Speech Motor Deficits in Cerebral Palsied Children
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 References • Ackermann, H., Hetrich, I., & Hehr, T. (1995). Oral diadochokinesis in • • • • • neurological dysarthrias. Folia phoniatrica et logopaedica, 47, 15-23. Amin-Zaki, L., Majeed, M. A., Elhassani, S. B., Clarkson, T. W., Greenwood, M. 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