摘要:

It has been proposed that auditory‐nerve fibers with characteristic frequencies (CFs) above the speech‐frequency range are important in speech perception when the signal‐to‐noise ratio in the speech frequency range is low [S. Greenberg, J. Phon.16, 139–149 (1988)]. If this is true, then it might be expected that recognition of speech at low signal‐to‐noise ratios would worsen with the addition of high‐pass noise sufficiently intense to mask information in high‐CF fibers. This hypothesis was tested for closed‐set recognition of vowels and spondees. Recognition was measured as a function of signal‐to‐noise ratio in speech‐shaped noise, with and without an intense high‐pass noise. The addition of high‐pass noise did not degrade vowel recognition. Spondee recognition decreased with the addition of the high‐pass noise at the highest levels of the speech‐shaped noise. However, this same decrease was seen when the spondees were low‐pass filtered to simulate downward spread of masking by the high‐pass noise. This indicates that the decrease in spondee recognition with high‐pass noise was due to masking of information in fibers with CFs in the speech range. Overall, these results suggest that fibers whose CFs are above the speech range are not necessary for speech perception in noise or in quiet.

ISSN:0001-4966    

DOI:10.1121/1.408343

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Frequency and duration discrimination thresholds of short rising and falling one‐formant speechlike transitions without a steady state were determined by means of same/different paired comparison tasks in two experiments. When frequency extent is varied (experiment 1), just noticeable differencesdecreasewith increasing transition duration. Expressed in Hz, thresholds are, on average, 70, 63, and 58 Hz for 20, 30, and 50 ms, respectively. However, when transition duration is varied at a constant frequency extent (experiment 2), difference limensincreasewith increasing duration and are, on average, 2.7, 4.5, and 4.9 ms for standard transitions of 20, 30, and 50 ms, respectively. The thresholds determined in the two experiments indicate that different psychoacoustical cues are used depending on whether final frequency (experiment 1) or transition duration (experiment 2) are varied. Both experiments were performed at two different frequency regions (between 200 and 700 Hz and between 500 and 1000 Hz), but the results did not differ per region. In addition, no significant differences were found between rising and falling transitions. Particular attention was paid to a methodological issue, viz., the extent to which sensitivity changes as a result of different proportions of catch trials. It was found that the listeners maintained the same response strategies throughout the tests, as their performance is similar, irrespective of the number of catch trials included in the testing sessions.

ISSN:0001-4966    

DOI:10.1121/1.408344

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The relationship between acoustic‐phonetic disturbances and lexical access was explored in an aphasic patient. M.L. had a restricted disturbance of phonemic discrimination that affected the discrimination of voicing contrasts in nonword stimuli. Despite this impairment, her discrimination of voicing contrasts in words and her comprehension of auditorily presented words containing voiced segments was excellent. Performance on lexical decision was impaired: M.L.’s rejection of nonwords was poor and her reaction times and error rates for word stimuli showed a trend toward being influenced by the lexical status (word or nonword) of the item that would be formed by a change in voicing. The results are consistent with a role for a phonemic code in auditory word recognition, coupled with lexical‐to‐acoustic/phonetic feedback, but are also compatible with the view that other access codes for the Phonological Input Lexicon are also available.

