摘要:

Temporal-integration functions and psychometric functions for detection were obtained in eight users of the Nucleus 22-electrode cochlear implant. Stimuli were 100-Hz, 200-μs/phase trains of biphasic pulses with durations ranging from 0.44 to 630.44 ms (1 to 64 pulses). Temporal-integration functions were measured for 21 electrodes. Slopes of these functions were considerably shallower than the 2.5 dB/doubling slopes typically observed in acoustic hearing. They varied widely across subjects and for different electrodes in a given subject, ranging from 0.06 to 1.94 dB/doubling of stimulus pulses, with a mean [standard deviation (s.d.)] value of 0.42 (0.38). Psychometric functions were measured for 11 of the same 21 electrodes. Slopes of psychometric functions also varied across subjects and electrodes, and were 2–20 times steeper than those reported by other investigators for normal-hearing and cochlear-impaired acoustic listeners. Slopes of individual psychometric functions for 1-, 2-, 4-, and 8-pulse stimuli ranged from 0.20 to1.84 log d/dBwith a mean (s.d.) value of 0.77 (0.45). Psychometric-function slopes did not vary systematically with stimulus duration in most cases. A clear inverse relation between slopes of psychometric functions and slopes of temporal-integration functions was observed. This relation was reasonably well described by a hyperbolic function predicted by the multiple-looks model of temporal integration [Viemeister and Wakefield, J. Acoust. Soc. Am.90, 858–865 (1991)]. Psychometric-function slopes tended to increase with absolute threshold and were inversely correlated with dynamic range, suggesting that observed differences in psychometric-function slopes across subjects and electrodes may reflect underlying differences in neural survival.

ISSN:0001-4966    

DOI:10.1121/1.418330

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This paper reports results of further experimentation on a previously developed physical model of the vocal-fold mucosa [Titze et al., J. Acoust. Soc. Am.97, 3080–3084 (1995)]. The effects of vocal-fold thickness, epithelial membrane thickness, and prephonatory glottal geometry on phonation threshold pressure were studied. Phonation threshold pressures in the range of 0.13 to 0.34 kPa were observed for an 11-mm-thick vocal fold with a 70-μm-thick “epithelial” membrane for different “mucosal” fluid viscosities. Higher threshold pressure was always obtained for thinner vocal folds and thicker membranes. In another set of experiments, lowest offset threshold pressure was obtained for a rectangular or a near-rectangular prephonatory glottis (with a glottal convergence angle within about±3°). It ranged from 0.07 to 0.23 kPa for different glottal half-widths between 2.0 and 6.0 mm. The threshold for more convergent or divergent glottal geometries was consistently higher. This finding only partially agrees with previous analytical work which predicts a lowest threshold for a divergent glottis. The discrepancy between theory and data is likely to be associated with flow separation from a divergent glottis.

ISSN:0001-4966    

DOI:10.1121/1.418331

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In this paper it is shown that at the edges of prosodic domains, initial consonant and final vowels have more extreme (less reduced) lingual articulations, which are called articulatory strengthening. Linguopalatal contact for consonants and vowels in different prosodic positions was compared, using reiterant-speech versions of sentences with a variety of phrasings read by three speakers of American English. Four prosodic domains were considered: the phonological word, the phonological (or intermediate) phrase, the intonational phrase, and the utterance. Domain-initial consonants show more linguopalatal contact than domain-medial or domain-final consonants, at three prosodic levels. Most vowels, on the other hand, show less linguopalatal contact in domain-final syllables compared to domain-initial and domain-medial. As a result, the articulatory difference between segments is greater around a prosodic boundary, increasing the articulatory contrast between consonant and vowels, and prosodic domains are marked at both edges. Furthermore, the consonant initial strengthening is generally cumulative, i.e., the higher the prosodic domain, the more linguopalatal contact the consonant has. However, speakers differed in how many and which levels were distinguished in this way. It is suggested that this initial strengthening could provide an alternative account for previously observed supralaryngeal declination of consonants. Acoustic duration of the consonants is also affected by prosodic position, and this lengthening is cumulative like linguopalatal contact, but the two measures are only weakly correlated.

ISSN:0001-4966    

DOI:10.1121/1.418332

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A number of different researchers have reported a substantial degree of variability in how American English /r/ coarticulates with neighboring segments. Acoustic and articulatory data were used to investigate this variability for speakers of “rhotic” American English dialects. Three issues were addressed: (1) the degree to which theF3trajectory is affected by segmental context and stress, (2) to what extent the data support a “coproduction” versus a “spreading” model of coarticulation, and (3) the degree to which the major acoustic manifestation of American English /r/—the time course ofF3—reflects tongue movement for /r/. TheF3formant trajectory durations were measured by automatic procedure and compared for nonsense words of the form /’waCrav/ and /wa’Crav/, where C indicates a labial, alveolar, or velar consonant. These durations were compared toF3trajectory durations in /’warav/ and /wa’rav/. In addition, formant values in initial syllables of words with and without /r/ were examined for effects of intervening consonant contexts. Results indicated similarF3trajectory durations across the different consonant contexts, and to a lesser degree across stress, suggesting that coarticulation of /r/ can be achieved by overlap of a stable /r/-related articulatory trajectory with movements for neighboring sounds. This interpretation, and the concordance ofF3time course with tongue movement for /r/, was supported by direct measures of tongue movement for one subject.

