Gerbil middle-ear sound transmission from 100 Hz to 60 kHz

Middle-ear sound transmission was evaluated as the middle-ear transfer admittance H(MY) (the ratio of stapes velocity to ear-canal sound pressure near the umbo) in gerbils during closed-field sound stimulation at frequencies from 0.1 to 60 kHz, a range that spans the gerbil's audiometric range. Similar measurements were performed in two laboratories. The H(MY) magnitude (a) increased with frequency below 1 kHz, (b) remained approximately constant with frequency from 5 to 35 kHz, and (c) decreased substantially from 35 to 50 kHz. The H(MY) phase increased linearly with frequency from 5 to 35 kHz, consistent with a 20-29 micros delay, and flattened at higher frequencies. Measurements from different directions showed that stapes motion is predominantly pistonlike except in a narrow frequency band around 10 kHz. Cochlear input impedance was estimated from H(MY) and previously-measured cochlear sound pressure. Results do not support the idea that the middle ear is a lossless matched transmission line. Results support the ideas that (1) middle-ear transmission is consistent with a mechanical transmission line or multiresonant network between 5 and 35 kHz and decreases at higher frequencies, (2) stapes motion is pistonlike over most of the gerbil auditory range, and (3) middle-ear transmission properties are a determinant of the audiogram.     

Finite element modeling of acousto-mechanical coupling in the cat middle ear

The function of the middle ear is to transfer acoustic energy from the ear canal to the cochlea. An essential component of this system is the tympanic membrane. In this paper, a new finite element model of the middle ear of the domestic cat is presented, generated in part from cadaver anatomy via microcomputed tomographic imaging. This model includes a layered composite model of the eardrum, fully coupled with the acoustics in the ear canal and middle-ear cavities. Obtaining the frequency response from 100 Hz to 20 kHz is a computationally challenging task, which has been accomplished by using a new adaptive implementation of the reduced-order matrix Padé-via-Lanczos algorithm. The results are compared to established physiological data. The fully coupled model is applied to study the role of the collagen fiber sublayers of the eardrum and to investigate the relationship between the structure of the middle-ear cavities and its function. Three applications of this model are presented, demonstrating the shift in the middle-ear resonance due to the presence of the septum that divides the middle-ear cavity space, the significance of the radial fiber layer on high frequency transmission, and the importance of the transverse shear modulus in the eardrum microstructure.     

Middle ear cavity and ear canal pressure-driven stapes velocity responses in human cadaveric temporal bones

Drive pressure to stapes velocity (V(st)) transfer function measurements are collected and compared for human cadaveric temporal bones with the drive pressure alternately on the ear canal (EC) and middle ear cavity (MEC) sides of the tympanic membrane (TM), in order to predict the performance of proposed middle-ear implantable acoustic hearing aids, as well as provide additional data for examining human middle ear mechanics. The chief finding is that, in terms of the V(st) response, MEC stimulation performs at least as well as EC stimulation below 8 kHz, provided that the EC is unplugged. Plugging the EC causes a reduced response for MEC drive below 2 kHz, due to a corresponding reduction of the pressure difference between the two sides of the TM. Between 8 and 11 kHz, the MEC drive transfer functions feature an approximately 17 dB drop in magnitude below the EC drive case, the cause of which remains unknown. The EC drive transfer functions reported here feature significantly less magnitude roll-off above 1 kHz than previous studies [with a slope of -2.3 vs -6.7 dB/octave for Aibara et al., Hear. Res. 152, 100-109 (2001)], and significantly more phase group delay (134 vs 62 micros for Aibara et al.).     

Transmission matrix analysis of the chinchilla middle ear

Despite the common use of the chinchilla as an animal model in auditory research, a complete characterization of the chinchilla middle ear using transmission matrix analysis has not been performed. In this paper we describe measurements of middle-ear input admittance and stapes velocity in ears with the middle-ear cavity opened under three conditions: intact tympano-ossicular system and cochlea, after the cochlea has been drained, and after the stapes has been fixed. These measurements, made with stimulus frequencies of 100-8000 Hz, are used to define the transmission matrix parameters of the middle ear and to calculate the cochlear input impedance as well as the middle-ear output impedance. This transmission characterization of the chinchilla middle ear will be useful for modeling auditory sensitivity in the normal and pathological chinchilla ear.     

Changes in auditory sensitivity with depth in a free-diving California sea lion (Zalophus californianus)

All current data on underwater hearing in pinnipeds are based on tests conducted in small tanks, and may not accurately represent the auditory functioning of free-ranging animals, especially if hearing sensitivity changes with water depth. Underwater auditory thresholds were determined for a California sea lion at depths ranging from 10 to 100 meters. The following results were obtained: (1) False alarm probabilities (responding in the absence of a signal) decreased significantly with depth, indicating that the sea lion adopted a more conservative response criterion in deeper water. (2) Hearing sensitivity generally worsened with depth. (3) There was a significant interaction between depth and frequency, the depth effect being most pronounced at 10 kHz and reversing at 35 kHz. Increasing pressure related to diving probably alters the impedance characteristics of the pinniped ear, in particular affecting the size of the middle-ear air space via expansion of cavernous tissue in the middle-ear cavity. These results show that the middle ear plays a functional role in underwater sound detection in sea lions. However, contrary to previous speculation, the presence of cavernous tissue in the sea lion middle ear does not appear to enhance sensitivity at depth.     

Wideband reflectance tympanometry in normal adults.

Acoustic impedance/reflectance measurements were made at various ear-canal pressures in 20 subjects with a clinical acoustic immittance instrument and an experimental impedance/reflectance system. Measurements were made over a frequency range of 226-2000 Hz with the clinical system and 125-11,310 Hz with the experimental system. For frequencies < or = 2.0 kHz, tympanograms obtained with the two systems are similar, with patterns that progress through the same orderly sequence with increasing frequency. Eardrum impedance measurements were also similar. There are small gender differences in middle-ear impedance. Reflectance patterns (reflectance versus frequency) at ambient ear-canal air pressure are characterized by high reflectance at low frequencies, two district minima at 1.2 and 3.5 kHz, increasing reflectance to 8.0 kHz, and decreasing reflectance above that frequency. Ear-canal pressure increases reflectance at low frequencies, decreases reflectance in the region of the minimum, and increases reflectance slightly at high frequencies. Reflectance tympanograms (reflectance versus ear-canal pressure) progress through a sequence of three patterns. At low frequencies, reflectance tympanograms are "V" shaped, indicating that pressure increases reflectance. At frequencies near the minimum reflectance, the pattern inverts, indicating that pressure decreases reflectance. At high frequencies, the patterns are flat, indicating that ear-canal pressure has little effect. Results presented for one patient suggest that reflectance tympanometry may be useful for detecting middle-ear pathology.     

磁力负刚度薄膜结构低频吸声特性

针对背腔深度较小的薄膜吸声结构难以实现低频吸声的问题,提出了磁力负刚度的解决方法。采用传递矩阵法,建立了负刚度薄膜吸声结构理论模型,分析得出该结构的声阻抗等同与大背腔常规薄膜吸声结构的声阻抗;阻抗管实验验证得出,在一定磁场条件下,不同背腔的负刚度薄膜吸声结构与无负刚度结构相比其共振频率显著下降,吸声系数曲线与理论结构吻合。负刚度机制能够降低薄膜吸声结构的共振频率,用较小背腔实现低频吸声,从而实现薄型低频吸声结构设计。      

A hierarchy of examples illustrating the acoustic coupling of the eardrum

Basic principles underlying the acoustic coupling of the eardrum are illustrated in the form of a hierarchy of examples ranging from a simple piston coupled to a semi-infinite acoustic duct, to a flexible partition coupled to a variable cross-section duct, and to a closed cavity. The hierarchy illuminates some of the limitations of various simplified elements commonly used to model the middle ear and demonstrates the necessity of treating the acoustics and the eardrum as an integrated subsystem. Results show that the tympanic cavity and the secondary middle-ear air chambers contribute fundamental features to the acoustic coupling of the ear. The nature of the acoustic coupling limits the passive energy absorption and transmission properties of the eardrum. The magnitude and frequency dependence of the energy dissipation within the ultrastructure of the partition, due to bending and transverse deflection, is discussed in analogy to possible dissipation mechanisms within the eardrum itself. Examples are provided for several simple systems reproducing some of the gross anatomical characteristics of the cat eardrum.     

Measurements of human middle ear forward and reverse acoustics: implications for otoacoustic emissions

Middle and inner ears from human cadaver temporal bones were stimulated in the forward direction by an ear-canal sound source, and in the reverse direction by an inner-ear sound source. For each stimulus type, three variables were measured: (a) Pec--ear-canal pressure with a probe-tube microphone within 3 mm of the eardrum, (b) Vst--stapes velocity with a laser interferometer, and (c) Pv--vestibule pressure with a hydrophone. From these variables, the forward middle-ear pressure gain (M1), the cochlear input impedance (Zc), the reverse middle-ear pressure gain (M2), and the reverse middle-ear impedance (M3) are directly obtained for the first time from the same preparation. These measurements can be used to fully characterize the middle ear as a two-port system. Presently, the effect of the middle ear on otoacoustic emissions (OAEs) is quantified by calculating the roundtrip middle-ear pressure gain Gme(RT) as the product of M1 and M2. In the 2-6.8 kHz region, absolute value(Gme(RT)) decreases with a slope of -22 dB/oct, while OAEs (both click evoked and distortion products) tend to be independent of frequency; this suggests a steep slope in vestibule pressure from 2 kHz to at least 4 kHz for click evoked OAEs and to at least 6.8 kHz for distortion product OAEs. Contrary to common assumptions, measurements indicate that the emission generator mechanism is frequency dependent. Measurements are also used to estimate the reflectance of basally traveling waves at the stapes, and apically generated nonlinear reflections within the vestibule.     

Modeling of the human middle ear using the finite-element method

In this study, a three-dimensional finite-element model (FEM) of the human middle ear was established, including features of the middle ear which were not considered in the previous model, i.e., the ligaments, tendons, I-S joint, loading of the cochlea, external auditory meatus (EAM), middle-ear cavities, etc. The unknown mechanical properties of these parts and the boundary conditions were determined so that the impedance obtained from the FEM analysis resembled the measurement values. The validity of this model was confirmed by comparing the motion of the tympanic membrane and ossicles obtained by this model with the measurement data, and the effects of the newly considered features on the numerically obtained results were examined. By taking the ligaments and tendons into account and assuming that the cochlea acts as a damper, with this model it was possible to realistically reproduce complex ossicular chain movement. It was found that the middle-ear cavities did not affect the vibration mode of the tympanic membrane. Although the EAM enhanced the sound pressure applied to the tympanic membrane compared with that at the entrance of the EAM, the pressure distribution on the surface of the tympanic membrane was not affected by the EAM.     

Development of an electroacoustic analogue model of the middle ear and acoustic reflex

Experimental measurements of changes in the acoustic admittance of the eardrum caused by stapedius muscle contractions in human subjects are used to develop and electroacoustic analogue model of the middle ear. In this model the stapedius muscle is included as an explicit functional unit. The acoustical characteristics of the external ear canal are also included. The model is extensively evaluated by comparing its properties with the known characteristics of real ears of humans and other animals. Subsequently, the model is used to predict the effects of the acoustic reflex on middle ear sound transmission, which cannot easily be measured in humans. The model predicts attenuation of potentially hazardous high level sounds at frequencies below 1 kHz of up to about 10 dB, but very little effect at higher frequencies unless the reflex-eliciting stimulus is of sufficient intensity to cause partial disarticulation of the incudo-stapedial joint by stapedius muscle contraction. Overall attenuation for typical industrial noises is unlikely to be greater than approximately 3 dB(A) and will probably be even less in practice, resulting in little effective protection from the harmful effects of high intensity noise. It is considered that the model will be of benefit in the analysis of middle ear function, including the interpretation of audiological measurements of eardrum impedance and acoustic reflex response. This should lead to more versatile diagnosis of peripheral auditory dysfunction than has been possible hitherto.     

Measurement of sound-pressure distribution in replicas of the oral cavity.

The spatial distributions of sound pressure in artificial oral cavities were measured to examine the characteristics of wave propagation in the vocal tract. The measurement was performed with plaster replicas of the oral cavity, and pure tones were used as the driving signals to obtain both amplitude and phase distributions at varied frequencies. Plane-wave propagation, which has been widely assumed for speech production models, was examined from the measured spatial distributions of sound pressure. Trajectories of media particles and vectorial maps of acoustic intensity, which can be computed from the measured pressure distributions, were also presented to visualize the acoustic field in the oral cavity. The results showed that at certain frequencies there existed points where sound pressure was absolutely zero, with the phase spatially circulating around them. Up to about 4 kHz, except at these certain frequencies, the wave front was almost one-dimensional, though an amplitude gradient was seen in the vertical direction.     

Acoustic mechanisms that determine the ear-canal sound pressures generated by earphones

In clinical measurements of hearing sensitivity, a given earphone is assumed to produce essentially the same sound-pressure level in all ears. However, recent measurements [Voss et al., Ear and Hearing (in press)] show that with some middle-ear pathologies, ear-canal sound pressures can deviate by as much as 35 dB from the normal-ear value; the deviations depend on the earphone, the middle-ear pathology, and frequency. These pressure variations cause errors in the results of hearing tests. Models developed here identify acoustic mechanisms that cause pressure variations in certain pathological conditions. The models combine measurement-based Thévenin equivalents for insert and supra-aural earphones with lumped-element models for both the normal ear and ears with pathologies that alter the ear's impedance (mastoid bowl, tympanostomy tube, tympanic-membrane perforation, and a "high-impedance" ear). Comparison of the earphones' Thévenin impedances to the ear's input impedance with these middle-ear conditions shows that neither class of earphone acts as an ideal pressure source; with some middle-ear pathologies, the ear's input impedance deviates substantially from normal and thereby causes abnormal ear-canal pressure levels. In general, for the three conditions that make the ear's impedance magnitude lower than normal, the model predicts a reduced ear-canal pressure (as much as 35 dB), with a greater pressure reduction with an insert earphone than with a supra-aural earphone. In contrast, the model predicts that ear-canal pressure levels increase only a few dB when the ear has an increased impedance magnitude; the compliance of the air-space between the tympanic membrane and the earphone determines an upper limit on the effect of the middle-ear's impedance increase. Acoustic leaks at the earphone-to-ear connection can also cause uncontrolled pressure variations during hearing tests. From measurements at the supra-aural earphone-to-ear connection, we conclude that it is unusual for the connection between the earphone cushion and the pinna to seal effectively for frequencies below 250 Hz. The models developed here explain the measured pressure variations with several pathologic ears. Understanding these mechanisms should inform the design of more accurate audiometric systems which might include a microphone that monitors the ear-canal pressure and corrects deviations from normal.     

Low-frequency characteristics of human and guinea pig cochleae

Previous physiological studies investigating the transfer of low-frequency sound into the cochlea have been invasive. Predictions about the human cochlea are based on anatomical similarities with animal cochleae but no direct comparison has been possible. This paper presents a noninvasive method of observing low frequency cochlear vibration using distortion product otoacoustic emissions (DPOAE) modulated by low-frequency tones. For various frequencies (15-480 Hz), the level was adjusted to maintain an equal DPOAE-modulation depth, interpreted as a constant basilar membrane displacement amplitude. The resulting modulator level curves from four human ears match equal-loudness contours (ISO226:2003) except for an irregularity consisting of a notch and a peak at 45 Hz and 60 Hz, respectively, suggesting a cochlear resonance. This resonator interacts with the middle ear stiffness. The irregularity separates two regions of the middle ear transfer function in humans: A slope of 12 dB/octave below the irregularity suggests mass-controlled impedance resulting from perilymph movement through the helicotrema; a 6-dB/octave slope above the irregularity suggests resistive cochlear impedance and the existence of a traveling wave. The results from four guinea pig ears showed a 6-dB/octave slope on either side of an irregularity around 120 Hz, and agree with published data.     

Enhancing interaural-delay-based extents of laterality at high frequencies by using "transposed stimuli"

An acoustic pointing task was used to determine whether interaural temporal disparities (ITDs) conveyed by high-frequency "transposed" stimuli would produce larger extents of laterality than ITDs conveyed by bands of high-frequency Gaussian noise. The envelopes of transposed stimuli are designed to provide high-frequency channels with information similar to that conveyed by the waveforms of low-frequency stimuli. Lateralization was measured for low-frequency Gaussian noises, the same noises transposed to 4 kHz, and high-frequency Gaussian bands of noise centered at 4 kHz. Extents of laterality obtained with the transposed stimuli were greater than those obtained with bands of Gaussian noise centered at 4 kHz and, in some cases, were equivalent to those obtained with low-frequency stimuli. In a second experiment, the general effects on lateral position produced by imposed combinations of bandwidth, ITD, and interaural phase disparities (IPDs) on low-frequency stimuli remained when those stimuli were transposed to 4 kHz. Overall, the data were fairly well accounted for by a model that computes the cross-correlation subsequent to known stages of peripheral auditory processing augmented by low-pass filtering of the envelopes within the high-frequency channels of each ear.     

