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Journal of the Acoustical Society of America

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Jul 2004

Volume 116, Issue 1, pp. 1-603

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Time–frequency analysis of auditory-nerve-fiber and basilar-membrane click responses reveal glide irregularities and non-characteristic-frequency skirts

Tai Lin and John J. Guinan, Jr.

J. Acoust. Soc. Am. Volume 116, Issue 1, pp. 405-416 (2004); (12 pages) | Cited 11 times

Online Publication Date: 01 Jul 2004

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Although many properties of click responses can be accounted for by a single, frequency-dispersive traveling wave exciting a single, characteristic-frequency (CF) resonance, some properties, such as waxing and waning cannot. Joint time–frequency distributions (TFDs) were used to help understand click responses of cat single auditory-nerve (AN) fibers (CFs<4 kHz) and published measurements of chinchilla basilar-membrane (BM) motion. For CFs>800 Hz, the peak energy of the response decreased in latency and frequency as the level increased, as expected. However, at high levels the trend reversed for AN, but not BM, responses. Normalized TFDs, which show the frequency with the peak energy at each response time, revealed glides, as previously reported. Classical theory predicts smooth, upward glides. Instead, at low CFs there were downward glides, and at other CFs glides had substantial irregularities. Finally, click skirts, defined as the longest-latency part of click responses, sometimes showed deviations from CF for above-threshold sound levels. Most of these phenomena are not explained by a single, frequency-dispersive traveling wave exciting a single CF resonance, but they can be accounted for by the interaction of two (or more) excitation drives with different latencies and frequency contents. © 2004 Acoustical Society of America.
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43.64.Kc Cochlear mechanics
43.64.Pg Electrophysiology of the auditory nerve

Prediction of the characteristics of two types of pressure waves in the cochlea: Theoretical considerations

Masayoshi Andoh and Hiroshi Wada

J. Acoust. Soc. Am. Volume 116, Issue 1, pp. 417-425 (2004); (9 pages) | Cited 3 times

Online Publication Date: 01 Jul 2004

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The aim of this study was to predict the characteristics of two types of cochlear pressure waves, so-called fast and slow waves. A two-dimensional finite-element model of the organ of Corti (OC), including fluid–structure interaction with the surrounding lymph fluid, was constructed. The geometry of the OC at the basal turn was determined from morphological measurements of others in the gerbil hemicochlea. As far as mechanical properties of the materials within the OC are concerned, previously determined mechanical properties of portions within the OC were adopted, and unknown mechanical features were determined from the published measurements of static stiffness. Time advance of the fluid–structure scheme was achieved by a staggered approach. Using the model, the magnitude and phase of the fast and slow waves were predicted so as to fit the numerically obtained pressure distribution in the scala tympani with what is known about intracochlear pressure measurement. When the predicted pressure waves were applied to the model, the numerical result of the velocity of the basilar membrane showed good agreement with the experimentally obtained velocity of the basilar membrane documented by others. Thus, the predicted pressure waves appeared to be reliable. Moreover, it was found that the fluid–structure interaction considerably influences the dynamic behavior of the OC at frequencies near the characteristic frequency. © 2004 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system
43.64.Kc Cochlear mechanics

A biophysical model of an inner hair cell

David G. Zeddies and Jonathan H. Siegel

J. Acoust. Soc. Am. Volume 116, Issue 1, pp. 426-441 (2004); (16 pages) | Cited 3 times

Online Publication Date: 01 Jul 2004

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Whole-cell patch-clamp recordings on isolated inner hair cells (IHCs) of guinea pig cochleae have revealed the presence of voltage-gated potassium channels. A biophysical model of an IHC is presented that indicates activation of slow voltage-gated potassium channels may lead to receptor potentials whose dc component decreases during the stimulus, and membrane potential hyperpolarizes when the stimulus is turned off. Both the decreasing dc and the hyperpolarization are, respectively, consistent with rapid adaptation and suppression of spontaneous rate in the auditory nerve. Receptor potentials recorded in vivo do not show these features, and when a nonspecific leak is included in the model to simulate microelectrode impalement, the model’s receptor potentials become similar to those in vivo. The nonspecific leak creates an electrical shunt that masks slow channel activity and allows the cell to depolarize. Both the decreasing dc and the hyperpolarization are sensitive to the resting potential. Because the reported resting potentials in vivo and in vitro differ greatly, the model is used to investigate homeostatic mechanisms responsible for the resting potential. It is found that the voltage-gated potassium channels have the greatest influence on the resting potential, but that the standing transducer current may be sufficient to eliminate the decreasing dc and after-stimulus hyperpolarization. © 2004 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system
43.64.Ld Physiology of hair cells
43.64.Wn Effects of noise and trauma on the auditory system

Periodogram based tests for distortion product otoacoustic emissions

Peter F. Craigmile and Wayne M. King

J. Acoust. Soc. Am. Volume 116, Issue 1, pp. 442-451 (2004); (10 pages)

Online Publication Date: 01 Jul 2004

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Distortion product otoacoustic emissions (DPOAEs) are an important nonbehavioral measure of cochlear function, which provides a close analogue of the behavioral pure-tone audiogram. DPOAEs are sinusoidal distortion products (DPs) produced by nonlinearities in the healthy cochlea. Detection of DPs is accomplished in the Fourier domain with a periodogram based test. The test compares the power in the DP periodogram bin to a noise estimate derived from a certain number of the surrounding bins. Statistical properties of this test to date have only been examined by constructing receiver operator characteristics curves derived from DPOAE measurements in normal and hearing impaired individuals. In this paper the null distribution of this order-statistic based test is explicitly derived, and via simulations intended to mimic the nonwhite features of real-ear noise measurements, the power of the test is demonstrated. These simulations demonstrate that a local F test is more powerful than this DPOAE test, with critical values that are easier to calculate. Although the power of both tests increase with an increasing number of bins, the improvement is negligible at around four bins. Since the power of both tests decrease at lower DP frequencies, it is not recommended to use a large number of bins. © 2004 Acoustical Society of America.
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43.64.Jb Otoacoustic emissions
43.60.Cg Statistical properties of signals and noise
43.60.Ac Theory of acoustic signal processing

Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds

John C. Middlebrooks

J. Acoust. Soc. Am. Volume 116, Issue 1, pp. 452-468 (2004); (17 pages) | Cited 5 times

Online Publication Date: 01 Jul 2004

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Interactions among the multiple channels of a cochlear prosthesis limit the number of channels of information that can be transmitted to the brain. This study explored the influence on channel interactions of electrical pulse rates and temporal offsets between channels. Anesthetized guinea pigs were implanted with 2-channel scala-tympani electrode arrays, and spike activity was recorded from the auditory cortex. Channel interactions were quantified as the reduction of the threshold for pulse-train stimulation of the apical channel by sub-threshold stimulation of the basal channel. Pulse rates were 254 or 4069 pulses per second (pps) per channel. Maximum threshold reductions averaged 9.6 dB when channels were stimulated simultaneously. Among nonsimultaneous conditions, threshold reductions at the 254-pps rate were entirely eliminated by a 1966-μs inter-channel offset. When offsets were only 41 to 123 μs, however, maximum threshold shifts averaged 3.1 dB, which was comparable to the dynamic ranges of cortical neurons in this experimental preparation. Threshold reductions at 4069 pps averaged up to 1.3 dB greater than at 254 pps, which raises some concern in regard to high-pulse-rate speech processors. Thresholds for various paired-pulse stimuli, pulse rates, and pulse-train durations were measured to test possible mechanisms of temporal integration. © 2004 Acoustical Society of America.
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43.64.Me Effects of electrical stimulation, cochlear implant
43.64.Qh Electrophysiology of the auditory central nervous system
43.66.Ts Auditory prostheses, hearing aids

Age reduces response latency of mouse inferior colliculus neurons to AM sounds

Henry Simon, Robert D. Frisina, and Joseph P. Walton

J. Acoust. Soc. Am. Volume 116, Issue 1, pp. 469-477 (2004); (9 pages) | Cited 1 time

Online Publication Date: 01 Jul 2004

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Age and stimulus rise time (RT) effects on response latency were investigated for inferior colliculus (IC) neurons in young-adult and old CBA mice. Single-unit responses were recorded to unmodulated and sinusoidal amplitude modulated (SAM) broadband noise carriers, presented at 35 to 80 dB SPL. Data from 63 young-adult and 76 old phasic units were analyzed to identify the time interval between stimulus onset and driven-response onset (latency). When controlling for stimulus sound level and AM frequency, significant age-related changes in latency were identified. Absolute latency decreased with age at all stimulus AM frequencies, significantly so for equivalent rise times (RT) ⩽ 12.5 ms. The linear correlation of latency with AM stimulus RT was significant for both young-adult and old units, and increased significantly with age. It is likely that both the decrease in absolute latency and the increase in latency/RT correlation with age are consistent with a reduction of inhibitory drive with age in the IC. These latency changes will result in age-related timing variations in brainstem responses to stimulus onsets, and therefore affect the encoding of complex sounds. © 2004 Acoustical Society of America.
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43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Ri Evoked responses to sounds
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