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Dec 2006

Volume 120, Issue 6, pp. 3429-EL89

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A nonlinear finite-element model of the newborn ear canal

Li Qi, Hengjin Liu, Justyn Lutfy, W. Robert J. Funnell, and Sam J. Daniel

J. Acoust. Soc. Am. Volume 120, Issue 6, pp. 3789-3798 (2006); (10 pages) | Cited 10 times

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A three-dimensional nonlinear finite-element model of a 22-day-old newborn ear canal is presented. The geometry is based on a clinical x-ray CT scan. A nonlinear hyperelastic constitutive law is applied to model large deformations. The Young’s modulus of the soft tissue is found to have a significant effect on the ear-canal volume change, which ranges from approximately 27% to 75% over the static-pressure range of ±3kPa. The effects of Poisson’s ratio and of the ratio C10:C01 in the hyperelastic model are found to be small. The volume changes do not reach a plateau at high pressures, which implies that the newborn ear-canal wall would not be rigid in tympanometric measurements. The displacements and volume changes calculated from the model are compared with available experimental data.
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43.64.Bt Models and theories of the auditory system
43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex

Laser interferometry measurements of middle ear fluid and pressure effects on sound transmission

Rong Z. Gan, Chenkai Dai, and Mark W. Wood

J. Acoust. Soc. Am. Volume 120, Issue 6, pp. 3799-3810 (2006); (12 pages) | Cited 17 times

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An otitis media with effusion model in human temporal bones with two laser vibrometers was created in this study. By measuring the displacement of the stapes from the medial side of the footplate, the transfer function of the middle ear, which is defined as the displacement transmission ratio (DTR) of the tympanic membrane to footplate, was derived under different middle ear pressure and fluid in the cavity with a correction factor for cochlear load. The results suggest that the DTR increases with increasing frequency up to 4k Hz when the middle ear pressure was changing from 0 to 20 or −20 cm H2O (e.g., ±196 daPa) and fluid level was increasing from 0 to a full middle ear cavity. The positive and negative pressures show different effects on the DTR. The effect of fluid on DTR varies between three frequency ranges: f<1k, between 1k and 4k, and f>4k Hz. These findings show how the efficiency of the middle ear system for sound transmission changes during the presence of fluid in the cavity and variations of middle ear pressure.
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43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Bt Models and theories of the auditory system

Columella footplate motion and the cochlear microphonic potential in the embryo and hatchling chicken

Young S. Kim, Timothy A. Jones, Mark E. Chertoff, and William C. Nunnally

J. Acoust. Soc. Am. Volume 120, Issue 6, pp. 3811-3821 (2006); (11 pages) | Cited 1 time

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A piezoelectric (PZE) vibrator was used to mechanically drive the columella footplate and stimulate the cochlea of chicken embryos and hatchlings. Our objectives were to characterize the motion of the PZE driver and determine the relationship between columella footplate motion (displacement/velocity) and the cochlear microphonic recorded from the recessus scala tympani (CMrst). At each frequency, displacement of the PZE driver probe tip was linearly related to the applied voltage over a wide range of attenuation levels (−60 to −20 dBre:50 Vp-p). The mean displacement across frequencies (100–4000 Hz) was 0.221±0.042 μmp-p for a constant applied voltage level of −20 dBre:50 Vp-p. Displacement was within 1.5 dB of the mean for this stimulus level at all frequencies except for 4000 Hz, where it was ∼ 3 dB higher (p<0.01). CMrst amplitudes in hatchlings were larger than amplitudes in embryos (p = 0.003). For a given frequency, CM was linearly related to footplate displacement and velocity at both ages. The transform ratio of CMrst/A (CM amplitude/displacement) increased at ∼ 6 dB/octave at frequencies between 100 and 1000 Hz in hatchlings suggesting that cochlear impedance (Zc) was resistive at these frequencies. In a large fraction of the embryos, Zc exhibited reactive behavior.
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43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Nf Cochlear electrophysiology
43.64.Yp Instruments and methods
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

L1,L2 maps of distortion-product otoacoustic emissions from a moth ear with only two auditory receptor neurons

Manfred Kössl and Frank Coro

J. Acoust. Soc. Am. Volume 120, Issue 6, pp. 3822-3831 (2006); (10 pages) | Cited 5 times

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The tympanal organ of the moth Empyreuma affinis emits physiologically vulnerable distortion-product otoacoustic emissions. To assess the nature of underlying mechanical nonlinearities, we measured L1,L2 maps by varying both stimulus levels. Two types of maps were found: (1) Maps containing dominant islands centered at the L1=L2 diagonal as it is typical for saturating nonlinearities that can be described by Boltzmann functions. In contrast to maps published for mammals and frogs, the shape of such islands includes sharp ridges at L1 or L2 levels close to 70 dB sound pressure level. This could be produced by a strongly asymmetric operating point of the respective transfer functions, consistent with the fact that the auditory sensory cells are not hair cells but primary mechanoreceptors with a single cilium. The saturating map components could be selectively reduced by acoustic suppression. (2) Maps where separated islands were less conspicuous but in which the dominant feature consisted of contour lines which were orthogonal to the L1 = 2L2 diagonal and could be generated by an expansive nonlinearity. Maps showing strong islands were found for f2 frequencies between 26.7 and 45 kHz, maps without strong islands for f2 between 42 and 57.5 kHz. This suggests a frequency-dependent change regarding the involved mechanical nonlinearities.
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43.64.Jb Otoacoustic emissions
43.64.Kc Cochlear mechanics

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

Carolina Abdala and Douglas H. Keefe

J. Acoust. Soc. Am. Volume 120, Issue 6, pp. 3832-3842 (2006); (11 pages) | Cited 20 times

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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.
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43.64.Jb Otoacoustic emissions
43.64.Kc Cochlear mechanics
43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
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