摘要:

Observers were required to detect 500‐, 110‐, or 20‐ms bursts of 250‐, 500‐, or 5000‐Hz tones presented in simultaneously gated narrow (30‐Hz) noise bands using standard two‐interval forced‐choice tracking procedures. The noise was in phase at the observers’ ears; the signal was in phase in one set of experiments and π radians out of phase in another. Three different ‘‘roving‐level’’ conditions were used: (1)fixedlevelthe noise‐power density,N0, was fixed (50 dB SPL), (2)inter‐intervalrovea random gain factor was chosen for every observation interval from a set uniformly distributed in decibels (40‐dB range; 0.1‐dB steps) to produceN0centered on 50 dB SPL. The gain factor affected signal and noise in both ears equally and thus left the signal‐to‐noise ratio, interaural phase differences and amplitude ratios unaffected, (3)interauralrovethe random gain varied from ear‐to‐ear in every observation interval. Reducing duration reduced BMLD’s in all conditions; roving levels reduced BMLD’s by small amounts except at 20 ms where interaural rove removes them. [This research was supported by The National Institutes of Health.]a)On leave from the Dept. of Exp. Psychol., Oxford.

ISSN:0001-4966    

DOI:10.1121/1.408850

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

In noisy and reverberant acoustical environments the human hearing system is capable of concentrating on a desired speaker, while attenuating undesired sounds like noise or reverberation. This so called ‘‘cocktail‐party processing’’ is reduced in hearing‐impaired persons. New hearing aid strategies try to imitate binaural processing principles to suppress interfering noise or reverberation in order to yield maximum speech intelligibility for the impaired listener. Two algorithms are described that reduce unwanted signal energies by attenuating sound that arises from the sides (lateral suppression) and that remove reverberation and short reflections. They were combined and implemented in real time on a multiprocessor setup to allow for adaptive adjustment of parameters and an optimal fit to the individual hearing loss. The noise reduction performance of the algorithms was tested with normal‐ and hearing‐impaired subjects. Subjective speech quality and speech intelligibility assessments as well as speech intelligibility measurements show that both groups benefit significantly from the preprocessing strategies in anechoic and reverberant acoustical situations with interfering speakers.

ISSN:0001-4966    

DOI:10.1121/1.408853

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

One of the assumptions underlying the calculation of almost everyd′ in the literature is that the distribution of sensations resulting from repeated presentation of a stimulus is normal and is equal to the distributions produced by the other stimuli in an experiment. This could be a reasonable approximation for pure tones, but it is doubtful whether it applies to more complex stimuli such as speech. A series of magnitude‐estimation experiments was carried out, in which subjects were asked to indicate the position of each stimulus on a line on a monitor screen, which ran either from ‘‘soft’’ to ‘‘loud’’ or from /p/ to /t/. The stimuli were practically identical to those used by [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am.51, 483–502 (1972), and by M. E. H. Schouten and A. J. van Hessen, J. Acoust. Soc. Am.92, 1841–1855 (1992)]. Training was done by means of identification of the same stimuli on a similar line, but now subdivided into segments. Each stimulus was presented for magnitude estimation 400 times before and 400 times after training; as a result, the shape and size of each distribution could be traced out.

ISSN:0001-4966    

DOI:10.1121/1.408856

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Human neural threshold tuning curves are derived using Allen’s [J. Acoust. Soc. Am.68, 1660–1670 (1980)] resonant tectorial membrane model of the cat cochlea by appropriately scaling the parameters. Because there is no measured neural threshold data available for the human to test the derived curves, a detection criterion, defined by a relationship among the bandwidth of the frequency tuning curves, expressed as an equivalent rectangular bandwidth (ERB), the width of the excitation patterns, expressed as an equivalent rectangular spread (ERS), and the psychophysical critical ratio, is explored and verified using cat data. The detection criterion can then be used to test the derived human curves using psychophysical data, and may also provide a deeper understanding of the frequency resolving properties of the cochlea.

ISSN:0001-4966    

DOI:10.1121/1.408810

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Only a few investigations concerning the analysis of poroelastic structures are directed toward solutions of specific problems [e.g., L. A. Taber, Int. J. Solids Structures29, 3125–3143 (1992), and references therein]. This paper addresses the derivation of a linear theory for vibrations of poroelastic shells. The three‐dimensional fundamental equations of poroelastic media are expressed in variational form [cf. L. Dormieux and C. Stolz, C. R. Acad. Sci.315(II), 407–412 (1992)]. The variational fundamental equations are obtained from the principle of virtual work through Friedrich’s transformation [M. C. Dökmeci, IEEE Trans. Ultrason. Ferroelec. Freq. ControlUFFC‐35, 775–787 (1988) and37, 369–385 (1990)]. The two‐dimensional theory of poroelastic shells is deduced from the variational equations using Mindlin’s method of reduction for the case when the fluid–solid coupling is included through Biot’s consolidation theory and the field quantities are taken to vary linearly across the shell thickness. The shear deformable linear theory accommodates the extensional, thickness, flexural, and coupled vibrations of poroelastic shells. Specialization in geometry, material properties, and vibrations is considered, the uniqueness of solutions is examined, and also, a numerical algorithm that is based on the method of moments is described for the vibrations of poroelastic shells.

