Left premotor cortex and allophonic speech perception in dyslexia: A PET study

Disorders of categorical perception has been put forward as a new account of phonological deficit in dyslexia (Serniclaes, W., Sprenger-Charolles, L., Carre, R. and Demonet, J.F., 2001. Perceptual discrimination of speech sounds in developmental dyslexia. J. Speech Lang. Hear. Res. 44, 384–399.) so...

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Published in:NeuroImage (Orlando, Fla.) Fla.), 2009-05, Vol.46 (1), p.241-248
Main Authors: Dufor, O., Serniclaes, W., Sprenger-Charolles, L., Démonet, J.-F.
Format: Article
Language:English
Subjects:
Adult
Brain - diagnostic imaging
Children & youth
Cognitive science
Dyslexia
Dyslexia - diagnostic imaging
Female
Humans
Image Interpretation, Computer-Assisted
Linguistics
Magnetic Resonance Imaging
Male
Neuroscience
Phonetics
Positron-Emission Tomography
Psychology
Speech
Speech Perception - physiology
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Summary:Disorders of categorical perception has been put forward as a new account of phonological deficit in dyslexia (Serniclaes, W., Sprenger-Charolles, L., Carre, R. and Demonet, J.F., 2001. Perceptual discrimination of speech sounds in developmental dyslexia. J. Speech Lang. Hear. Res. 44, 384–399.) so that dyslexic subjects tend to discriminate phoneme instances within a given phonemic category rather than between categories, possibly witnessing the persistence of phonemic boundaries of ‘allophones’ that may be relevant to other languages although not to one's mother tongue (Serniclaes, W., Van Heghe, S., Mousty, P., Carre, R. and Sprenger-Charolles, L., 2004. Allophonic mode of speech perception in dyslexia. J. Exp. Child Psychol. 87, 336–361.). The brain correlates of within- and between-category discrimination were explored using a /ba/–/da/ phonetic continuum and H 2 15O PET in 14 dyslexic and 16 control adult readers; subjects discriminated a set of stimuli pairs, first in a ‘naïve’ (acoustic) condition and, after debriefing about the stimuli identity, in a speech (phonemic) condition (Dufor, O., Serniclaes, W., Sprenger-Charolles, L. and Demonet, J.F., 2007. Top-down processes during auditory phoneme categorization in dyslexia: a PET study. NeuroImage 34, 1692–1707.). While discrimination of ‘between’ pairs improved in all subjects following debriefing, ‘within’ stimuli yielded variable performance; some subjects kept discriminating them, while best categorizers judged them identical. Correlation analyses between acoustic-to-speech changes in brain activity and in ‘within’-pair discrimination, and between control and dyslexic groups, revealed a criss-crossed correlation pattern in the left BA6 so that the higher the activity the better the categorization in control subjects whereas the higher the activity the more increased ‘within’ discrimination in dyslexic subjects. Therefore, in average readers, enhanced activity in the left BA6 likely contributes to optimizing phoneme categorization via refined speech motor coding. In dyslexic subjects showing sensitivity to ‘within’-category cues, activity enhancement in this region might suggest the persistence of motor coding for allophonic representations of speech.
ISSN:1053-8119
1095-9572
DOI:10.1016/j.neuroimage.2009.01.035