摘要:

We have measured the ultrasonic attenuation parameters α0andnof several biological fluidsinvitroin the frequency range 2.8–6.8 MHz, using frequency shift and/or a sinc (⋅) sidelobe ratio technique. The parameters α0andndescribe the frequency‐dependent attenuation via a power‐law model, i.e., α( f)=α0 f n, wherefis frequency. The samples investigated were blood, pus, cyst fluid, bile, and infected hematoma. It was found that the values of α0span approximately the range between 0.03–0.3 dB cm−1MHz−n, and values ofnrange from about 1.1–1.3.

ISSN:0001-4966    

DOI:10.1121/1.391097

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The nonlinear transfer of energy among modes of different frequencies on a vibrating string is investigated both theoretically and experimentally. The nonlinearity is associated with the well‐known variation of string tension caused by the vibration modes, but it is essential that at least one of the end supports has finite mechanical admittance if there is to be any mode coupling. If the nonrigid bridge support has zero admittance in a direction parallel to the string, the coupling is of third order in the mode amplitudes. For a more realistic model in which the string changes direction as it passes over a bridge of finite admittance there are additional coupling terms of second order. The first mechanism gives driving terms of frequency 2ωn±ωmwhere ωnand ωmare, respectively, the angular frequencies of thenth andmth modes present on the string, while the second mechanism gives driving terms of angular frequencies 2ωnand 2ωm. Analysis shows that modes absent from the initial excitation of the string can be driven to appreciable amplitude by these mechanisms, reaching their maximum amplitude after a time typically of order 0.1 s. Modes that are in nearly harmonic frequency relationship behave simply but coupling of modes that are appreciably inharmonic may give rise to rapid amplitude fluctuations. A simple experiment with a wire deflected by a bridge of elastic cord and plucked so as to eliminate a particular mode from the initial excitation provided general semiquantitative confirmation of the theoretical predictions.

ISSN:0001-4966    

DOI:10.1121/1.391007

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Two groups of 5‐ to 11‐month‐old infants were tested for their ability to discriminate within‐utterance intensity variations similar to those associated with linguistic stress. A visually reinforced discrimination procedure was used to determine sensitivity to increments in peak intensity for a final position, synthetic CVC syllable within either a bisyllabic (CVCVC) or a trisyllablic (CVCVCVC) context. Discrimination performance was above chance for a 2‐dB increment, and improved for 4‐ and 6‐dB increments. In addition, infants were more sensitive to intensity increments in the bisyllablic as compared to the trisyllabic context. Infant sensitivity for within‐utterance intensity variations is sufficient for the detection of some linguistic stress contrasts.

ISSN:0001-4966    

DOI:10.1121/1.391110

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A computer editing technique was used to remove varying amounts of voicing from the syllable‐final closure intervals of naturally produced tokens of /pqb, pqd, pqg, pag, pig, pug/. Vowels for all six syllables were approximately the same duration, and the final release bursts were retained. Identification results showed that voiceless responses tended to occur in relatively large numbers when all of the closure voicing and, in most cases, a portion of the preceding vowel‐to‐consonant (VC) transition had been removed. A second experiment demonstrated that removal of final release bursts had very little effect on the identification functions. Acoustic measurements were made in an attempt to gain information about the acoustic bases of the listeners’ voiced–voiceless judgments. In general, stimuli that subjects tended to identify as voiceless showed higher first‐formant offset frequencies and shorter intensity decay times than stimuli that subjects tended to identify as voiced. However, for stops following /i/ and /u/ these acoustic differences were relatively small. We were unable to find a single acoustic measure, or any combination of measures, that clearly explained the listeners’ voiced–voiceless decisions.

ISSN:0001-4966    

DOI:10.1121/1.391094

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The identifiability of isolated vowels (/V/) was compared to that of vowels in consonantal context (/pVp/) when subjects performed a monitoring task. On successive blocks of trials in a test series, the subjects listened for instances of one or another of nine monophthongal vowels (/i,I,q,1,v,a,c,U,u/) and identified each test item as being an instance or not. On average, resulting false alarm errors occurred significantly less often in the /pVp/ condition, consistent with the previous finding that vowel perception may be aided by consonantal context. This beneficial effect of context was found to be restricted to the class of open vowels, however, with perception of the close vowels being somewhat hindered by context. The error data for misses also showed an interaction between context and vowel height. Various accounts of the interaction are considered.

ISSN:0001-4966    

DOI:10.1121/1.391114

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The performance of eight naive observers in learning to identify speech spectrograms was studied over a 2‐month period. Single tokens from a 50‐word phonetically balanced (PB) list were recorded by several talkers and displayed on a Spectraphonics Speech Spectrographic Display system. Identification testing occurred immediately after daily training sessions. After approximately 20 h of training, naive subjects correctly identified the 50 PB words from a single talker over 95% of the time. Generalization tests with the same words were then carried out with different tokens from the original talker, new tokens from another male talker, a female talker, and finally, a synthetic talker. The generalization results for these talkers showed recognition performance at 91%, 76%, 76%, and 48%, respectively. Finally, generalization tests with a novel set of PB words produced by the original talker were also carried out to examine in detail the perceptual strategies and visual features that subjects abstracted from the training set. Our results demonstrate that even without formal training in phonetics or acoustics naive observers can learn to identify visual displays of speech at very high levels of accuracy. Analysis of subjects’ performance in a verbal protocol task demonstrated that they rely on salient visual correlates of many phonetic features in speech.

ISSN:0001-4966    

DOI:10.1121/1.391035

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Two aspects of the relation between cubic‐difference‐tone (CDT) generation and suppression were investigated in normal hearing listeners. First, the effects of narrow‐band noise and sinusoids on the two processes were examined using a forward‐masking paradigm. Within individual listeners, cubic difference bands (CDBs) behaved much like CDTs whereas the suppression effects produced by narrow‐band noise were substantially less than those produced by sinusoids. These results suggest that at least partially different processes underlie the two phenomena. Second, the role of suppression in the difference between forward‐ and simultaneous‐masking estimates of CDB amplitude was investigated. The data across listeners were highly variable but indicated a more complicated interpretation than that proposed by Shannon and Houtgast [J. Acoust. Soc. Am.68, 825–829 (1980)].

ISSN:0001-4966    

DOI:10.1121/1.391034

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Detectability of a 400‐ms, 1000‐Hz pure‐tone signal was examined in bandlimited noise where different spectral regions were given similar waveform envelope characteristics. As expected, in random noise the threshold increased as the noise bandwidth was increased up to a critical bandwidth, but remained constant for further increases in bandwidth. In the noise with envelope coherence however, thresholddecreasedwhen the noise bandwidth was made wider than the critical bandwidth. The improvement in detectability was attributed to a process by which energy outside the critical band is used to help differentiate signal from masking noise, provided that the waveform envelope characteristics of the noise inside and outside the critical band are similar. With flanking coherent noise bands either lower or higher in frequency than a noise band centered on the signal, it was next determined that the frequency relation and remoteness of the coherent noise did not particularly influence the magnitude of the unmasking effect. An interpretation in terms of nonsimultaneous masking was reconciled with some aspects of the data, and with an interpretation in terms of across‐frequency temporal pattern analysis. This paradigm, in which detection is based upon across‐frequency temporal envelope coherence, was termed ‘‘comodulation masking release.’’ Comodulation offers a controlled way to investigate some of the mechanisms which permit signals to be detected at adverse signal‐to‐noise ratios.

ISSN:0001-4966    

DOI:10.1121/1.391005

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

It has often been advanced that pitch is a two‐dimensional perceptual attribute, its two dimensions being: (1) tone height, a perceptual quality monotonically related to frequency; and (2) tone chroma, a quality shared by tones forming an octave interval. However, given that many musically uneducated adults do not seem to perceive tone chroma, this model is controversial. We investigated the sensitivity of three‐month‐old infants to tone chroma by means of a behavioral habituation–dishabituation procedure. Infants were presented with two successive melodic sequences of pure tones, the second sequence being a distorted version of the first one. The distortion consisted in shifting the frequency of some of the original tones, through a seventh or a ninth for some infants, through an octave for others. In the former case, infants displayed significant novelty reactions. In the latter case, significant novelty reactions were observed when the two sequences differed in melodic contour, but not when they had the same contour. These results suggest that young infants are sensitive to both tone height and tone chroma, and thus that tone chroma perception does not necessitate some form of musical experience.

ISSN:0001-4966    

DOI:10.1121/1.391006

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Recent studies of temporal resolution in hearing‐impaired listeners indicate that many ears with cochlear damage exhibit elevated temporal gap thresholds. The deviations from normal may be large, for equivalent‐SPL comparisons, but are often small or absent for equivalent‐SL comparisons. In the present experiment, we examine the premise that SL effects in gap resolution are independent of sound pressure level. Normal hearing subjects used a Békésy procedure to track the minimum level of an octave‐band signal at 1 kHz needed to keep a periodic temporal gap at threshold. Performance functions were generated to show stimulus intensity as a function of gap duration, for gaps from 25 ms to the smallest detectable value. In separate conditions, the level of a white‐noise background was varied to shift the subject’s audibility threshold. Results indicate that the limits of resolution are largely invariant with SPL, but criterion sensation levels for resolution are progressively reduced at higher SPL. It is concluded that gap thresholds from normal and impaired ears should be compared for equivalent SPL; comparisons made with SL equated are likely to underestimate the consequence of cochlear damage on resolving capacity.

ISSN:0001-4966    

DOI:10.1121/1.391008

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP