Ear asymmetries in middle-ear, cochlear, and brainstem responses in human infants

In 2004, Sininger and Cone-Wesson examined asymmetries in the signal-to-noise ratio (SNR) of otoacoustic emissions (OAE) in infants, reporting that distortion-product (DP)OAE SNR was larger in the left ear, whereas transient-evoked (TE)OAE SNR was larger in the right. They proposed that cochlear and brainstem asymmetries facilitate development of brain-hemispheric specialization for sound processing. Similarly, in 2006 Sininger and Cone-Wesson described ear asymmetries mainly favoring the right ear in infant auditory brainstem responses (ABRs). The present study analyzed 2640 infant responses to further explore these effects. Ear differences in OAE SNR, signal, and noise were evaluated separately and across frequencies (1.5, 2, 3, and 4 kHz), and ABR asymmetries were compared with cochlear asymmetries. Analyses of ear-canal reflectance and admittance showed that asymmetries in middle-ear functioning did not explain cochlear and brainstem asymmetries. Current results are consistent with earlier studies showing right-ear dominance for TEOAE and ABR. Noise levels were higher in the right ear for OAEs and ABRs, causing ear asymmetries in SNR to differ from those in signal level. No left-ear dominance for DPOAE signal was observed. These results do not support a theory that ear asymmetries in cochlear processing mimic hemispheric brain specialization for auditory processing.     

The effect of superior-canal opening on middle-ear input admittance and air-conducted stapes velocity in chinchilla

The recent discovery of superior semicircular canal (SC) dehiscence syndrome as a clinical entity affecting both the auditory and vestibular systems has led to the investigation of the impact of a SC opening on the mechanics of hearing. It is hypothesized that the hole in the SC acts as a "third window" in the inner ear which shunts sound-induced stapes volume velocity away from the cochlea through the opening in the SC. To test the hypothesis and to understand the third window mechanisms the middle-ear input admittance and sound-induced stapes velocity were measured in chinchilla before and after surgically introducing a SC opening and after patching the opening. The extent to which patching returned the system to the presurgical state is used as a control criterion. In eight chinchilla ears a statistically significant, reversible increase in low-frequency middle-ear input admittance magnitude occurred as a result of opening the SC. In six ears a statistically significant reversible increase in stapes velocity was observed. Both of these changes are consistent with the hole creating a shunt pathway that increases the cochlear input admittance.     

Acoustics of the human middle-ear air space

The impedance of the middle-ear air space was measured on three human cadaver ears with complete mastoid air-cell systems. Below 500 Hz, the impedance is approximately compliance-like, and at higher frequencies (500-6000 Hz) the impedance magnitude has several (five to nine) extrema. Mechanisms for these extrema are identified and described through circuit models of the middle-ear air space. The measurements demonstrate that the middle-ear air space impedance can affect the middle-ear impedance at the tympanic membrane by as much as 10 dB at frequencies greater than 1000 Hz. Thus, variations in the middle-ear air space impedance that result from variations in anatomy of the middle-ear air space can contribute to inter-ear variations in both impedance measurements and otoacoustic emissions, when measured at the tympanic membrane.     

A human nonlinear cochlear filterbank.

Some published cochlear filterbanks are nonlinear but are fitted to animal basilar membrane (BM) responses. Others, like the gammatone, are based on human psychophysical data, but are linear. In this article, a human nonlinear filterbank is constructed by adapting a computational model of animal BM physiology to simulate human BM nonlinearity as measured by psychophysical pulsation-threshold experiments. The approach is based on a dual-resonance nonlinear type of filter whose basic structure was modeled using animal observations. In modeling the pulsation threshold data, the main assumption is that pulsation threshold occurs when the signal and the masker produce comparable excitation, that is the same filter output, at the place of the BM best tuned to the signal frequency. The filter is fitted at a discrete number of best frequencies (BFs) for which psychophysical data are available for a single listener and for an average response of six listeners. The filterbank is then created by linear regression of the resulting parameters to intermediate BFs. The strengths and limitations of the resulting filterbank are discussed. Its suitability for simulating hearing-impaired cochlear responses is also discussed.     

Miscible displacement of non-Newtonian fluids in a vertical tube

The influence of rheology on the miscible displacement of a viscous fluid by a less viscous, Newtonian one in a vertical tube is studied experimentally as a function of the flow velocity. For Newtonian displaced fluids the transient residual film thickness is nearly of the tube radius at large viscosity ratios between the two fluids in agreement with experimental and numerical results from the literature. For shear-thinning fluids with a zero yield stress (mostly xanthan-water solutions), decreases down to of the radius for the most concentrated solutions. For fluids with a non-zero yield stess, further decreases down to 24-25% of the radius. The orders of magnitude of these values can be obtained through numerical simulations (commercial code) for the various types of fluids. Instabilities of the film at its boundary develop downstream and lead to a reduction of the final thickness of the film at longer times: this reduction is larger for lower viscosity ratios and larger velocities.Received: 15 February 2003, Published online: 8 July 2003PACS: 47.20.Gv Hydrodynamic stability: Viscous instability - 83.60.Wc Rheology: Flow instabilities     

Distortion product otoacoustic emissions for hearing threshold estimation and differentiation between middle-ear and cochlear disorders in neonates

Our aim in the present study was to apply extrapolated DPOAE I/O-functions [J. Acoust. Soc. Am. 111, 1810-1818 (2002); 113, 3275-3284 (2003)] in neonates in order to investigate their ability to estimate hearing thresholds and to differentiate between middle-ear and cochlear disorders. DPOAEs were measured in neonates after birth (mean age = 3.2 days) and 4 weeks later (follow-up) at 11 test frequencies between f2 = 1.5 and 8 kHz and compared to that found in normal hearing subjects and cochlear hearing loss patients. On average, in a single ear hearing threshold estimation was possible at about 2/3 of the test frequencies. A sufficient test performance of the approach is therefore suggested. Thresholds were higher at the first measurement compared to that found at the follow-up measurement. Since thresholds varied with frequency, transitory middle ear dysfunction due to amniotic fluid instead of cochlear immaturity is suggested to be the cause for the change in thresholds. DPOAE behavior in the neonate ears differed from that found in the cochlear hearing loss ears. From a simple model it was concluded that the difference between the estimated DPOAE threshold and the DPOAE detection threshold is able to differentiate between sound conductive and cochlear hearing loss.     

Effects of middle-ear immaturity on distortion product otoacoustic emission suppression tuning in infant ears

Distortion product otoacoustic emission (DPOAE) measures of cochlear function, including DPOAE suppression tuning curves and input/output (I/O) functions, are not adultlike in human infants. These findings suggest the cochlear amplifier might be functionally immature in newborns. However, many noncochlear factors influence DPOAEs and must be considered. This study examines whether age differences in DPOAE I/O functions recorded from infant and adult ears reflect maturation of ear-canal/middle-ear function or cochlear mechanics. A model based on linear middle-ear transmission and nonlinear cochlear generation was developed to fit the adult DPOAE I/O data. By varying only those model parameters related to middle-ear transmission (and holding cochlear parameters at adult values), the model successfully fitted I/O data from infants at birth through age 6 months. This suggests that cochlear mechanics are mature at birth. The model predicted an attenuation of stimulus energy through the immature ear canal and middle ear, and evaluated whether immaturities in forward transmission could explain the differences consistently observed between infant and adult DPOAE suppression. Results show that once the immaturity was compensated for by providing infants with a relative increase in primary tone level, DPOAE suppression tuning at f2= 6000 Hz was similar in adults and infants.     

The development of middle-ear admittance in the hamster.

A high-frequency admittance meter was developed and used to study the maturation of physiological function in the middle ear of neonatal golden hamsters (Mesocricetus auratus). The middle-ear input admittance in the frequency range of 0.8-1.8 kHz was measured in animals ranging in age from 6 to 69 days postpartum. Admittance magnitude was found to increase steadily with age, beginning on day 16, to asymptotic values at each test frequency. There were no obvious differences in admittance growth rates within the range of frequencies tested. However, an analysis of the slopes of the admittance ma;nitude frequency response curves revealed an increase from 4.6 dB/octave for animals 25 days old or younger, to 6.3 dB/octave for all older animals. This difference between younger and older subjects indicates that the development of the middle ear in the golden hamster is more complex than a simple increase in pure compliance.     

Comparison of WKB calculations and experimental results for three-dimensional cochlear models.

The WKB asymptotic method is applied to the calculation of cochlear models with square scala cross section, for which the fluid motion is fully three dimensional. The analysis begins with the exact solution for wave propagation in a duct with constant properties. This solution is somewhat tedious but straightforward, since it requires a Fourier series expansion across the duct. Then with the formulation of Whitham [Linear and Nonlinear Waves (Wiley, New York, 1974)], the approximate solution is readily generated for the duct with properties which vary slowly along the length. Numerical calculations are carried out for the experimental models of Cannel [Ph.D. thesis, Univ. of Warwick (1969)] and Helle [Dr.-Ing. disser., Technische Univ., Müchen (1974)] who furnish quantitative details of both "basilar membrane" response and model parameters. Without any free parameters for adjusting, the present WKB solution shows quite satisfactory agreement with the experimental model results. Computer time is reasonable; the calculation of displacement envelope and phase at a number of stations along the cochlea for a given frequency requires only one second of CPU time. Thus the credibility and practically of the approach is established for the investigation of yet more realistic and more elaborate cochlear models.     

Finite-element analysis of middle-ear pressure effects on static and dynamic behavior of human ear

A finite-element analysis for static behavior of middle ear under variation of the middle-ear pressure was conducted in a 3D model of human ear by combining the hyperelastic Mooney-Rivlin material model and geometry nonlinearity. An empirical formula was then developed to calculate material parameters of the middle-ear soft tissues as the stress-dependent elastic modulus relative to the middle-ear pressure. Dynamic behavior of the middle ear in response to sound pressure in the ear canal was predicted under various positive and negative middle-ear pressures. The results from static analysis indicate that a positive middle ear pressure produces the static displacements of the tympanic membrane (TM) and footplate more than a negative pressure. The dynamic analysis shows that the reductions of the TM and footplate vibration magnitudes under positive middle-ear pressure are mainly determined by stress dependence of elastic modulus. The reduction of the TM and footplate vibrations under negative pressure was caused by both the geometry changes of middle-ear structures and the stress dependence of elastic modulus.     

From realistic to simple models of associating fluids. II. Primitive models of ammonia,ethanol and models of water revisited

Recently developed methodology to construct primitive models of associating fluids directly from realistic intermolecular potential functions is applied to ammonia, ethanol and several models of water. Hard cores of the molecules are pictured as fused hard-sphere bodies defined by composite short-range repulsions, and the Coulombic repulsions and attractions are approximated by hard-sphere and square-well potentials, respectively. Hard-sphere diameters are determined directly from the parent potential using a theoretical route and the range of the square-well attraction is adjusted using constraints imposed on hydrogen bonding. It is shown that the developed primitive models, despite their simplicity and lack of any long-range interactions, are able to reproduce the structural properties (the set of the site–site correlation functions) of the parent realistic models and may thus serve well as a reference in the perturbation theory.     

Effects of short-term auditory deprivation on speech production in adult cochlear implant users.

Speech production parameters of three postlingually deafened adults who use cochlear implants were measured: after 24 h of auditory deprivation (which was achieved by turning the subject's speech processor off); after turning the speech processor back on; and after turning the speech processor off again. The measured parameters included vowel acoustics [F1, F2, F0, sound-pressure level (SPL), duration and H1-H2, the amplitude difference between the first two spectral harmonics, a correlate of breathiness] while reading word lists, and average airflow during the reading of passages. Changes in speech processor state (on-to-off or vice versa) were accompanied by numerous changes in speech production parameters. Many changes were in the direction of normalcy, and most were consistent with long-term speech production changes in the same subjects following activation of the processors of their cochlear implants [Perkell et al., J. Acoust. Soc. Am. 91, 2961-2978 (1992)]. Changes in mean airflow were always accompanied by H1-H2 (breathiness) changes in the same direction, probably due to underlying changes in laryngeal posture. Some parameters (different combinations of SPL, F0, H1-H2 and formants for different subjects) showed very rapid changes when turning the speech processor on or off. Parameter changes were faster and more pronounced, however, when the speech processor was turned on than when it was turned off. The picture that emerges from the present study is consistent with a dual role for auditory feedback in speech production: long-term calibration of articulatory parameters as well as feedback mechanisms with relatively short time constants.     

Fast numerical solution of nonlinear nonlocal cochlear models

A fast full second order time-step algorithm for some recently proposed nonlinear, nonlocal active models for the inner ear is analyzed here. In particular, we emphasize the properties of discretized systems and the convergence of a hybrid direct-iterative solver for its approximate solution in view of the parameters of the continuous model. We found that the proposed solver is faster than standard sparse direct solvers for all the considered discrete models.Numerical tests confirm that the proposed techniques are crucial in order to get fast and reliable simulations.     

Ear-canal acoustic admittance and reflectance measurements in human neonates. II. Predictions of middle-ear in dysfunction and sensorineural hearing loss

This report describes relationships between middle-ear measurements of acoustic admittance and energy reflectance (YR) and measurements of hearing status using visual reinforcement audiometry in a neonatal hearing-screening population. Analyses were performed on 2638 ears in which combined measurements were obtained [Norton et al., Ear Hear. 21, 348-356 (2000)]. The measurements included distortion-product otoacoustic emissions (DPOAE), transient evoked otoacoustic emissions (TEOAE), and auditory brainstem responses (ABR). Models to predict hearing status using DPOAEs, TEOAEs, or ABRs were each improved by the addition of the YR factors as interactions, in which factors were calculated using factor loadings from Keefe et al. [J. Acoust. Soc. Am. 113, 389-406 (2003)]. This result suggests that information on middle-ear status improves the ability to predict hearing status. The YR factors were used to construct a middle-ear dysfunction test on 1027 normal-hearing ears in which DPOAE and TEOAE responses were either both present or both absent, the latter condition being viewed as indicative of middle-ear dysfunction. The middle-ear dysfunction test classified these ears with a nonparametric area (A) under the relative operating characteristic curve of A = 0.86, and classified normal-hearing ears that failed two-stage hearing-screening tests with areas A = 0.84 for DPOAE/ABR, and A = 0.81 for TEOAE/ABR tests. The middle-ear dysfunction test adequately generalized to a new sample population (A = 0.82).     

Lattice-gas and lattice-Boltzmann models of miscible fluids

We introduce new lattice-gas and lattice-Boltzmann models for simulating miscible fluids in two dimensions. The inclusion of a nonlocal interaction produces a lattice gas with lower diffusivity than achieved before. To overcome some observed unphysical properties of this lattice gas, we introduce a lattice-Boltzmann analogue of the model. We first formulate a miscible two-component lattice-Boltzmann model with local interactions only, and show that its diffusivity is determined by an eigenvalue of the linearized collision operator. Diffusivity is then reduced by including nonlocal interactions. The utility of the model is demonstrated by a simulation of two-dimensional viscous fingering.     

Some solvable models of nonuniform classical fluids

A model classical fluid is constructed by assuming that the direct correlation functionc(r – r) is independent of any applied external field. Thermodynamic consistency requires thatc(r – r) 0, and permits explicit representation of the model by a many-body interaction potential. In the canonical ensemble, the model shows a phase transition to an infinite density condensed phase, but in the grand canonical ensemble only an anomalous transition to zero density vapor is found to stably exist.     

A comparison of various nonlinear models of cochlear compression

The vibration response of the basilar membrane in the cochlea to sinusoidal excitation displays a compressive nonlinearity, conventionally described using an input-output level curve. This displays a slope of 1 dB/dB at low levels and a slope m < 1 dB/dB at higher levels. Two classes of nonlinear systems have been considered as models of this response, one class with static power-law nonlinearity and one class with level-dependent properties (using either an automatic gain control or a Van der Pol oscillator). By carefully choosing their parameters, it is shown that all models can produce level curves that are similar to those measured on the basilar membrane. The models differ, however, in their distortion properties, transient responses, and instantaneous input-output characteristics. The static nonlinearities have a single-valued instantaneous characteristic that is the same at all input levels. The level-dependent systems are multi-valued with an almost linear characteristic, for a given amplitude of excitation, whose slope varies with the excitation level. This observation suggests that historical attempts to use functional modeling (i.e., Wiener of Volterra series) may be ill founded, as these methods are unable to represent level-dependent nonlinear systems with multi-valued characteristics of this kind.     

Chirotropical phenomena in biological fluids and their homochiral models

The strong and non-monotonous dependence of chirotropical properties of biological fluids and their homochiral models on the concentration of chiral substance was found, which is associated with the formation of complex, supramolecular structures that consecutively replace each other, viz., molecular associations and strings, and with an increase in the magnitude of the delocalization of the excited electron states of chromophore groups. The rule of consistent change in the sign of chirality was formulated upon the formation of chiral phases, which replace each other.