摘要:

The simple model introduced in Part I [J. Acoust. Soc. Am.102, 413–429 (1997)] is used to simulate the response of the cochlea to three stimulus tones. The focus is on “emission suppression tuning curves” constructed using a third tone to suppress the cubic distortion tone emission (CDT,2 f1−f2) generated by two primary tones at frequenciesf1andf2(intensitiesL1andL2). A criterion decrease (here, 5 dB) of the CDT emission amplitude defines the2 f1−f2emission suppression tuning curve. Applying traditional tuning curve measures to emission suppression tuning curves appears ineffective in determining the underlying cochlear amplifier characteristics. However, it is shown that there are three characteristics of emission suppression tuning curves which are particularly useful: (1) the “f2threshold” which is the level of the third tone,L3,required for the criterion CDT amplitude decrease, under the condition that the third tone frequency,f3,is approximately equal tof2;(2) the “shoulder threshold” similarly defined forf3≪f2;and (3) the “tuning width,”w40.The tuning width is defined to be the distance (in octaves) from the frequencyf2to the upperf3frequency for which there is a criterion CDT decrease, in this case using theL3level which is 40 dB above thef2threshold. Model calculations appropriate to gerbils show that these measures are most accurately related to the underlying cochlear amplifier characteristics for parameters where the primary stimulus amplitudes satisfyL1/L2>20 dBand for whichL1is 25 dB or more below the sharp “notch” seen in the two tone input–output function. In this parameter region, the cochlear amplifier characteristics are related to measured quantities by the relationshipswr≅w40andGa≅TE+w40gp.Here,Gais the gain (dB) of the cochlear amplifier, defined as the total increase in cochlear response over the passive response,wris the distance (octaves) over which the active cochlear response rises to a maximum, andgpis the passive increase (dB/octave) of the traveling wave along the basilar membrane. The measured quantities areTE,the difference (dB) between the shoulder threshold and thef2threshold, and the tuning width,w40(octaves), defined above. Model predictions are confirmed by measurements in adult gerbils.

ISSN:0001-4966    

DOI:10.1121/1.421101

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The deformation response of a guinea pig outer hair cell is modeled for mechanical and electrical stimulation up to 25 kHz. The analysis uses a Fourier series technique for a finite length cell surrounded internally and externally by a much larger continuum of viscous fluid. The analytical solution predicts that outer hair cell length changes occur due to applied mechanical or electrical stimulation without significant resonance, characteristic of a highly damped system. The deformation is found to have little attenuation up to a corner frequency of about 2 kHz for long cells and 10 kHz for short cells, in agreement with published experimental results. For electrical loading of 1 mV across the lateral cell wall, deformation for short cells is calculated to be greater than 1 nm for frequencies up to 20 kHz. These results support the proposition thatin vivothe outer hair cell modifies the character of basilar membrane deformation on a cycle-by-cycle basis. An estimate of the capability of the cell to supply energy to the basilar membrane is given based on published values of outer hair cell material properties.

ISSN:0001-4966    

DOI:10.1121/1.421126

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

In a profile-analysis task, the effect of randomly perturbing the amplitudes of the components of multi-tone stimuli was studied in two experiments. In the first experiment, thresholds for a signal added in-phase to the central component of a standard were measured for different numbers of components in two conditions. In one condition thresholds were measured in blocks for six different “jagged” standards, and in another, thresholds were measured when one of the six standards was chosen randomly on a presentation-by-presentation basis. Regardless of condition, thresholds did not depend on the numbers of components and increased magnitude of perturbation increased thresholds. Moreover, the slope relating thresholds to number of components did not increase with increasing magnitude of perturbation. In the second experiment, the signal consisted of an increase in amplitude of the central components and a decrease in amplitude of the outer components of the standard (a stimulus type which has been shown to maximize the change in threshold with increasing number of components). The amplitudes of component tones were selected randomly on a presentation-by-presentation basis. Thresholds fell with increases in the number of components, but the slope relating thresholds to numbers of components did not change as the magnitude of perturbation increased. The latter result contrasts with that reported by Kidd et al. [J. Acoust. Soc. Am.90, 1340–1354 (1991)].

ISSN:0001-4966    

DOI:10.1121/1.421124

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The ability to identify the frequency of the incremented component in a multitone complex was assessed in two conditions, both using the same 11-tone complexes (fixed frequency, equilog spaced, random phases). In the standard-plus-signal complex all components had equal level, except one of the inner nine, which was incremented in level by an in-phase addition of a sinusoid of the same frequency (the signal). The overall level and signal position were randomly varied on each presentation. In the “Standard-absent” condition the standard-plus-signal complex was presented first, and it was followed by a single sinusoid either at the signal frequency or at that of an adjacent component (below or above). In the “Standard-present” condition, a complex with equal-level components (the standard complex) was also presented on each trial, either before or after the standard-plus-signal complex (in random order). These two complexes were followed by the single sinusoid. In both conditions, the subjects had to indicate whether the signal frequency was the same as or different from the frequency of the single sinusoid. In a third condition, the ability to discriminate between the standard complex and the standard-plus-signal complex (with signal frequency uncertainty) was investigated. In all three conditions, thresholds for the increment in level for each signal frequency were estimated by the use of nine independent interleaved adaptive procedures. Results showed that the ability to identify the signal frequency was at least as good as the ability to discriminate between the two complexes. The results suggest that an increase in pitch strength of the incremented component is a possible cue in profile analysis tasks.

ISSN:0001-4966    

DOI:10.1121/1.421102

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A maximum-likelihood method was applied in measurements of frequency and intensity discrimination for aged and young normal-hearing subjects with closely matched audiograms. This method was preferred over other psychophysical procedures because it is efficient and controls experimental variance, features that are highly desirable for testing aged subjects. In order to implement the method, psychometric functions for each task were also measured from young subjects using a constant-stimuli procedure. For the young subjects, the differential thresholds obtained from these two procedures were generally comparable. Further, both sets of data were consistent with previous literature, indicating that the maximum-likelihood method was successfully applied for frequency and intensity discrimination. A frequency-dependent difference between young and aged subjects in both frequency and intensity discrimination was observed. Even with closely matched audiograms, aged subjects demonstrated poorer discrimination abilities than young subjects. The age-related difference was always largest at 500 Hz and decreased as frequency increased.

ISSN:0001-4966    

DOI:10.1121/1.421127

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

An alternative for the Liljencrants–Fant (LF) glottal-pulse model is presented. This alternative is derived from the Rosenberg model. Therefore, it is called the Rosenberg++ model. In the derivation a general framework is used for glottal-pulse models. The Rosenberg++ model is described by the same set ofTorRparameters as the LF model but it has the advantage over the LF model that it is computationally more efficient. It is compared with the LF model in a psychoacoustic experiment, from which it is concluded that in a practical situation it is capable of producing synthetic speech which is perceptually equivalent to speech generated with the LF model.

ISSN:0001-4966    

DOI:10.1121/1.421103

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The effect of digital processing, which slows the speed of speech (speech-rate) without changing its pitch, has been examined. The processing is intended to make speech communication easier by allowing more time for cognitive processing when the listening situation is difficult, for example, when listening to a foreign language, or when the user has a hearing loss. The speech-rate slowing makes use of a pitch-synchronous partial expansion of the waveform in the time domain. The processing was evaluated using a simulation of hearing loss which has been shown to lead to reduced intelligibility for normally hearing subjects. The simulation included the major consequences of cochlear hearing loss; loudness recruitment, threshold elevation, and reduced frequency selectivity. Two simulations were used: a moderate flat hearing loss with auditory filters broadened by a constant factor of three (B3R2); and the same loss with linear amplification applied prior to the simulation processing(B3R2+).Two expansion rates were used for the speech-rate slowing, 1.25 and 1.50. The intelligibility of sentences in speech-shaped noise was measured. For both simulation conditions, the speech-rate slowing did not give any improvement in intelligibility. Rather, in conditionB3R2+the slowing produced statistically significant deleterious effects on intelligibility. The results suggest that artificial speech-rate slowing will not improve the intelligibility of speech in noise for hearing-impaired people who have the type of cochlear damage simulated in this test.

ISSN:0001-4966    

DOI:10.1121/1.421123

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

People with cochlear hearing loss often have considerable difficulty in understanding speech in the presence of background sounds. In this paper the relative importance of spectral and temporal dips in the background sounds is quantified by varying the degree to which they contain such dips. Speech reception thresholds in a 65-dB SPL noise were measured for four groups of subjects: (a) young with normal hearing; (b) elderly with near-normal hearing; (c) young with moderate to severe cochlear hearing loss; and (d) elderly with moderate to severe cochlear hearing loss. The results indicate that both spectral and temporal dips are important. In a background that contained both spectral and temporal dips, groups (c) and (d) performed much more poorly than group (a). The signal-to-background ratio required for 50% intelligibility was about 19 dB higher for group (d) than for group (a). Young hearing-impaired subjects showed a slightly smaller deficit, but still a substantial one. Linear amplification combined with appropriate frequency-response shaping (NAL amplification), as would be provided by a well-fitted “conventional” hearing aid, only partially compensated for these deficits. For example, group (d) still required a speech-to-background ratio that was 15 dB higher than for group (a). Calculations of the articulation index indicated that NAL amplification did not restore audibility of the whole of the speech spectrum when the speech-to-background ratio was low. For unamplified stimuli, the SRTs in background sounds were highly correlated with absolute thresholds, but not with age. For stimuli with NAL amplification, the correlations of SRTs with absolute thresholds were lower, but SRTs in backgrounds with spectral and/or temporal dips were significantly correlated with age. It is proposed that noise with spectral and temporal dips may be especially useful in evaluating possible benefits of multi-channel compression.

ISSN:0001-4966    

DOI:10.1121/1.421128

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A method is presented for using a small number of bandpass filters and banks of parallel comb filters to analyze the tempo of, and extract the beat from, musical signals of arbitrary polyphonic complexity and containing arbitrary timbres. This analysis is performed causally, and can be used predictively to guess when beats will occur in the future. Results in a short validation experiment demonstrate that the performance of the algorithm is similar to the performance of human listeners in a variety of musical situations. Aspects of the algorithm are discussed in relation to previous high-level cognitive models of beat tracking.

ISSN:0001-4966    

DOI:10.1121/1.421129

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The importance of individual identity and kinship has been demonstrated in the social behavior of many nonhuman primates, with some evidence suggesting that individually distinctive acoustic features are present in their vocalizations as well. In order to systematically test whether acoustic cues to identity are reliably present across the vocal repertoire of rhesus monkeys (Macaca mulatta), we examinedcoos,grunts, andnoisy screamsproduced by adult females of two free-ranging groups. First, acoustic analyses were used to characterize spectral patterning, the fundamental frequency, and temporal characteristics of these three distinct call types. Vocalizations were then classified by caller identity, based on discriminant function analyses. Results showed that coos (rich, harmonically structured sounds) were markedly more distinctive by caller than were either grunts or noisy screams, and that spectral-patterning measures related to vocal tract filtering effects were the most reliable markers of individual identity. Grunts (pulsed, noisy calls) were classified at lower, but above-chance rates and spectral patterning cues were again critical in this sorting. Noisy screams (continuous, broadband noise bursts that could include a high-frequency, periodic component) could not be reliably sorted by caller. Playback experiments conducted with the screams showed no response differences when listening animals heard vocalizations produced by kin or nonkin individuals. This result was strikingly different from the corresponding outcome of a previous test with coo calls, but consistent with the acoustic analysis. Implications of these findings for vocal production mechanisms in nonhuman primates and previous studies of rhesus monkey vocalizations are discussed.

ISSN:0001-4966    

DOI:10.1121/1.421104

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP