摘要:

Two experiments were conducted involving the auditory localization aftereffect, in which the perceptual lateralization of a test sound having an interaural time difference (ITD) shifts away from that of a prior adapting sound having a different ITD. First, the frequency selectivity of the aftereffect was examined for sinusoids presented through headphones, with various combinations of adapter and test frequencies below 800 Hz, using the method of constant stimuli. The magnitude of the aftereffect was found to be largest when the frequencies of the two tones were similar, and virtually disappeared at a frequency difference of one-half octave. Second, the ITD selectivity of the aftereffect was examined for 400-Hz sinusoids. Subjects’ judgments of lateralization were measured directly in terms of the perceived azimuth of the test tone for various combinations of adapter and test ITDs in the range of±625 μs.The magnitude of the aftereffect was found to be largest when adapter and test ITDs differed by approximately 250 μs. These results were successfully simulated by an interaural cross-correlation model having gain control. The results are consistent with the idea that the gain of ITD-selective units, located after binaural interaction but before across-frequency integration, is changed by recent input.

ISSN:0001-4966    

DOI:10.1121/1.423064

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Analytical solutions are presented for the correlation between the envelopes of certain narrow-band stimuli that are typically used in experiments on binaural unmasking and on Comodulation Masking Release (CMR). These stimuli consist of two maskers with identical envelopes and a signal that is added to one of the maskers. If the two maskers have the same center frequency and are presented to the right and left ear, the stimulus resembles a binauralMoSmcondition. If the two maskers have different center frequencies, we have a CMR condition with one flanking band. The solutions for the envelope correlation differ depending on whether the envelope correlation is expressed as normalized cross correlation or as normalized cross covariance (Pearson product-moment correlation). The envelope correlation depends on the statistics of the masker and the signal whereas the waveform correlation depends on neither. This influence only disappears for the normalized envelopecross correlationprovided that the masker level is much higher than the signal level. In this case the envelope cross correlation is approximately equal to the square root of the waveform correlation. It is argued that the different properties of both types of envelope correlation are of relevance for CMR research.

ISSN:0001-4966    

DOI:10.1121/1.423065

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

An adaptive noise cancellation scheme based on two-stage adaptive filtering as proposed by Van Compernolle [Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing(IEEE, New York, 1990)] was tested for two identical directional microphones mounted in an endfire configuration within a single behind-the-ear (BTE) hearing aid. Speech intelligibility tests were carried out with two normal hearing subjects and three hearing aid users with moderate hearing losses, in a realistic test environment using open set words and sentences. A significant improvement, on average more than 5 dB, of speech reception threshold (SRT) in background noise was obtained.

ISSN:0001-4966    

DOI:10.1121/1.423066

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Videostroboscopy is an examination which yields a permanent record of the moving vocal folds. Thus, it allows the diagnosis of abnormalities which contribute to voice disorders. In this paper, in order to find and quantify the deformation of the vocal folds in videostroboscopic recordings, an active contours- (snakes) based approach is used to delineate the vocal folds in each frame of the videostroboscopic image sequence. After this delineation, a new elastic registration algorithm is used to register the vocal fold contours between adjacent frames of the video sequence. This algorithm is based on the regularization principle and is very effective when large deformations are present. A least-squares approach is used to fit an affine model to the displacement vectors found by elastic registration. The parameters of this model, rotation, translation, and deformation along two principle axes, quantify the deformation and allow the succinct characterization of the videostroboscopic recordings based on the deformations that occurred. Experiments are shown with synthetic and real videostroboscopic data that demonstrate the value of the proposed approach.

ISSN:0001-4966    

DOI:10.1121/1.423067

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Age-related changes in the laryngeal system can be perceived as altered vocal pitch and increased pitch variability. However, reports vary as to the nature and extent of an age effect on fundamental frequency(F0)for analyses taken over long segments of connected speech. Analysis ofF0across a smaller time frame may be more informative. Young speakers show an increase inF0associated with phonetically governed devoicing gestures that is likely mediated by increased vocal fold stiffness. Anatomic and neurophysiologic changes in the aged larynx may limit the role of increased vocal fold stiffness in the devoicing gesture. This study tests the hypothesis that aged speakers show a smaller increase inF0in association with the devoicing gesture for production of an intervocalic voiceless obstruent than do young speakers. Normal young and aged speakers produced a short sentence containing an intervocalic voiceless obstruent. Measures ofF0were obtained for ten cycles before voice offset and ten cycles after voice onset. Young speakers showed a small increase inF0during devoicing whereas aged speakers showed a decrease inF0during devoicing. Aged speakers seem to rely more on vocal fold abduction rather than a combination of abduction and tensing to achieve devoicing.

ISSN:0001-4966    

DOI:10.1121/1.423068

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

In recent years there has been a great deal of interest in demonstrations of the so-called “Perceptual-Magnet Effect” (PME). In these studies, AX-discrimination tasks purportedly reveal that discriminability of speech sounds from a single category varies with judged phonetic “goodness” of the sounds. However, one possible confound is that category membership is determined by identification of sounds in isolation, whereas, discrimination tasks include pairs of stimuli. In the first experiment of the current study, identifications and goodness judgments were obtained for vowels (/i/–/e/) presented in pairs. A substantial shift in phonetic identity was evidenced with changes in the context vowel. In a second experiment, listeners participated in an AX-discrimination task with the vowel pairs from the first experiment. Using the contextual identification functions from the first experiment, predictions of discriminability were calculated using the classic tenets of Categorical Perception. Obtained discriminability functions were well accounted for by predictions from identification. There was no additional unexplained variance that required the proposal of “perceptual magnets.” These results suggest that PME may be nothing more than further demonstration that general discriminability is greater for cross-category stimulus pairs than for within-category pairs.

ISSN:0001-4966    

DOI:10.1121/1.423087

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Head-related transfer functions (HRTFs) were used to create spatialized stimuli for presentation through earphones. Subjects performed forced-choice, identification tests during which allowed response directions were indicated visually. In each experimental session, subjects were first presented with auditory stimuli in which the stimulus HRTFs corresponded to the allowed response directions. The correspondence between the HRTFs used to generate the stimuli and the directions was then changed so that response directions no longer corresponded to the HRTFs in the natural way. Feedback was used to train subjects as to which spatial cues corresponded to which of the allowed responses. Finally, the normal correspondence between direction and HRTFs was reinstated. This basic experimental paradigm was used to explore the effects of the type of feedback provided, the complexity of the simulated acoustic scene, the number of allowed response positions, and the magnitude of the HRTF transformation subjects had to learn. Data showed that (1) although subjects may not adapt completely to a new relationship between physical stimuli and direction, response bias decreases substantially with training, and (2) the ability to resolve different HRTFs depends both on the stimuli presented and on the state of adaptation of the subject.

ISSN:0001-4966    

DOI:10.1121/1.423088

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A series of experiments was performed in which subjects were trained to interpret auditory localization cues arising from locations different from their normal spatial positions. The exact pattern of mean response to these alterations (as a function of time) was examined in order to begin to develop a quantitative model of adaptation. Mean responses were roughly proportional to the normal position associated with the localization cues presented. As subjects adapted, the best-fit slope (relating mean response and normal position) changed roughly exponentially with time. The exponential rate and adaptation asymptote were found for each subject in each experiment, as well as the rate and asymptote of readaptation to normal cues. The rate of adaptation does not show any statistical dependence on experimental conditions; however, the asymptote of the best-fit slope varied with the strength of the transformation used in each experiment. This result is consistent with the hypothesis that subjects cannot adapt to a nonlinear transformation of auditory localization cues, but instead adapt to a linear approximation of the transformation. Over time, performance changes exponentially towards the best-fit linear approximation for the transformation used in a particular experiment, and the rate of this adaptation does not depend upon the transformation employed.

ISSN:0001-4966    

DOI:10.1121/1.423107

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The efficacy of audio-visual interactions in speech perception comes from two kinds of factors. First, at theinformationlevel, there is some “complementarity” of audition and vision: It seems that some speech features, mainly concerned with manner of articulation, are best transmitted by the audio channel, while some other features, mostly describing place of articulation, are best transmitted by the video channel. Second, at theinformation processinglevel, there is some “synergy” between audition and vision: The audio-visual global identification scores in a number of different tasks involving acoustic noise are generally greater than both the auditory-alone and the visual-alone scores. However, these two properties have been generally demonstrated until now in rather global terms. In the present work, audio-visual interactions at thefeaturelevel are studied for French oral vowels which contrast three series, namely front unrounded, front rounded, and back rounded vowels. A set of experiments on the auditory, visual, and audio-visual identification of vowels embedded in various amounts of noise demonstrate that complementarity and synergy in bimodal speech appear to hold for a bundle ofindividualphonetic features describing place contrasts in oral vowels. At the information level (complementarity), in the audio channel the height feature is the most robust, backness the second most robust one, and rounding the least, while in the video channel rounding is better than height, and backness is almost invisible. At the information processing (synergy) level, transmitted information scores show that all individual features are better transmitted with the ear and the eye together than with each sensor individually.

ISSN:0001-4966    

DOI:10.1121/1.423069

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The sinuous instability wave of a planar air jet is excited by localized acoustic flow across the nozzle. Phase velocity and the growth exponent are found from synchronous hot-wire measurements made beyond the excited region, where the profile is approximately sech-squared. In the observed range of scaled radian frequency, 0.02–1.33 (the stability limit), results agree with real-frequency (spatially growing) analysis but not with complex-frequency (temporally growing) analysis. The latter predicts smaller phase velocity at low frequencies and has been questioned in edgetone analysis. In further tests, the acoustic driving signal is made independent of downstream distance, as in an organ pipe. The jet deflection is then the sum of acoustic convection and of the instability wave, summing to zero at the nozzle, as proposed by Fletcher, Elder, and others. The instability-wave theory applies to linear behavior in the inviscid limit and therefore to a hypothetical nonspreading jet. The local velocity profile width must be considered in relating to a physical jet. In a flue organ pipe oscillating at equilibrium amplitude the stability-wave theory is not applicable near the lip, where the laminar flow assumed in the theory disappears and the jet deflection exceeds the range of linear behavior. Direct sound generation by the jet is investigated briefly.

ISSN:0001-4966    

DOI:10.1121/1.423089

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP