Speech Motor Deficits in Cerebral Palsied Children: An Acoustic-Perceptual Approach 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 Emily Lin, PhD1, Chia-Ling Chen, MD, PhD2, 3, & Chao-Chin Lee, BSLT1
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)
Aetiology of CP (Little, 1862) Birth Asphyxia Birth Asphyxia (Denhoff, 1976; Blair & Stanley, 1997; Hagberg et al., 2001) Intrauterine viral infections e.g. Rubella & Cytomegalo-virus (CMV) Intrauterine viral infections e.g. Rubella & Cytomegalovirus (CMV) Low gestation age (Denhoff, 1976; Hagberg & Mallard, 2000; Blair & Stanley, 1993; Stanley, 1997) Maternal thyroid abnormalities Low Apgar scores (Nelson & Ellenberg, 1981) Cerebral Palsy (Risk Factors) (Blair & Stanley, 1993; Stanley, 1997) Perinatal exposure: Methyl mercury Multiple gestation (Amin-Zaki, Majeed, Elhassani et al., 1979; Stanley, 1997) (Nelson & Grether, 1999) Iodine deficiency Male gender: 1.9:1 to 0.99:1 (M:F) (Blair & Stanley, 1997) (Pharoah, Buttfield & Hetzel, 1971)
Speech Characteristics of CP ↓ Speech Intelligibility ↓ Speech Naturalness (Kent, Netsell, & Abbs, 1978) • Prosody • Slow rate • Arythmatic (Hixon & Hardy, 1964) (Andrews, 1999) (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)
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) Vowel Space (F1-F2 Plot)
Vowel Working Space & Speech Intelligibility Cerebral Palsy (CP) Multiple Sclerosis (MS) Amyotrophic Lateral Sclerosis (ALS) Normal Speakers Parkinson’s Disease (PD) • Tjaden & Wilding (2004) • MS (N=15), PD (N=12) & controls (N=15) • Corner vowels: /i/, /a/, /ӕ/ & /u/ in habitual, loud & slow (passage) • Perceptualanalysis & Acoustic analysis • Size of vowel working space area & speech intelligibility seems to be unrelated in MS group • Tjaden & Wilding (2005) • 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 & Acousticanalysis • 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) • 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) • Liu et al. (2005) • Mandarin speakers with CP (N=20) & controls (N=10); • Corner vowels: /i/, /a/ & /u/ in habitual speaking rate; • Perceptualanalysis & Acoustic analysis; • Significant correlation between vowel working space & speech intelligibility • Fourakis (1991) • Healthy individuals (N=8 ) • 9 vowels in different 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 • Perceptualanalysis & Acousticanalysis • 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: • Syllable length • Consonant length • Vowel length • Formant analysis of vowels (Baken, 1987) : • 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: 2005 Paul Boersma & David Weenink) • Moment analysis
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%
100 Sub1 Sub2 80 Sub3 Sub4 Percent Sub5 60 correct Sub6 (in %) 40 20 0 Consonant Vowel Tone Type of Phoneme Results • Consonants exhibited the lowest rate of correct productions.
Distribution of Consonant Errors • Frequency of correct production lower than 40%: • / /, / /, / /, / / (retroflex): Subjects 1 to 4 • /ts’/ (aspirated affricate): Subjects 2 and 6
Speech Moments 1 & 2 • 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 • Vowels following incorrectly produced consonants exhibited a more • compressed vowel space than those following correctly produced consonants.
Consonant Length • 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 • 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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