ISSN:0001-4966    

DOI:10.1121/1.418333

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This study investigated the acoustic characteristics of voicing in the production of fricative consonants. The fricatives [f v s z] were used in combination with the vowels [i e a o u]to create CV syllables, which were produced by four subjects both in a context condition (following voiced and voiceless velar stops) and in isolation. Analyses were conducted of the time course of glottal excitation during the fricative noise interval in the voiced and voiceless fricative stimuli. Results showed that the patterns of voicing in the fricative noise interval were influenced by the voicing characteristics of preceding stop consonants. Nonetheless, these carryover coarticulatory effects were short-lived, influencing only the first 10’s of ms of the following segment. Despite the influence of phonetic context on the patterns of voicing, an acoustic measure relating to the presence or absence of glottal excitation at the acoustic boundaries of the fricative noise reliably classified a majority (93%) of the fricative consonants in terms of the phonetic category of voicing. Thus, while phonetic context affected the patterns of glottal excitation in the fricative noise interval, it did not affect the criterial attribute associated with the phonetic category of voicing.

ISSN:0001-4966    

DOI:10.1121/1.418334

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Ten postlinguistically deaf adults who used the Nucleus Cochlear Implant System and SPEAK speech coding strategy responded to vowels, consonants, words, and sentences presented sound-only at 70, 60, and 50 dB sound-pressure level. Highest group mean scores were at a raised-to-loud level of 70 dB for consonants (73%), words (44%), and sentences (87%); the highest score for vowels (70%) was at a conversational level of 60 dB. Lowest group mean scores were at a soft level of 50 dB for vowels (56%), consonants (47%), words (10%), and sentences (29%); all except subject 7 had some open-set speech recognition at this level. For the conversational level (60 dB), group mean scores for sentences and words were 72% and 29%, respectively. With this performance and sound-pressure level, it was observed that these subjects communicated successfully in a variety of listening situations. Given these subjects’ speech recognition scores at 60 dB and the fact that 70 dB does not simulate the vocal effort used in everyday speaking situations, it is suggested that cochlear implant candidates and implantees be evaluated with speech tests presented at 60 dB instead of the customary 70 dB sound-pressure level to simulate benefit provided by implants in everyday life. Analysis of individuals’ scores at the three levels for the four speech materials revealed different patterns of speech recognition among subjects (e.g., subjects 1 and 5). Future research on the relation between stimuli, sound processing, and subjects’ responses associated with these different patterns may provide guidelines to select parameter values with which to map incoming sound onto an individual’s electrical dynamic range between threshold and maximum acceptable loudness level to improve speech recognition.

ISSN:0001-4966    

DOI:10.1121/1.418383

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Many damselfishes perform a courtship behavior known as the signal jump, in which they rise in the water column and then rapidly swim downward while producing a pulsed sound. Pulsed sounds produced during the signal jump of the damselfishDascyllus albisellawere analyzed to determine whether they were correlated with the signal jump distance or speed, and how they changed with propagation. No statistical relationship was found between signal jump speed or distance with the number of pulses, pulse period, or change in the peak frequency of pulses in a call. If echoes were present in the sound, the change in echo delay would likely have been too small for damselfish to detect. Sounds attenuated with distance such that the signal-to-noise ratio decreased from 17–25 dB at 1 to 2 m to 5–10 dB at 11 to 12 m. It is unlikely thatD. albisellacan detect sounds at or beyond 11–12 m from the sound source, based on noise masking data from other fishes. Pulse period is least affected by propagation when compared to peak frequency, pulse duration, interpulse interval, and coefficient of variation of pulse amplitudes within a call. These results suggest that the sound produced during the signal jump functions over short distances and that the pulse period provides the most reliable basis for signal identification.

ISSN:0001-4966    

DOI:10.1121/1.418425

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Approximations for leaky wave coupling coefficients and background scattering contributions are usually derived by assuming the shell response is governed by thin shell theory. Comparisons are described with approximations derived by other methods for a thick spherical shell at frequencies above coincidence. The variation of the phase of the coupling coefficient from numerical evaluation of the Watson transformation residue by Kargl [Ph.D. thesis, Washington State University (1990)] is evident in an analytical approximation. The phase of the background includes inertial and wave-kinematic contributions and is related to research by Gaunaurd and Werby [J. Acoust. Soc. Am.90, 2536–2550 (1991)]. The inertial contribution to the background phase is derived directly from the reflectivity of a plate in the limit of small phase shift for propagation across the thickness of the shell. The frequency and angle dependence of the phase of the exact reflection coefficient of a plate (having the same thickness as the shell) is also examined.

ISSN:0001-4966    

DOI:10.1121/1.418384

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The purpose of this Letter is to present an exact analytical solution for sound propagation in ducts with a quadratic mean temperature profile. Using appropriate transformations, the one-dimensional wave equation for ducts with an axial mean temperature gradient was reduced to the hypergeometric differential equation, whose solution can be expressed in terms of hypergeometric functions. The analysis neglects the effects of mean flow and is therefore valid only for small mean Mach numbers.

ISSN:0001-4966    

DOI:10.1121/1.418385

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The aim of this Comment is to show that, when the normal velocity of the transducer is no longer constant, the algorithm that has been recently proposed by Wu et al. [J. Acoust. Soc. Am.99, 1339–1348 for Part I and 1349–1359 for Part II (1996)] cannot eliminate aliasing nor remove the phase error in the angular spectrum. In fact, in recent articles, Wu et al. proposed and used a new numerical algorithm for eliminating the aliasing in the spectrum. Moreover, they have shown that the phase error can be easily removed. In their investigation they used a planar transducer and linear array. To show the effectiveness of their algorithm, the normal velocity of the planar transducer or of the elementary transducers (in the case of the array) has been supposed constant.

ISSN:0001-4966    

DOI:10.1121/1.418388

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP