摘要:

The impulse response for the acoustic radiation coupling between two disks has been found in a closed analytic form for the case of a transmitter larger in diameter than a coaxially aligned receiver. In order to verify experimentally the derived expression piezoelectric transducers were used as transmitters and receivers. An analysis of piezoelectric transduction is presented in order to account for transduction effects in the experimental system. Discrete time models of the transmitter and receiver processes valid for times less than one reverberation period are formed based on Redwood’s equivalent circuits adapted byz‐transform techniques. Recurrence relationships are derived and used in the manner of digital filters to calculate the transducer output due to any type of input. In the case of the transmitter, the force acting on the front face is calculated for any applied electrical waveform, whereas the receiver model calculates the voltage generated across the device due to any force function acting on the receiver face. The transducer models are used in conjunction with the disk to disk impulse response to calculate the voltage generated across the receiver due to any electrical waveform applied to the transmitter. Responses measured experimentally in water are presented and compared with predicted waveforms; receiver amplifier insertion characteristics are included in the model and a correction is made to take into account ultrasonic absorption by water. Good agreement is shown between the predicted and measured waveforms.

ISSN:0001-4966    

DOI:10.1121/1.391419

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A thermodynamic method for measuring the acoustic nonlinearity parameterB/Ain tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20° to 37 °C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues.

ISSN:0001-4966    

DOI:10.1121/1.391420

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

In this article, we examine the effects of changing speaking rate and syllable stress on the space–time structure of articulatory gestures. Lip and jaw movements of four subjects were monitored during production of selected bisyllabic utterances in which stress and rate were orthogonally varied. Analysis of the relative timing of articulatory movements revealed that the time of onset of gestures specific to consonant articulation was tightly linked to the timing of gestures specific to the flanking vowels. The observed temporal stability was independent of large variations in displacement, duration, and velocity of individual gestures. The kinematic results are in close agreement with our previously reported EMG finding [B. Tulleretal., J. Exp. Psychol.: HPP8, 460–472 (1982a)] and together provide evidence for relational invariants in articulation.

ISSN:0001-4966    

DOI:10.1121/1.391421

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Listeners’ abilities to learn to hear all the details of an initially unfamiliar sequence of ten 45‐ms tones were studied by tracking detection thresholds for each tonal component over a prolonged period of training. After repeated listening to this sequence, the presence or absence of individual tones could be recognized, even though they were attenuated by 40–50 dB relative to the remainder of the pattern. Threshold‐tracking histories suggest that listeners tend to employ two different learning strategies, one of which is considerably more efficient. Special training by reducing stimulus uncertainty and extending the duration of the target component was effective in increasing the rate of threshold improvement. Strategies acquired with the first pattern studied generalized to new sequences of tones. The possible implications of these results for the perceptual learning of speech or other auditory codes are discussed.

ISSN:0001-4966    

DOI:10.1121/1.391422

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Measures of frequency selectivity from forward masking suggest sharper tuning than those from simultaneous masking. To account for this result, various interpretations involving additional tuning mechanisms have been proposed. In the present study, it is shown that a simple multiplicative relation between on‐frequency forward and off‐frequency simultaneous masking predicts this result quite well. The relation assumes that changes in masking produced by separating the masker from the signal in frequency, in time, and in both frequency and time are related to one another by Weber’s law. The accuracy of the predictions suggests that the limits of auditory frequency selectivity are already established in simultaneous masking and that special interpretations involving additional tuning mechanisms are not required to account for the difference between simultaneous and forward measures. Implications for a dB scale of masking are discussed.

ISSN:0001-4966    

DOI:10.1121/1.391423

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Band‐narrowing estimates of the critical bandwidth (CB) are consistently larger than critical‐ratio (CR) estimates for the same signal frequency. Bilger [inHearingandDavis:EssaysHonoringHallowellDavis, edited by S. K. Hirshetal. (Washington U. P., St. Louis, 1976), p. 191] proposed that this difference could be accounted for by reference to intensity‐discrimination performance [CR(Hz)/CB(Hz)=ΔI/I]. To test this hypothesis, band‐narrowing, critical‐ratio, and intensity‐discrimination data were collected for four normally hearing, well‐trained listeners. Signal frequency was 2000 Hz and two noise levels were used: 20 and 50 dBN0. The relations proposed by Bilger among critical‐bandwidth estimates from band‐narrowing experiments, critical‐ratio estimates from pure‐tone detection in wideband noise, and intensity discrimination for a critical‐band‐wide noise in wideband noise are not supported by the results of individual listeners, or results averaged across listeners.

ISSN:0001-4966    

DOI:10.1121/1.391424

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Four experiments were performed in an attempt to refine the measurement of psychophysical tuning curves (PTCs). PTCs were determined using sinusoidal signals and narrow‐band noise maskers, in both simultaneous and forward masking. In experiment I a fixed low‐level notched noise was gated with the masker in order to restrict off‐frequency listening and to eliminate ‘‘confusions’’ between the signal and masker in forward masking. In contrast to previous work, this procedure produced PTCs with similar round tips in both simultaneous and forward masking. The PTCs differed mainly in that the high‐frequency skirts were steeper in forward masking. Experiment II compared PTCs with and without an additional notched‐noise masker, for a number of signal levels. The notched noise had the effect of broadening the tips of the PTCs, this effect being greater in forward masking than in simultaneous masking. With increasing signal level the high‐frequency skirt of the PTC became slightly steeper, and the low‐frequency skirt slightly shallower. Experiment III studied the effect of signal duration on PTCs determined in simultaneous masking. Duration had little effect when off‐frequency listening was restricted with a fixed notched‐noise masker, but had a substantial effect in the absence of such a masker. Experiment IV studied the effect of signal delay in forward masking. When off‐frequency listening was restricted and the signal levels adjusted to produce similar masker levels at threshold for each delay, the shape of the PTC was not affected by delay. It is concluded that, when PTCs are determined in the presence of notched noise, suppression is probably responsible for most of the differences between simultaneous and forward masking. Previous work may have overestimated the influence of suppression, because it did not control off‐frequency listening and/or provide appropriate detection cues in forward masking.

ISSN:0001-4966    

DOI:10.1121/1.391425

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The just‐noticeable‐difference in frequency (jndf) for complex signals with triangular spectral envelopes is found to depend on the envelope slope. For shallow slopes (<140 dB/oct), jndfincreases with decreasing slope. Addition of noise also impairs frequency discrimination within a region of about 20 dB above masked threshold. This is found for both maskers used: a wideband noise and a narrow‐band masker which is below the signal in frequency. When wideband noise is used, frequency discrimination of complex signals with shallow slopes deteriorates more rapidly with decreasing signal‐to‐noise ratio than it does when the signals have steep spectral slopes.

ISSN:0001-4966    

DOI:10.1121/1.391347

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The human psychophysical adaptation literature infers the existence of channels in the auditory system sensitive to frequency modulation (FM) from selective increases in FM detection thresholds following adaptation with FM stimuli. Using this psychophysical paradigm to characterize the attributes of feature‐sensitive channels requires knowledge of the phenomenon’s stability over repeated testing. In this study FM detection thresholds were measured in human subjects with continued testing over numerous sessions. During adapting intervals within the sessions either FM upsweeps or silence was presented. Exposure to FM upsweeps initially resulted in an increase in FM detection thresholds by a factor of 2 to 3 relative to those measured following silence. These initial threshold elevations decreased markedly with repeated testing (more than five 30‐min experimental sessions). Final threshold differences between adapted and nonadapted conditions approached zero. In one subject, such asymptotic threshold values were regained in a single session, after a 4‐month hiatus. The findings suggest multiple determinants of the selective adaptation function, as well as a reevaluation of inferred mechanisms.

ISSN:0001-4966    

DOI:10.1121/1.391399

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A purpose of this study was to determine the values of exponents of psychophysical functions for the discomfort produced by whole‐body vertical vibration. In addition, the applicability of a method of predicting the average stimulus intensity of a stimulus the intensity of which varies with time was investigated. The first experiment investigated the effect on discomfort of the duration of vibration (for durations of 2, 5, 10, 20, and 50 s) and of the vibration acceleration magnitude [for 0.5, 0.75, 1.11, 1.67, and 2.5 ms−2(rms) at 8 Hz]. The magnitude estimation method was used. The results show that the logarithm of the magnitude estimates is in linear proportion to both the logarithm of the acceleration and the logarithm of the duration. The values of exponents for acceleration and duration were 0.96 and 0.56, respectively. In the second experiment, the point of subjective equality of each of 16 nonsteady vibrations was measured and compared with the stimulus intensity predicted by means of the method proposed by the authors. Good agreement was found between the measured and predicted stimulus intensity and it was confirmed that the predicting method could be applied to vibration as well as to noise.

ISSN:0001-4966    

DOI:10.1121/1.391400

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP