摘要:

The goals of this study were to characterize tongue surface displacement during production of bilabial stops and to refine current estimates of vocal-tract wall impedance using direct measurements of displacement in the vocal tract during closure. In addition, evidence was obtained to test the competing claims of passive and active enlargement of the vocal tract during voicing. Tongue displacement was measured and tongue compliance was estimated in four subjects during production of /aba/ and /apa/. All subjects showed more tongue displacement during /aba/ than during /apa/, even though peak intraoral pressure is lower for /aba/. In consequence, compliance estimates were much higher for /aba/, ranging from 5.1 to8.5×10−5 cm3/dyn.Compliance values for /apa/ ranged from 0.8 to2.3×10−5 cm3/dynfor the tongue body, and0.52×10−5for the single tongue tip point that was measured. From combined analyses of tongue displacement and intraoral pressure waveforms for one subject, it was concluded that smaller tongue displacements for /p/ than for /b/ may be due to active stiffening of the tongue during /p/, or to intentional relaxation of tongue muscles during /b/ (in conjunction with active tongue displacement during /b/).

ISSN:0001-4966    

DOI:10.1121/1.419729

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Previous studies have convincingly shown that the weight assigned to vocalic formant transitions in decisions of fricative identity for fricative-vowel syllables decreases with development. Although these same studies suggested a developmental increase in the weight assigned to the noise spectrum, the role of the aperiodic-noise portions of the signals in these fricative decisions have not been as well-studied. The purpose of these experiments was to examine more closely developmental shifts in the weight assigned to the aperiodic-noise components of the signals in decisions of syllable-initial fricative identity. Two experiments used noises varying along continua from a clear /s/ percept to a clear /∫/ percept. In experiment 1, these noises were created by combining /s/ and /∫/ noises produced by a human vocal tract at different amplitude ratios, a process that resulted in stimuli differing primarily in the amplitude of a relatively low-frequency (roughly 2.2-kHz) peak. In experiment 2, noises that varied only in the amplitude of a similar low-frequency peak were created with a software synthesizer. Both experiments used synthetic /ɑ/ and /u/ portions, and efforts were made to minimize possible contributions of vocalic formant transitions to fricative labeling. Children and adults labeled the resulting stimuli as /s/ vowel or /∫/ vowel. Combined results of the two experiments showed that children’s responses were less influenced than those of adults by the amplitude of the low-frequency peak of fricative noises.

ISSN:0001-4966    

DOI:10.1121/1.419730

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Vowel recognition was assessed for eight, cochlear implant patients who use the Ineraid’s six-electrode array. Recognition was tested in three conditions: with the Ineraid after years of experience; with a CIS processor at fitting of the processor; and with the CIS processor after 1 month’s experience. At the time of fitting of the CIS processor, vowel recognition was not superior to that with the Ineraid. Recognition improved significantly over the period of a month. At 1 month, performance was significantly better with the CIS processor than with the Ineraid. This outcome is interpreted to mean that remapping of the vowel space is necessary following fitting with the CIS processor and some of the remapping occurs over a time period of days or weeks, rather than hours. Vowel errors at one month could be accounted for by two mechanisms. One is that patients attended to low-frequency channels at the expense of high-frequency channels, or could not use information in high-frequency channels. The second is that, for diphthongs, patients could not detect frequency change over the course of the utterance.

ISSN:0001-4966    

DOI:10.1121/1.419731

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Human and monkey perception of the American English liquid /ra–la/ contrast was compared using various synthetic continua in which the normal spectral and temporal cues were either complete, partial, or altered in various ways. Two experiments compared human and monkeydiscriminationof the various continua using a low-uncertainty repeating-standard procedure. Results showed that, while human sensitivity was best at the human phoneme boundary, monkey sensitivity was best inside the /ra/ category. Also, while humans were more sensitive than monkeys to temporal variation in the stimuli, monkeys were more sensitive than humans to spectral variation, particularly for stimuli inside the /ra/ category. Two additional experiments compared human and monkeyidentificationof the /ra–la/ continua using a higher-uncertainty go/nogo identification procedure. Monkeys performed as accurately as humans (including one native Spanish and one native Hindi listener) in identifying the stimuli. However, human and monkey “phoneme boundaries” were in different places, with monkey boundaries shifted more toward /ra/ than human boundaries. These results suggest that human boundaries may be based on some sort of specific linguistic knowledge. Despite these boundary differences, monkeys showed a trading relation comparable to that of humans, indicating that the /ra–la/ trading relation has a psychoacoustic basis and that linguistic knowledge is not a necessary prerequisite for it to occur.

ISSN:0001-4966    

DOI:10.1121/1.419732

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The effect of loudness recruitment and threshold elevation together with reduced frequency selectivity have been simulated to examine the combined effect of the two major consequences of cochlear hearing loss on the intelligibility of speech in speech-shaped noise. In experiment 1, four conditions were simulated: a moderate flat loss with auditory filters broadened by a factor of three (B3R2); a moderate-to-severe sloping loss with auditory filters broadened by a constant factor of three (B3RX); and these conditions with linear amplification applied prior to the simulation processing (B3R2+, B3RX+). For conditions B3R2 and B3RX, performance was markedly worse than for a control condition (normal hearing, condition R1) tested in a previous study. For conditions B3R2+ and B3RX+, linear amplification improved performance considerably. However, performance remained below that for condition R1 by between 5% and 19%. In experiment 2 the broadening of the auditory filters was made more realistic by making it a function of the absolute threshold at the center frequency of the auditory filter. Three different hearing losses were simulated: a moderate-to-severe sloping loss with variable broadening of the auditory filters (BXRX); the same moderate-to-severe sloping loss with linear amplification (BXRX+); and the same broadening of the auditory filters but without the simulation of loudness recruitment and threshold elevation (BX). For condition BXRX, performance was markedly worse than in condition R1, while performance in condition BX was somewhat worse than for condition R1. For condition BXRX+, linear amplification according to the NAL procedure improved performance to a large extent but it remained worse than for condition R1. The results are consistent with previous evidence indicating that only part of the decrease of performance produced by actual cochlear hearing loss can be compensated by conventional linear hearing aids.

ISSN:0001-4966    

DOI:10.1121/1.419733

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Two important aspects of singers’F0control have been investigated: vibrato extent and intonation. From ten commercially available compact disc recordings of F. Schubert’sAve Maria, 25 tones were selected for analysis. Fundamental frequency was determined by spectrograph analysis of a high overtone at each turning point of the vibrato undulations. It was found that the mean vibrato extent for individual tones ranged between±34and±123 centand that the mean across tones and singers amounted to±71 cent.Informal measurements on Verdi opera arias showed much higher figures. With regard to intonation substantial departures from equally tempered tuning were found for individual tones. A tone’s vibrato extent was found to have a negative correlation with tone duration and a positive correlation with intonation.

ISSN:0001-4966    

DOI:10.1121/1.419735

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The fluctuating pressure inside a violin is investigated at theA0(main air) resonance, under the assumption that the walls are kept rigid. Three effects are shown to contribute to a reduction in the fluctuating pressure near the violin’s f-holes. The strongest effect arises from a tendency to form a standing wave within the relatively long, thin shape of the upper bout. A second and smaller effect arises from the violin’s nonuniform shape, and is modeled by treating the upper bout as an acoustical waveguide with nonuniform cross section. A third effect is associated with the Green’s function of an acoustical radiator, and will significantly reduce the fluctuating pressure in the immediate vicinity of the violin’s f-hole. Experimental verification of the theory is obtained by measuring the fluctuating pressure inside a rectangular box, with the resonance being driven by a small loudspeaker located outside the aperture.

ISSN:0001-4966    

DOI:10.1121/1.419736

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The effect of temperature and thermal dose (equivalent minutes at 43 °C) on ultrasonic attenuation in fresh dog muscle, liver, and kidneyin vitro, was studied over a temperature range from room temperature to 70 °C. The effect of temperature on ultrasonic absorption in muscle was also studied. The attenuation experiments were performed at 4.32 MHz, and the absorption experiments at 4 MHz. Attenuation and absorption increased at temperatures higher than 50 °C, and eventually reached a maximum at 65 °C. The rate of change of tissue attenuation as a function of temperature was between 0.239 and 0.291Np m−1 MHz−1 °C−1over the temperature range 50–65 °C. A change in attenuation and absorption was observed at thermal doses of 100–1000 min, where a doubling of these loss coefficients was observed over that measured at 37 °C, presumably the result of changes in tissue composition. The maximum attenuation or absorption was reached at thermal dosages on the order of107min. It was found that the rate at which the thermal dose was applied (i.e., thermal dose per min) plays a very important role in the total attenuation absorption. Lower thermal dose rates resulted in larger attenuation coefficients. Estimations of temperature-dependent absorption using a bioheat equation based thermal model predicted the experimental temperature within 2 °C.

ISSN:0001-4966    

DOI:10.1121/1.419737

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Elementary theory underlying the relationship between the number of scatterers per resolution cell(N)and echo intensity signal-to-noise ratio (SNR) is reviewed. A relationship between the probability density functions for estimates ofNandSNR2is derived. This relationship is validated using a computer simulation. Phantom andin vitroexperiments are described. In one set of experiments on phantoms, empirical distributions of estimates ofNandSNR2are measured and compared to theoretical predictions. The utility ofSNR2for discrimination of phantoms with different values forNis assessed using receiver operating characteristic (ROC) analysis. In another set of experiments, the frequency dependence of theSNR2estimate is investigated for a two-component phantom and for excised dog kidney. It is shown that the frequency dependence of the SNR can help to identify the presence of two or more scattering components that are spatially mixed. With regard to kidney data, measurements performed both parallel and perpendicular to the predominant nephron orientation are reported. The observed anisotropy is compared to the anisotropy of backscatter coefficient encountered in previous investigations.

ISSN:0001-4966    

DOI:10.1121/1.419738

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

We investigated the potential damage inflicted on erythrocytes by acoustic radiation force when the cells are concentrated by a 500-kHz ultrasonic standing wave at the pressure node. The extent of the damage was estimated from the concentrations of potassium ions, iron complexes, and lactate dehydrogenase released from the cells. After 2 min of ultrasound irradiation at12.8 mJ/m3,the cells concentrated on the pressure node, with a cell distribution half-width of 138 μm; no significant release of intracellular components was detected, even after 15 min of irradiation. The results indicate that even small ions like potassium are not released as a result of ultrasound irradiation on cell membranes without cavitation, and they demonstrate the potential use of acoustic radiation force for concentrating living cells in biomedical applications.

ISSN:0001-4966    

DOI:10.1121/1.421009

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP