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ERP correlates of Speech Processing in Dyslexia

Milene Bonte, Lisa v/d Plas and Leo Blomert

University of Maastricht, The Netherlands M.Bonte@Psychology.Unimaas.Nl

Abstract

Dyslexics perform below average on a large variety of experimental phonological tasks. It is not clear so far, how this relates to phonological processing during on-line speech perception. In two consecutive studies we employed two different experimental approaches to compare behavioural and event-related potential (ERP) measures of implicit phonological processing during speech perception in normal-reading and dyslexic children (7-10 years). In both studies we used paradigms which induce phonological processing without requiring subjects to perform a phonological task. In the first experiments we used an auditory lexical decision task in combination with phonological onset priming. Behavioural and ERP data obtained in these priming experiments suggested different pre-lexical phonological processing in dyslexics. Both ERP morphology and phonological priming effects indicated specific processing anomalies in neural sources underlying the N1 and the N250. In the second study we use an oddball paradigm to further explore these anomalies. We investigate whether ERP data of dyslexics and normal readers indicate a different sensitivity to the statistical regularity of phonological sequences in the native language. Preliminary ERP results of normal subjects show larger MMN responses to nonwords consisting of highly frequent as compared to infrequent phoneme sequences. We are currently testing dyslexic children to find out whether their MMN responses do or do not show a similar sensitivity. In this way it is possible to reveal whether the basis for a phonological core deficit is to be found in the hard-wired spoken language system.

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