摘要:

Previous work suggests that stabilities in articulator phasing, over changes in speech rate and stress, support the underlying perceptual stability of syllabic structures over such changes [B. Tuller and S. Kelso, J. Acoust. Soc. Am.76, 1030–1036 (1984)]. Control of articulator phasing may, therefore, be an important part of the communicative act. If this is the case, it might be expected that the acoustic manifestations of articulator phase (i.e., relative duration of acoustic segments) have a more important influence on judgments of syllabic structure than the absolute durations of acoustic events. To investigate this possibility, synthetic waveforms corresponding to the v + c + v sequence /ipi/ were created. The acoustic events manipulated were duration of the initial and final v's and the position of a burst corresponding to a /p release/ in the intervocalic interval. Preliminary results suggest that judgments of syllabic structure (e.g., /i♯pi/ vs /ip♯i/) are, indeed, more affected by relative durations of the acoustic events than by their absolute durations. [Work supported in part by Louisiana Lions' Foundation and UNO Chancellor's Fellowship.]Also at Kresge Hearing Res. Lab., LSU Medical Ctr., New Orleans, LA 70122.

ISSN:0001-4966    

DOI:10.1121/1.2028339

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Previous research has shown that the Hindi retroflex‐dental contrast among stop consonants is not easily differentiated by English speakers even after some training. In the present study, subjects were given four days of training (768 trials) in a categorial AX discrimination task on full (unmodified) or truncated tokens of naturally produced breathy‐voiced [důha] vs [důha]. Truncation involved removing the vowel from the syllables. Half the subjects were given category knowledge during training (i.e., response forms listed the identity of the first token of each pair). Truncation of the stimuli resulted in better performance during training, but the advantage did not transfer to post tests with the full syllables. Category knowledge resulted in greater improvement during training on both truncated and full syllables. It also led to better performance on the post test of full syllables only for subjects trained on full syllables. Large individual differences found in each training condition suggest that subjects' strategies may be more important than stimulus and task variables in predicting success in perceptual differentiation of non‐native contrasts.

ISSN:0001-4966    

DOI:10.1121/1.2028344

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Discrimination of a heard target word from phonologically similar and dissimilar items was investigated in seventeen 3.5‐ to 4.5‐year olds and nine adults using a two‐choice reaction time (RT) procedure. The target word (“little”) differed from the similar items (e.g., “lettle”) on a single acoustic‐phonetic segment and from the dissimilar items (e.g., “cookie”) on all four acoustic‐phonetic segments. Predictions based on the similarity neighborhood model (Luce, 1986) and the cohort model (Marslen‐Wilson and Tyler, 1980) were (1) since word neighborhoods are less dense in children than in adults, children should show a smaller difference between their RTs to similar and dissimilar items than adults; (1) RTs for correct responses should be faster for dissimilar than for similar items; (3) children should false alarm more to similar than to dissimilar items; and (4) for the similar items, the later in the sequence of acoustic‐phonetic segments the change occurs, the more easily confused the item should be with the target, generating higher false alarm rates. Results supported all predictions except the last, suggesting the cohort model may not provide an adequate description of young children's on line processing.

ISSN:0001-4966    

DOI:10.1121/1.2028350

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A theoretical model is established to study the direct transmission of sound through a finite cylindrical double shell. Shells comply with Donnells' equations and the theory includes constantly spaced stiffeners in axial and circumferential directions. However, this is limited in the case of a large number of stiffeners. The acoustical excitation is a plane wave located in an infinite medium outside the shell. The two internal media are homogeneous. Absorption is taken into consideration by a complex wavenumber. The direct transmission calculation includes the fluid structure coupling with light fluid assumption and mechanical links between shells. There is a distributed stiffness of constant value per unit length in the radial direction and along circumferential lines. The solution of the equations is obtained by a modal method. The acoustical pressure in each medium and the vibratory behavior of shells is given. An application to aircraft design is presented. Numerical results show the comparison between structural linkage and air gap effects on the transmission of sound inside the inner cavity. [Work supported by Aerospatiale Soc., Toulouse, France.]

ISSN:0001-4966    

DOI:10.1121/1.2028353

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Weak radiator analysis attempts to answer the question how should a structure respond at a given frequency such that it radiates sound least efficiently? Use of the boundary element method leads to a quadratic expression for the total radiated power from a structure formulated in terms of the surface velocity distribution on the structure. This quadratic power expression, formulated at the surface, represents the basis for the technique. Constrained optimization applied to the expression for power leads to that response shape that radiates sound least efficiently. The constraint considered here corresponds to a nonzero velocity at some point on the surface, equivalent to a drive point. More general constraints are possible, such as nonzero mean‐square velocity. Weak radiator analysis is demonstrated through its application to a centrally driven, 760 × 610 mm plate, forming one side of a box. The resulting weak radiator shapes are unique, i.e., they do not correspond to the mode shapes of either a simply supported or clamped plate.

ISSN:0001-4966    

DOI:10.1121/1.2028361

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The use of high‐frequency acoustics to study biogeographic boundaries is entering a new phase with the development of hardware and software that enable estimates of total biomass, number of scatterers, and individual size, all as a function of distance from the echo sounder. For macrozooplankton and micronekton, the relationship between target strength (TS) and the physical size of the scatterer in terms of length, wet weight, or dry weight is of crucial concern. Recent study of a variety of zooplankton taxa has revealed relationships that indicate TS increases as a function of organism volume, not cross‐sectional area, as usually assumed. New models of sound scattering from plankton appear to be required as recent work illustrates [T. K. Stanton, J. Acoust. Soc. Am.86, 1499–1510 (1989)]. Although more specific information about the identity of sound scatterers is presently difficult to extract from the acoustic returns, ongoing studies of the size frequency distribution of oceanic zooplankton suggest that in particular geographic regions and depths, specific taxa occupy a specific range of sizes. Accurate estimates of a number of organisms, in particular, size categories can, in such cases, be used to estimate numbers of individuals in these taxonomic groups. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2028365

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Acoustics is used to determine the relationship between current flow, temperature structure, and biological processes at fronts. In 1985 surveys were made of acoustic volume reverberation at the boundary of the slope water and the Gulf Stream, 120 km northeast of Cape Hatteras, using towed 70‐kHz sonars. Scattering theory and net samples suggest the scatterers were macrozooplankton of about 2‐cm length. Two‐dimensional images of 200‐m depth by several kilometers distance give views of internal biological patches across the front. From them the spatial arrangement and behavior of animals have been observed and animal type inferred. For large‐scale surveys covering several hundred kilometers and days, obtained during April 1989 (BioSYNOP program), a synoptic view, from which the influence of large meanders of the Gulf Stream on the macrozooplankton can be observed, was obtained. Finally, better resolution of animal type, function, and size is possible with multifrequency sonar. Multicolor imaging of 38‐, 70‐, and 200‐kHz sonar profiles suggest a difference in the animal size composition between the Gulf Stream and adjacent waters. [Work supported by ONR and NSERC of Canada.]

ISSN:0001-4966    

DOI:10.1121/1.2028366

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Cutaneous low‐threshold mechanoreceptors transmit information about innocuous deformations of the skin that occur duing contact with stimulus objects as well as during normal motoric behaviors. Movement across the skin not only elicits motion‐sensitive responses in individual mechanoreceptors, but sequentially activates different spatially adjacent populations of mechanoreceptors to sites along the path of motion. Psychophysical tests of subject's capacity to distinguish opposing direction to tactile motion across the skin (i.e., of directional sensitivity) provide quantitative indices of the integrity of peripheral mechanoreceptors, as well as of central neural mechanisms to which they project. It will be shown that in neurologically normal subjects, directional sensitivity (i) is a curvilinear function of the velocity of stimulus movement, (ii) increases linearly with the length of skin transversed, and (iii) varies grossly in proportion to the innervation density of the fast and slowly adapting type I mechanoreceptors. Since injury to peripheral sensory nerves results in alterations in the mechanoreceptors' spatial‐ and temporal‐encoding properties, directional sensitivity is often impaired. The degree of impairment can be quantitatively characterized by alterations in the slope andxintercept of the relationship between directional sensitivity (d′ units) and the length of skin traversed.

ISSN:0001-4966    

DOI:10.1121/1.2028369

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Using the method described previously, mechanoreceptor‐specific vibrotactile perception thresholds have been determined at the fingertips (digits 3 and 5) of a series of 24 chain saw operators, 83% of whom reported symptoms of intermittent or persistent numbness, and/or episodic white fingers. Motor and sensory nerve conduction velocities were then recorded from the median and ulnar nerves in each hand and arm, as well as motor distal latencies, following conventional procedures. If the results are compared with normative values from nonvibration exposed, symptom‐free, manual workers (and the limit of normality is taken to be two standard deviations from the mean value), 71% and 29% of sawyers reported symptoms are found to possess abnormal vibrotactile thresholds and sensory nerve conduction velocities, respectively. Of the workers at present not reporting symptoms, 50% and 89% are found to possess normal vibrotactile thresholds and sensory velocities, respectively. Performance measures of the two objective tests will be discussed that attempt to account for the subjective nature of symptom reporting.

ISSN:0001-4966    

DOI:10.1121/1.2028372

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Current emergency response plans and preparedness at commercial nuclear power plants include means for notifying the public surrounding the facility in a situation involving real or potential radiological hazards. An alerting system may employ various means, including, for example, fixed sirens or mobile siren vehicles. In this paper emergency planning concepts and guidance are reviewed and an assessment of a set of recently collected data at operating plants is provided. Data were gathered from event notification reports on both inadvertent soundings and failures of sirens over about a 3‐yr period. Siren system vulnerabilities are discussed; in addition, some insights are provided on rates of occurrence of both false alarms and failures, and likely causes of these events.

ISSN:0001-4966    

DOI:10.1121/1.2028379

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP