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Journal of the Acoustical Society of America

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Dec 2001

Volume 110, Issue 6, pp. 2811-3330

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Origin of the bell-like dependence of the DPOAE amplitude on primary frequency ratio

Andrei N. Lukashkin and Ian J. Russell

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3097-3106 (2001); (10 pages) | Cited 13 times

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For low and medium sound pressure levels (SPLs), the amplitude of the distortion product otoacoustic emission (DPOAE) recorded from guinea pigs at the 2f1-f2 frequency is maximal when f2/f1 ≈ 1.23 and decreases for lower and higher f2/f1 ratios. The high-ratio slope of the DPOAE dependence on the ratio of the primary frequencies might be anticipated since the f1 amplitude at the f2 place is expected to decrease for higher f2/f1 ratios. The low-ratio slope of the dependence at low and medium SPLs of the primaries is actually one slope of a notch. The DPOAE amplitude recovers from the notch when the f2/f1 ratio is further reduced. In two-dimensional space formed by the f2/f1 ratio, and the levels of the primaries, the notch is continuous and has a level-dependent phase transition. The notch is identical to that seen in DPOAE growth functions. Similar notches and phase transitions were observed for high-order and high-frequency DPOAEs. Theoretical analysis reveals that a single saturating nonlinearity is capable of generating similar amplitude notch and phase transition when the f2/f1 ratio is decreased because of the increase in f1 amplitude at the DPOAE generation place (f2 place). The difference between the DPOAE recorded from guinea pigs and humans is discussed in terms of different position of the operating point of the DPOAE generating nonlinearity. © 2001 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system
43.64.Jb Otoacoustic emissions
43.64.Kc Cochlear mechanics

A human nonlinear cochlear filterbank

Enrique A. Lopez-Poveda and Ray Meddis

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3107-3118 (2001); (12 pages) | Cited 27 times

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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. © 2001 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system

Distortion product otoacoustic emission input/output functions in normal-hearing and hearing-impaired human ears

Patricia A. Dorn, Dawn Konrad-Martin, Stephen T. Neely, Douglas H. Keefe, Emily Cyr, and Michael P. Gorga

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3119-3131 (2001); (13 pages) | Cited 30 times

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DPOAE input/output (I/O) functions were measured at 7f2 frequencies (1 to 8 kHz; f2/f1 = 1.22) over a range of levels (−5 to 95 dB SPL) in normal-hearing and hearing-impaired human ears. L1-L2 was level dependent in order to produce the largest 2 f1-f2 responses in normal ears. System distortion was determined by collecting DP data in six different acoustic cavities. These data were used to derive a multiple linear regression model to predict system distortion levels. The model was tested on cochlear-implant users and used to estimate system distortion in all other ears. At most but not all f2’s, measurements in cochlear implant ears were consistent with model predictions. At all f2 frequencies, the ears with normal auditory thresholds produced I/O functions characterized by compressive nonlinear regions at moderate levels, with more rapid growth at low and high stimulus levels. As auditory threshold increased, DPOAE threshold increased, accompanied by DPOAE amplitude reductions, notably over the range of levels where normal ears showed compression. The slope of the I/O function was steeper in impaired ears. The data from normal-hearing ears resembled direct measurements of basilar membrane displacement in lower animals. Data from ears with hearing loss showed that the compressive region was affected by cochlear damage; however, responses at high levels of stimulation resembled those observed in normal ears. © 2001 Acoustical Society of America.
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43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Jb Otoacoustic emissions

Effects of draining cochlear fluids on stapes displacement in human middle-ear models

Richard M. Lord, Eric W. Abel, Zhigang Wang, and Robert P. Mills

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3132-3139 (2001); (8 pages) | Cited 1 time

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Displacement-frequency characteristics of the stapes footplate were measured in five human temporal bones before and after draining the vestibule. Measurements were made in the 0.125–8 kHz range at 80 dB input sound pressure level, using a laser Doppler vibrometer. A circuit model was also used to predict stapes displacement. The temporal bone studies show a slight decrease in stapes footplate displacement at low frequency, and little change above 1 kHz. The displacement change is not as great as that found by other investigators or predicted by the model. There is little difference in stapes motion in temporal bones when the inner ear is intact or drained. © 2001 Acoustical Society of America.
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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

Multicomponent stimulus interactions observed in basilar-membrane vibration in the basal region of the chinchilla cochlea

William S. Rhode and Alberto Recio

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3140-3154 (2001); (15 pages) | Cited 6 times