ISSN:0001-4966    

DOI:10.1121/1.408816

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The beamlike vibration of a thin circular cylindrical shell with attached thin flat plates at each end is considered. Two mechanisms of the plates’ influence are considered: First, the plates have no stiffness in their own plane, but have stiffness in the direction transverse to their plane; and second, the plates have stiffness in their own plane, but not in the transverse direction. It is shown that the frequency bands are, to a large extent, influenced by each of the above mechanisms. The equations used for the shell vibration are based on a simplification concerning the neglect of the axial bending moment in the shell. The boundary condition equations (equations of contact) lead to a characteristic equation of beamlike vibration of the shell with attached plates. The resonance frequencies for the shell with the plates are determined by experiment also. The results of the calculation of the resonance frequencies, taking into account the plane displacements of the plates, are close to the frequency determined experimentally.

ISSN:0001-4966    

DOI:10.1121/1.408821

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

For many profoundly hearing‐impaired speech reading is the most important means of communication; amplified speech may provide, at best, additional information to speech reading. In an attempt to improve audio‐visual communication, speech pattern elements that were thought to be most beneficial as a supplement to lip‐reading were analyzed. The elements were fundamental frequency (f0), voicing, and the first two formants (F1andF2). With these elements auditory stimuli were pro‐duced with different encodings for voiced speech fragments. In theF1F2encoding both formants were represented by two adjacent harmonics off0around each formant frequency; in theF1encoding by two harmonics off0aroundF1. In thef0encoding fundamental frequency was encoded as a single sine wave. In all cases white noise was used during voiceless speech. Out of 20 profoundly hearing‐impaired subjects, all subjects but one showed a considerable improvement in lipreading scores when supplemented with an auditory stimulus. In most cases highest scores were obtained with the natural speech condition. For four subjects theF1‐encoded signal provided highest scores. Relations among intelligibility scores and dynamic range, gap detection, and difference limen for frequency will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.408749

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

There have been many attempts in the past to systematically attribute the physical properties of speech to subjective characteristics. The aim of this study was to look in more detail at how objective properties interact to contribute to the shape of performance‐intensity functions for individual words. The interaction of such features as speech level, familiarity, and spectral consistency were found to be complex but enlightening. In this study the largest effect is due to familiarity, however this is shown not to be as important under some conditions and for subsets of words with particular characteristics. Although the results shown by no means explain the whole story of speech perception, they do provide some insight into the play of factors for the fairly simple case of monosyllabic words. [This work was supported by the National Physical Laboratory, Teddington, UK.]

ISSN:0001-4966    

DOI:10.1121/1.408829

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Behavioral and neurophysiologic correlates of pitch and phoneme perception were investigated in a 42‐year‐old male with a unilateral cortical lesion (due to left hemisphere frontal‐temporal‐parietal craniotomy). Functional impairment of his speech perception ability was reflected in his behavioral performance. Electrophysiologic measures (ABR, MLR, MMN) were used to assess the underlying neurophysiologic processes. In the behavioral experiment the stimuli were synthesized syllables differing in place of articulation (/da/, /ga/) and pitch (high, low). The pitch and place differences were equally discriminable. A same‐different behavioral discrimination task revealed that the subjects discrimination of pitch was intact, however his discrimination of place was severly impaired. The mismatch negativity (MMN) auditory‐evoked potential is a pre‐attentive neurophysiologic index of acoustic change. Of interest was whether the MMN would reflect the selective impairment in phonetic perception at a pre‐attentive level. Results revealed that the MMN was elicited by pitch differences in speech stimuli but not by place differences (i.e., consistent with behavioral discrimination). Thus the MMN appears to reflect the distinct neuroanatomic sites that underlie processing of different auditory stimulus attributes. Theoretical implications for neurophysiologic processes underlying pitch and place of articulation perception will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.408785

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Perceptual and acoustic descriptions of children’s articulatory errors typically have focused upon consonant productions, as compared to vowel productions. In the present investigation, three subject groups (15 misarticulating children age 4 to 6 who were referred for clinical services, 15 normally articulating 4‐ to 6‐year‐old children, and 15 young adult subjects) produced multiple repetitions of single syllable target words embedded in a carrier phrase. Midpoint (target) formant frequencies of selected vowels were measured and the resulting vowel quadrilaterals were then compared across subject groups to determine if children with so‐called phonological delays characterized primarily by consonant misarticulations produced vowel spaces similar or different from normally articulating children. This is an interesting question because the focus on consonants in misarticulating children implies that speech production is guided by segmental strategies, when in fact many children in the 4‐ to 6‐year‐old range may be aware of the segmental structure of speech. Perhaps, then, misarticulating children produce vowel spaces that reflect a more global speech delay.

ISSN:0001-4966    

DOI:10.1121/1.408788

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP