Temporal Aspects of Aerodynamic Segments of Velopharyngeal Coarticulation in Children and Adults
Fadwa Khwaileh. MA
Seunghee Ha. PhD
University of Tennessee, Knoxville
Coarticulation
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Coarticulation refers to the fact that a phonological segment is not realized identically in all environments, but often varies adhering to the characteristics of an adjacent segment (Kühnert & Nolan, 1999).
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two types of coarticulatory effects: z Forward (anticipatory) articulators are adjusted during a previous segment in anticipation for the following phonetic segment (Kent & Minifie, 1977)
z Backward (carryover) a given sound is affected by the sounds preceding it
Velopharyngeal Coarticulation
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Refers to the spreading of the articulatory effect of the nasal sound onto adjacent segments
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In VNC sequence, velar lowering coincids with the tongue movement toward the position of the vowel
In NVC sequence velar elevation started during or after oral constriction for the nasal (Kent, Carney & Severeid 1974)
This pattern of movement is responsible for the vowels before and after the nasal to be nasalized.
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deviation causes excessive nasality to be perceived. Velopharyngeal Coarticulation
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The knowledge of the extent of VPC is important in clinical settings
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The differentiation between normal and abnormal degrees of nasality is crucial to intervention decisions. An acoustic study found that the degree of anticipatory and carryover VPC in children with a repaired cleft palate was greater than in normal children (Ha, Sim, Zhi, & Kuehn 2004) .
Developmental patterns of VP
coarticulation
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Studies yielded inconsistent results regarding antic. VPC
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Adults showed greater antic.VPC than children,
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Greater nasal airflow at the midpoint of the initial vowel in /ini/ with
increasing age ( Thomson & Hixon, 1979).
Similar extent and degree of nasalization b/w children and
adults(Flege, 1988).
Adults demonstrate shorter proportional duration of antic. VPC than
children (Ha & Kuehn, 2006)
Studies agreed that children & adults show similar degree
of carr. VPC
Different underlying mechanisms: (Bell-Berti, 1993).
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Antic. coarticulation involves high neuromotor control,
Carr.coarticulation is largely attributed to mechanical and inertial
forces acting on the articulators
Effect of vowel height on VPC
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Studies reported that in nasal contexts, high vowels are realized
with less VP opening than low vowels. (Al-Bamerni, 1983; Bell-Berti et al., 1979)
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Acoustic studies reported longer duration for VPC effect on high
vowels compared to low vowels. (Ha et al., 2004; Ha & Kuehn, 2006)
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Aerodynamic studies reported nasal airflow was found to be
substantially greater for high vowels than for the low vowels in
vowel-nasal contexts (Lubker & Moll, 1965; Young, Zajac, Mayo & Hooper, 2001)
z Increased tongue height results in an increased
constriction in the oral cavity, more air is directed through
the nasal cavity (Hajek, 1997)
Purpose of the study
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To compare the temporal domain of antic. and carr.
VPC b/w children and adults by measuring duration
of nasal airflow segments.
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To determine the effect of vowel height on the
duration of antic.VPC.
Participants
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A total of 26 subjects participated
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9 younger children (5-8 years-old). 6 males, 3 females
9 older children (9-11 years-old). 5 males, 4 females
8 adults (18+ years-old). 4 males, 4 females
No history of speech, language, hearing problems,
or orofacial anomalies
No upper respiratory infections at the time of the
data collection.
English as their first language.
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3 children were bilingual
Speech Sample
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Subjects produced
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/ama/ 5 times X 3 trials
/imi/ 5 times X 3 trials
Participants used self-determined rate, pitch and
loudness
Practiced the test words before collecting speech
samples
Instrumentation
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Pressure-flow technique
Temporal Measurements
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Temporal measurements are defined as the
following
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Total word duration
Nasal onset interval
Nasal consonant interval
Nasal offset interval
10% of peak nasal flow
Statistical Analyses
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Proportional duration was calculated to control the
influence of different speech rates Ratios were measured
by dividing each interval into the total word duration X 100.
Means and st.dev. for prop. durations
Repeated measures of ANOVA was used to determine
possible age (three levels), vowel height (two levels)
effects.
Post hoc for differences among age groups.
Results
Age group effect
Significant age group
effect on the duration of
antic. VPC (F = 16.65,
P = 0)
z Younger children are
sig. different than both
older children and
adults (P =0)
zNo sig. Diff. b/w older
children and adults
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sig. Age group
effect on the duration of
nasal cons. And
duration of carr.VPC (F
=.749, P > .05), (F =
1.255, P > .05)
40.0
35.0
30.0
T i m e (m s )
zNo
Duration of nasal flow segments in /ama/
25.0
adults
20.0
15.0
older children
young children 10.0
5.0
0.0
onset /ama/
nasal/ama/
offset/ama/
Age group effect
zSignificant
zNo
sig. Age group effect
on the duration of nasal
cons. And duration of
carr.VPC (F =.695, P >
.05), (F = 2.713, P > .05)
Duration of nasal flow segments in /imi/
T i m e (m s )
age group
effect on the duration of
antic. VPC (F = 13.451, P
= 0)
z Younger children are sig.
different than both older
children (P =0) and adults
(P =.004)
zNo sig. Diff. b/w older
children and adults (P >
.05)
45
40
35
30
25
20
15
10
5
0
adults
older children
young children onset /imi/
nasal/imi/
offset/imi/
Vowel height effect on
duration of antic. VPC
zNo
zDuration
of nasal airflow is
not affected by vowel height
• Volume of nasal airlfow
Vowel height effect om anti. VPC
35
30
25
T i m e (m s )
sig. Vowel height effect
on the duration of antic. VPC
across all age groups (F =
.021, P > .05)
zNo sig. Interaction between
vowel height and age group
(F = .806, P > .05)
20
onset /ama/
15
onset /imi/
10
5
0
adults
older children
young children
Discussion
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Duration of carr.VPC was similar for all age groups.
Consistient with previous studies (e.g, Ha & Kuehn, 2006)
Duration of carr. VPC was longer than the duration
of antic. VPC for all age groups
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Results supports the idea of different underlying
mechanisms for anti. and carr. Coarticulatory effects
(Bell-Berti,
1993)
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Antic. Coarticulation involves high motor control of the
speech mechanism.
Carr. Coarticulation involves mechanical and enertial
forces which might be constant in children and adults
Discussion
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Younger children show longer antic. VPC than
adults and older children.
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Children may have taken longer time than adults to
achieve oral constriction following velum lowering for the
nasal consonant
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Children take more time to organize their speech
(Nittrouer et al. 1989)
Discussion
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Duration of antic. VPC in high vowel context
is not different from low level context.
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Duration of the nasal airflow segment is not
related to the increased perception of nasality in
high vowel contexts compared to low vowels
ones.
Direct association between nasal airflow
magnitude and vowel height (Lubker & Moll, 1965; Young, Zajac, Mayo
& Hooper, 2001)
Conclusions
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Anticipatory and carryover coarticulation have
different underlying mechanisms
VPC patterns in older children (9-11 years of
age) is similar to those of adults and different
than those of younger children (5-8 years of
age).
Increased perceived nasality on high vowel
context is related to magnitude of nasal flow
rather than duration of nasal flow
References
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