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Development of coarticulation in German children: Articulatory locus equations



The present study investigates the development of coarticulation in German children between 3 and 7 years of age. To quantify coarticulation degree, we will not only apply the commonly used method of Locus Equations (LE) on the acoustic signal, but also on the articulation recorded with ultrasound, which so far has been rarely done in children (Noiray et al., 2013). This allows us to directly track dynamic movements instead of inferring (co)articulation from the acoustic signal. Coarticulation can be viewed as connecting single speech sounds by varying degrees of articulatory overlap. While some aspects of coarticulation are claimed to be universal, resulting from anatomic properties (e.g., overlap of labial consonants and lingual vowels), others are not that predictable and may be language-specific (e.g., vowel-to-vowel coarticulation). The way children acquire the coarticulatory patterns of their native language has been discussed intensively (i.e., holistic versus segmental theory). The present study extends previous work by investigating coarticulation with a broader set of phonemes, multiple age groups, and in both acoustics and articulation. Five cohorts of monolingual German children (3 to 7 years of age) as well as an adult control group are tested. Stimuli are elicited in a repetition task embedded in a child friendly setting. The prerecorded acoustic stimuli consist of disyllabic pseudo words following the pattern C1V1C2V2, preceded by the carrier word " eine " (/͜ aɪnə/). Within the stressed first syllable (C1V1), C1 is /b/, /d/, /g/, or /z/ and V1 one of the tense, long vowels /i/, /y/, /u/, /a/, /e/, and /o/. The second CV syllable consisting of the same consonant set as C1 plus the neutral vowel /ə/ is added to the syllable of interest such that C2 is never equal to C1, resulting in three different contexts per C1V1. In total, there are 72 different pseudo words. Besides the CV coarticulation within the pseudo word, the carrier phrase enables the investigation of V-to-V anticipatory coarticulation from V1 on the preceding schwa. At Ultrafest VII we will present the first results for CV coarticulation in the cohort of 5 year-olds and adults. During the recordings, children are comfortably seated in an adjustable car seat. They are recorded with a portable ultrasound system (Sonosite Edge, sr: 48Hz) with a small probe fixed on a custom-made probe holder. The probe holder was designed to allow for natural vertical motion of the jaw but prevent motion in the lateral and horizontal translations. It is positioned straight below the participant's chin to record the tongue on the midsagittal plane. Ultrasound video data are collected with synchronized audio speech signal (microphone Sennheiser, sr: 48 KHz) on a computer. In addition to tongue motion, a video camera (Sony, sr: 50Hz) records the participant's face to track the labial articulation as well as head and probe motion enabling us to correct the data from a jaw-based to a head-based coordinate system. As for the analysis, target words in the acoustic speech signal as well as relevant tongue data are extracted using custom-made Praat and Matlab programs. Acoustic LE measures of the CV coarticulation will be based on the F2 transitions between the very onset of V1 and its midpoint, while the articulatory analysis will focus on the highest tongue point's motion between C1 and V1. As the ultrasound allows us to track motion earlier than is visible in the acoustic signal, we will not only use the onset of the vowel but move further into the consonant to find early cues of the vowel's influence on the tongue shape.
Development of Coarticulation in German Children:
Articulatory Locus Equations
Coarticulation, defined as varying degrees of articulatory overlap between speech seg-
ments, is a crucial mechanism for fluency. When learning to speak, children have to develop
their languages coarticulatory patterns. No study has yet investigated CV coarticulation and
its development in German (but reanalysis for adults [1]). Tradition-
ally, acoustic Locus Equations (LE) are used to measure coarticu-
latory degree. Second formant frequencies at vowel onset and
midpoint are plotted on the y- and x-axis to obtain consonant-spe-
cific regression lines [e.g., 2, 3, 4]. Recently, LE metrics have been
successfully extended to articulation by plotting the horizontal posi-
tion of the highest point of the tongue instead of F2 [e.g. 5, 6].
Research Questions
1) What is the German coarticulation hierarchy for places of articulation in adults?
2) Do 5 year-old children already show the adult-like pattern?
3) Are vowel impacts evident only at the offset of consonants or already during the closure?
1) More coarticulation for labials and velars is expected than for alveolars.
2) Yes, as they did in other languages [e.g., 5], but we expect more variability in children.
3) We expect traces of the vowels already in the middle of the consonant.
Elina Rubertus
, Dzhuma Abakarova
, Mark Tiede
, Jan Ries
, Aude Noiray
University of Potsdam,
Haskins Laboratories
This work was supported by the DFG GZ: NO 1098/2-1
We thank the whole LOLA team for their great work: Helene
Killmer-Rumpf, Lisa Roehle, Liuba Carpova, Michelle
Golchert, Stefanos Tserkezis, & Stella Krüger.
Special thanks go to our adult and child participants (and their
parents) who made it easy and fun for us to collect our data.
Contact Information
Elina Rubertus
Laboratory for Oral Language Acquisition
University of Potsdam
Department Linguistics
[1] Iskarous, K., Mooshammer, C., Hoole, P., Recasens, D., Shadle, C. H., Saltzman, E., & Whalen, D. H. (2013).
The coarticulation/invariance scale: Mutual information as a measure of coarticulation resistance, motor synergy,
an articulatory invariance. JASA, 134.
[2] Gibson, T. & Ohde, R. N. (2007). F2 Locus equations: Phonetic descriptors of coarticulation in 17- to 22-
month-old children. JSLHR, 30.
[3] Sussman, H. M., Hoemeke, K. A., McCaffrey, H. A. (1992). Locus equations as an index of coarticulation for
place of articulation distinctions in children. JSHR, 35.
[4] Sussman, H. M., Duder, C., Dalston, E., & Cacciatore, A. (1999). An acoustic analysis of the development of
CV coarticulation: A case study. JSLHR, 42.
[5] Noiray, A., Ménard, L., & Iskarous, K. (2013). The development of motor synergies in children: ultrasound and
acoustic measurements. JASA, 133.
[6] Barbier, G., Perrier, P., Ménard, L., Payan, Y., Tiede, M.K., Perkell, J. S. (2013). Speech planning as an index
of speech motor control maturity. 14th Annual Conference of the International Speech Communication
Association (Interspeech 2013), Lyon : France
[7] Nittrouer, S., Studdert-Kennedy, M., & Neely, S. (1996). How children learn to organize their speech gestures:
Further evidence from fricative vowel syllables. JSHR, 39.
11 5-year-olds (4 f, age range: 5;00 - 5;07 y) & 4 adults (2 f, age range:
22 27 y), all native German speakers without known hearing or language
Disyllabic trochaic pseudo words in
carrier phrase: /͜aɪnə/ C
always tense
18 C
syllables x 3 times
in each of 2 contexts (C
108 stimuli in randomized blocks
Repetition task in SOLLAR in child-friendly set-up
Prerecorded auditory stimuli
Participantsrepetitions recorded with
Microphone (acoustic signal for formant detection & synchronization)
Ultrasound (midsagittal tongue contour for articulatory analysis)
Video camera (lip movement and head correction)
/b/ /y:/ /b/
/d/ + /u:/ + /d/ + /ǝ/
/g/ /a:/ /g/
1) Coarticulation hierarchy
Our data provide consistent evidence that the German
hierarchy of places of articulation regarding the
amount of coarticulation is
/b/ > /g/ >> /d/.
This corroborates with previous results from other
languages, suggesting this hierarchy to be universal.
Possibly because of biomechanical properties: As /b/ is
a labial consonant, the tongue is free to shape for the
upcoming vowel, allowing for a high degree of
coarticulation. /g/ is relatively free in its place of
articulation ranging from velar to palatal realizations
depending on the following vowel without affecting its
perception. For the alveolar /d/ in contrast, the tongue
is quite constrained in its shape, so anticipation of
upcoming vowels is only possible to a small extent.
2) Childrens coarticulation
The 5-year old children show exactly the same
coarticulation pattern as the adult control group.
Contrary to our expectations, their productions show
less variability than those of the adults, indicated by
higher r
values. However, the adult control group only
contains 4 speakers, while more variability in children
may be accounted for by a larger group size. Interest-
ingly, all consonants show a higher coarticulation
degree in children than in adults. This might be an
indication of less fine-grained articulatory movements
possibly resulting from an immature speech motor
control as suggested by the holistic theory [7].
3) Early impact of the vowel
In both cohorts we find strong impacts of the following
vowel not only at the offset of the consonant (C100),
but already at the temporal midpoint (C50).
Anticipation of the upcoming vowel thus starts early
and increases the closer we get to its midpoint (i.e.,
higher slopes for C100 than C50). Going even further
back in time would allow us to get an idea of how early
anticipatory coarticulation starts.
Traditional F2 Locus Equations
To compare these results from the articulatory domain
with the traditional measure of acoustic LEs, we are
currently working on a reliable formant detection
technique for child speech.
1. Introduction 2. Method
3. Data Analysis 5. Discussion & Conclusion
4. Results
Acoustic Processing
Semi-automatic labeling
Points of interest for the analysis:
Consonant midpoint (C50)
Consonant offset (C100)
Vowel midpoint (V50)
Articulatory Processing
Semi-automatic tongue contour detection at
C50, C100, & V50 using SOLLARContours in Matlab
Extraction of horizontal position (x) of the highest
point of the tongue dorsum (TD)
Statistical Analysis
Regression analyses for horizontal position of TD
at C50 versus V50
at C100 versus V50
Front Back
... The development of lingual coarticulation in alveolar stops produced by typically developing children has been addressed in a number of studies (e.g., Sussman et al., 1992;Goodell & Studdert-Kennedy, 1993;Sussman et al., 1999;Noiray et al., 2013;Rubertus et al., 2015;Zharkova et al., 2015b). Alveolar consonants in children's productions have generally been demonstrated to undergo smaller vowel-related coarticulatory effects than labial and velar consonants, thus yielding consonant-specific patterns similar to those observed in adults (cf. ...
... Similar findings for voiceless stops were reported in a study of 4-to-5-year-old Canadian French speaking children by Noiray et al. (2013), who, in addition to acoustic locus equations, used articulatory locus equations, based on horizontal changes of the highest point of the tongue. Smaller coarticulation for the alveolar stop than for non-alveolar stops has also been found in German speaking 5-year-old children, in an ultrasound study by Rubertus et al. (2015). Noiray et al. (2013) interpreted their results by referring to Iskarous et al. (2010), who showed that locus equations are directly related to an articulator synergy between the tongue body and the tongue tip. ...
... The study provided additional information to that reported in locus equation studies of coarticulation in children (e.g., Sussman et al., 1992;Sussman et al., 1999;Noiray et al., 2013;Rubertus et al., 2015). Specifically, ultrasound tongue shape data were used, including information on the root of the tongue. ...
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In this study, vowel-on-consonant lingual coarticulation at [t] closure offset was compared in 5-year-old children and 13-year-old adolescents. The study aimed to establish whether, by the end of the closure, children from the younger age group adjust the tongue shape to the following vowels to the same extent as adolescents. Ten 5-year-olds and ten 13-year-olds, all speakers of Scottish Standard English, produced [t]-vowel syllables with the vowels [i] and [a], in a carrier phrase. Measures of tongue shape based on midsagittal ultrasound imaging data were used to compare anticipatory coarticulation and within-speaker variability across groups. Both age groups changed the extent of tongue dorsum bunching in order to coarticulate the consonant with the following vowels. The 5-year-old children, unlike the adolescents, did not consistently modify the bunching location within the tongue curve to accommodate the tongue shape to that of the upcoming vowel. Token-to-token variability was significantly greater in the younger age group. The results suggest that vowel-on-[t] coarticulatory patterns produced by typically developing children are affected by the development of motor control, with articulatory constraints on the tongue limiting the extent of lingual coarticulation in 5-year-old children. The findings on typical coarticulation development are relevant for clinical practice, and they highlight the need for more detailed descriptions of how phonetic characteristics of speech sounds affect coarticulation throughout childhood.
... However the number of ultrasound studies of speech production in children has been steadily growing over the last decade, and methodological advances have led to younger age groups being targeted in research studies (e.g., Song et al., 2013;Magloughlin, 2016;Rubertus et al., 2015;Yip et al., 2015), as well as using quantification methods that could be employed to identify covert contrasts (e.g., Ménard and Noiray, 2011;Noiray et al., 2013;Klein et al. 2013;Zharkova et al., 2015aZharkova et al., , 2015b. ...
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Ultrasound tongue imaging has become a promising technique for detecting covert contrasts, due to the developments in data analysis methods that allow for processing information on tongue shape from young children. An important feature concerning analyses of ultrasound data from children who are likely to produce covert contrasts is that the data are likely to be collected without head-to-transducer stabilisation, due to the speakers’ age. This article is a review of the existing methods applicable in analysing data from non-stabilised recordings. The article describes some of the challenges of ultrasound data collection from children, and analysing these data, as well as possible ways to address those challenges. Additionally, there are examples from typical and disordered productions featuring covert contrasts, with illustrations of quantifying differences in tongue shape between target speech sounds.
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The study aims to investigate the development of coarticulation in 5-year old German children. The main goal was to examine the way different aspects of consonant production vary on a quantitative coarticulation -invariance scale as a function of age. To achieve this goal, we employed Mutual Information (MI), a method that has been used to measure coarticulation degree by quantifying independence between two variables (Iskarous et al., 2013).
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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. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America. The article can also be found at
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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.
Locus equations were investigated as a phonetic index for children's production of stop + vowel tokens. Locus equations are straight-line regression fits to data points formed by plotting onsets of F2 transitions along the ordinate and their corresponding midvowel nuclei along the abscissa. Such functions for adult speech have been found to be extremely linear with slope and y-intercept values contrastively distinctive across place of articulation. Sixteen children, aged 3-5 years, produced /bVt/, /dVt/, and /gVt/ tokens embedded in a carrier phrase and repeated in randomized order a minimum of three times. Six medial vowel contexts were used [i, I, ae, [symbol: see text], a, u]. Both individual and group mean scatterplots were extremely linear and highly remniscent of adult prototypes. While labial and velar slopes exhibited some degree of overlap, labial versus alveolar and alveolar versus velar slopes were significantly different. All y-intercepts as a function of place of articulation were significantly different. Compared to adult norms, intersubject variability of slope and y-intercept ranges were greater for children. Locus equations can provide a phonetic descriptor for a child's attainment of stop place categories seeking to achieve the adult standard of a balance between coarticulatory adjustments and contrastive distinctiveness.
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.
The general purpose of this research was to describe coarticulation across voiced stop consonant place of articulation in 10 children younger than 2 years of age. A total of 1,182 voiced stop CV productions was analyzed using the locus equation metric, which yielded 3 regression lines that described the relation of F2 onset and F2 vowel for /bV/, /dV/, and /gV/ productions. The results revealed significant differential effects for slope and y-intercept as a function of stop consonant place of articulation. The ordering of the mean slope values for stop consonant place of articulation was /g/>/b/ and /d/, indicating that /g/ was produced with significantly greater coarticulation than /b/ or /d/. However, the unique vowel allophonic pattern of [g] coarticulation reported in the literature for English-speaking adults was generally not learned by these young children. Group and individual coarticulation trends are described in relation to developmental theories of sound acquisition. Results suggest that early coarticulation patterns are phoneme specific.
Speech planning as an index of speech motor control maturity. 14th Annual Conference of the International Speech Communication Association
  • G Barbier
  • P Perrier
  • L Ménard
  • Y Payan
  • M K Tiede
  • J S Perkell
Barbier, G., Perrier, P., Ménard, L., Payan, Y., Tiede, M.K., Perkell, J. S. (2013). Speech planning as an index of speech motor control maturity. 14th Annual Conference of the International Speech Communication Association (Interspeech 2013), Lyon : France