Psychophysical tuning curves at very high frequencies

For most normal-hearing listeners, absolute thresholds increase rapidly above about 16 kHz. One hypothesis is that the high-frequency limit of the hearing-threshold curve is imposed by the transmission characteristics of the middle ear, which attenuates the sound input [Masterton et al., J. Acoust. Soc. Am. 45, 966-985 (1969)]. An alternative hypothesis is that the high-frequency limit of hearing is imposed by the tonotopicity of the cochlea [Ruggero and Temchin, Proc. Nat. Acad. Sci. U.S.A. 99, 13206-13210 (2002)]. The aim of this study was to test these hypotheses. Forward-masked psychophysical tuning curves (PTCs) were derived for signal frequencies of 12-17.5 kHz. For the highest signal frequencies, the high-frequency slopes of some PTCs were steeper than the slope of the hearing-threshold curve. The results also show that the human auditory system displays frequency selectivity for characteristic frequencies (CFs) as high as 17 kHz, above the frequency at which absolute thresholds begin to increase rapidly. The findings suggest that, for CFs up to 17 kHz, the high-frequency limitation in humans is imposed in part by the middle-ear attenuation, and not by the tonotopicity of the cochlea.     

Distortion product otoacoustic emission suppression tuning and acoustic admittance in human infants: birth through 6 months

Previous work has reported non-adultlike distortion product otoacoustic emission (DPOAE) suppression in human newborns at f2=6000 Hz, indicating an immaturity in peripheral auditory function. In this study, DPOAE suppression tuning curves (STCs) were recorded as a measure of cochlear function and acoustic admittance/reflectance (YR) in the ear canal recorded as a measure of middle-ear function, in the same 20 infants at birth and through 6 months of age. DPOAE STCs changed little from birth through 6 months, showing excessively narrow and sharp tuning throughout the test period. In contrast, several middle-ear indices at corresponding frequencies shifted systematically with increasing age, although they also remained non-adultlike at 6 months. Linear correlations were conducted between YR and DPOAE suppression features. Only two correlations out of 76 were significant, and all but three YR variables accounted for <10% of the variance in DPOAE suppression tuning. The strongest correlation was noted between admittance phase at 5700 Hz and STC tip-to-tail (R=0.49). The association between middle-ear variables and DPOAE suppression may be stronger during other developmental time periods. Study of older infants and children is needed to fully define postnatal immaturity of human peripheral auditory function.     

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.     

Middle-ear response in the chinchilla and its relationship to mechanics at the base of the cochlea

The responses of the malleus and the stapes to sinusoidal acoustic stimulation have been measured in the middle ears of anesthetized chinchillas using the M?ssbauer technique. With "intact" bullas (i.e., closed except for venting via capillary tubing), the vibrations of the tip of the malleus reach a maximal peak velocity of about 2 mm/s in responses to 100-dB SPL tones in the frequency range 500-6000 Hz; vibration velocity diminishes toward lower frequencies with a slope of about 6 dB/oct. Opening the bulla widely increases the responses to low-frequency stimuli by as much as 16 dB. At low frequencies, malleus response sensitivity with either open or intact bullas far exceeds all previous measurements in cats and matches or exceeds such measurements in guinea pigs. Whether measured in open or intact bullas, phase-versus-frequency curves closely approximate those predicted from the magnitude-versus-frequency curves by minimum phase theory. The stapes responses are similar to those of the malleus, except that stapes response magnitude is lower, on the average, by 7.5 dB at frequencies below 2 kHz and 10.7 dB at 2 kHz and above. Comparison of the responses of the middle ear with those of the basilar membrane at a site 3.5 mm from the stapes indicates that, at frequencies below 150 Hz, the basilar membrane displacement is proportional to stapes acceleration. At frequencies between 150 and 2000 Hz, basilar membrane displacement is proportional to stapes velocity.