Cross-modal effects of letters on the MMN to speech sounds reveals deficient letter - speech sound processing in children with dyslexia
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1
Faculty of Psychology and Neuroscience, Maastricht University, Netherlands
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2
Maastricht Brain Imaging Center, M-BIC, Netherlands
According to the phonological deficit hypothesis, the core deficit in dyslexia relates to degraded speech sound representations which hamper the acquisition and automation of letter - speech sound (LS) associations necessary for learning to read. While phonological processing has been investigated extensively in children with dyslexia, the consequences of the assumed phonological deficit for single LS processing has received far less attention. The present study is the first to report neural correlates of single LS processing in dyslexic children.
Recently the mismatch negativity (MMN) was successfully employed to investigate neural correlates of LS processing in eight and eleven year old and in adult non-impaired readers. An effect of letters on the MMN to speech sounds was interpreted as reflecting early and automatic LS integration. The development towards adult-like LS integration appeared to extend over multiple years: No integration in eight year olds and integration, but not adult-like, in eleven year olds. Additionally, a late effect, referred to as the Late Negativity, was observed around 650 ms after speech sound onset in eight and eleven year olds but not in adults. Since eight year olds know the relation between letters and speech sounds and the effect of letters on speech sound processing was only apparent on the Late Negativity, it was suggested to reflect less automated LS association.
In the present study, the same MMN paradigm was used to investigate LS processing in eleven year old children with dyslexia. Results revealed no early integration effects but only a late association effect, which resembled mostly the results in eight year old non-impaired readers with approximately one year of reading experience. This indicates that eleven year old children with dyslexia are still at a very early level of LS processing. Our results are supported by a recent fMRI-study revealing lower LS integration effects even in adults with dyslexia.
The present results furthermore confirmed the existence of a Late Negativity around 650 ms after stimulus onset which was clearly distinguishable from the often described Late MMN appearing around 450 ms. The Late Negativity was not observed to speech sounds in isolation and might thus reflect cross-modal association effects. Although there is a trade off with measuring time, the present study shows that the use of longer epochs might, depending on the research question, gain important insights.
Conference:
MMN 09
Fifth Conference on Mismatch Negativity (MMN) and its Clinical and Scientific Applications, Budapest, Hungary, 4 Apr - 7 Apr, 2009.
Presentation Type:
Poster Presentation
Topic:
Poster Presentations
Citation:
Froyen
D,
Willems
G,
Walter
A and
Blomert
L
(2009). Cross-modal effects of letters on the MMN to speech sounds reveals deficient letter - speech sound processing in children with dyslexia.
Conference Abstract:
MMN 09
Fifth Conference on Mismatch Negativity (MMN) and its Clinical and Scientific Applications.
doi: 10.3389/conf.neuro.09.2009.05.122
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Received:
26 Mar 2009;
Published Online:
26 Mar 2009.
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Correspondence:
Dries Froyen, Faculty of Psychology and Neuroscience, Maastricht University, 6200 MD Maastricht, Netherlands, Netherlands.d.froyen@psychology.unimaas.nl