Anticipatory coarticulation in the speech of adults and young children: acoustic, perceptual, and video data

Temporal, spectral and amplitude characteristics of the Greek fricative /s/ in hearing-impaired and normal-hearing speech

Fricatives, and especially sibilants, are very frequently misarticulated by speakers with hearing loss. Misarticulations can result in phonemic contrast weakening or loss, compromising intelligibility. The present study focuses on the examination of acoustic characteristics of the Greek alveolar fricative /s/, an articulatorily demanding sound, produced by young adult speakers with profound hearing impairment and with normal hearing. An array of variables was examined using mixed-effects and random forest models aiming to assess the effectiveness of various measures in differentiating hearing-impaired and normal-hearing /s/ production. Significant differences were found in spectral and amplitude measures, but not in temporal measures. In hearing-impaired speech, spectral slope and RMS amplitude had significantly lower values, indicating a more distributed spectrum, suggestive of decreased flow velocity through the fricative constriction. Also, a trend for concentration of energy at lower frequencies was observed suggesting more posterior fricative articulation than normal. Moreover, measures capturing the variation of frequency and amplitude over time revealed different patterns of sibilance development across time than normal, denoting the production of a less well-formed or less sibilant /s/ by speakers with hearing impairment. The investigation of contextual effects on /s/ in hearing-impaired speech showed increased spectral variance, negative skewness and lower kurtosis in the labial (rounded) context /u/ in relation to the nonlabial contexts /i/ and /a/, indicating a more diffuse, less compact spectrum with concentration at high frequencies. Findings are discussed in relation to previous literature on fricative production by speakers with hearing impairment and normal hearing in Greek and other languages.

Developmental differences in perceptual anticipation underlie different sensitivities to coarticulatory dynamics

Anticipatory coarticulation is an indispensable feature of speech dynamics contributing to spoken language fluency. Research has shown that children speak with greater degrees of vowel anticipatory coarticulation than adults - that is, greater vocalic influence on previous segments. The present study examined how developmental differences in anticipatory coarticulation transfer to the perceptual domain.Using a gating paradigm, we tested 29 seven-year-olds and 93 German adult listeners with sequences produced by child and adult speakers, hence corresponding to low versus high vocalic anticipatory coarticulation degrees. First, children predicted vowel targets less successfully than adults. Second, greater perceptual accuracy was found for low compared to highly coarticulated speech. We propose that variations in coarticulation degrees reflect perceptually important differences in information dynamics and that listeners are more sensitive to fast changes in information than to a large amount of vocalic information spread across long segmental spans.

Criteria for creating new standard reading passages for the assessment of speech and voice: A Delphi consensus study

Standard reading passages allow for the study of the integrated functions of speech and voice components in contextual, running speech, with target stimuli in a controlled environment. In both clinical practice and research, these texts provide rapid insight into the characteristics of the patient's speech, with fewer hesitations than in conversational speech and better predictability by the evaluator. Although a plethora of texts exist in different languages, they present various limitations. A specifically created standardised text in each language allowing for an ecological assessment of speech and voice functions, meeting most required criteria for standard speech and voice assessment and adapted to the target language's cultural and linguistic specificities, would therefore be an interesting option. However, no guidelines exist for the creation of such a reading passage. This article describes the international Delphi consensus study carried out to identify a minimal set of criteria to take into account when creating standard reading passages for an overall speech and voice assessment in adolescents and adults. This survey was conducted in three consecutive rounds; forty experts participated in the first round, with a total dropout of 17% from round 1 to round 3. It results in a minimal set of ten criteria which were selected by a majority of the experts and were rated as most important. This set contains five phoneme-level, two word-level, two sentence-level criteria and one global-level criterion. It can be used as a general guideline for the creation of standard reading passages in Indo-European Romance and Germanic languages such as English, French and German. The construction of a new reading passage in French following this guideline is briefly described.

The coarticulation-duration relationship in early Quechua speech

Evidence from acoustic and articulatory phonetics suggests that children coarticulate more than adults, but previous work has focused on the instantiation of coarticulation with phonology in a typologically homogeneous sample. The interplay of coarticulation with children's speaking rate has also been ignored. How do coarticulation and speaking rate (duration) interact over the course of development, and does the interaction manifest differently across distinct morphological environments? To answer this, the current study measured the speech patterns of bilingual Quechua-Spanish children (5-10 years) and adults. Coarticulation and duration were measured in two word environments, within morphemes and across morpheme boundaries. Unsurprisingly, adults consistently coarticulated more in shorter duration sequences, in both morphological environments. The children's coarticulation-duration patterns, however, varied by morphological environment. Additionally, the children's speech patterns, but not the adults', were sensitive to prosodic length: children produced increasingly shorter phones in words with more syllables. It is suggested that the differences between adults and children are attributable to adults' faster speaking rate and increased dominance in Quechua.

Practice and experience predict coarticulation in child speech

Much research in child speech development suggests that young children coarticulate more than adults. There are multiple, not mutually-exclusive, explanations for this pattern. For example, children may coarticulate more because they are limited by immature motor control. Or they may coarticulate more if they initially represent phonological segments in larger, more holistic units such as syllables or feet. We tested the importance of several different explanations for coarticulation in child speech by evaluating how four-year-olds' language experience, speech practice, and speech planning predicted their coarticulation between adjacent segments in real words and paired nonwords. Children with larger vocabularies coarticulated less, especially in real words, though there were no reliable coarticulatory differences between real words and nonwords after controlling for word duration. Children who vocalized more throughout a daylong audio recording also coarticulated less. Quantity of child vocalizations was more predictive of the degree of children's coarticulation than a measure of receptive language experience, adult word count. Overall, these results suggest strong roles for children's phonological representations and speech practice, as well as their immature fine motor control, for coarticulatory development.

Acquisition and Acoustic Patterns of Southern American English /l/ in Young Children

Purpose The aim of the current study was to examine /l/ developmental patterns in young learners of Southern American English, especially in relation to the effect of word position and phonetic contexts. Method Eighteen children with typically developing speech, aged between 2 and 5 years, produced monosyllabic single words containing singleton /l/ in different word positions (pre- vs. postvocalic /l/) across different vowel contexts (high front vs. low back) and cluster /l/ in different consonant contexts (/pl, bl/ vs. /kl, gl/). Each production was analyzed for its accuracy and acoustic patterns as measured by the first two formant frequencies and their difference (F1, F2, and F2-F1). Results There was great individual variability in /l/ acquisition patterns, with some 2- and 3-year-olds reaching 100% accuracy for prevocalic /l/, while others were below 70%. Overall, accuracy of prevocalic /l/ was higher than that of postvocalic /l/. Acoustic patterns of pre- and postvocalic /l/ showed greater differences in younger children and less apparent differences in 5-year-olds. There were no statistically significant differences between the acoustic patterns of /l/ coded as perceptually acceptable and those coded as misarticulated. There was also no apparent effect of vowel and consonant contexts on /l/ patterns. Conclusion The accuracy patterns of this study suggest an earlier development of /l/, especially prevocalic /l/, than has been reported in previous studies. The differences in acoustic patterns between pre- and postvocalic /l/, which become less apparent with age, may suggest that children alter the way they articulate /l/ with age. No significant acoustic differences between acceptable and misarticulated /l/, especially postvocalic /l/, suggest a gradient nature of /l/ that is dialect specific. This suggests the need for careful consideration of a child's dialect/language background when studying /l/.

What anticipatory coarticulation in children tells us about speech motor control maturity

PURPOSE

This study aimed to evaluate the role of motor control immaturity in the speech production characteristics of 4-year-old children, compared to adults. Specifically, two indices were examined: trial-to-trial variability, which is assumed to be linked to motor control accuracy, and anticipatory extra-syllabic vowel-to-vowel coarticulation, which is assumed to be linked to the comprehensiveness, maturity and efficiency of sensorimotor representations in the central nervous system.

METHOD

Acoustic and articulatory (ultrasound) data were recorded for 20 children and 10 adults, all native speakers of Canadian French, during the production of isolated vowels and vowel-consonant-vowel (V1-C-V2) sequences. Trial-to-trial variability was measured in isolated vowels. Extra-syllabic anticipatory coarticulation was assessed in V1-C-V2 sequences by measuring the patterns of variability of V1 associated with variations in V2. Acoustic data were reported for all subjects and articulatory data, for a subset of 6 children and 2 adults.

RESULTS

Trial-to-trial variability was significantly larger in children. Systematic and significant anticipation of V2 in V1 was always found in adults, but was rare in children. Significant anticipation was observed in children only when V1 was /a/, and only along the antero-posterior dimension, with a much smaller magnitude than in adults. A closer analysis of individual speakers revealed that some children showed adult-like anticipation along this dimension, whereas the majority did not.

CONCLUSION

The larger trial-to-trial variability and the lack of anticipatory behavior in most children-two phenomena that have been observed in several non-speech motor tasks-support the hypothesis that motor control immaturity may explain a large part of the differences observed between speech production in adults and 4-year-old children, apart from other causes that may be linked with language development.

Spoken Language Development and the Challenge of Skill Integration

The development of phonological awareness, the knowledge of the structural combinatoriality of a language, has been widely investigated in relation to reading (dis)ability across languages. However, the extent to which knowledge of phonemic units may interact with spoken language organization in (transparent) alphabetical languages has hardly been investigated. The present study examined whether phonemic awareness correlates with coarticulation degree, commonly used as a metric for estimating the size of children's production units. A speech production task was designed to test for developmental differences in intra-syllabic coarticulation degree in 41 German children from 4 to 7 years of age. The technique of ultrasound imaging allowed for comparing the articulatory foundations of children's coarticulatory patterns. Four behavioral tasks assessing various levels of phonological awareness from large to small units and expressive vocabulary were also administered. Generalized additive modeling revealed strong interactions between children's vocabulary and phonological awareness with coarticulatory patterns. Greater knowledge of sub-lexical units was associated with lower intra-syllabic coarticulation degree and greater differentiation of articulatory gestures for individual segments. This interaction was mostly nonlinear: an increase in children's phonological proficiency was not systematically associated with an equivalent change in coarticulation degree. Similar findings were drawn between vocabulary and coarticulatory patterns. Overall, results suggest that the process of developing spoken language fluency involves dynamical interactions between cognitive and speech motor domains. Arguments for an integrated-interactive approach to skill development are discussed.

Back From the Future: Nonlinear Anticipation in Adults' and Children's Speech

Purpose This study examines the temporal organization of vocalic anticipation in German children from 3 to 7 years of age and adults. The main objective was to test for nonlinear processes in vocalic anticipation, which may result from the interaction between lingual gestural goals for individual vowels and those for their neighbors over time. Method The technique of ultrasound imaging was employed to record tongue movement at 5 time points throughout short utterances of the form V1#CV2. Vocalic anticipation was examined with generalized additive modeling, an analytical approach allowing for the estimation of both linear and nonlinear influences on anticipatory processes. Results Both adults and children exhibit nonlinear patterns of vocalic anticipation over time with the degree and extent of vocalic anticipation varying as a function of the individual consonants and vowels assembled. However, noticeable developmental discrepancies were found with vocalic anticipation being present earlier in children's utterances at 3-5 years of age in comparison to adults and, to some extent, 7-year-old children. Conclusions A developmental transition towards more segmentally-specified coarticulatory organizations seems to occur from kindergarten to primary school to adulthood. In adults, nonlinear anticipatory patterns over time suggest a strong differentiation between the gestural goals for consecutive segments. In children, this differentiation is not yet mature: Vowels show greater prominence over time and seem activated more in phase with those of previous segments relative to adults.

Leveraging audiovisual speech perception to measure anticipatory coarticulation

A noninvasive method for accurately measuring anticipatory coarticulation at experimentally defined temporal locations is introduced. The method leverages work in audiovisual (AV) speech perception to provide a synthetic and robust measure that can be used to inform psycholinguistic theory. In this validation study, speakers were audio-video recorded while producing simple subject-verb-object sentences with contrasting object noun rhymes. Coarticulatory resistance of target noun onsets was manipulated as was metrical context for the determiner that modified the noun. Individual sentences were then gated from the verb to sentence end at segmental landmarks. These stimuli were presented to perceivers who were tasked with guessing the sentence-final rhyme. An audio-only condition was included to estimate the contribution of visual information to perceivers' performance. Findings were that perceivers accurately identified rhymes earlier in the AV condition than in the audio-only condition (i.e., at determiner onset vs determiner vowel). Effects of coarticulatory resistance and metrical context were similar across conditions and consistent with previous work on coarticulation. These findings were further validated with acoustic measurement of the determiner vowel and a cumulative video-based measure of perioral movement. Overall, gated AV speech perception can be used to test specific hypotheses regarding coarticulatory scope and strength in running speech.

On the development of gestural organization: A cross-sectional study of vowel-to-vowel anticipatory coarticulation

In the first years of life, children differ greatly from adults in the temporal organization of their speech gestures in fluent language production. However, dissent remains as to the maturational direction of such organization. The present study sheds new light on this process by tracking the development of anticipatory vowel-to-vowel coarticulation in a cross-sectional investigation of 62 German children (from 3.5 to 7 years of age) and 13 adults. It focuses on gestures of the tongue, a complex organ whose spatiotemporal control is indispensable for speech production. The goal of the study was threefold: 1) investigate whether children as well as adults initiate the articulation for a target vowel in advance of its acoustic onset, 2) test if the identity of the intervocalic consonant matters and finally, 3) describe age-related developments of these lingual coarticulatory patterns. To achieve this goal, ultrasound tongue imaging was used to record lingual movements and quantify changes in coarticulation degree as a function of consonantal context and age. Results from linear mixed effects models indicate that like adults, children initiate vowels’ lingual gestures well ahead of their acoustic onset. Second, while the identity of the intervocalic consonant affects the degree of vocalic anticipation in adults, it does not in children at any age. Finally, the degree of vowel-to-vowel coarticulation is significantly higher in all cohorts of children than in adults. However, among children, a developmental decrease of vocalic coarticulation is only found for sequences including the alveolar stop /d/ which requires finer spatiotemporal coordination of the tongue’s subparts compared to labial and velar stops. Altogether, results suggest greater gestural overlap in child than in adult speech and support the view of a non-uniform and protracted maturation of lingual coarticulation calling for thorough considerations of the articulatory intricacies from which subtle developmental differences may originate.

The dynamics of voiceless sibilant fricative production in children between 7 and 13 years old: An ultrasound and acoustic study

This study reports on dynamic tongue shape and spectral characteristics of sibilant fricatives /s/ and /ʃ/ in Scottish English speaking children aged between 7 and 13 years old. The sequences /əCa/ and /əCi/ were produced by 40 children, with ten participants in each age group, and two-year intervals between successive groups. Productions of the same sequences by ten adults were used for comparison with the children's data. Quantitative dynamic analyses were carried out on spectral information and on ultrasound imaging data on tongue shape. All age groups differentiated between the two consonants in the fricative centroid and in tongue shape. Vowel-on-consonant effects showed consonant-specific patterns across age groups without a consistent increase or decrease in the extent of coarticulation with increasing age. The extent of discriminability between the two fricatives increased with age on both acoustic and articulatory measures. Younger speakers were generally more variable than older speakers. Complementary findings from the centroid and tongue shape measures suggest that age-related differences are due to the ongoing maturation of controlling the tongue in coordination with other articulators, particularly the jaw, throughout childhood.

How Do Children Organize Their Speech in the First Years of Life? Insight From Ultrasound Imaging

PURPOSE

This study reports on a cross-sectional investigation of lingual coarticulation in 57 typically developing German children (4 cohorts from 3.5 to 7 years of age) as compared with 12 adults. It examines whether the organization of lingual gestures for intrasyllabic coarticulation differs as a function of age and consonantal context.

METHOD

Using the technique of ultrasound imaging, we recorded movement of the tongue articulator during the production of pseudowords, including various vocalic and consonantal contexts.

RESULTS

Results from linear mixed-effects models show greater lingual coarticulation in all groups of children as compared with adults with a significant decrease from the kindergarten years (at ages 3, 4, and 5 years) to the end of the 1st year into primary school (at age 7 years). Additional differences in coarticulation degree were found across and within age groups as a function of the onset consonant identity (/b/, /d/, and /g/).

CONCLUSIONS

Results support the view that, although coarticulation degree decreases with age, children do not organize consecutive articulatory gestures with a uniform organizational scheme (e.g., segmental or syllabic). Instead, results suggest that coarticulatory organization is sensitive to the underlying articulatory properties of the segments combined.

An Ultrasound Study of the Development of Lingual Coarticulation during Childhood

BACKGROUND/AIMS

There is growing evidence that coarticulation development is protracted and segment-specific, and yet very little information is available on the changes in the extent of coarticulation across different phonemes throughout childhood. This study describes lingual coarticulatory patterns in 6 age groups of Scottish English-speaking children between 3 and 13 years old.

METHODS

Vowelon-consonant anticipatory coarticulation was analysed using ultrasound imaging data on tongue shape from 4 consonants that differ in the degree of constraint, i.e., the extent of articulatory demand, on the tongue.

RESULTS

Consonant-specific age-related patterns are reported, with consonants that have more demands on the tongue reaching adolescent-like levels of coarticulation in older age groups. Within-speaker variability in tongue shape decreases with increasing age.

CONCLUSION

Reduced coarticulation in the youngest age group may be due to insufficient tongue differentiation. Immature patterns for lingual consonants in 5- to 11-year-olds are explained by the goal of producing the consonant target overriding the goal of coarticulating the consonant with the following vowel.

Fricative Contrast and Coarticulation in Children With and Without Speech Sound Disorders

PURPOSE

The purpose of this study was, first, to expand our understanding of typical speech development regarding segmental contrast and anticipatory coarticulation, and second, to explore the potential diagnostic utility of acoustic measures of fricative contrast and anticipatory coarticulation in children with speech sound disorders (SSD).

METHOD

In a cross-sectional design, 10 adults, 17 typically developing children, and 11 children with SSD repeated carrier phrases with novel words with fricatives (/s/, /ʃ/). Dependent measures were 2 ratios derived from spectral mean, obtained from perceptually accurate tokens. Group analyses compared adults and typically developing children; individual children with SSD were compared to their respective typically developing peers.

RESULTS

Typically developing children demonstrated smaller fricative acoustic contrast than adults but similar coarticulatory patterns. Three children with SSD showed smaller fricative acoustic contrast than their typically developing peers, and 2 children showed abnormal coarticulation. The 2 children with abnormal coarticulation both had a clinical diagnosis of childhood apraxia of speech; no clear pattern was evident regarding SSD subtype for smaller fricative contrast.

CONCLUSIONS

Children have not reached adult-like speech motor control for fricative production by age 10 even when fricatives are perceptually accurate. Present findings also suggest that abnormal coarticulation but not reduced fricative contrast is SSD-subtype-specific.

SUPPLEMENTAL MATERIALS

S1: https://doi.org/10.23641/asha.5103070. S2 and S3: https://doi.org/10.23641/asha.5106508.

The perceived clarity of children's speech varies as a function of their default articulation rate

The current study investigated whether variation in children's default articulation rate might reflect individual differences in the development of articulatory timing control, which predicts a positive correlation between rate and perceived clarity (motor skills hypothesis), or whether such variation is better attributed to speech external factors, which predicts that faster rates result in poorer target attainment (undershoot hypothesis). Two different speech samples were obtained from 54 typically developing children (5;2 - 7;11). Six utterances were extracted from each sample and measured for articulation rate and segmental duration. Fourteen adult listeners rated the utterances for clarity (enunciation). Acoustic correlates of perceived clarity, pitch, and vowel quality were also measured. The findings were that age-dependent and individual differences in children's default articulation rates were due to segmental articulation and not to suprasegmental changes. The rating data indicated that utterances produced at faster rates were perceived as more clearly articulated than those produced at slower rates, regardless of a child's age. Vowel quality measures predicted perceived clarity independently of articulation rate. Overall, the results support the motor skills hypothesis: Faster default articulation rates emerge from better articulatory timing control.

Spatial and temporal lingual coarticulation and motor control in preadolescents

PURPOSE In this study, the authors compared coarticulation and lingual kinematics in preadolescents and adults in order to establish whether preadolescents had a greater degree of random variability in tongue posture and whether their patterns of lingual coarticulation differed from those of adults. METHOD High-speed ultrasound tongue contour data synchronized with the acoustic signal were recorded from 15 children (ages 10-12 years) and 15 adults. Tongue shape contours were analyzed at 9 normalized time points during the fricative phase of schwa-fricative-/a/ and schwa-fricative-/i/ sequences with the consonants /s/ and /ʃ/. RESULTS There was no significant age-related difference in random variability. Where a significant vowel effect occurred, the amount of coarticulation was similar in the 2 groups. However, the onset of the coarticulatory effect on preadolescent /ʃ/ was significantly later than on preadolescent /s/, and also later than on adult /s/ and /ʃ/. CONCLUSIONS Preadolescents have adult-like precision of tongue control and adult-like anticipatory lingual coarticulation with respect to spatial characteristics of tongue posture. However, there remains some immaturity in the motor programming of certain complex tongue movements.

Toward improved spectral measures of /s/: results from adolescents

PURPOSE

This article introduces theoretically driven acoustic measures of /s/ that reflect aerodynamic and articulatory conditions. The measures were evaluated by assessing whether they revealed expected changes over time and labiality effects, along with possible gender differences suggested by past work.

METHOD

Productions of /s/ were extracted from various speaking tasks from typically speaking adolescents (6 boys, 6 girls). Measures were made of relative spectral energies in low- (550-3000 Hz), mid- (3000-7000 Hz), and high-frequency regions (7000-11025 Hz); the mid-frequency amplitude peak; and temporal changes in these parameters. Spectral moments were also obtained to permit comparison with existing work.

RESULTS

Spectral balance measures in low-mid and mid-high frequency bands varied over the time course of /s/, capturing the development of sibilance at mid-fricative along with showing some effects of gender and labiality. The mid-frequency spectral peak was significantly higher in nonlabial contexts, and in girls. Temporal variation in the mid-frequency peak differentiated ±labial contexts while normalizing over gender.

CONCLUSIONS

The measures showed expected patterns, supporting their validity. Comparison of these data with studies of adults suggests some developmental patterns that call for further study. The measures may also serve to differentiate some cases of typical and misarticulated /s/.

The development of motor synergies in children: ultrasound and acoustic measurements

The present study focuses on differences in lingual coarticulation between French children and adults. The specific question pursued is whether 4-5 year old children have already acquired a synergy observed in adults in which the tongue back helps the tip in the formation of alveolar consonants. Locus equations, estimated from acoustic and ultrasound imaging data were used to compare coarticulation degree between adults and children and further investigate differences in motor synergy between the front and back parts of the tongue. Results show similar slope and intercept patterns for adults and children in both the acoustic and articulatory domains, with an effect of place of articulation in both groups between alveolar and non-alveolar consonants. These results suggest that 4-5 year old children (1) have learned the motor synergy investigated and (2) have developed a pattern of coarticulatory resistance depending on a consonant place of articulation. Also, results show that acoustic locus equations can be used to gauge the presence of motor synergies in children.

The breadth of coarticulatory units in children and adults

PURPOSE

To assess, in children and adults, the breadth of coarticulatory movements associated with a single rounded vowel.

METHOD

Upper and lower lip movements were recorded from 8 young adults and 8 children (aged 4-5 years). A single rounded versus unrounded vowel was embedded in the medial position of pairs of 7-word/7-syllable sentences.

RESULTS

Both children and adults produced movement trajectories associated with lip rounding that were very broad temporally (i.e., movement duration lasting 45% to 56% of the sentence). Some effects appeared to extend across the entire utterance. There were no differences between children and adults in the extent of the coarticulatory effect. However, children produced relatively variable movements associated with lip rounding.

CONCLUSIONS

These data support the hypothesis that, for young children and adults, broad chunks of output have been planned by the onset of implementation of a sentence. This implies that, based on a change in a single phoneme, the motor commands to the muscles are altered for the production of the entire sentence.

Temporal features of articulation from childhood to adolescence: an electropalatographic investigation

This study was designed to investigate the development of articulatory timing from mid-childhood to late adolescence. Productions of sentences containing /t/, /l/, /s/, and /k/ were produced by 48 children and adults (aged 6-38 years) and captured using the Reading Electropalatography3 (EPG3) system. Mean duration of the sentences and the approach, closure/stable constriction, and release phases of consonant articulation were calculated. In addition, temporal coordination of lingual gestures and the intra-subject articulatory timing variation were investigated across the ages. Results reveal some distinct differences in duration and temporal coordination of lingual gestures between 6- to 7-year-olds and mature speakers, with continual refinement of articulatory control indicated into late adolescence. Differences in articulatory stability, in contrast, were not significant. The present findings may form a platform for development of a more descriptive model of motor speech development.

Articulation rate in preschool children: a 3-year longitudinal study

BACKGROUND

Speaking rate has implications for both clinical practice and an understanding of normal and disordered communication processes. Fundamental information on speaking rate is required by the clinician for the appropriate management of those disorders with disturbances of rate or those in which rate modification strategies are applied. One measure of speaking rate, articulation rate, excludes pause time and measures the speed with which articulators move. A developmental assessment of articulation rate is of particular interest because of its implications for changes in temporal motor aspects of speech production in development.

AIMS

The fundamental aim was to provide longitudinal and normative data on articulation rate in a group of preschool children. The following questions were asked. What are the articulation rates and variability in rate at ages 4, 5 and 6, and is there a developmental trend? Are speaking context, utterance length and gender significant variables?

METHODS & PROCEDURES

Speech samples from four speaking contexts, spontaneous, imitated, automatic (represented by nursery rhyme narration) and repetition, were elicited from 16 normally developing children (eight boys and eight girls) at ages 4, 5 and 6. Utterances were measured in syllables per second for runs of speech without pauses within each speaking context.

OUTCOMES & RESULTS

In contrast to expectation, articulation rate did not increase significantly with age. Neither did variability of rate decrease with age. Results suggest that the course of development is non-linear. Automatic speech and repetition were significantly faster than imitated speech. An interaction between imitated speech and variability was found at age 4. Considerable individual differences in rate were identified. There were no gender differences and no correlations between articulation rate and utterance length.

CONCLUSIONS

Unique information is provided on the development of speaking rate in preschool children together with additional normative data. The results have both theoretical and clinical implications. The data should assist the clinician in the assessment and diagnosis of rate and in rate modification management. Caution should be exercised in generalizing the results of the study in view of the small sample size and other factors.

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.

Perception of coarticulatory information in normal speech and dysarthria

PURPOSE

This study addressed three research questions: (a) Can listeners use anticipatory vowel information in prevocalic consonants produced by talkers with dysarthria to identify the upcoming vowel? (b) Are listeners sensitive to interspeaker variation in anticipatory coarticulation during prevocalic consonants produced by healthy talkers and/or talkers with dysarthria, as measured by vowel identification accuracy? (c) Is interspeaker variation in anticipatory coarticulation reflected in measures of intelligibility?

METHOD

Stimuli included 106 CVC words produced by 20 speakers with either Parkinson's disease or multiple sclerosis or by 16 healthy controls characterized by an operationally defined normal, under, or over level of anticipatory vowel coarticulation. Ten listeners were presented with prevocalic consonants for identification of the vowel. Ten additional listeners judged single-word intelligibility. An analysis of variance was used to determine differences in vowel identification accuracy and intelligibility as a function of speaker group, coarticulation level, and vowel type.

RESULTS

Listeners accurately identified vowels produced by all speaker groups from the aperiodic portion of prevocalic consonants, but interspeaker variations in strength of coarticulation did not strongly affect vowel identification accuracy or intelligibility.

CONCLUSIONS

Listeners appear to be tuned to similar types of information in the acoustic speech stream irrespective of the source or speaker, and any perceptual effects of interspeaker variation in coarticulation are subtle.

The emergence of mature gestural patterns in the production of voiceless and voiced word-final stops

The organization of gestures was examined in children's and adults' samples of consonant-vowel-stop words differing in stop voicing. Children (5 and 7 years old) and adults produced words from five voiceless/voiced pairs, five times each in isolation and in sentences. Acoustic measurements were made of vocalic duration, and of the first and second formants at syllable center and voicing offset. The predicted acoustic correlates of syllable-final voicing were observed across speakers: vocalic segments were shorter and first formants were higher in words with voiceless, rather than voiced, final stops. In addition, the second formant was found to differ depending on the voicing of the final stop for all speakers. It was concluded that by 5 years of age children produce words ending in stops with the same overall gestural organization as adults. However, some age-related differences were observed for jaw gestures, and variability for all measures was greater for children than for adults. These results suggest that children are still refining their organization of articulatory gestures past the age of 7 years. Finally, context effects (isolation or sentence) showed that the acoustic correlates of syllable-final voicing are attenuated when words are produced in sentences, rather than in isolation.

Variability in /s/ production in children and adults: evidence from dynamic measures of spectral mean

Previous research has found developmental decreases in temporal variability in speech. Relatively less work has examined spectral variability, and, in particular, variability in consonant spectra. This article examined variability in productions of the consonant /s/ by adults and by 3 groups of children, with mean ages of 3;11 (years;months), 5;04, and 8;04. Specifically, it measured the influence of age, phonetic context, and syllabic context on variability. Spectral variability was estimated by measuring dynamic spectral characteristics of multiple productions of /s/ in sV, spV, and swV sequences, where the vowel was either /a/ or /u/. Mean duration, variability in duration, and coarticulation were also measured. Children were found to produce /s/ with greater temporal and spectral variability than adults. Duration and coarticulation were comparable across the 4 age groups. Spectral variability was greater in swV contexts than in sV or spV sequences. The lack of consistent effects of phonetic context on spectral variability suggests that the developmental differences were related to subtle variability in place of articulation for /s/ in the children's productions.

An acoustic analysis of the development of CV coarticulation: a case study

This study analyzed stop consonant-vowel productions from babbling to meaningful speech in a single female child spanning the period from age 7 months to age 40 months. A total of 7,888 utterances (3,103 [bV], 3,236 [dV], and 1,549 [gV]) were analyzed to obtain frequencies at F2 onset and F2 at vocalic center for each utterance. A linear regression line ("locus equation") was fit to the cluster of F2 coordinates per stop place category produced during each month. The slope of the regression lines provided a numerical index of vowel-induced coarticulation on consonant productions. Labial, alveolar, and velar CV productions followed distinct articulatory paths toward adult-like norms of coarticulation. Inferences about the gradual emergence of segmental independence of the consonant and vowel in the three stop place environments were made from locus equation scatterplots and mean F2 onset and F2 midvowel frequencies obtained across babbling, early words, and natural speech.

Development of adaptive phonetic gestures in children: evidence from vowel devoicing in two different dialects of Japanese

High vowels between voiceless consonants are often devoiced in many languages, as well as in many dialects of Japanese. This phenomenon can be hypothesized to be a consequence of the adaptive organization of the laryngeal gestures to various conditions, including dialectal requirements. If this theory is correct, it may be possible to predict developmental changes in vowel devoicing based on the developmental improvement in the dialect-specific organization of the laryngeal gestures. To test this expectation, the developmental properties of vowel devoicing were investigated for 72 children of 4 and 5 years of age, and 37 adults in two dialects of Japanese. One was the Osaka dialect, with a low devoicing rate, and the other the Tokyo dialect, with a high devoicing rate. In the Tokyo dialect, the devoicing rate of children significantly increased and reached an adultlike level by the age of 5 years, whereas it remained low irrespective of age in Osaka. The vowel devoicing of 5-year-old children exhibited the same characteristics as that of the adults of their respective dialect. These results suggest that children growing up with the Tokyo dialect acquire the articulatory gestures which do not inhibit vowel devoicing by the age of 5 years, whereas children growing up with the Osaka dialect acquire those which inhibit the devoicing of vowels by the same age. The results fit in well with the predictions of the gestural account of vowel devoicing. It is also suggested that learning dialect-specific adaptive strategies to coordinate voicing and devoicing gestures as required to attain an adultlike vowel devoicing pattern is a long process: By the age of 5 years children have completed enough of this process to become members of their dialectal community.

A comparison of intergestural patterns in deaf and hearing adult speakers: implications from an acoustic analysis of disyllables

Coarticulation studies in speech of deaf individuals have so far focused on intrasyllabic patterning of various consonant-vowel sequences. In this study, both inter- and intrasyllabic patterning were examined in disyllables /symbol see text #CVC/ and the effects of phonetic context, speaking rate, and segment type were explored. Systematic observation of F2 and durational measurements in disyllables minimally contrasting in vocalic ([i], [u,][a]) and in consonant ([b], [d]) context, respectively, was made at selected locations in the disyllable, in order to relate inferences about articulatory adjustments with their temporal coordinates. Results indicated that intervocalic coarticulation across hearing and deaf speakers varied as a function of the phonetic composition of disyllables (b_b or d_d). The deaf speakers showed reduced intervocalic coarticulation for bilabial but not for alveolar disyllables compared to the hearing speakers. Furthermore, they showed less marked consonant influences on the schwa and stressed vowel of disyllables compared to the hearing controls. Rate effects were minimal and did not alter the coarticulatory patterns observed across hearing status. The above findings modify the conclusions drawn from previous studies and suggest that the speech of deaf and hearing speakers is guided by different gestural organization.

Acoustic characteristics of /s/ in adolescents

The goal of the current study was to construct a reference database against which misarticulations of /s/ can be compared. Acoustic data for 26 typically speaking 9- to 15-year-olds were examined to resolve measurement issues in acoustic analyses, including alternative sampling points within the /s/ frication; the informativeness of linear versus Bark transformations of each of the 4 spectral moments of /s/ (Forrest, Weismer, Milenkovic, & Dougall, 1988); and measurement effects associated with linguistic context, age, and sex. Analysis of the reference data set indicates that acoustic characterization of /s/ is appropriately and optimally (a) obtained from the midpoint of /s/, (b) represented in linear scale, (c) reflected in summary statistics for the 1 st and 3rd spectral moments, (d) referenced to individual linguistic-phonetic contexts, (e) collapsed across the age range studied, and (f) described individually by sex.

How children learn to organize their speech gestures: further evidence from fricative-vowel syllables

Previous studies with fricative-vowel (FV) syllables have shown that the difference in overall spectrum between fricatives is less in children's speech than in that of adults, but that fricative noises show greater differences in the region of the second formant (F2) as a function of the upcoming vowel than those of adults at corresponding points in the fricative. These results have been interpreted as evidence that children produce fricatives that are not spatially differentiated as those of adults and that children initiate vowel gestures earlier during syllable production than adults do (Nittrouer, Studdert-Kennedy, & McGowan, 1989). The goals of the present study were (a) to replicate the previous age-related difference for F2 with FV syllables; (b) to test the alternative interpretation that age-related differences in fricative f2 reflect age-related differences in vocal-tract geometry; (c) to determine whether age-related differences in F2 (and so, by inference, in articulatory organization) might extend beyond the syllable boundaries, perhaps into the schwa of a preceding unstressed syllable; and (d) determine if gestures other than fricative gestures show less spatial differentiation in children's than in adults' speech. To these ends, F2 frequencies were measured in schwa-fricative-vowel utterances (consisting of the fricatives /s/ and [symbol:see text] and of the vowels /i/ and /a/) from 40 speakers (10 each of the ages of 3, 5, 7 years, and adults) at three locations (for the entire schwa, for 10 ms of fricative noise centered at 30 ms before voicing onset, and 10 pitch periods from vocalic center). Results of several analyses supported four conclusions: (a) the earlier finding was replicated; (b) age-related differences in vocal-tract geometry could not explain the age-related difference in vowel effects on fricative noise; (c) children master intersyllabic gestural organization prior to intrasyllabic gestural organization; and (d) unlike fricative gestures, children's vowel gestures are more spatially distinct than those of adults.

Effects of lexical meaning and practiced productions on coarticulation in children's and adults' speech

This investigation examined the effect of familiarity with a speech target on the magnitude of the coarticulation observed in children (aged 3, 5, and 7 years) and adults. For the purposes of this investigation, coarticulation was defined as the effect that a following vowel, /i/ or /u/, had on the frequency value of the second formant (F2) in the preceding fricative, /s/ or /f/. Familiarity with the spoken targets was examined through the manipulation of two factors: (a) the presence or absence of lexical meaning and (b) the extent to which speakers were allowed to practice an item prior to recording. Results of acoustic measurements confirm that the children exhibited a greater effect of a following vowel on the preceding fricative when compared to adults. Nonmeaningful production items appeared to exhibit a greater effect of the vowel on the preceding fricative than meaningful production items, regardless of age of the individual. Limited motor practice did not have an effect on degree of fricative-vowel coarticulation in production items for any of the age groups. For the productions in this investigation, the primary coarticulatory effect was intrasyllabic.

Perception of coarticulatory cues in the speech of children with profound hearing loss and children with normal hearing

Two experiments investigated the perception of coarticulatory cues in the speech of children with profound hearing loss and children with normal hearing. To examine anticipatory coarticulation, five repetitions of the syllables [section i section u ti tu ki ku] produced by nine children with hearing loss and nine children with normal hearing were edited to include only the aperiodic consonantal portion. To explore perseveratory coarticulation, comparable segments were excised from the syllables [i section u section it ut it uk]. The stimuli had been analyzed previously in two acoustic studies of coarticulation (Baum & Waldstein, 1991; Waldstein & Baum, 1991). Ten listeners were presented with the aperiodic segment and were asked to identify the missing vowel. Overall, listeners' vowel identification was better for the productions by children with normal hearing than for those by children with hearing loss. In anticipatory contexts, listeners were able to identify the absent vowel with better-than-chance accuracy for all productions by both groups except the [i] tokens following [section] produced by children with hearing loss. In perseveratory contexts, identification accuracy was significantly above chance for all except the [i] tokens preceding [t] produced by children with normal hearing, but only for [u] tokens produced by children with hearing loss. Identification accuracy was better in anticipatory than in perseveratory contexts for both speaker groups' productions. The patterning of vowel identification, however, differed for the two speaker groups in anticipatory but not perseveratory contexts.

The emergence of mature gestural patterns is not uniform: evidence from an acoustic study

Previous studies investigating the organization of articulatory gestures present conflicting accounts of age-related differences in the execution of the articulatory gestures themselves and in the organization of those gestures. Several methodological differences may help to explain these contradictions: First, different studies have used different measures, all of which reflect vocal-tract activity to varying extents; second, the articulatory gestures being analyzed differed across studies; third, the phonetic composition of syllables has varied; and finally, utterance length, and therefore complexity, has varied across studies. The purpose of this study was to investigate the possibility that the reason these methodological differences have led to contradictory results is because the emergence of mature gestural patterns in children's speech is not uniform. To accomplish this goal, detailed acoustic analyses were performed on schwa-stop-vowel utterances from adults and from children (3, 5, and 7 years of age). Temporal measures showed that some acoustic segments were longer in children's than in adults' samples, whereas others were similar in duration. Formant frequencies indicated that vocal-tract opening and closing achieve adult-like patterns of movement by the age of 3 years, but children's tongue gestures are constrained by phonetic context more than those of adults until at least the age of 7 years. Taken together, these results suggest that the pace of development for learning to produce and to coordinate articulatory gestures is not uniform. Thus, the contradictions in findings among earlier studies may very well reflect differences in choices of measurement and utterances to be analyzed, both of which may lead to evaluations of different aspects of gestural patterning.

Acoustic evidence for the development of gestural coordination in the speech of 2-year-olds: a longitudinal study

Studies of child phonology have often assumed that young children first master a repertoire of phonemes and then build their lexicon by forming combinations of these abstract, contrastive units. However, evidence from children's systematic errors suggests that children first build a repertoire of words as integral sequences of gestures and then gradually differentiate these sequences into their gestural and segmental components. Recently, experimental support for this position has been found in the acoustic records of the speech of 3-, 5-, and 7-year-old children, suggesting that even in older children some phonemes have not yet fully segregated as units of gestural organization and control. The present longitudinal study extends this work to younger children (22- and 32-month-olds). Results demonstrate clear differences in the duration and coordination of gestures between children and adults, and a clear shift toward the patterns of adult speakers during roughly the third year of life. Details of the child-adult differences and developmental changes vary from one aspect of an utterance to another.