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Childhood Apraxia of Speech (CAS): Neurophysiological evidence of phonological involvement Reem Khamis Dakwar, Melissa Randazzo & Karen Froud ASHA 2008
Childhood Apraxia of Speech (CAS): Neurophysiological evidence of phonological involvement
Reem Khamis Dakwar, Melissa Randazzo & Karen Froud
ASHA 2008
Background
• No single validated list of diagnostic features of CAS (Shriberg et al., 1997)
• Approximately 50 different features used by SLPs in the field (Forrest, 2003)
• It is debated in the literature whether CAS is specifically a linguistic impairment (Crary, 1984) or a motor planning impairment (Edwards, 1984)
Theoretical Perspectives
• Input processing deficit
• Organization or Representation
• Output processing deficit• Motor programming or
Prearticulatory sequencing deficit
Shriberg, Aram and Kwiatkowski, 1997
EEG• Noninvasive method for measuring electrical
potentials generated by brain activity• High temporal resolution ( useful for looking at
language)• Experiments can be done without overt participation
from subjects ( useful for working with children)• EEG is a measure of continuous brain activation
(voltages)• To look at event-related activations (ERPs), we
average together segments of the continuous recording time-locked to stimuli
Mismatch negativity• A negative deflection in the ERP• The brain’s “automatic change-detection
response” (Näätänen et al., 1997)• Present large numbers of a frequent
stimulus (ta ta ta ta ta)• Plus an infrequent stimulus (“oddball”) (ta
ta ta ta da ta )• MMN: negativity peaking around 150-250
milliseconds after the oddball is presented• MMN is completely automatic, does not
require (conscious) attention• Reflects formation of traces in auditory
sensory memory (Näätänen, 2001)• Can use this mismatch to study language-
specific phonetic representations (Conboy et al, 2008)
Picture adapted from Sharma et al., 1993
Aim of the study
• To compare ERPs to standard and deviant syllables between children with CAS and typically developing controls
• Standard: /pa/• Phonemic deviant: /ba/
pa
Stimuli: standard
VOT: 50msecDuration: 500msec
ba
Stimuli: phonemic contrast
VOT: 5msecDuration: 500msec
Pilot study participants
CAS • n=5 (1 male, 4 females)• Mean age = 6.8 years • All right-handed• Diagnosis of CAS by
neurologist or SLP
Control• n=5 (3 males, 2 females)• Mean age = 7.3 years• All right-handed• 1 control was a sibling of
a CAS participant
Experiment• Continuous EEG recordings
were made while children watched an age appropriate movie of their choosing
• Sounds were presented through earphones at a comfortable listening level
• 128-channel Geodesic Sensor nets, digitally sampled via a high-impedance amplifier at 250Hz, impedances maintained below 40kΩ
Data analysis procedures
Raw EEG data
Select sections of data based on onset of stimuli
Remove noise from data
Detect and remove artifacts
Average over all remaining trials for
each participant
Combine averaged results from other
participants
May re-reference, baseline correct,
remontage, average channels together
For each condition in the experiment:
segmentation
Noise reductionNotch filter
High / low pass filters
Bad channel replacementReject artifact trials
Averaged Event
Related Potential
(ERP)
Grand-averaged
Event Related Potential
(ERP)
Look at time
course
Look at ERP
distribution
Look at time
course
Look at ERP
distribution
Statistical comparison with other conditions
Results: Controls
**
**
** p <0.05
Results: Apraxic group
** p <0.05
**
Discussion • Phonological representation in CAS
– Pilot results provide preliminary evidence from a neurophysiological standpoint that there is phonological involvement in CAS
• EEG is an effective method for investigating neural correlates of phonological representation
• Early phonetic perception and language outcomes• Need for further studies
– Longitudinal studies of children with CAS– Subgroups of children with mild vs severe CAS– Other differences in speech perception – e.g. allophonic
contrasts
Thank you
Neurocognition of Language LabTeachers College, Columbia University
525 West 120th Street, New York, NY 10027www.tc.edu/neurocog
References
Crary, M.A. (1984). A neurolinguistic perspective on developmental dyspraxia, Communicative Disorders, 9 (3), 33-49.
Edwards,M. (1984). Disorders of Articulation. New York: Springer-Verlag.
Forrest, K. (2003). Diagnostic criteria of developmental apraxia of speech used by speech-language pathologists. American Journal of Speech-Language Pathology, 12, 376-380.
Sharma, A., Kraus, N., McGee, T., Carrell, T., and Nicol, T.(1993). Acoustic versus phonetic representation of speech as reflected by the mismatch-negativity event related potential. Electroencephalographic Clinical Neurophysiology, 88 (1), 64-71/
Shriberg, L.D., Aram, D.M., and Kwiatkowsi, J. (1997). Developmental Apraxia of Speech: I. Descriptive and theoretical perspectives. Journal of Speech, Language, and Hearing Research, 40, 273-285.