摘要:

This study was designed to measure the ultrasonic attenuation within phantoms and tissue samples over a broad bandwidth and at many angles of incidence with respect to intrinsic orientations in order to elucidate both the frequency and angular dependence of the attenuation coefficient. Significant angular dependence, or anisotropy, of the attenuation was observed in canine myocardium (maximum to minimum ratio: 2.2 to 1) and a tissue mimicking phantom of oriented graphite fibers in gelatin (max to min: 2 to 1). In control studies, insignificant anisotropy was observed in the attenuation in canine liver samples and phantoms with graphite powder suspended in gelatin. Comparisons of the magnitude of variations of the oriented‐fiber phantom to that predicted by a viscous relative motion model are presented.

ISSN:0001-4966    

DOI:10.1121/1.399751

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The internal spectra of several air jet excited Helmholtz resonators with natural frequencyf0of approximately 250 Hz, as a function of jet speedvbetween 0 and 5000 cm/s, were surveyed. Above the edge tone region the frequency of oscillation ranged between 140–305 Hz. Domains of jet speed in which a single frequency Helmholtz mode occurs are separated by narrow transition zones where Helmholtz modes of very low amplitude having two different frequencies either produce a heterodyne or alternate. The Helmholtz mode is excited throughout the range ofvconsidered. Harmonics of the Helmholtz mode occur in the highest and next to highest domains and frequency mixing between it and the lowest standing wave mode occurs in the highest domain. In the highest domain a standing wave mode at approximately 6f0cooperatively excites the Helmholtz mode. An approximate linear model incorporating an empirical dispersion relation is used to explain the major features of frequency versus jet speed behavior. The effects of varying jet width and neck length are examined.

ISSN:0001-4966    

DOI:10.1121/1.399698

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The transfer functions between acceleration and force (‘‘accelerance’’) at the driving point and radiation efficiencies for the top plates of guitars have been investigated. A vibration exciter was used for driving the guitar at the bridge and the transfer functions and cross‐power spectra were measured at the driving point with the aid of an impedance head. The frequency spectrum of the accelerance function determined in this manner showed good agreement with those reported for the same guitar using a different excitation and measurement method. The output acoustic intensity was measured with a sound‐intensity probe and the radiated sound power from the top plate was determined. The radiation efficiency, determined from the ratio of the top plate radiated sound power and the input power, is presented for different guitars and for a guitar with a modified top plate.

ISSN:0001-4966    

DOI:10.1121/1.399699

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The feasibility of using the linear predictive coding (LPC) technique to replace the voicing sources of tracheoesophageal speech was explored. Four vowels, [i], [a], [e], [u], and one diphthong [ou], produced by two male and two female tracheoesophageal speakers were analyzed by the LPC autocorrelation method. Normalized prediction error functions were used to choose the algorithm and the control parameters of the analysis. Poles of the vocal tract transfer function were selected from frames whose normalized prediction errors were close to minimum with criteria derived from transfer functions of normally produced vowels. Vowels were synthesized with the reconstructed transfer function and a synthesized excitation input. Results of an identification task indicated that the synthesized vowels were highly intelligible, and the gender of the speaker was better identified from the synthesized vowels than from the original tracheoesophageal vowels.

ISSN:0001-4966    

DOI:10.1121/1.399700

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In a variety of experiments and paradigms, researchers have attempted to determine whether or not speech perception is specialized by comparing perception of speech syllables to perception of nonspeech analogs. While nonspeech analogs appear optimal as comparisons to speech because they are acoustically similar without being recognized as speechlike, it is argued that the comparison they offer is confounded and uninterpretable. Two experiments are designed to show that, in auditory perception generally where acoustic signals are causal consequences of mechanical events, perceptual experiences are of the mechanical events themselves, not of the acoustic signal. This has two consequences. One is that there is a confounding in comparisons of speech with sine wave analogs that, whereas the one perceived as speech also has a definite causal source, the other, perceived as nonspeech, has an indeterminate or ambiguous source. A second is that response patterns in classification tasks such as those used in the literature comparing speech to nonspeech will reflect properties of the perceived sound‐producing event; they will not provide a clear window on auditory system processes used to recover event properties. Experiment 3 is designed to show that perception of many acoustic‐signal‐producing events can appear to be special by the logic of speech–sine wave comparisons—even events that cannot plausibly be supposed to involve a specialization.

ISSN:0001-4966    

DOI:10.1121/1.399701

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The perception of voicing in final velar stop consonants was investigated by systematically varying vowel duration, change in offset frequency of the final first formant (F1) transition, and rate of frequency change in the finalF1 transition for several vowel contexts. Consonant–vowel–consonant (CVC) continua were synthesized for each of three vowels, [i,I,æ], which represent a range of relatively low to relatively high‐F1 steady‐state values. Subjects responded to the stimuli under both an open‐ and closed‐response condition. Results of the study show that both vowel duration andF1 offset properties influence perception of final consonant voicing, with the salience of theF1 offset property higher for vowels with high‐F1 steady‐state frequencies than low‐F1 steady‐state frequencies, and the opposite occurring for the vowel duration property. WhenF1 onset and offset frequencies were controlled, rate of theF1 transition change had inconsistent and minimal effects on perception of final consonant voicing. Thus the findings suggest that it is the termination value of theF1 offset transition rather than rate and/or duration of frequency change, which cues voicing in final velar stop consonants during the transition period preceding closure.

ISSN:0001-4966    

DOI:10.1121/1.399702

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A group of prelinguistically profoundly hearing impaired children, between 7 and 11 years of age, were trained in the perception of vowel duration and place, the fricative /s/, and manner of articulation (/m/ vs /b/ and /s/ vs /t/) distinctions, using information provided by a multiple‐channel electrotactile aid (Tickle Talker), and through aided hearing. Training was provided in the tactile‐plus‐aided hearing (TA) and tactile (T) conditions. Speech feature recognition tests were conducted in the TA, T, and aided hearing (A) conditions, during pre‐training, training, and post‐training phases. Test scores in the TA and T conditions were significantly greater than scores in the A condition for all tests, suggesting that perception of these features was improved when the tactile aid was worn. Test scores in the training and post‐training phases were significantly greater than in the pretraining phase, suggesting that the training provided was responsible for the improvement in feature perception. Statistical analyses demonstrated a significant interaction between the main effects of condition and phase, suggesting that training improved perception in the TA and T conditions, but not in the A condition. Post‐training and training test scores were similar suggesting that the perceptual skills acquired during training were retained after the removal of training. Recognition of trained features improved for trained, as well as for untrained words.

ISSN:0001-4966    

DOI:10.1121/1.399703

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The main goal of this study was to investigate the efficacy of four vibrotactile speechreading supplements. Three supplements provided single‐channel encodings of fundamental frequency (F0). Two encodings involved scaling and shifting glottal pulses to pulse rate ranges suited to tactual sensing capabilities; the third transformedF0 to differential amplitude of two fixed‐frequency sinewaves. The fourth supplement added to one of theF0 encodings a second vibrator indicating high‐frequency speech energy. A second goal was to develop improved methods for experimental control. Therefore, a sentence corpus was recorded on videodisc using two talkers whose speech was captured by video, microphone, and electroglottograph. Other experimental control issues included use of visual‐alone control subjects, a multiple‐baseline, single‐subject design replicated for each of 15 normal‐hearing subjects, sentence and syllable pre‐ and post‐tests balanced for difficulty, and a speechreading screening test for subject selection. Across 17 h of treatment and 5 h of visual‐alone baseline testing, each subject performed open‐set sentence identification. Covariance analyses showed that the single‐channel supplements provided a small but significant benefit, whereas the two‐channel supplement was not effective. All subjects improved in visual‐alone speechreading and maintained individual differences across the experiment. Vibrotactile benefit did not depend on speechreading ability.

ISSN:0001-4966    

DOI:10.1121/1.399704

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Languages differ in their inventories of distinctive sounds and in their systems of contrast. Here, it is proposed that this observation may have predictive value with respect to how extensively various phones are coarticulated in particular languages. This hypothesis is based on three assumptions: (1) There are ‘‘output constraints’’ on just how a given phone can be articulated; (2) output constraints are, at least in part, affected by language‐particular systems of phonetic contrast; and (3) coarticulation is limited in a way that respects those output constraints. Together, these assumptions lead to the expectation that, in general, languages will tend to tolerate less coarticulation just where extensive coarticulation would lead to confusion of contrastive phones. This prediction was tested by comparing acoustic measures of anticipatory vowel‐to‐vowel coarticulation in languages that differ in how they divide up the vowel space into contrastive units. The acoustic measures were the first and second formant frequencies, measured in the middle and at the end of the target vowels /a/ and /e/, followed by /pV/, where /V/ was /i,e,a,o,u/. Two languages (Ndebele and Shona) with the phonemic vowels /i,e,a,o,u/ were found to have greater anticipatory coarticulation for the target vowel /a/ than does a language (Sotho) that has a more crowded mid‐ and low‐vowel space, with the phonemic vowels /i,e,q,a,co,u/. The data were based on recordings from three speakers of each of the languages.

ISSN:0001-4966    

DOI:10.1121/1.399705

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Speech error data have been used to argue for the psychological reality of distinctive features and phonemes as well as the hierarchical ordering levels of processing for speech production. The models of production that have emerged from analysis of these data are nearly unanimous in characterizing (implicitly or explicitly) the motor output level as entirely governed by prior selection and processing of larger units, especially the phoneme. This study reports on the laboratory elicitation of sublexical speech errors by means of tongue twisters. Simultaneous audio and electromyographic recordings were analyzed. Where possible, single‐motor unit discrimination was carried out to preclude the possibility of signal contamination by activation of adjacent musculature. The results indicate that traditional methods of data collection on which most speech error corpora are based are inadequate. Production models based on these corpora are not supported by the electromyographic data and must accordingly be revised.

ISSN:0001-4966    

DOI:10.1121/1.399706

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP