[TS-1.3] A behavioural and ERP investigation of letter-sound processing: Is a lack of automaticity a proximal cause of dyslexia?

Nash, H. 1 , Hulme, C. 1 , McArthur, G. 2 , Mahajan, Y. 3 , Gooch, D. 4 & Snowling, M. 5

2 Macquarie University
3 University of Western Sydney
4 Royal Holloway
5 University of Oxford

Drawing on evidence from neuroimaging studies Blomert proposed that the proximal cause of dyslexia is a deficit in forming automatic connections between letters and phonemes. Using fMRI Blau et al, (2009; 2010) found reduced integration of letter-phoneme pairs in dyslexics and using the cross-modal MMN the same research group found evidence for integration in adults and older children but not in younger or dyslexic children (Froyen et al, 2008; 2009; 2010). In a pilot study we collected data from developing and more advanced readers using a priming task in which we compared targets in related (prime was the same letter/phoneme) and unrelated (neutral prime) conditions. We conducted two experiments, in the first a letter prime preceded a phoneme target and in the second the phoneme was the prime and the letter the target. We found that both groups were faster to respond to the target in the related condition, at both a long (500ms) and short (0ms) ISI. Therefore, exposure to a letter/phoneme facilitated the subsequent processing of the same phoneme/letter, suggesting that the two representations are integrated. In addition, we found that priming from letters-to-phonemes was a predictor of decoding. In the main study we collected behavioural and EEG data from dyslexic children, age-matched and reading -matched controls. In the behavioural experiments we found that children in all 3 groups showed evidence of integration. However, preliminary analyses of ERPS suggested group differences. The age-matched controls showed an effect of related letters on phonemes in the central region and an effect of related phonemes on letters in the left parietal region, but these effects were weaker in the dyslexics and reading-matched controls. There was some evidence of an effect emerging later in the latter 2 groups, possibly reflecting differences in latency or the role of attentional processing.