ISSN:0001-4966    

DOI:10.1121/1.408345

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The masking of speech by amplitude‐modulated and unmodulated speech‐spectrum noise has been evaluated by the measurement of monaural speech recognition in such noise on young and elderly subjects with normal‐hearing and elderly hearing‐impaired subjects with and without a hearing aid. Sinusoidal modulation with frequencies covering the range 2–100 Hz, as well as an irregular modulation generated by the sum of four sinusoids in random phase relation, was used. Modulation degrees were 100%, ±6 dB, and ±12 dB. Root mean‐square sound pressure level was equal for modulated and unmodulated maskers. For the normal‐hearing subjects, essentially all types of modulated noise provided some release of speech masking as compared to unmodulated noise. Sinusoidal modulation provided more release of masking than the irregular modulation. The release of masking increased with modulation depth. It is proposed that the number and duration of low‐level intervals are essential factors for the degree of masking. The release of masking was found to reach a maximum at a modulation frequency between 10 and 20 Hz for sinusoidal modulation. For elderly hearing‐impaired subjects, the release of masking obtained from amplitude modulation was consistently smaller than in the normal‐hearing groups, presumably related to changes in auditory temporal resolution caused by the hearing loss. The average speech‐to‐noise ratio required for 30% correct speech recognition varied greatly between the groups: For young normal‐hearing subjects it was −15 dB, for elderly normal‐hearing it was −9 dB, for elderly hearing‐impaired subjects in the unaided listening condition it was +2 dB and in the aided condition it was +3 dB. The results support the conclusion that within the methodological context of the study, age as well as sensorineural hearing loss, as such, influence speech recognition in noise more than what can be explained by the loss of audibility, according to the audiogram and the masking noise spectrum.

ISSN:0001-4966    

DOI:10.1121/1.408346

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Ultrasonic pulse arrival time and energy level variations introduced by propagation through human abdominal wall specimens have been measured. A hemispheric transducer transmitted an ultrasonic pulse that was detected by a linear array transducer after propagation through an abdominal wall section. The array was translated in the elevation direction to collect data over a two‐dimensional aperture. Differences in arrival time and energy level between the measured waveforms and calculated references that account for geometric delay and spreading were found. Plots of waveforms compensated for geometric path, maps of time delay differences and energy level fluctuations, and statistics derived from these for water paths and tissue paths characterize the measurement system and describe the time delay differences and energy level fluctuations caused by 14 different human abdominal wall specimens. Repeated measurements using the same specimens show that individual tissue path measurements are reproducible, the results depend on specimen position, and frozen storage of a specimen for three months does not appear to alter the time delay differences and energy level fluctuations produced by the specimen. Comparison of measurements at room and body temperature indicates that appreciably higher time delay differences occur at body temperature while energy level fluctuations and time delay difference patterns are less affected. For the 14 different abdominal wall specimens, the rms time delay differences and energy level fluctuations have average values of 43.0 ns and 3.30 dB, respectively, and the associated correlation lengths of the time delay differences and energy level fluctuations are 7.90 and 2.28 mm, respectively. The spatial patterns of time delay difference and energy level fluctuation in the reception plane appear largely uncorrelated, although some background variations in energy level fluctuation are similar to features in time delay difference maps. The results provide important new information about the variety and range of ultrasonic wave front arrival and energy variations caused by transmission through abdominal wall.

ISSN:0001-4966    

DOI:10.1121/1.408347

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Focus degradation produced by abdominal wall has been compensated using a least‐mean‐square error estimate of arrival time. The compensation was performed on data from measurements of ultrasonic pulses from a curved transducer that emits a hemispheric wave and simulates a point source. The pulse waveforms were measured in a two‐dimensional aperture after propagation through a water path and after propagation through 14 different specimens of human abdominal wall. Time histories of the virtual point source were reconstructed by removing the time delays produced by geometric path differences and also removing time shifts produced by propagation inhomogeneities in the case of compensation, finding the complex amplitudes of the Fourier harmonics across the aperture, calculating the Fraunhofer diffraction pattern of each harmonic, and summing the patterns. This process used a least‐mean‐square error solution for the relative delay expressed in terms of the arrival time differences between neighboring points and included an algorithm to determine arrival time differences when correlation based estimates were unsatisfactory due to dissimilarity of neighboring waveforms. Comparisons of reconstructed time histories in the image plane show that the −10‐dB effective radius of the focus for reception through abdominal wall without compensation for inhomogeneities averaged 48% greater than the corresponding average effective radius for ideal waveforms, while time‐shift compensation reduced the average −10‐dB effective radius to a value that is only 4% greater than for reception of ideal waveforms. The comparisons also indicate that the average ratio of energy outside an ellipsoid defined by the −10‐dB effective widths to the energy inside that ellipsoid is 1.81 for uncompensated tissue path data and that time‐shift compensation reduced this average to 0.93, while the corresponding average for ideal waveforms was found to be 0.35. These results show that time‐shift compensation yields a significant improvement over the uncompensated case although other factors must be considered to achieve an ideal diffraction limited focus.

ISSN:0001-4966    

DOI:10.1121/1.408348

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

It is shown for a flow field with vorticity, that even if the velocityuis axisymmetric, the term [(∇×u)⋅∇)]uis, in general, nonzero. In his treatment of acoustic streaming near a rigid sphere, Lane [J. Acoust. Soc. Am.27, 1082 (1955)] dropped this term; this is probably why his results differ from those of others.

ISSN:0001-4966    

DOI:10.1121/1.408349

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The absorption and velocity of ultrasound at 21 MHz and the shear viscosity were measured for water solutions of poly (sodium 4‐styrenesulfonate) as a function of concentration and temperature. The molecular weight of the polymer is 70 000. The concentrations used were 1%, 5%, and 9% by weight, and the temperatures were 25, 30, 35, 40, and 45 °C. The absorption or α/f2decreases almost linearly with increasing temperature at a given concentration and increases with concentration at a given temperature. The velocity is a linearly increasing function of the temperature and also increases with concentration at a given temperature. In addition, the shear viscosity decreases linearly with temperature and increases with concentration.

ISSN:0001-4966    

DOI:10.1121/1.408350

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Recent measurements of sonoluminescence produced by a single, stable, pulsating gas bubble indicate that the spectrum can be modeled by that for a blackbody at a temperature of nearly 40 000 K [R. Hiller, S. J. Putterman, and B. P. Barber, ‘‘Spectrum of synchronous picosecond sonoluminescence,’’ Phys. Rev. Lett.69, 1182 (1992)]. These results are in contrast with earlier measurements of the spectrum which is modeled by electronic transitions of rotational and vibrational bands within specific elements of the host liquid [E. B. Flint and K. S. Suslick, ‘‘The temperature of cavitation,’’ Science253, 1397 (1991)]. It is suggested that the single‐bubble SL observed by Hilleretal. is intrinsically different from the multiple‐bubble SL observed by Flint and Suslick. In the former case, symmetric bubble collapse leads to shock wave formation in the gas; in the latter case, asymmetric bubble collapse leads to liquid jets that penetrate the hot bubble interior and result principally in incandescence of the host liquid.

ISSN:0001-4966    

DOI:10.1121/1.408351

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Bies and Hansen [J. Acoust. Soc. Am.88, 2743–2754 (1990)] have proposed an alternative formulation of the relationship between noise exposure and noise‐induced hearing impairment to that presented in International Standard ISO 1999 to demonstrate that the interpretation of the standard is not unique. J. H. Macrae [J. Acoust. Soc. Am.90, 2513–2516 (1991)] has shown that neither the Bies and Hansen formulation nor the International Standard accounts for observed deterioration in hearing threshold levels at 4000 Hz associated with aging in war veterans with noise‐induced permanent threshold shift (NIPTS). Thus Macrae has shown that at present there is no formulation which accounts for all epidemiological data. It is shown that Macrae’s data provides an opportunity to extend the formulation of Bies and Hansen without altering in any way their representation of the International Standard database to represent the new epidemiological data for post exposure provided by Macrae as well. A similar extension of the formulation of Kraak and co‐investigators may be shown. If the International Standard is corrected, as suggested by Macrae, and the extensions of the formulations of Bies and Hansen and of Kraak and co‐investigators are accepted, then there will be three formulations which account for all of the epidemiological data.

ISSN:0001-4966    

DOI:10.1121/1.408272

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP