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Development of coarticulation in German children: Articulatory locus equations

  • December 2015
DOI:10.13140/RG.2.1.5098.8881
  • Conference: Ultrafest VII
  • At: Hog Kong
Authors:
Elina Rubertus at Universität Potsdam
Elina Rubertus
Dzhuma Abakarova at Universität Potsdam
Dzhuma Abakarova
Mark Tiede
Mark Tiede
Mark Tiede
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Jan Ries at Universität Potsdam
Jan Ries
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Abstract

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.
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Development of Coarticulation in German Children:
Articulatory Locus Equations
Background
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 language’s 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?
Predictions
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
a
, Dzhuma Abakarova
a
, Mark Tiede
b
, Jan Ries
a
, Aude Noiray
a
a
University of Potsdam,
b
Haskins Laboratories
Acknowledgements
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
rubertus@uni-potsdam.de
http://www.uni-potsdam.de/lola
References
[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.
Participants
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
impairment
Stimuli
Disyllabic trochaic pseudo words in
carrier phrase: /͜aɪnə/ C
1
V
1
C
2
V
2
• V
1
always tense
• C
1
≠ C
2
18 C
1
V
1
syllables x 3 times
in each of 2 contexts (C
2
)
108 stimuli in randomized blocks
Procedure
Repetition task in SOLLAR in child-friendly set-up
• Prerecorded auditory stimuli
• Participants’ repetitions recorded with
• Microphone (acoustic signal for formant detection & synchronization)
• Ultrasound (midsagittal tongue contour for articulatory analysis)
• Video camera (lip movement and head correction)
/i:/
/b/ /y:/ /b/
/d/ + /u:/ + /d/ + /ǝ/
/g/ /a:/ /g/
/e:/
/o:/
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) Children’s 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
2
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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... 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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Speech planning as an index of speech motor control maturity. 14th Annual Conference of the International Speech Communication Association
  • Jan 2013
  • 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