Articulatory movement characteristics of labial consonant productions by children and adults

One purpose of the present investigation was to attempt to better understand articulatory movement characteristics of children's speech, particularly as they might relate to the question of why acoustic measures of children's segment durations are often longer than those of adults. In order to address this issue and to consider other general characteristics of children's speech production development, a variety of data was obtained from three groups of children and from a group of adults using strain gauge instrumentation to monitor superior-inferior lip and jaw displacement and peak velocity. Results indicate that the children's peak velocity and articulatory displacement measures were in many respects quite similar to those of the adults, although certain differences were observed. For a number of measures, there were also few peak velocity or displacement differences observed among the three age groups of children, despite the fact that they spanned about a six-year age range. In general, it appears that even when children and adults produce consonant sounds that are perceptually "correct," articulatory differences can be observed among their productions.     

Effects of rate and bite block manipulations on kinematic characteristics of children's speech

The purpose of the present study was to investigate kinematic characteristics of the speech of children and adults under three speaking conditions. The effects of requiring subjects to produce speech stimuli were studied as they spoke: in a normal manner; at a faster than normal rate; and while holding a bite block between their molars to restrict mandibular movement. Using a strain gauge monitoring system, superior-inferior lip and jaw movement data were collected from 24 subjects--six in each of three groups of normally developing children and an adult control group. For the normal condition, it was found that net peak velocity (i.e., the sum of the peak velocities of the individual articulators) was quite comparable among the three groups of children and the adults. Net peak velocity increased significantly for all four groups of subjects when they spoke at a fast rate, but it did not increase significantly in the bite block condition. For most measures, there were typically no differences in peak velocity across the various speaking conditions when comparing the three groups of children to one another. In general, articulatory displacement data showed patterns quite similar to those of the peak velocity data. In addition to the displacement and peak velocity data, pilot data are discussed concerning temporal properties of articulatory phases and also concerning maximum, nonspeech articulatory gestures.     

Temporal characteristics of nasalization in children and adult speakers of American English and Korean during production of three vowel contexts

The purpose of this study was to identify and compare the temporal characteristics of nasalization in relation to (1) languages, (2) vowel contexts, and (3) age groups. Two distinct acoustic energies from the mouth and nose were recorded during speech production (/pamap, pimip, pumup/) using two microphones to obtain the absolute and proportional measurements on the acoustic temporal characteristics of nasalization. Twenty-eight normal adults (14 American English and 14 Korean speakers) and 28 normal children (14 American English and 14 Korean speakers) participated in this study. In both languages, adults showed shorter duration of nasalization than children within all three vowel contexts. The high vowel context revealed longer duration of nasalization than the low vowel context in both languages. There was no significant difference of temporal characteristics of nasalization between American English and Korean. Nasalization showed different timing characteristics between children and adults across vowel contexts. The results are discussed in association with developmental coarticulation and the relationship between acoustic consequences of articulatory events and vowel height.     

Lip-jaw and tongue-jaw coordination during rate-controlled syllable repetitions

The present study investigated the relationship between functionally relevant compound gestures and single-articulator component movements of the jaw and the constrictors lower lip and tongue tip during rate-controlled syllable repetitions. In nine healthy speakers, the effects of speaking rate (3 vs 5 Hz), place of articulation, and vowel type during stop consonant-vowel repetitions (/pa/, /pi/, /ta/, /ti/) on the amplitude and peak velocity of differential jaw and constrictor opening-closing movements were measured by means of electromagnetic articulography. Rather than homogeneously scaled compound gestures, the results suggest distinct control mechanisms for the jaw and the constrictors. In particular, jaw amplitude was closely linked to vowel height during bilabial articulation, whereas the lower lip component amplitude turned out to be predominantly rate sensitive. However, the observed variability across subjects and conditions does not support the assumption that single-articulator gestures directly correspond to basic phonological units. The nonhomogeneous effects of speech rate on articulatory subsystem parameters indicate that single structures are differentially rate sensitive. On average, an increase in speech rate resulted in a more or less proportional increase of the steepness of peak velocity/amplitude scaling for jaw movements, whereas the constrictors were less rate sensitive in this respect. Negative covariation across repetitions between jaw and constrictor amplitudes has been considered an indicator of motor equivalence. Although significant in some cases, such a relationship was not consistently observed across subjects. Considering systematic sources of variability such as vowel height, speech rate, and subjects, jaw-constrictor amplitude correlations showed a nonhomogeneous pattern strongly depending on place of articulation.     

Articulatory dynamics of loud and normal speech

A comparison was made between normal and loud productions of bilabial stops and stressed vowels. Simultaneous recordings of lip and jaw movement and the accompanying audio signal were made for four native speakers of Swedish. The stimuli consisted of 12 Swedish vowels appearing in an /i'b_b/ frame and were produced with both normal and increased vocal effort. The displacement, velocity, and relative timing associated with the individual articulators as well as their coarticulatory interactions were studied together with changes in acoustic segmental duration. It is shown that the production of loud as compared with normal speech is characterized by amplification of normal movement patterns that are predictable for the above articulatory parameters. In addition, it was observed that the acoustic durations of bilabial stops were shortened, whereas stressed vowels were lengthened during loud speech production. Two interpretations of the data are offered, viewing loud articulatory behavior as a response to production demands and perceptual constraints, respectively.     

The acoustic bases for gender identification from children's voices.

The purpose of this study was to examine the acoustic characteristics of children's speech and voices that account for listeners' ability to identify gender. In Experiment I, vocal recordings and gross physical measurements of 4-, 8-, 12-, and 16-year olds were taken (10 girls and 10 boys per age group). The speech sample consisted of seven nondiphthongal vowels of American English (/ae/ "had," /E/ "head," /i/ "heed," /I/ "hid," /a/ "hod," /inverted v/ "hud," and /u/ "who'd") produced in the carrier phrase, "Say /hVd/ again." Fundamental frequency (f0) and formant frequencies (F1, F2, F3) were measured from these syllables. In Experiment II, 20 adults rated the syllables produced by the children in Experiment I based on a six-point gender rating scale. The results from these experiments indicate (1) vowel formant frequencies differentiate gender for children as young as four years of age, while formant frequencies and f0 differentiate gender after 12 years of age, (2) the relationship between gross measures of physical size and vocal characteristics is apparent for at least 12- and 16-year olds, and (3) listeners can identify gender from the speech and voice of children as young as four years of age, and with respect to young children, listeners appear to base their gender ratings on vowel formant frequencies. The findings are discussed in relation to the development of gender identity and its perceptual representation in speech and voice.     

The relationship of vocal tract shape to three voice qualities

Three-dimensional vocal tract shapes and consequent area functions representing the vowels [i, ae, a, u] have been obtained from one male and one female speaker using magnetic resonance imaging (MRI). The two speakers were trained vocal performers and both were adept at manipulation of vocal tract shape to alter voice quality. Each vowel was performed three times, each with one of the three voice qualities: normal, yawny, and twangy. The purpose of the study was to determine some ways in which the vocal tract shape can be manipulated to alter voice quality while retaining a desired phonetic quality. To summarize any overall tract shaping tendencies mean area functions were subsequently computed across the four vowels produced within each specific voice quality. Relative to normal speech, both the vowel area functions and mean area functions showed, in general, that the oral cavity is widened and tract length increased for the yawny productions. The twangy vowels were characterized by shortened tract length, widened lip opening, and a slightly constricted oral cavity. The resulting acoustic characteristics of these articulatory alterations consisted of the first two formants (F1 and F2) being close together for all yawny vowels and far apart for all the twangy vowels.     

A modeling investigation of articulatory variability and acoustic stability during American English /r/ production

This paper investigates the functional relationship between articulatory variability and stability of acoustic cues during American English /r/ production. The analysis of articulatory movement data on seven subjects shows that the extent of intrasubject articulatory variability along any given articulatory direction is strongly and inversely related to a measure of acoustic stability (the extent of acoustic variation that displacing the articulators in this direction would produce). The presence and direction of this relationship is consistent with a speech motor control mechanism that uses a third formant frequency (F3) target; i.e., the final articulatory variability is lower for those articulatory directions most relevant to determining the F3 value. In contrast, no consistent relationship across speakers and phonetic contexts was found between hypothesized vocal-tract target variables and articulatory variability. Furthermore, simulations of two speakers' productions using the DIVA model of speech production, in conjunction with a novel speaker-specific vocal-tract model derived from magnetic resonance imaging data, mimic the observed range of articulatory gestures for each subject, while exhibiting the same articulatory/acoustic relations as those observed experimentally. Overall these results provide evidence for a common control scheme that utilizes an acoustic, rather than articulatory, target specification for American English /r/.     

Audibility-based predictions of speech recognition for children and adults with normal hearing

This study investigated the relationship between audibility and predictions of speech recognition for children and adults with normal hearing. The Speech Intelligibility Index (SII) is used to quantify the audibility of speech signals and can be applied to transfer functions to predict speech recognition scores. Although the SII is used clinically with children, relatively few studies have evaluated SII predictions of children's speech recognition directly. Children have required more audibility than adults to reach maximum levels of speech understanding in previous studies. Furthermore, children may require greater bandwidth than adults for optimal speech understanding, which could influence frequency-importance functions used to calculate the SII. Speech recognition was measured for 116 children and 19 adults with normal hearing. Stimulus bandwidth and background noise level were varied systematically in order to evaluate speech recognition as predicted by the SII and derive frequency-importance functions for children and adults. Results suggested that children required greater audibility to reach the same level of speech understanding as adults. However, differences in performance between adults and children did not vary across frequency bands.     

The acoustical significance of tongue, lip, and larynx maneuvers in rounded palatal vowels

The acoustical consequences of articulatory maneuvers of [y] are studied in model experiments in order to obtain insights into articulator programming and speech motor control by elucidating the role of each component maneuver of a speech segment in setting up vocal tract resonance conditions for the spectral features of the speech wave. The maneuvers of [y] are found to provide a maximum and stable plain-flat spectral contrast with [i]. The results can be generalized to different vocal tract sizes. Tongue retraction and larynx depression are rejected as compensations to counteract labial undershoot. Larynx depression is complementary to lip rounding and restores spectral sensitivity to palatal and pharyngeal tongue movements otherwise disturbed by the labial activity. Spectral sensitivity then remains the same for [i] and [y], and there is no need for separate compensation programs for each of these phones.     

Speech intelligibility and spatial release from masking in young children

Children between the ages of 4 and 7 and adults were tested in free field on speech intelligibility using a four-alternative forced choice paradigm with spondees. Target speech was presented from front (0 degrees); speech or modulated speech-shaped-noise competitors were either in front or on the right (90 degrees). Speech reception thresholds were measured adaptively using a three-down/one-up algorithm. The primary difference between children and adults was seen in elevated thresholds in children in quiet and in all masked conditions. For both age groups, masking was greater with the speech-noise versus speech competitor and with two versus one competitor(s). Masking was also greater when the competitors were located in front compared with the right. The amount of masking did not differ across the two age groups. Spatial release from masking was similar in the two age groups, except for in the one-speech condition, when it was greater in children than adults. These findings suggest that, similar to adults, young children are able to utilize spatial and/or head shadow cues to segregate sounds in noisy environments. The potential utility of the measures used here for studying hearing-impaired children is also discussed.     

Different phase-stable relationships of the upper lip and jaw for production of vowels and diphthongs.

Relational invariants have been reported in the timing of articulatory gestures across suprasegmental changes, such as rate and stress. In the current study, the relative timing of the upper lip and jaw was investigated across changes in both suprasegmental and segmental characteristics of speech. The onset of upper lip movement relative to the vowel-to-vowel jaw cycle during intervocalic bilabial production was represented as a phase angle, and analyzed across changes in stress, vowel height, and vowel/diphthong identity. Results indicated that the relative timing of the upper lip and jaw varied systematically with changes in stress and vowel/diphthong identity, while remaining constant across changes in vowel height. It appears that modifications in relative timing may be due to adjustments in the jaw cycle as a result of the compound nature of jaw movement for diphthongs as compared to vowels, with further modifications due to the effect of stress on these compound movements.     

Economy of effort in different speaking conditions. I. A preliminary study of intersubject differences and modeling issues

This study explores the hypothesis that clear speech is produced with greater "articulatory effort" than normal speech. Kinematic and acoustic data were gathered from seven subjects as they pronounced multiple repetitions of utterances in different speaking conditions, including normal, fast, clear, and slow. Data were analyzed within a framework based on a dynamical model of single-axis frictionless movements, in which peak movement speed is used as a relative measure of articulatory effort (Nelson, 1983). There were differences in peak movement speed, distance and duration among the conditions and among the speakers. Three speakers produced the "clear" condition utterances with movements that had larger distances and durations than those for "normal" utterances. Analyses of the data within a peak speed, distance, duration "performance space" indicated increased effort (reflected in greater peak speed) in the clear condition for the three speakers, in support of the hypothesis. The remaining four speakers used other combinations of parameters to produce the clear condition. The validity of the simple dynamical model for analyzing these complex movements was considered by examining several additional parameters. Some movement characteristics differed from those required for the model-based analysis, presumably because the articulators are complicated structurally and interact with one another mechanically. More refined tests of control strategies for different speaking styles will depend on future analyses of more complicated movements with more realistic models.     

Controlling changes in vocal tract resistance.

There is some evidence that speech aerodynamics follows the rules of a regulating system. The purpose of the present study was to assess how the speech system manages perturbations that produce "errors" within the system. Three experimental approaches were used to evaluate the physiological responses to an imposed change in airway resistance. The first involved subjects with varying degrees of velopharyngeal inadequacy. The second and third approaches involved noncleft subjects whose airway was perturbed by bleed valves and bite blocks during consonant productions. The pressure-flow technique was used to measure aerodynamic variables associated with the production of test consonants. The results of this study provide additional evidence that the speech system actively responds to perturbations in ways that tend to minimize a change in consonant speech pressures. The degree of success in stabilizing pressures appears to reflect the capability of the system to use whatever articulatory and respiratory responses are available.     

A qualitative dynamic analysis of reiterant speech production: phase portraits, kinematics, and dynamic modeling

The departure point of the present paper is our effort to characterize and understand the spatiotemporal structure of articulatory patterns in speech. To do so, we removed segmental variation as much as possible while retaining the spoken act's stress and prosodic structure. Subjects produced two sentences from the "rainbow passage" using reiterant speech in which normal syllables were replaced by /ba/ or /ma/. This task was performed at two self-selected rates, conversational and fast. Infrared LEDs were placed on the jaw and lips and monitored using a modified SELSPOT optical tracking system. As expected, when pauses marking major syntactic boundaries were removed, a high degree of rhythmicity within rate was observed, characterized by well-defined periodicities and small coefficients of variation. When articulatory gestures were examined geometrically on the phase plane, the trajectories revealed a scaling relation between a gesture's peak velocity and displacement. Further quantitative analysis of articulator movement as a function of stress and speaking rate was indicative of a language-modulated dynamical system with linear stiffness and equilibrium (or rest) position as key control parameters. Preliminary modeling was consonant with this dynamical perspective which, importantly, does not require that time per se be a controlled variable.     

Coherence in children's speech perception.

Studies with adults have demonstrated that acoustic cues cohere in speech perception such that two stimuli cannot be discriminated if separate cues bias responses equally, but oppositely, in each. This study examined whether this kind of coherence exists for children's perception of speech signals, a test that first required that a contrast be found for which adults and children show similar cue weightings. Accordingly, experiment 1 demonstrated that adults, 7-, and 5-year-olds weight F2-onset frequency and gap duration similarly in "spa" versus "sa" decisions. In experiment 2, listeners of these same ages made "same" or "not-the-same" judgments for pairs of stimuli in an AX paradigm when only one cue differed, when the two cues were set within a stimulus to bias the phonetic percept towards the same category (relative to the other stimulus in the pair), and when the two cues were set within a stimulus to bias the phonetic percept towards different categories. Unexpectedly, adults' results contradicted earlier studies: They were able to discriminate stimuli when the two cues conflicted in how they biased phonetic percepts. Results for 7-year-olds replicated those of adults, but were not as strong. Only the results of 5-year-olds revealed the kind of perceptual coherence reported by earlier studies for adults. Thus, it is concluded that perceptual coherence for speech signals is present from an early age, and in fact listeners learn to overcome it under certain conditions.     

Acoustical Analysis of Speech in Progressive Supranuclear Palsy

Background

Dysarthria often is an early and prominent clinical feature of progressive supranuclear palsy (PSP). Based on perceptual analyses, speech impairment in PSP reportedly consists of prominent hypokinetic and spastic components with occasional ataxic features.

Objective

To measure objectively and quantitatively different speech parameters in PSP as compared with Parkinson's disease (PD) by acoustical analysis and to correlate these parameters with disease duration, global motor, and speech impairment and with the subtype of disease (Richardson's syndrome [RS] vs parkinsonian type of PSP [PSP-P]).

Patients and Methods

Twenty-six patients with clinical diagnosis of PSP (n = 14 classified as RS and n = 12 classified as PSP-P) and 30 age- and gender-matched patients with clinical diagnosis of PD were tested. Speech examination was based on the acoustical analysis of a standardized four-sentence reading task. Several speech variables were measured to assess phonation, intonation variability, speech velocity, and articulatory precision. All participants were tested according to Unified Parkinson's Disease Rating Scale/Motor Score (UPDRS-III) and staged according to Hoehn and Yahr stages. Global speech intelligibility was evaluated on the basis of the UPDRS-III speech item.

Results

In the PSP group, speech velocity, intonation variability, and the fraction of intraword pauses as a measure of articulatory precision were significantly reduced, whereas the percentage of speech pauses was prolonged as compared with the PD group. Only in the male PSP patients, vowel articulation was found to be impaired. Global speech performance was worse in the PSP group in comparison with the PD group and showed a correlation to some distinct speech dimensions. No differences of speech variables were seen between RS and PSP-P patients.

Conclusions

PSP patients feature a mixed type of dysarthria with hypokinetic and spastic components that differ significantly from the speech performance of PD speakers. This probably reflects the widespread neuropathological changes in PSP comprising basal ganglia as well as pontine and further brainstem regions.     

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.     

Effects of frequency modulated tones and vowel formants on perioral muscle activity during isometric lip rounding

Two studies were conducted to assess the sensitivity of perioral muscles to vowel-like auditory stimuli. In one study, normal young adults produced an isometric lip rounding gesture while listening to a frequency modulated tone (FMT). The fundamental of the FMT was modulated over time in a sinusoidal fashion near the frequency ranges of the first and second formants of the vowels /u/ and /i/ (rate of modulation = 4.5 or 7 Hz). In another study, normal young adults produced an isometric lip rounding gesture while listening to synthesized vowels whose formant frequencies were modulated over time in a sinusoidal fashion to simulate repetitive changes from the vowel /u/ to /i/ (rate of modulation = 2 or 4 Hz). The FMTs and synthesized vowels were presented binaurally via headphones at 75 and 60 dB SL, respectively. Muscle activity from the orbicularis oris superior and inferior and from lip retractors was recorded with surface electromyography (EMG). Signal averaging and spectral analysis of the rectified and smoothed EMG failed to show perioral muscle responses to the auditory stimuli. Implications for auditory feedback theories of speech control are discussed.     

Effect of masker type and age on speech intelligibility and spatial release from masking in children and adults

Speech recognition in noisy environments improves when the speech signal is spatially separated from the interfering sound. This effect, known as spatial release from masking (SRM), was recently shown in young children. The present study compared SRM in children of ages 5-7 with adults for interferers introducing energetic, informational, and/or linguistic components. Three types of interferers were used: speech, reversed speech, and modulated white noise. Two female voices with different long-term spectra were also used. Speech reception thresholds (SRTs) were compared for: Quiet (target 0 degrees front, no interferer), Front (target and interferer both 0 degrees front), and Right (interferer 90 degrees right, target 0 degrees front). Children had higher SRTs and greater masking than adults. When spatial cues were not available, adults, but not children, were able to use differences in interferer type to separate the target from the interferer. Both children and adults showed SRM. Children, unlike adults, demonstrated large amounts of SRM for a time-reversed speech interferer. In conclusion, masking and SRM vary with the type of interfering sound, and this variation interacts with age; SRM may not depend on the spectral peculiarities of a particular type of voice when the target speech and interfering speech are different sex talkers.