square for 8 h per day during five consecutive days) and NZW rabbits as control group (n = 6, not exposed to any WBV) were participated. A(dp) and noise floor levels (L(nf)) were examined on three occasions: day 0 (i.e., baseline), day 8 (i.e., immediately 1 h after exposure), and day 11 (i.e., 72 h following exposure) with f(2) frequencies ranging from 500 to 10,000 Hz and primaries L(1) and L(2) levels of 65 and 55 dB sound pressure level, respectively. Main effects were statistically found to be significant for group, time, and frequency (p < 0.05). DPOAE amplitudes were significantly larger for rabbits exposed to WBV, larger on day 8 and larger for mid to high f(2) frequencies (at and above 5,888.50 Hz). Main effects were not statistically found to be significant for ear (p > 0.05). Also, four statistically significant interactions including time by ear, time by frequency, group by frequency, and group by time were detected (p < 0.05). Contrary to the main hypothesis, DPOAE amplitudes were significantly larger for rabbits exposed to WBV. WBV exposure significantly led to enhanced mean A(dp) at mid to high frequencies rather than at low ones.     

Three approaches for estimating the elastic modulus of the tympanic membrane

The function of the middle ear is to resolve the acoustic impedance mismatch between the air in the ear canal and the fluid of the inner ear. Without this impedance matching, very little acoustic energy would be absorbed into the cochlea. The first step in this process is the tympanic membrane (TM) converting sound in the ear canal into vibrations of the middle ear bones. Understanding how the TM manages its task so successfully over such a broad frequency range should lead to more satisfactory and less variable TM repairs (myringoplasty). In addition, understanding the mechanics of the TM is necessary to improve the coupling between ossicular prostheses and the TM. Mathematical models have played a central role in helping the research community understand the mechanics of the eardrum. However, all models require parameters as inputs. Unfortunately, most of the parameters needed for modeling the TM are not well known. In this work, several approaches for inferring the material properties of the TM are explored. First, constitutive modeling is used to estimate an elastic modulus based on the elastic modulus of collagen and experimentally observed fiber densities. Second, experimental tension and bending test results from the literature are re-interpreted using composite laminate theory. Lastly, dynamic measurements of the cat TM are used in conjunction with a composite shell model to bound the material parameters. Values from the literature, both measurement and modeling efforts, and from the present analysis are brought together to form a coherent picture of the TM's material properties. In the human, the data bound the elastic modulus between 0.1 and 0.3 GPa. In the cat, the data suggest a range of 0.1-0.4 GPa. These values are significantly higher than previous estimates.     

Non‐invasive optical assessment of viscosity of middle ear effusions in otitis media

Eustachian tube dysfunction can cause fluid to collect within the middle ear cavity and form a middle ear effusion (MEE). MEEs can persist for weeks or months and cause hearing loss as well as speech and learning delays in young children. The ability of a physician to accurately identify and characterize the middle ear for signs of fluid and/or infection is crucial to provide the most appropriate treatment for the patient. Currently, middle ear infections are assessed with otoscopy, which provides limited and only qualitative diagnostic information. In this study, we propose a method utilizing cross‐sectional depth‐resolved optical coherence tomography to noninvasively measure the diffusion coefficient and viscosity of colloid suspensions, such as a MEE. Experimental validation of the proposed technique on simulated MEE phantoms with varying viscosity and particulate characteristics is presented, along with some preliminary results from in vivo and ex vivo samples of human MEEs.

In vivo Optical Coherence Tomography (OCT) image of a human tympanic membrane and Middle Ear Effusion (MEE) (top), with a CCD image of the tympanic membrane surface (inset). Below is the corresponding time‐lapse M‐mode OCT data acquired along the white dotted line over time, which can be analyzed to determine the Stokes–Einstein diffusion coefficient of the effusion.     

Middle ear transmission in the grass frog, Rana temporaria

The anuran middle ear serves to transmit eardrum vibrations to the inner ear. In order to do this efficiently, the eardrum and middle ear must operate as an impedance transformer matching the low impedance of air to the higher impedance of the fluid-filled inner ear. In amniotes, one of the mechanisms used to achieve impedance transformation is to have the middle ear work as a force-amplifying lever system. Here, we present evidence that the grass frog middle ear also implements a lever system. The columellar footplate, which sits in the oval window, is firmly connected to the otic capsule along its ventral edge. Therefore, simple in-out movement of the columella is prevented while a rotational movement around the footplate's ventral edge is possible. The latter movement pattern was confirmed by laser vibrometry measurements of eardrum and footplate vibrations. The results showed that the footplate vibrations were 20–30 dB weaker than those of the eardrum and that the two structures vibrated 180° out of phase (at low frequencies). The lever ratio was approximately 6, i.e. somewhat higher than lever ratios reported for amniotes. Hence, the middle ear lever probably makes a significant contribution to impedance matching in frogs. Accepted: 1 July 1997     

A three-dimensional finite element model of round window membrane vibration before and after stapedotomy surgery

Piston stapes prostheses are implanted in patients with refractory conductive or mixed hearing loss due to stapes otosclerosis to stimulate the perilymph with varying degrees of success. The overclosure effect described by the majority of researchers affects mainly low and medium frequencies, and a large number of patients report a lack of satisfactory results for frequencies above 2 kHz. The mechanics of perilymph stimulation with the piston have not been studied in a systematic manner. The objective of this study was to assess the influence of stapedotomy surgery on round window membrane vibration and to estimate the postoperative outcomes using the finite element (FE) method. The study hypothesis is that the three-dimensional FE model developed of the human inner ear, which simulates the round window (RW) membrane vibration, can be used to assess the influence of stapedotomy on auditory outcomes achieved after the surgical procedure. An additional objective of the study was to enable the simulation of RW membrane vibration after stapedotomy using a new type of stapes prosthesis currently under investigation at Warsaw University of Technology. A three-dimensional finite element (FE) model of the human inner ear was developed and validated using experimental data. The model was then used to simulate the round window membrane vibration before and after stapedotomy surgery. Functional alterations of the RW membrane vibration were derived from the model and compared with the results of experimental measurements from temporal bones of a human cadaver. Piston stapes prosthesis implantation causes an approximately fivefold (14 dB) lower amplitude of the RW membrane vibrations compared with normal anatomical conditions. A satisfactory agreement between the FE model and the experimental data was found. The new prosthesis caused an increase of 20–30 dB in the RW displacement amplitude compared with the 0.4-mm piston prosthesis. In all frequencies, the FE model predicted a RW displacement curve that was above the experimental curves for the normal ear. The stapedotomy can be well simulated by the FE model to predict the auditory outcomes achieved following this otosurgery procedure. The 3D FE model developed in this study may be used to optimize the geometry of a new type of stapes prosthesis in order to achieve a similar sound transmission through the inner ear as for a normal middle ear. This should provide better auditory outcomes for patients with stapedial otosclerosis.     

Small tympanic membrane perforations in the inferior quadrants do not impact the manubrium vibration in guinea pigs

Background

It has been believed that location of the perforation has a significant impact on hearing loss. However, recent studies have demonstrated that the perforation sites had no impact on hearing loss. We measured the velocity and pattern of the manubrium vibration in guinea pigs with intact and perforated eardrum using a laser Doppler vibrometer in order to determine the effects of different location perforations on the middle ear transfer functions.

Methods

Two bullas from 2 guinea pigs were used to determine stability of the umbo velocities, and 12 bullas from six guinea pigs to determine the effects of different location perforations on sound transmission. The manubrium velocity was measured at three points on the manubrium in the frequencies of 0.5–8 kHz before and after a perforation was made. The sites of perforations were in anterior-inferior (AI) quadrants of left ears and posterior-inferior (PI) quadrants of right ears.

Results

The manubrium vibration velocity losses were noticed in the perforated ears only below 1.5 kHz. The maximum velocity loss was about 7 dB at 500 Hz with the PI perforation. No significant difference in the velocity loss was found between AI and PI perforations. The average ratio of short process velocity to the umbo velocity was approximately 0.5 at all frequencies. No significant differences were found before and after perforation at all frequencies (p>0.05) except 7 kHz (p = 0.004) for both AI and PI perforations.

Conclusions

The manubrium vibration velocity losses from eardrum perforation were frequency-dependent and the largest losses occur at low frequencies. Manubrium velocity losses caused by small acute inferior perforations in guinea pigs have no significant impact on middle ear sound transmission at any frequency tested. The manubrium vibration axis may be perpendicular to the manubrium below 8 kHz in guinea pigs.     

Establishing bioequivalence of racemic venlafaxine formulations using stereoselective assay method: Is it necessary?

A bioequivalence study for venlafaxine generic formulation was conducted as an open label, balanced, randomized, two‐way crossover, single‐dose study. In this study, a comparison of various pharmacokinetic parameters of venlafaxine hydrochloride 150 mg modified release capsules of Ranbaxy and EFEXOR®‐XR 150 mg capsules of Wyeth, in healthy, adult, male, human subjects under fasting condition was performed to conclude bioequivalence. Venlafaxine and its major active metabolite O‐desmethylvenlafaxine (ODV) are racemates. The “(S)‐(+)” and “(R)‐(−)” enantiomers of venlafaxine and ODV are established as being active. Hence, subject samples were analyzed using nonstereoselective and stereoselective assay methods. Both (S)‐(+) and (R)‐(−) enantiomers of venlafaxine and ODV showed similar absorption and disposition. The 90% confidence intervals for venlafaxine, (R)‐(−)‐venlafaxine as well as (S)‐(+)‐venlafaxine were within acceptance range concluding bioequivalence. The results obtained by stereoselective assay were comparable to the nonstereoselective analysis, as sum of concentrations of (S)‐(+)‐ and (R)‐(−)‐enantiomers of venlafaxine and ODV. The mean (S)‐(+)/(R)‐(−) ratios of the enantiomers of venlafaxine and ODV at various time points were consistent in the study subjects. Therefore, the estimation of venlafaxine and ODV using nonstereoselective assay method is effective in distinguishing formulation differences (if any) in bioequivalence studies in a cost‐effective manner. Chirality, 2011. © 2011 Wiley‐Liss, Inc.     

Does body size predict the buzz‐pollination frequencies used by bees?

Body size is an important trait linking pollinators and plants. Morphological matching between pollinators and plants is thought to reinforce pollinator fidelity, as the correct fit ensures that both parties benefit from the interaction. We investigated the influence of body size in a specialized pollination system (buzz‐pollination) where bees vibrate flowers to release pollen concealed within poricidal stamens. Specifically, we explored how body size influences the frequency of buzz‐pollination vibrations. Body size is expected to affect frequency as a result of the physical constraints it places on the indirect flight muscles that control the production of floral vibrations. Larger insects beat their wings less rapidly than smaller‐bodied insects when flying, but whether similar scaling relationships exist with floral vibrations has not been widely explored. This is important because the amount of pollen ejected is determined by the frequency of the vibration and the displacement of a bee's thorax. We conducted a field study in three ecogeographic regions (alpine, desert, grassland) and recorded flight and floral vibrations from freely foraging bees from 27 species across four families. We found that floral vibration frequencies were significantly higher than flight frequencies, but never exceeded 400 Hz. Also, only flight frequencies were negatively correlated with body size. As a bee's size increased, its buzz ratio (floral frequency/flight frequency) increased such that only the largest bees were capable of generating floral vibration frequencies that exceeded double that of their flight vibrations. These results indicate size affects the capacity of bees to raise floral vibration frequencies substantially above flight frequencies. This may put smaller bees at a competitive disadvantage because even at the maximum floral vibration frequency of 400 Hz, their inability to achieve comparable thoracic displacements as larger bees would result in generating vibrations with lower amplitudes, and thus less total pollen ejected for the same foraging effort.     

Hearing in the African lungfish (Protopterus annectens): pre-adaptation to pressure hearing in tetrapods?

Lungfishes are the closest living relatives of the tetrapods, and the ear of recent lungfishes resembles the tetrapod ear more than the ear of ray-finned fishes and is therefore of interest for understanding the evolution of hearing in the early tetrapods. The water-to-land transition resulted in major changes in the tetrapod ear associated with the detection of air-borne sound pressure, as evidenced by the late and independent origins of tympanic ears in all of the major tetrapod groups. To investigate lungfish pressure and vibration detection, we measured the sensitivity and frequency responses of five West African lungfish (Protopterus annectens) using brainstem potentials evoked by calibrated sound and vibration stimuli in air and water. We find that the lungfish ear has good low-frequency vibration sensitivity, like recent amphibians, but poor sensitivity to air-borne sound. The skull shows measurable vibrations above 100 Hz when stimulated by air-borne sound, but the ear is apparently insensitive at these frequencies, suggesting that the lungfish ear is neither adapted nor pre-adapted for aerial hearing. Thus, if the lungfish ear is a model of the ear of early tetrapods, their auditory sensitivity was limited to very low frequencies on land, mostly mediated by substrate-borne vibrations.     

Middle ear epithelial mucin production in response to interleukin-6 exposure in vitro

OBJECTIVES: To investigate the role of the inflammatory cytokine interleukin-6 (IL-6) in the regulation of mucin secretion by middle ear epithelia. MATERIALS AND METHODS: Primary chinchilla middle ear epithelial cultures were established and exposed to IL-6 in a dose- and time-dependent manner. Mucin secretion was characterized by exclusion chromatography and liquid scintillation. RESULTS: Epithelial cultures exposed to increasing doses of IL-6 demonstrated greater amounts of mucin secretion (p=0.018). Additionally, cultures exposed to IL-6 at 50 ng/ml showed significant increased secretion of mucin over control in time-dependent experiments at 6-, 15- and 24-h time points (p=0.003). CONCLUSIONS: IL-6 upregulates mucin secretion from cultured middle ear epithelial cells in a dose- and time-dependent manner. Elucidating the effect of specific cytokines on the regulation of mucin secretion is vital to understanding the pathophysiology of otitis media and the development of novel therapeutic strategies.     

Middle-ear dynamics before and after ossicular replacement

The mechanism of hearing involves conduction of mechanical vibrations along the ossicular chain to the inner ear. An acoustic wave is collected and transformed as it passes down the ear canal and impacts on the tympanic membrane (ear drum). The drum is connected to the inner-ear by three ossicle bones (malleus, incus, and stapes) in a complex arrangement, which serves to further transform the mechanical vibration before it reaches the cochlea of the inner ear. What is the mechanical function of the ossicular chain, and what are the biomechanical consequences of surgical reconstruction with prostheses? To answer these questions, a three-dimensional finite element model of the outer ear canal and middle ear was generated. The dynamical behaviour was predicted for the normal ear, and an ear reconstructed with partial and total ossicular replacement prostheses. For the normal ear, stapes amplitudes of 1x10(-8) m at low frequencies decrease to 4x10(-10)m at approximately 3kHz with several resonance peeks in between, most significantly at approximately 1kHz. Thereafter a further resonance is predicted at 4kHz associated with the ear canal. The behaviour is changed fundamentally by adding a prosthesis; the partial replacement increases the vibratory coupling of the drum and the stapes compared to the normal ear whereas the total replacement does the opposite, and is predicted to have the disadvantage of bringing several new resonances of the ossicular chain into the hearing range. It is hypothesised that the function of the malleus-incus-stapes arrangement is to link the drum to the oval window with the flexibility required for impedance matching but the rigidity to prevent unconstrainable resonances from occurring in the hearing range. If this is true, then the structural stiffness of ossicular chain is the critical design variable for middle-ear replacement prostheses.     

The effects of variable mass and geometry, pretwist, shear deformation and rotatory inertia on the resonant frequencies of intact long bones: A finite element model analysis

The influence of pretwist, nonuniformities in mass and flexural stiffness, rotatory inertia and shear deformation on the natural frequencies of intact bones is evaluated by means of a linear elastic, finite-element model which has been programmed for solution on the digital computer. Theoretical results are compared to the results on the forced vibration of intact canine radii obtained experimentally by Thompson. Surprisingly, inclusion of fairly large pretwist angles (from −14° to 12° for one specimen) had little affect on the first three frequencies of transverse vibration in either the cranial or lateral directions. Inclusion of shear deformation reduced the third-mode frequency in the stiffest (lateral) direction by about six per cent, otherwise shear deformation played a minor role in determining natural frequencies. Similarly, rotatory inertia had negligible influence up to the third natural frequency.

The predominant influence on the first three natural frequencies of transverse vibration could be attributed to the variations in mass and flexural stiffness along the length of the test specimens. Different effective moduli of elasticity are required to yield correct absolute values for the frequencies which correspond to experimental findings, thus implying the presence of some inhomogeneities in material properties around the bone cross-section and/or along its length.     

Biomechanical and neurophysiological studies on audition in eared and earless harlequin frogs (Atelopus)

Tissue displacement of various body surfaces and the auditory midbrain sensitivities to sound were measured in Atelopus species with or without a tympanic middle ear (“eared” and “earless”, respectively). Tissue displacement (vibration) of body regions was measured by laser Doppler vibrometer . The body wall directly overlying the lung is most dramatically displaced by sound pressure in all species tested. The otic (lateral head) region showed low displacement in earless species, but significant displacement to high-frequency sound in eared species. Peak tissue displacement of the body wall occurred within the frequency range of each species' advertisement vocalization. Peak tissue displacement of the otic region of the eared species also occurred within these frequencies. Multi-unit neurophysiological recordings of the auditory midbrain (torus semicircularis) also were obtained. Auditory sensitivity curves showed three distinct regions of sensitivity at low, middle, and high frequencies, the latter located within the frequency range of each species' advertisement vocalization. The correlation between auditory midbrain sensitivity and tissue displacement of the body wall region at advertisement vocalization frequencies, suggests that the body wall/lungs serve as the route of sound transfer to the inner ear in earless species and possibly in the eared species as well. Accepted: 4 April 1998