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Multicomponent stimuli consisting of two to seven tones were used to study suppression of basilar-membrane vibration at the 3–4-mm region of the chinchilla cochlea with a characteristic frequency between 6.5 and 8.5 kHz. Three-component stimuli were amplitude-modulated sinusoids (AM) with modulation depth varied between 0.25 and 2 and modulation frequency varied between 100 and 2000 Hz. For five-component stimuli of equal amplitude, frequency separation between adjacent components was the same as that used for AM stimuli. An additional manipulation was to position either the first, third, or fifth component at the characteristic frequency (CF). This allowed the study of the basilar-membrane response to off-CF stimuli. CF suppression was as high as 35 dB for two-tone combinations, while for equal-amplitude stimulus components CF suppression never exceeded 20 dB. This latter case occurred for both two-tone stimuli where the suppressor was below CF and for multitone stimuli with the third component=CF. Suppression was least for the AM stimuli, including when the three AM components were equal. Maximum suppression was both level- and frequency dependent, and occurred for component frequency separations of 500 to 600 Hz. Suppression decreased for multicomponent stimuli with component frequency spacing greater than 600 Hz. Mutual suppression occurred whenever stimulus components were within the compressive region of the basilar membrane. © 2001 Acoustical Society of America.
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43.64.Kc Cochlear mechanics

DPOAE suppression tuning: Cochlear immaturity in premature neonates or auditory aging in normal-hearing adults?

Carolina Abdala

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3155-3162 (2001); (8 pages) | Cited 9 times

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Previous work has shown that distortion product otoacoustic emission (DPOAE) suppression tuning curves (STCs) recorded from premature neonates are narrower than adult STCs at both low and high frequencies. This has been interpreted to indicate an immaturity in cochlear function prior to term birth. However, an alternative explanation for this finding is that adult DPOAE STCs are broadened and reflect cochlear hair cell loss in normal-hearing adults due to aging, and natural exposure to noise and ototoxins. This alternative hypothesis can be tested by studying suppression tuning in normal-hearing school-aged children. If normal-hearing children, who have not aged significantly or been exposed to noise/ototoxins, have DPOAE suppression tuning similar to adults, the auditory aging hypothesis can be ruled out. However, if children have tuning similar to premature neonates and dissimilar from adults, it implicates aging or other factors intrinsic to the adult cochlea. DPOAE STCs were recorded at 1500, 3000, and 6000 Hz using optimal parameters in normal-hearing children and adults. DPOAE STCs collected previously from premature neonates were used for age comparisons. In general, results indicate that tuning curves from children are comparable to adult STCs and significantly different from neonatal STCS at 1500 and 6000 Hz. Only the growth of suppression was not adultlike in children and only at 6000 Hz. These findings do not strongly support the auditory aging hypothesis as a primary explanation for previously observed neonatal–adult differences in DPOAE suppression tuning. It suggests that these age differences are most likely due to immaturities in the neonatal cochlea. However, nonadultlike suppression growth observed in children at 6000 Hz warrants further attention and may be indicative of subtle alternations in the adult cochlea at high frequencies. © 2001 Acoustical Society of America.
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43.64.Kc Cochlear mechanics

Energy-independent factors influencing noise-induced hearing loss in the chinchilla model

Roger P. Hamernik and Wei Qiu

J. Acoust. Soc. Am. Volume 110, Issue 6, pp. 3163-3168 (2001); (6 pages) | Cited 8 times

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The effects on hearing and the sensory cell population of four continuous, non-Gaussian noise exposures each having an A-weighted Leq = 100 dB SPL were compared to the effects of an energy-equivalent Gaussian noise. The non-Gaussian noise conditions were characterized by the statistical metric, kurtosis (β), computed on the unfiltered, β(t), and the filtered, β(f ), time-domain signals. The chinchilla (n = 58) was used as the animal model. Hearing thresholds were estimated using auditory-evoked potentials (AEP) recorded from the inferior colliculus and sensory cell populations were obtained from surface preparation histology. Despite equivalent exposure energies, the four non-Gaussian conditions produced considerably greater hearing and sensory cell loss than did the Gaussian condition. The magnitude of this excess trauma produced by the non-Gaussian noise was dependent on the frequency content, but not on the average energy content of the impacts which gave the noise its non-Gaussian character. These results indicate that β(t) is an appropriate index of the increased hazard of exposure to non-Gaussian noises and that β(f ) may be useful in the prediction of the place-specific additional outer hair cell loss produced by non-Gaussian exposures. The results also suggest that energy-based metrics, while necessary for the prediction of noise-induced hearing loss, are not sufficient. © 2001 Acoustical Society of America.
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43.64.Wn Effects of noise and trauma on the auditory system
43.66.Ed Auditory fatigue, temporary threshold shift
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