摘要:

An assay utilizing luminescent bacteria,Photobacteriumphosphoreum, was adapted to assess the antibacterial effects of acoustic energy. Acoustic pressures up to 67 kPa in the 100‐ to 800‐Hz frequency range were applied to bacteria freely suspended in a liquid medium. Bacterial luminescence decreased after sonication, thus showing sensitivity to the effects of acoustic energy. This decreased luminescence was linearly related to exposure duration, appeared independent of acoustic frequency in this range, and was significantly heightened by the presence of cavitation. High‐frequency components of the acoustic emission were recorded from the sonicated fluid, and it was found that the decrease in luminescence due to sonication was directly related to the logarithm of the acoustic emission. Viability studies on exposed bacteria indicated a diminution of luminescence without bacterial death. The potential use of luminescent bacteria in assessing the biological effects of acoustic energy‐generating systems is discussed.

ISSN:0001-4966    

DOI:10.1121/1.399974

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A method is discussed for measuring the acoustical impedance of woodwind instruments that is relatively fast and insensitive to the ambient acoustical noise. The apparatus is essentially made of a measurement head, which is an approximately cylindrical cavity fitted with two microphones (in practice often three or more for technical reasons) and, at one of its ends, a loudspeaker; the other end is connected to the acoustical cavity under study (the instrument). The loudspeaker emits acoustical chirps and the signals provided by the microphones are Fourier transformed with the help of a microcomputer, which also extracts from the results the acoustical impedance as a function of frequency. A relatively high dynamic range is needed in order to match the high quality factor of the resonances of musical instruments, especially at low frequencies. To meet this requirement, it was found necessary to take into account the acoustical losses inside the head as well as the mutual perturbation of the microphones or various perturbations arising from geometrical imperfections of the cavity. This can be done automatically and without long calculations by using a calibration method, based on the successive use of three reference cavities, which are described and discussed in detail in this article. The method has been tested with cylindrical cavities and gives satisfactory results in terms of peak positions and heights. Impedance curves of clarinets have also been measured. The three‐calibration technique eliminates several sources of systematics and corrects automatically for various perturbations, such as perturbations of the acoustical field by the microphones, and allows the study of instruments of various diameters.

ISSN:0001-4966    

DOI:10.1121/1.399975

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A digital processing method is described for altering spectral contrast (the difference in amplitude between spectral peaks and valleys) in natural utterances. Speech processed with programs implementing the contrast alteration procedure was presented to listeners with moderate to severe sensorineural hearing loss. The task was a three alternative (/b/,/d/, or /g/) stop consonant identification task for consonants at a fixed location in short nonsense utterances. Overall, tokens with enhanced contrast showed moderate gains in percentage correct stop consonant identification when compared to unaltered tokens. Conversely, reducing spectral contrast generally reduced percent correct stop consonant identification. Contrast alteration effects were inconsistent for utterances containing /d/. The observed contrast effects also interacted with token intelligibility.

ISSN:0001-4966    

DOI:10.1121/1.399976

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Perception models based on different kinds of acoustic data were compared with respect to their capacity to predict perceptual confusions between the Swedish stops [b,d,Δ,g] in systematically varied vowel contexts. Fragments of VC:V utterances read by a male speaker were presented to listeners. The resulting confusions were especially numerous between short stimulus segments following stop release, and formed a regular pattern depending mainly on the acute/grave dimension of the following vowel. The acoustic distances calculated were based on: (1) filter band spectra; (2)F2andF3at the CV boundary and in the middle of the following vowel; (3) the duration of the burst (=transient + noise section). Both the spectrum‐based and the formant‐based models provided measures of acoustic distance (dissimilarity) that revealed regular patterns. However, the predictive capacity of both models was improved by including the time‐varying properties of the stimuli in the distance measures. The highest correlation between predicted and observed percent confusions,r=0.85, was obtained with the formant‐based model in combination with burst length data. The asymmetries in the listeners’ confusions were also shown to be predictable, given acoustic data on the following vowel.

ISSN:0001-4966    

DOI:10.1121/1.399977

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The contribution of extraneous sounds to the perceptual estimation of the first‐formant (F1) frequency of voiced vowels was investigated using a continuum of vowels perceived as changing from /I/ to /q/ asF1 was increased. Any phonetic effects of adding extraneous sounds were measured as a change in the position of the phoneme boundary on the continuum. Experiments 1–5 demonstrated that a pair of extraneous tones, mistuned from harmonic values of the fundamental frequency of the vowel, could influence perceived vowel quality when added in theF1 region. PerceivedF1 frequency was lowered when the tones were added on the lower skirt ofF1, and raised when they were added on the upper skirt. Experiments 6 and 7 demonstrated that adding a narrow‐band noise in theF1 region could produce a similar pattern of boundary shifts, despite the differences in temporal properties and timbre between a noise band and a voiced vowel. The data are interpreted using the concept of the harmonic sieve [Duifhuisetal., J. Acoust. Soc. Am.71, 1568–1580 (1982)]. The results imply a partial failure of the harmonic sieve to exclude extraneous sounds from the perceptual estimation ofF1 frequency. Implications for the nature of the hypothetical harmonic sieve are discussed.

ISSN:0001-4966    

DOI:10.1121/1.399978

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A number of studies, involving English, Swedish, French, and Spanish, have shown that, for sequences of rounded vowels separated by nonlabial consonants, both EMG activity and lip protrusion diminish during the intervocalic consonant interval, producing a ‘‘trough’’ pattern. A two‐part study was conducted to (a) compare patterns of protrusion movement (upper and lower lip) and EMG activity (orbicularis oris) for speakers of English and Turkish, a language where phonological rules constrain vowels within a word to agree in rounding and (b) determine which of two current models of coarticulation, the ‘‘look‐ahead’’ and ‘‘coproduction’’ models, best explained the data. Results showed Turkish speakers producing ‘‘plateau’’ patterns of movement rather than troughs, and unimodal rather than bimodal patterns of EMG activity. In the second part of the study, one prediction of the coproduction, model, that articulatory gestures have stable profiles across contexts, was tested by adding and subtracting movement data signals to synthesize naturally occurring patterns. Results suggest English and Turkish may have different modes of coarticulatory organization.

ISSN:0001-4966    

DOI:10.1121/1.400349

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Individual and group loudness relations were obtained at a frequency in the region of impaired hearing for 100 people, 98 with bilateral cochlear impairment. Slope distributions were determined from absolute magnitude estimation (AME) and absolute magnitude production (AMP) of loudness; they were also derived from cross‐modality matching (CMM) and AME of apparent length. With respect to both the means and the individual slope values, the two distributions closely agree. More than half of the measured deviations are less than 20%, with an overall average of −1.5%, meaning that transitivity is preserved for bilaterally impaired individuals. Moreover, over the stimulus range where cochlear impairment steepens the loudness function, both the group means and the individual slope values are clearly larger than in normal hearing. The results also show that, for groups of people with approximately similar losses, the standard deviation is a nearly constant proportion of the mean slope value giving a coefficient of variation of about 27% in normal and impaired hearing. This indicates, in accord with loudness matching, that the size of the slopes depends directly on the degree of hearing loss. The results disclose that loudness measurements obtained by magnitude scaling are able to reveal the operating characteristic of the ear for individuals.

ISSN:0001-4966    

DOI:10.1121/1.399979

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

It is estimated that 22% of the masking observed in many traditional tone‐in‐noise detection experiments is due to uncertainty associated with trial‐to‐trial variation in the noise waveform.

ISSN:0001-4966    

DOI:10.1121/1.399980

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In part I of this study [van Rooijetal., J. Acoust. Soc. Am.86, 1294–1309 (1989)], the validity and manageability of a test battery comprising auditive (sensitivity, frequency resolution, and temporal resolution), cognitive (memory performance, processing speed, and intellectual abilities), and speech perception tests (at the phoneme, spondee, and sentence level) were investigated. In the present article, the results of a selection of these tests for 72 elderly subjects (aged 60–93 years) are analyzed by multivariate statistical techniques. The results show that the deterioration of speech perception in the elderly consists of two statistically independent components: (a) a large component mainly representing the progressive high‐frequency hearing loss with age that accounts for approximately two‐thirds of the systematic variance of the tests of speech perception and (b) a smaller component (accounting for one‐third of the systematic variance of the speech perception tests) mainly representing a general performance decrement due to reduced mental efficiency, which is indicated by a general slowing of performance and a reduced memory capacity. Although both components are correlated with age, it was found that the balance between auditive and cognitive contributions to speech perception performance did not change with age.

ISSN:0001-4966    

DOI:10.1121/1.399981

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The bandwidths for summation at threshold were measured for subjects with normal hearing and subjects with sensorineural hearing loss. Thresholds in quiet and in the presence of a masking noise were measured for complex stimuli consisting of 1 to 40 pure‐tone components spaced 20 Hz apart. The single component condition consisted of a single pure tone at 1100 Hz; additional components were added below this frequency, in a replication of the Gässler [Acustica4, 408–414 (1954)] procedure. For the normal subjects, thresholds increased approximately 3 dB per doubling of bandwidth for signal bandwidths exceeding the critical bandwidth. This slope was less for the hearing‐impaired subjects. Summation bandwidths, as estimated from two‐line fits, were wider for the hearing‐impaired than for the normal subjects. These findings provide evidence that hearing‐impaired subjects integrate sound energy over a wider‐than‐normal frequency range for the detection of complex signals. A second experiment used stimuli similar to those of Spiegel [J. Acoust. Soc. Am.66, 1356–1363 (1979)], and added components both above and below the frequency of the initial component. Using these stimuli, the slope of the threshold increase beyond the critical bandwidth was approximately 1.5 dB per doubling of bandwidth, thus replicating the Spiegel (1979) experiment. It is concluded that the differences between the Gässler (1954) and Spiegel (1979) studies were due to the different frequency content of the stimuli used in each study. Based upon the present results, it would appear that the slope of threshold increase is dependent upon the direction of signal expansion, and the size of the critical bands into which the signal is expanded.

ISSN:0001-4966    

DOI:10.1121/1.399982

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP