Speech Motor Deficits in
Cerebral Palsied Children:
An Acoustic-Perceptual Approach
Emily Lin, PhD1, Chia-Ling Chen, MD, PhD2, 3, & Chao-Chin Lee, BSLT1
1Department
of Communication Disorders, University of Canterbury, Christchurch, New Zealand
2Department of Physical Medicine and Rehabilitation, Chang Gung Memorial and Children Hospital,
Taoyuan, Taiwan
3Department of Physical Therapy, Chang Gung University, Taoyuan, Taiwan
The 5th Asia Pacific Conference on Speech, Language and Hearing
Brisbane, Australia
July 9-13, 2007
Research Question
• What are the acoustic measures useful for
detecting incorrect speech productions in
children with cerebral palsy?
Why Acoustic Measures?
• Acoustic recording is non-invasive.
• Acoustic signal is
• Objective/instrumental
• A link between speech production and perception,
allowing for assessment of:
– Placement/movement of articulators (e.g., tongue) or vocal tract
configuration
– Speech intelligibility
Purpose of the Study
• To identify acoustic measures sensitive to
changes of speech motor control in cerebral
palsied children related to the perception of
speech production errors
Cerebral Palsy (CP)
Definition (Blaire & Watson, 2006):
• a disorder of movement or posture
• related to static (non-progressive) abnormality in the brain
• acquired early in life (before or after birth; when the brain is
still immature and developing)
Prevalence:
• 1 (Cerebral Palsy Society of New Zealand, 2000) or 2 (Platt & Pharoah,
1995; Blair, 2001; Hagberg, Hagberg, Beckung & Uvebrant, 2001) per
1000 live births.
Motor Signs of CP
•
•
•
•
•
•
•
•
Rigidity
Flaccidity
Spasticity (increased rigidity in a group of muscles)
Ataxia (poor coordination)
Dyskinesia (jerky motion)
Athetosis (weak but controllable movement)
Tremor
Chorea (involuntary uncontrollable movements of
body and face along with marked incoordination of
limbs)
(Little, 1862)
(Denhoff, 1976;
Hagberg & Mallard, 2000;
Blair & Stanley, 1993;
Stanley, 1997)
(Blair & Stanley, 1993;
Stanley, 1997)
Intrauterine
viral infections
e.g. Rubella &
CytomegaloCytomegalovi
virus
(CMV)
rus (CMV)
Maternal
thyroid
abnormalities
Birth
Asphyxia
Low
gestation
age
Cerebral
Palsy
(Denhoff, 1976;
Blair & Stanley, 1997;
Hagberg et al., 2001)
Low Apgar
scores
(Nelson &
Ellenberg,
1981)
(Risk Factors)
(Amin-Zaki, Majeed,
Elhassani et al., 1979;
Stanley, 1997)
Perinatal
exposure:
Methyl
mercury
Multiple
gestation
Iodine
deficiency
(Pharoah, Buttfield & Hetzel, 1971)
Male
gender:
1.9:1 to
0.99:1
(M:F)
(Nelson & Grether, 1999)
(Blair & Stanley, 1997)
Cerebral Palsy (CP)
Diagnosis:
Types of CP:
Prevalence:
(Cerebral Palsy Society of New
Spastic CP
Athetoid CP
Ataxic CP
70-80%
10-20%
5-10%
Zealand, 2007)
Damage to the:
(Rutherford, 1950)
● Pyramidal tract,
motor cortex /
corticospinal tract
● Improper
absorption of
GABA
● Hypertonicity
Characterized by:
(Levitt, 1995; Rutherford, 1950)
● Varies in degree of
intelligence (may be
more impaired than
athetoid CP)
● Epilepsies
● Abnormalities of the
rib cage
● Extrapyramidal
motor system &/or
● Pyramidal tract &
● Cerebellum
● Basal ganglia
● Hypertonicity &
hypotonicity – changes
with time
● Balancing issues
● Athetosis
● Disturbed
awareness of motion &
sense of direction
● Intelligence varies
from good to very high
● Visual and auditory
processing
● Emotionally labial
● Intellectual
impairment
Articulation
(Kent, Netsell, & Abbs, 1978)
(Hixon & Hardy, 1964)
Prosody
Prosody
•↓ rate
• Slow rate
•Short phrases
Arythmatic
• •Arhymatic
•Imprecise
consonants
•Distorted vowels
Spastic/
weak
muscle tone
& impaired
coordination
↓ Speech Intelligibility
↓ Speech Naturalness
Voice
•Dysarthria
•Harsh quality
•Strain & strangle
quality
•Pitch breaks
(Andrews, 1999)
Resonance
•Hypernasality
(Hardy, 1961; Kent & Netsell, 1978)
Speech Pattern in CP
• Dysarthria* is often found in CP speech
– Frequency of dysarthria in CP: 31%-88%
* Dysarthria is characterized by centralized vowel articulation as well as
reduced articulatory precision for fricatives and affricates (Ansel and
Kent, 1992)
• Highly variable:
Pattern and severity depends on the underlying
pathophysiology
– Spastic CP: low pitch, hypernasality, pitch breaks, breathy voice,
excess & equal stress (Workinger & Kent, 1991)
– Athetoid CP: irregular articulatory breakdowns, inappropriate
silences, prolonged intervals and speech sounds, excessive loudness
variation, voice breaks
(Yorkston, Beukelman, Strand, & Bell, 1999)
Vowel Space (F1-F2 Plot)
Formants 1 (F1) & 2 (F2):
• Critical to vowel
perception (Peterson &
Barney, 1952)
• F1 relates to tongue
height & F2 to tongue
advancement (Kent et
al., 1999)
• Related to overall
speech intelligibility
(Turner, Tjaden &
Weismer, 1995; Ansel
& Kent, 1992; Liu,
Tsao & Kuhl, 2005;
Liu, Tseng & Tsao,
2000; Whitehill &
Ciocca, 20)
Multiple
Sclerosis (MS)
Tjaden &
Wilding (2004)
• MS (N=15), PD
(N=12) & controls
(N=15)
• Corner vowels: /i/,
/a/, /ӕ/ & /u/ in
habitual, loud & slow
(passage)
• Perceptual analysis
& Acoustic analysis
• Size of vowel
working space area &
speech intelligibility
seems to be unrelated
in MS group
Tjaden &
Wilding (2005)
Amyotrophic
Lateral
Sclerosis (ALS)
Weismer, Martin,
Kent & Kent (1992)
Turner, Tjaden &
Weismer (1995)
Weismer, Laures,
Jeng, Kent & Kent
(2000)
• ALS (N=10) & controls
(N=19)
• Corner vowels: /ӕ/, /a/
& /u/ in habitual & fast
speaking rate
• Perceptual analysis &
Acoustic analysis
• Increased rate resulted
in reduced vowel
working space, but no
change in speech
intelligibility
Weismer, Jeng,
Laures, Kent &
Kent (2001)
Tjaden, Rivera,
Wilding & Turner
(2005)
Parkinson’s
Disease (PD)
Weismer et al.
(2001)
• PD (N=10), ALS
(N=10) & controls
(N=19);
• Corner vowels: /i/,
/ӕ/, /a/ & /u/ in
habitual rate &
intensity;
• Perceptual analysis
& Acoustic analysis;
• Vowel working
space reduced (no
significance for PD);
correlated with
speech intelligibility
(reduced in both
groups)
Tjaden &
Wilding (2004)
Tjaden et
al.(2005)
Cerebral
Palsy (CP)
Normal
Speakers
Liu et al. (2005)
Fourakis (1991)
• Mandarin speakers
with CP (N=20) &
controls (N=10);
• 9 vowels in different
• Corner vowels: /i/,
/a/ & /u/ in habitual
speaking rate;
• Perceptual analysis
& Acoustic analysis;
• Significant
correlation between
vowel working space
& speech intelligibility
• Healthy individuals
(N=8 )
rate & stress
• Vowel working space
was largest during slow
stressed speech
Bradlow, Toretta
& Pisoni (1996)
• Healthy individuals
(N= 20)
• Vowels: /i/, /a/ & /oʊ/
in habitual speaking
rate
• Perceptual analysis &
Acoustic analysis
• Increased vowel
space area were
positively correlated
with increased
intelligibility
Summary of Literature Review
• Spastic type is most prevalent in CP.
• Dysarthria is a common feature in CP speech.
• Involuntary abnormal prosodic pattern can be
an indication of speech motor deficits.
• Acoustic-perceptual studies revealed a positive
relationship between vowel space and speech
intelligibility in CP, suggesting that vowel
space may be a useful acoustic measure for
detecting speech motor difficulties.
Hypothesis
• Acoustic difference between incorrectly and
correctly produced speech sounds can be used
to detect subtle articulatory changes and reflect
loss of phonemic contrast (and thus
compromised speech intelligibility).
Research Design
• Subjects as own controls
• Compare error rates in producing different
phonemic contrasts
• Describe the temporal and spectral
characteristics of the acoustics of the
incorrectly produced vowels and consonants
Method
• Convenience sampling:
– Cerebral Palsied Children referred to the Department
of Pediatric Rehabilitation at Chang-Gung Memorial
Hospital (Tao-Yuan, Taiwan) in 2005
• Subject Selection:
– Inclusion criteria:
 Cerebral palsied children
 Native speakers of Mandarin
– Exclusion criteria:
 Mental retardation
 Hearing impairment
 Cognitive and sensory impairment
 Epilepsy
Subjects
• Age: 7 – 15 years
• 1 female (spastic quadriplegia*) and
5 males (2 spastic quadriplegia & 3 spastic diplegia*)
*Quadriplegia: four limb involvement with unsymmetrical
severity on two sides;
Diplegia: four limb involvement with symmetrical severity on
both sides and with the lower limb involvement usually more
severe than the upper limb
Subject’s Task
• Read a list of 140 Mandarin 2-word phrases
[CV(N)-CV(N)]* containing minimal pairs
contrasting consonants (21), vowels (16), and
tones (4)
– Each of the 140 items was read twice in a sequence
– Words were presented in the form of orthography with
phonemic transcription on the side.
– Examples:
“ratio”: /pi3 li4/
“grain of rice”: /mi3 li4/
* C = consonant; V = vowel; N = nasal
Recording Procedure
• Subject seated in a quiet room and asked to
perform subject’s task, with the recording
device in place.
– Microphone placed 15 cm from the lips
– Direct digitization (Sampling rate: 44KHz)
– No modeling was provided
Listeners and Listener’s Task
• Two native Mandarin speakers trained in the field of
•
speech pathology
Error Identification Task:
– Listen to acoustic signals played back through a computer
sound card and speakers
• One 2-word phrase at a time
• Repeated listening allowed
– Circle, on the word list, vowels, consonants, and tones
perceived to be incorrectly produced
– Perform the task individually, being blind to the CP type
– Repeat the whole session a second time (for reliability
analysis)
Acoustic Measurement
•
Temporal measures:
–
–
–
•
Formant analysis of vowels (Baken, 1987) :
–
–
•
Syllable length
Consonant length
Vowel length
Formant 1 frequency (F1)
Formant 2 frequency (F2)
FFT spectral moment analysis of consonants
(Forrest, Weismer, Milenkovic, & Dougall, 1988):
–
–
Moment 1 (M1): mean
Moment 2 (M2): standard deviation
Analysis Software
• TF32 (copyright:
2000 Paul Milenkovic)
– Time lengths of individual vowels & consonants
– F1 & F2 frequencies: LPC (Linear Predictive
Coding) algorithm
• PRATT (copyright:
– Moment analysis
2005 Paul Boersma & David Weenink)
Reliability
• Perceptual identification of production errors:
– Intra-judge total reliability:
• Consonant: 88.4%, 92.4%
• Tone: 86.7%, 84.9%
• Vowel: 81.5%, 84.7%
– Inter-judge total reliability:
• Consonant: 85.4%
• Vowel: 80.6%
• Tone: 65.6%
• Acoustic measurement:
Measure-remeasure reliability (20% data):
• Consonant length: 97.9
• Syllable length: 94.9%
• Vowel length: 93.7%
• Speech Moment 1: 95.4%
• Speech Moment 2: 93.1%
• F1: 82.6%
• F2: 73.3%
Results
100
Sub1
Sub2
Sub3
Sub4
Sub5
Sub6
80
Percent
correct 60
(in %)
40
20
0
Consonant Vowel
Tone
Type of Phoneme
• Consonants exhibited the lowest rate of correct productions.
Distribution of Consonant Errors
100
80
Percent
correct 60
(in %)
40
20
0
Sub1
Sub2
Sub3
Sub4
Sub5
Sub6
m t p l p' t . k t ' . h k' s f ts t' ts' n t ' .
Consonant
• Frequency of correct production lower than 40%:
 / /, / /, / /, / / (retroflex): Subjects 1 to 4
 /ts’/ (aspirated affricate): Subjects 2 and 6
`
Speech Moments 1 & 2
3500
3000
2500
M2
(SD) 2000
1500
1000
Correct
Incorrect
500
0
0
1000
2000
3000
4000
5000
M1
(Mean, in Hz)
• Incorrect consonants cluster more together in the M1-M2 plot than their correct counterparts.
 M1 & M2 were lower for incorrect consonant production involving frication or affrication.
 M1 & M2: When produced correctly, retroflexed tend to have lower M1 & M2 than their
non-retroflexed counterparts. But incorrect productions were inconsistent.
 M1: When produced correctly, un-aspirated plosives were lowered than their aspirated
counterparts. But incorrect productions were inconsistent.
Vowel Space
2800
2600
/i/
Correct consonant
Incorrect consonant
/i/
2400
F2
(in Hz)
2200
2000
/a/
1800
/a/
1600
1400
/u/
1200
1000
400
/u/
500
600
700
800
900
1000
1100
F1
(in Hz)
• Vowels following incorrectly produced consonants exhibited a more
compressed vowel space than those following correctly produced consonants.
Consonant Length
250
200
Correct
Incorrect
*
*
Consonant
150
Length
(in msec)
100
50
0
First syllable
Second syllable
Position
• Incorrectly produced consonants (n = 98) were significantly longer than
correctly produced ones (n = 618) in both first-word/syllable (T =43284.5,
p < 0.001) and second-word/syllable positions (T = 65669, p < 0.001).
Vowel Length
500
*
Correct
Incorrect
400
Vowel
Length 300
(in msec)
200
100
0
First syllable
Second syllable
Position
• Incorrectly produced consonants (n = 98) were found to be associated with
vowels significantly shorter than vowels in correctly produced consonants
(n = 618) only in the first-word/syllable position (T = 29378, p = 0.003) but
not in the second-word/syllable position (T = 56302, p = 0.567).
Summary
• Error Patterns:
– No difference between diplegia & quadriplegia
– Mostly consonant errors (esp. frication, affrication, retroflex)
• Acoustic characteristics of incorrect production:
– Consonant:
Consonant length prolonged
Retroflexed consonants:
- M1 contrast inconsistent
Fricatives and affricates:
– Lower M1: suggesting a more posterior tongue placement
– Lower M2: suggesting less diffusion of frication noise
Summary - continued
– Vowels following incorrect consonants:
Vowel length shortened
Vowel space compressed, suggesting
 Production: more restrained vocal tract shaping
 Perception: less speech intelligibility
Clinical Implications
• Temporal and spectral measures are useful for
detecting subtle changes in speech motor control.
• The found impact of an incorrect consonant on
the vowel immediately following it suggests that
vowel manipulation (e.g., change in length or
extent of jaw opening) may help compensating
for the loss of vowel clarity as well as overall
speech intelligibility (i.e., reversing the adverse
effect with anticipatory coarticulation).
Follow-up
• Increased sample size
• Effect of facilitation strategies (rate,
overarticulation)
• Listening task effect: blinded phonemic
(especially tone) transcription task vs. error
identification task with known phonemic
representations
• Effect of spectral analysis software
Conclusion
• Spastic CP exhibits mostly consonant errors,
which are associated with a compressed vowel
space.
• Tone errors may be a secondary problem for
CP children but this requires further studies
examining the effect of listening task.
• A selection of temporal and spectral measures
are useful for differentiating correct and
incorrect productions by CP children.
Acknowledgement
• Fiona Yip, BSLT, Department of
Communication Disorders, University of
Canterbury
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