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Journal of the Acoustical Society of America

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Dec 2010

Volume 128, Issue 6, pp. EL355-3830

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Recovery of distortion-product otoacoustic emissions after a 2-kHz monaural sound-exposure in humans: Effects on fine structures

Miguel Angel Aranda de Toro, Rodrigo Ordoñez, Karen Reuter, and Dorte Hammersh⊘i

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3568-3576 (2010); (9 pages)

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A better understanding of the vulnerability of the fine structures of distortion-product otoacoustic emissions (DPOAEs) after acoustic overexposure may improve the knowledge about DPOAE generation, cochlear damage, and lead to more efficient diagnostic tools. It is studied whether the DPOAE fine structures of 16 normal-hearing human subjects are systematically affected after a moderate monaural sound-exposure of 10 min to a 2-kHz tone normalized to an exposure level LEX,8h of 80 dBA. DPOAEs were measured before and in the following 70 min after the exposure. The experimental protocol allowed measurements with high time and frequency resolution in a 1/3-octave band centered at 3 kHz. On average, DPOAE levels were reduced approximately 5 dB in the entire measured frequency-range. Statistically significant differences in pre- and post-exposure DPOAE levels were observed up to 70 min after the end of the sound exposure. The results show that the effects on fine structures are highly individual and no systematic change was observed.
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43.64.Jb Otoacoustic emissions
43.64.Wn Effects of noise and trauma on the auditory system

A two-dimensional cochlear fluid model based on conformal mapping

Hannes Lüling, Jan-Moritz P. Franosch, and J. Leo van Hemmen

J. Acoust. Soc. Am. Volume 128, Issue 6, pp. 3577-3584 (2010); (8 pages)

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Using conformal mapping, fluid motion inside the cochlear duct is derived from fluid motion in an infinite half plane. The cochlear duct is represented by a two-dimensional half-open box. Motion of the cochlear fluid creates a force acting on the cochlear partition, modeled by damped oscillators. The resulting equation is one-dimensional, more realistic, and can be handled more easily than existing ones derived by the method of images, making it useful for fast computations of physically plausible cochlear responses. Solving the equation of motion numerically, its ability to reproduce the essential features of cochlear partition motion is demonstrated. Because fluid coupling can be changed independently of any other physical parameter in this model, it allows the significance of hydrodynamic coupling of the cochlear partition to itself to be quantitatively studied. For the model parameters chosen, as hydrodynamic coupling is increased, the simple resonant frequency response becomes increasingly asymmetric. The stronger the hydrodynamic coupling is, the slower the velocity of the resulting traveling wave at the low frequency side is. The model’s simplicity and straightforward mathematics make it useful for evaluating more complicated models and for education in hydrodynamics and biophysics of hearing.
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43.64.Kc Cochlear mechanics
43.64.Bt Models and theories of the auditory system
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