摘要:

The in-plane and bending stiffnesses of the outer hair cell wall are characteristics crucial to the understanding of force and energy transmission between cochlear elements. A mathematical interpretation is given of the micropipet experiment directed at determining the outer hair cell wall stiffness. On the basis of the microstructural observation of the wall showing that it comprises protein networks with different elastic properties, the model of an orthotropic cylindrical shell is used. The boundary-value problem is analyzed corresponding to the stress–strain state of the wall (shell) caused by the action of the micropipet. The solution is given in terms of Fourier series with respect to the circumferential coordinate. An asymptotic analysis of the solution is developed and an approximate formula for the length of the tongue aspirated within the pipet is derived. This leads to an analytical expression for the stiffness parameter measured in the micropipet experiment in terms of Young’s moduli and Poisson’s ratios of the wall. This expression is an important part of the estimation of the elastic constants of the wall.

ISSN:0001-4966    

DOI:10.1121/1.421216

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The outer hair cell makes both passive and active contributions to basilar membrane mechanics. The outer hair cell mechanics is strongly coupled to the elastic properties of the cell lateral wall. The lateral wall experiences both in-plane deformations and bending under physiological and experimental conditions. To characterize the outer hair cell wall, the model of an orthotropic cylindrical shell is used. The elastic constants of the wall are estimated by solving a set of three equations based on the analyses of three independent experiments. The first equation is derived from a new interpretation of the micropipet experiment; the other two are obtained from the axial loading and the osmotic challenge experiments. The two Young’s moduli corresponding to the longitudinal and circumferential directions and two Poisson’s ratios are estimated. The longitudinal, circumferential, and mixed modes of the bending stiffness are also estimated. The sensitivity of the derived constants to the variation of the cell axial stiffness, which has been measured by several independent groups, is examined. The new estimates are also compared with results obtained by using the assumption of the wall isotropy.

ISSN:0001-4966    

DOI:10.1121/1.421217

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

In experiment 1, masking patterns were obtained with a tonal masker that was sinusoidally amplitude modulated (SAM) at a rate of 8 Hz and a depth(m)of 1.0. The signal was centered at a masker peak or masker valley. Masker frequency(fm)was 750, 1350, or 2430 Hz, and signal frequency(fs)ranged from 0.8 to1.62 fm.Thresholds were generally higher for a signal in a masker peak than in a masker valley. The magnitude of this peak-to-valley (PV) difference was governed byfs/fm,rather than byfs,and was largest forfs>fm.The PV differences were smallest at the lowestfm,at least whenfs>fm.In experiment 2, growth-of-masking functions were measured (fm=1350 Hz,fs=1.44fm). The masker was modulated at a depth(m)of 1.0, 0.75, or 0.50. These thresholds were compared with those obtained with an unmodulated masker in forward or simultaneous masking. The comparisons suggest that thresholds for a signal at a peak of an 8-Hz SAM masker are due to simultaneous masking, while those in a valley are due primarily to forward masking whenm=1.0or simultaneous masking whenm=0.75or 0.50. For these masker depths, the PV difference first increased but then decreased as masker level increased from 60 to 90 dB SPL. This was a consequence of the slope of the masking function for peak placement changing from a value greater than 2.0 to a value of 1.0 at the highest signal levels (an effect that was also observed with the unmodulated simultaneous masker), a result that may be understood in terms of basilar membrane nonlinearity.

ISSN:0001-4966    

DOI:10.1121/1.421247

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Loudness-intensity functions for click stimuli were obtained from 30 adult listeners having normal(n=10),flat(n=10),or sloping(n=10)high-frequency cochlear hearing loss configurations. The procedure of cross-modality matching (CMM) between loudness and perceived line length [R. P. Hellman and C. H. Meiselman, J. Speech Hear. Res.31, 605–615 (1988); J. Acoust. Soc. Am.88, 2596–2606 (1990); J. Acoust. Soc. Am.93, 966–975 (1993)] was used to validate their loudness growth functions. Mean group loudness exponents were similar to those reported in recent investigations that utilized pure tone stimuli, further supporting the validity and reliability of the CMM task as an estimate of the loudness growth function. The results also suggest that the mean loudness function for clicks is similar to the function obtained with tonal stimuli at least for listeners with moderately impaired hearing or better. Moreover, CMM produced less variability than the more conventional psychophysical methods of magnitude estimation and production for the groups with cochlear hearing loss. Toward direct application of the CMM technique, in lieu of absolute exponential slope values, the individually determined loudness growth function over a range of intensities should be compared to the normal mean function for calculations of deviations.

ISSN:0001-4966    

DOI:10.1121/1.421218

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Thresholds were measured for a 6-kHz sinusoidal signal presented within a 500-ms masker. The masker was either a bandpass Gaussian noise of varying bandwidth, or a sinusoid of the same frequency as the signal. The spectrum level of the noise masker was kept constant at 20 dB SPL, and the level of the sinusoidal masker was 40 dB SPL. Thresholds for signal durations between 2 and 300 ms were measured for masker bandwidths ranging from 60 to 12 000 Hz. The masker was spectrally centered around 6 kHz. For masker bandwidths less than 600 Hz, the slope of the temporal integration function decreased with decreasing masker bandwidth. The results are not consistent with current models of temporal integration or temporal resolution. It is suggested that the results at narrow bandwidths can be understood in terms of changes in the power spectrum of the stimulusenvelopeor modulation spectrum. According to this view, the onset and offset ramps of the signal introduce detectable high-frequency components into the modulation spectrum, which provide a salient cue in narrowband maskers. For broadband maskers, these high-frequency components are masked by the inherent rapid fluctuations in the masker envelope. Additionally, for signal durations between 7 and 80 ms, signal thresholds decreased by up to 5 dB as the masker bandwidth increased from 1200 to 12 000 Hz. The mechanisms underlying this effect are not yet fully understood.

ISSN:0001-4966    

DOI:10.1121/1.421229

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Adaptive linear filtering can improve effective speech-to-noise ratios by attenuating spectral regions with intense noise components to reduce the noise’s spread of masking onto speech in neighboring regions. This mechanism was examined in static listening conditions for seven individuals with sensorineural hearing loss. Subjects were presented with nonsense syllables in an intense octave-band noise centered on 0.5, 1, or 2 kHz. The nonsense syllables were amplified to maximize the articulation index; the noises were the same for all subjects. The processing consisted of applying frequency-selective attenuation to the speech-plus-noise with the goal of attenuating the frequency region containing the noise by various amounts. Consonant recognition scores and noise masking patterns were collected in all listening conditions. When compared with masking patterns obtained from normal-hearing subjects, all hearing-impaired subjects had higher masked thresholds at frequencies below, within, and above the masker band except for one subject who demonstrated additional masking above the masker only. Frequency-selective attenuation resulted in both increases and decreases in consonant recognition scores. Increases were associated with a release from upward spread of masking. Decreases were associated with applying too much attenuation such that speech energy within the masker band that was audible before processing was partially below threshold after processing. Fletcher’s [Speech and Hearing in Communication(Van Nostrand, New York, Reference 1953)] version of articulation theory (without modification) accounted for individual subject differences within the range of variability associated with the consonant recognition test in almost every instance. Hence, primary factors influencing speech reception benefits are characterized by articulation theory. Fletcher’s theory appears well-suited to guide the design of control algorithms that will maximize speech recognition for individual listeners.

ISSN:0001-4966    

DOI:10.1121/1.423106

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Thresholds for the detection of a tone added in-phase to the carrier of a fully modulated SAM tone were measured. In some conditions the signal was added to a single SAM tone, and in other conditions the signal was added to the sum of three or more SAM tones. Level equalization ensured that the addition of the tonal signal did not lead to increases in energy. When multiple SAM tone maskers were used, a small number of reproducible maskers were tested, each masker being composed of SAM tones with a variety of relative modulator phases. The maskers were eitherfixedacross intervals and trials,rovedacross trials but fixed across intervals, orrandomlychosen across both intervals and trials. The frequency separation between the signal-centered and off-frequency SAM tones was also varied. For small signal-centered/off-frequency SAM tone frequency separations, a separation ratio of 1.3, thresholds in thefixedcondition depend on the relative modulator phases, and a simple mixture model reasonably predicted thresholds in therovingcondition based on thresholds in thefixedcondition for two of the three observers. For signal-centered/off-frequency SAM tone frequency separation factor of 1.68, effects of relative modulator phases were not obtained. Thresholds in thetarget-alonecondition were generally superior to thresholds measured with the comodulated masker. Comodulated thresholds were better thantarget-alonethresholds only when level equalization was not used, and so the addition of the signal led to increases in level.

ISSN:0001-4966    

DOI:10.1121/1.421219

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Age differences in auditory suppression were examined by comparing auditory-filter shapes obtained with simultaneous and forward masking at 2 kHz in young and elderly normal-hearing listeners. To compensate for the decay of forward masking, growth of masking functions were used to transform thresholds obtained with a notched-noise masker to the level of a continuous noise band that would give the same threshold values. Although both age groups exhibited smaller equivalent rectangular bandwidths (ERBs) when the filters derived from transformed thresholds were obtained with forward masking, the change from simultaneous to nonsimultaneous masking was significantly greater for young adults. Measures of the low-(Pl)and high-(Pu)frequency sides of the filters for young listeners indicated that the slopes of both sides increased following a change from simultaneous to forward masking but that the high-frequency side exhibited significantly greater sharpening. Filter slopes (both upper and lower) for older adults, in contrast, did not differ between the two masking procedures. The findings from the study are discussed as reflecting possible age differences in auditory suppression. However, it is also noted that conclusions regarding differences between filter shapes derived with simultaneous and forward masking are limited to filter parameters determined with transformed (as described above) thresholds.

ISSN:0001-4966    

DOI:10.1121/1.421220

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The present experiment investigated the effect of onset asynchrony on listeners’ ability to make relative intensity comparisons between a 1-kHz tone and a band of noise high-pass filtered at 3 kHz. In the synchronous condition, the tone and noise were gated on and off simultaneously. In the two asynchronous conditions, either the tone was gated on before the noise or vice versa, both stimuli terminating simultaneously. In the sequential condition, the offset of the tone coincided with the onset of the noise. The task of the six listeners was to indicate in which of the two presentation intervals the level of the tone was incremented relative to that of the noise. To deter the use of strategies based on successive, within-channel level comparisons, the overall level of the stimuli was randomized on each presentation. For all listeners thresholds were lowest in the synchronous condition, and highest in the sequential condition, the difference ranging from approximately 7 to 18 dB (signalre:pedestal amplitude). Furthermore, five of the six listeners had significantly lower thresholds in the noise-leading condition than in the tone-leading condition, the average difference across listeners being approximately 5 dB. The results are discussed in terms of auditory grouping and the possible strategies available to the listeners.

ISSN:0001-4966    

DOI:10.1121/1.421232

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The two experiments reported here examine how an inter-aural time difference (ITD) interacts with two other cues, mistuning and onset asynchrony, in reducing the contribution of a single frequency component to the perception of a vowel’s identity. Previous experiments have shown that although ITD is generally rather ineffective at segregating a simultaneous harmonic frequency component from a vowel, it can produce some segregation when listeners have already been exposed to the isolated segregated component. A difference in ITD increases segregation overall in experiment 1 where the to-be-segregated component can also have a different onset time from the remainder of the vowel, and experiment 2 shows a similar result when the to-be-segregated component is mistuned. However, segregation by ITD is present just as strongly on trials when there is neither mistuning nor a difference in onset-time as on trials where these additional cues are present. Segregation on trials when there is neither mistuning nor a difference in onset-time is however larger in the present experiment which mixed all conditions together than in similar trials in an earlier experiment that had a blocked design [C. J. Darwin and R. W. Hukin, J. Acoust. Soc. Am.102, 2316–2324 (1997)]. The results show that segregation by ITD increases when other more potent cues are present in the experiment.

ISSN:0001-4966    

DOI:10.1121/1.421221

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP