Kinematic, acoustic, and perceptual analyses of connected speech produced by parkinsonian and normal geriatric adults

Acoustic and kinematic analyses, as well as perceptual evaluation, were conducted on the speech of Parkinsonian and normal geriatric adults. As a group, the Parkinsonian speakers had very limited jaw movement compared to the normal geriatrics. For opening gestures, jaw displacements and velocities produced by the Parkinsonian subjects were about half those produced by the normal geriatrics. Lower lip movement amplitude and velocity also were reduced for the Parkinsonian speakers relative to the normal geriatrics, but the magnitude of the reduction was not as great as that seen in the jaw. Lower lip closing velocities expressed as a function of movement amplitude were greater for the Parkinsonian speakers than for the normal geriatrics. This increased velocity of lower lip movement may reflect a difference in the control of lip elevation for the Parkinsonian speakers, an effect that increased with the severity of dysarthria. Acoustically, the Parkinsonian subjects had reduced durations of vocalic segments, reduced formant transitions, and increased voice onset time compared to the normal geriatrics. These effects were greater for the more severe, compared to the milder, dysarthrics and were most apparent in the more complex, vocalic gestures.     

Effects of noise on speech production: acoustic and perceptual analyses

Acoustical analyses were carried out on a set of utterances produced by two male speakers talking in quiet and in 80, 90, and 100 dB SPL of masking noise. In addition to replicating previous studies demonstrating increases in amplitude, duration, and vocal pitch while talking in noise, these analyses also found reliable differences in the formant frequencies and short-term spectra of vowels. Perceptual experiments were also conducted to assess the intelligibility of utterances produced in quiet and in noise when they were presented at equal S/N ratios for identification. In each experiment, utterances originally produced in noise were found to be more intelligible than utterances produced in the quiet. The results of the acoustic analyses showed clear and consistent differences in the acoustic-phonetic characteristics of speech produced in quiet versus noisy environments. Moreover, these accounts differences produced reliable effects on intelligibility. The findings are discussed in terms of: (1) the nature of the acoustic changes that taken place when speakers produce speech under adverse conditions such as noise, psychological stress, or high cognitive load: (2) the role of training and feedback in controlling and modifying a talker's speech to improve performance of current speech recognizers; and (3) the development of robust algorithms for recognition of speech in noise.     

Effects of categorization and discrimination training on auditory perceptual space

Psychophysical phenomena such as categorical perception and the perceptual magnet effect indicate that our auditory perceptual spaces are warped for some stimuli. This paper investigates the effects of two different kinds of training on auditory perceptual space. It is first shown that categorization training using nonspeech stimuli, in which subjects learn to identify stimuli within a particular frequency range as members of the same category, can lead to a decrease in sensitivity to stimuli in that category. This phenomenon is an example of acquired similarity and apparently has not been previously demonstrated for a category-relevant dimension. Discrimination training with the same set of stimuli was shown to have the opposite effect: subjects became more sensitive to differences in the stimuli presented during training. Further experiments investigated some of the conditions that are necessary to generate the acquired similarity found in the first experiment. The results of these experiments are used to evaluate two neural network models of the perceptual magnet effect. These models, in combination with our experimental results, are used to generate an experimentally testable prediction concerning changes in the brain's auditory maps under different training conditions.     

Coarticulation in sequences of two nonhomorganic stop consonants: perceptual and acoustic evidence

This study investigated whether any perceptually useful coarticulatory information is carried by the release burst of the first of two successive, nonhomorganic stop consonants. The CV portions of natural VCCV utterances were replaced with matched synthetic stimuli from a continuum spanning the three places of stop articulation. There was a sizable effect of coarticulatory cues in the natural-speech portion on the perception of the second stop consonant. Moreover, when the natural VC portions including the final release burst were presented in isolation, listeners were significantly better than chance at guessing the identity of the following, "missing" syllable-initial stop. The hypothesis that the release burst of a syllable-final stop contains significant coarticulatory information about the place of articulation of a following, nonhomorganic stop was further confirmed in acoustic analyses which revealed significant effects of CV context on the spectral properties of the release bursts. The relationship between acoustic stimulus properties and listeners' perceptual responses was not straightforward, however.     

Acoustic and perceptual characteristics of voicing in fricatives and fricative clusters.

Several types of measurements were made to determine the acoustic characteristics that distinguish between voiced and voiceless fricatives in various phonetic environments. The selection of measurements was based on a theoretical analysis that indicated the acoustic and aerodynamic attributes at the boundaries between fricatives and vowels. As expected, glottal vibration extended over a longer time in the obstruent interval for voiced fricatives than for voiceless fricatives, and there were more extensive transitions of the first formant adjacent to voiced fricatives than for the voiceless cognates. When two fricatives with different voicing were adjacent, there were substantial modifications of these acoustic attributes, particularly for the syllable-final fricative. In some cases, these modifications leads to complete assimilation of the voicing feature. Several perceptual studies with synthetic vowel-consonant-vowel stimuli and with edited natural stimuli examined the role of consonant duration, extent and location of glottal vibration, and extent of formant transitions on the identification of the voicing characteristics of fricatives. The perceptual results were in general consistent with the acoustic observations and with expectations based on the theoretical model. The results suggest that listeners base their voicing judgments of intervocalic fricatives on an assessment of the time interval in the fricative during which there is no glottal vibration. This time interval must exceed about 60 ms if the fricative is to be judged as voiceless, except that a small correction to this threshold is applied depending on the extent to which the first-formant transitions are truncated at the consonant boundaries.     

Statistically robust evidence of stochastic resonance in human auditory perceptual system

In human perception, exogenous noise is known to yield a masking effect, i.e. an increase of the perceptual threshold relative to a stimulus acting on the same modality. However, somehow counter-intuitively, the opposite mechanism can occasionally occur: a decrease of the perceptual threshold for a non-vanishing, virtuous amount of noise. This mechanism, called stochastic resonance, is deemed to provide important information about the role of noise in the human brain. In this paper, we investigate stochastic resonance in a detection task in the auditory modality. Normal-hearing participants were asked to judge the presence of acoustic stimuli of different intensity and superimposed to different levels of white noise. The matrix-like outcomes of a behavioural experiment were fitted by a two-dimensional, noise-dependent psychometric function. The fit revealed a statistically significant stochastic resonance in 43% of the experimental runs. We conclude that, in the auditory modality, stochastic resonance is a tiny effect that, under conventional circumstances, is largely overrun by standard masking.     

Pattern of BOLD signal in auditory cortex relates acoustic response to perceptual streaming

Background

The ultrasonic vocalizations (USV) of courting male mice are known to possess a phonetic structure with a complex combination of several syllables. The genetic mechanisms underlying the syllable sequence organization were investigated.

Results

This study compared syllable sequence organization in two inbred strains of mice, 129S4/SvJae (129) and C57BL6J (B6), and demonstrated that they possessed two mutually exclusive phenotypes. The 129S4/SvJae (129) strain frequently exhibited a "chevron-wave" USV pattern, which was characterized by the repetition of chevron-type syllables. The C57BL/6J strain produced a "staccato" USV pattern, which was characterized by the repetition of short-type syllables. An F1 strain obtained by crossing the 129S4/SvJae and C57BL/6J strains produced only the staccato phenotype. The chevron-wave and staccato phenotypes reappeared in the F2 generations, following the Mendelian law of independent assortment.

Conclusions

These results suggest that two genetic loci control the organization of syllable sequences. These loci were occupied by the staccato and chevron-wave alleles in the B6 and 129 mouse strains, respectively. Recombination of these alleles might lead to the diversity of USV patterns produced by mice.     

Production of contrast between sibilant fricatives by children with cochlear implants

Speech production by children with cochlear implants (CIs) is generally less intelligible and less accurate on a phonemic level than that of normally hearing children. Research has reported that children with CIs produce less acoustic contrast between phonemes than normally hearing children, but these studies have included correct and incorrect productions. The present study compared the extent of contrast between correct productions of /s/ and /∫/ by children with CIs and two comparison groups: (1) normally hearing children of the same chronological age as the children with CIs and (2) normally hearing children with the same duration of auditory experience. Spectral peaks and means were calculated from the frication noise of productions of /s/ and /∫/. Results showed that the children with CIs produced less contrast between /s/ and /∫/ than normally hearing children of the same chronological age and normally hearing children with the same duration of auditory experience due to production of /s/ with spectral peaks and means at lower frequencies. The results indicate that there may be differences between the speech sounds produced by children with CIs and their normally hearing peers even for sounds that adults judge as correct.     

Acoustic analyses and perceptual data on anticipatory labial coarticulation in adults and children

The present study investigated anticipatory labial coarticulation in the speech of adults and children. CV syllables, composed of [s], [t], and [d] before [i] and [u], were produced by four adult speakers and eight child speakers aged 3-7 years. Each stimulus was computer edited to include only the aperiodic portion of fricative-vowel and stop-vowel syllables. LPC spectra were then computed for each excised segment. Analyses of the effect of the following vowel on the spectral peak associated with the second formant frequency and on the characteristic spectral prominence for each consonant were performed. Perceptual data were obtained by presenting the aperiodic consonantal segments to subjects who were instructed to identify the following vowel as [i] or [u]. Both the acoustic and the perceptual data show strong coarticulatory effects for the adults and comparable, although less consistent, coarticulation in the speech stimuli of the children. The results are discussed in terms of the articulatory and perceptual aspects of coarticulation in language learning.     

Reiterant speech: an acoustic and perceptual validation

Reiterant speech, or nonsense syllable mimicry, has been proposed as a way to study prosody, particularly syllable and word durations, unconfounded by segmental influences. Researchers have shown that segmental influences on durations can be neutralized in reiterant speech. If it is to be a useful tool in the study of prosody, it must also be shown that reiterant speech preserves the suprasegmental duration and intonation differences relevant to perception. In the present study, syllable durations for nonreiterant and reiterant ambiguous sentences were measured to seek evidence of the duration differences which can enable listeners to resolve surface structure ambiguities in nonreiterant speech. These duration patterns were found in both nonreiterant and reiterant speech. A perceptual study tested listeners' perception of these ambiguous sentences as spoken by four "good" speakers--speakers who neutralized intrinsic duration differences and whose sentences were independently rated by skilled listeners as good imitations of normal speech. The listeners were able to choose the correct interpretation when the ambiguous sentences were in reiterant form as well as they did when the sentences were spoken normally. These results support the notion that reiterant speech is like nonreiterant speech in aspects which are important in the study of prosody.     

Differences in fricative production between children and adults: evidence from an acoustic analysis of /sh/ and /s/

Speech samples of 12 speakers (8 children and 4 adults) producing the fricatives /s/ and/sh/ followed by the vowels /i/ and /u/ were analyzed to locate the major spectral prominences. Results showed that the fricative low-frequency prominences for children's samples differed from those of adults in three important ways: (1) They were generally higher in frequency; (2) they were greater in amplitude relative to higher frequency regions; and (3) they showed greater effects of vowel context. The first finding can be explained by a simple scaling of adult models of fricative production to accommodate children's smaller vocal tracts. The other two findings suggest, however, that there are other anatomical and articulatory differences between children and adults affecting fricative production. The data presented here suggest that one important difference may be the relative sizes of the fricative constriction and the glottal opening.     

Effects of postlingual deafness on speech production: implications for the role of auditory feedback

This study investigated some effects of postlingual deafness on speech by exploring selected properties of consonants, vowels, and suprasegmentals in the speech of seven totally, postlingually deafened individuals. The observed speech properties included parameters that function as phonological contrasts in English, as well as parameters that constitute primarily phonetic distinctions. The results demonstrated that postlingual deafness affects the production of all classes of speech sounds, suggesting that auditory feedback is implicated in regulating the phonetic precision of consonants, vowels, and suprasegmentals over the long term. In addition, the results are discussed in relation to factors that may influence the degree of speech impairment, such as age at onset of deafness.     

Interactions of speaking condition and auditory feedback on vowel production in postlingually deaf adults with cochlear implants

This study investigates the effects of speaking condition and auditory feedback on vowel production by postlingually deafened adults. Thirteen cochlear implant users produced repetitions of nine American English vowels prior to implantation, and at one month and one year after implantation. There were three speaking conditions (clear, normal, and fast), and two feedback conditions after implantation (implant processor turned on and off). Ten normal-hearing controls were also recorded once. Vowel contrasts in the formant space (expressed in mels) were larger in the clear than in the fast condition, both for controls and for implant users at all three time samples. Implant users also produced differences in duration between clear and fast conditions that were in the range of those obtained from the controls. In agreement with prior work, the implant users had contrast values lower than did the controls. The implant users' contrasts were larger with hearing on than off and improved from one month to one year postimplant. Because the controls and implant users responded similarly to a change in speaking condition, it is inferred that auditory feedback, although demonstrably important for maintaining normative values of vowel contrasts, is not needed to maintain the distinctiveness of those contrasts in different speaking conditions.     

Effects of acoustic overstimulation on spectral and temporal processing in the amphibian auditory nerve

Activity of isolated auditory-nerve fibers in tree frogs (Eleutherodactylus coqui) exposed to continuous 3-min tones of different intensities at their characteristic frequencies (CFs) was recorded. Period histograms show a retardation in the preferred phase of discharge during and after the cessation of the exposure. Postexposure phase shift is concomitant with an elevation in CF thresholds and related to the level of tone exposure above threshold. Vector strength does not show comparable trends of change; postexposure shifts are related to preexposure CF thresholds. Recovery of phase retardation is rapid; units exposed to successive 3-min tones of the same intensities with intervals of 10-14 min between exposures experienced similar changes in their patterns of temporal discharge. Micromechanical changes affecting stereocilia stiffness or structural alterations in the tectorial membrane of the amphibian papilla may underly the transitory phase shifts observed in traumatized anuran auditory fibers.     

Effects of interaural decorrelation and acoustic spectrum on detecting the motion of an auditory target

The ability to detect the motion of an auditory target based on dynamic changes in interaural time differences was measured as a function of interaural correlation and acoustic spectrum in a single-interval forced-choice design. Three subjects listened to headphone-presented noise containing a dynamic linear change in interaural delay (500 μs/s). The stimulus spectrum was broadband (0.1 to 10 kHz), highpass above 1.5 kHz, or lowpass below 1.2 kHz, and interaural correlation ranged from 0.1 to 1.0. Subject performance was nearly identical for the broadband and lowpass conditions, with near perfect detection for interaural correlations of 0.5 or greater, and above threshold (d′ > 1) detection for a correlation of 0.3. Performance was near random when the correlation was 0.1. In the highpass condition, performance rapidly deteriorated from substantially above threshold (d′ > 2) to random level as interaural correlation was reduced from 1.0 to 0.7. This rapid decline in performance at high frequencies may be explained in terms of interaural envelope decorrelation. The text was submitted by the authors in English.     

The acoustic and perceptual effects of two noise-suppression algorithms

Internal noise generated by hearing-aid circuits can be audible and objectionable to aid users, and may lead to the rejection of hearing aids. Two expansion algorithms were developed to suppress internal noise below a threshold level. The multiple-channel algorithm's expansion thresholds followed the 55-dB SPL long-term average speech spectrum, while the single-channel algorithm suppressed sounds below 45 dBA. With the recommended settings in static conditions, the single-channel algorithm provided lower noise levels, which were perceived as quieter by most normal-hearing participants. However, in dynamic conditions "pumping" noises were more noticeable with the single-channel algorithm. For impaired-hearing listeners fitted with the ADRO amplification strategy, both algorithms maintained speech understanding for words in sentences presented at 55 dB SPL in quiet (99.3% correct). Mean sentence reception thresholds in quiet were 39.4, 40.7, and 41.8 dB SPL without noise suppression, and with the single- and multiple-channel algorithms, respectively. The increase in the sentence reception threshold was statistically significant for the multiple-channel algorithm, but not the single-channel algorithm. Thus, both algorithms suppressed noise without affecting the intelligibility of speech presented at 55 dB SPL, with the single-channel algorithm providing marginally greater noise suppression in static conditions, and the multiple-channel algorithm avoiding pumping noises.     

Saturation of the acoustic waves produced by pulsed arcs

Rapid simultaneous measurements of the arc current and voltage and the emitted acoustic wave were made on a small 20 A DC arc in open air, which was subjected to current pulses ranging in amplitude from 0·4 kA to 40 kA and in rise time from 10^?4 s to 10^?7 s. The results show that for a rise time Δt < 10^?5s, the amplitude of the pressure wave generated by the arc no longer varies with Δt but remains constant for a given amplitude of the current pulse. An additional study shows that this saturation is accompanied by a modification in the electrical behaviour of the arc, which suggests that the observed saturation is due to the arc itself and not to absorption of the pressure wave in the surrounding air.     

Compensation strategies for a lip-tube perturbation of French [u]: an acoustic and perceptual study of 4-year-old children

The relations between production and perception in 4-year-old children were examined in a study of compensation strategies for a lip-tube perturbation. Acoustic and perceptual analyses of the rounded vowel [u] produced by twelve 4-year-old French speakers were conducted under two conditions: normal and with a 15-mm-diam tube inserted between the lips. Recordings of isolated vowels were made in the normal condition before any perturbation (N1), immediately upon insertion of the tube and for the next 19 trials in this perturbed condition, with (P2) or without articulatory instructions (P1), and in the normal condition after the perturbed trials (N2). The results of the acoustic analyses reveal speaker-dependent alterations of F1, F2, and/or F0 in the perturbed conditions and after the removal of the tube. For some subjects, the presence of the tube resulted in very little change; for others, an increase in F2 was observed in P1, which was generally reduced in some of the 20 repetitions, but not systematically and not continuously. The use of articulatory instructions provided in the P2 condition was detrimental to the achievement of a good acoustic target. Perceptual data are used to determine optimal combinations of F0, F1, and F2 (in bark) related to these patterns. The data are compared to a previous study conducted with adults [Savariaux et al., J. Acoust. Soc. Am. 106, 381-393 (1999)].     

金属点蚀过程声发射源机制研究

研究了腐蚀特别是点蚀过程产生应力波,即声发射(AE)的源机制,估算了单个钝化膜破裂所产生的薄板表面位移量级,并用实验进行了论证。作者提出,利用板波声发射理论加上参数识别方法,可将腐蚀过程产生的声发射信号同背景噪声相区别。