[PS-1.25] Deficient letter processing in developmental dyslexia: What are the processes involved?

Fernandes, T. 1 , Vale, A. P. 2 , Castro, S. L. 1 , Morais, J. 3 & Kolinsky, R. 3, 4

1 Universidade do Porto, Portugal
2 Universidade de Trás-os-Montes e Alto Douro, Portugal
3 Université Libre de Bruxelles, ULB, Belgium
4 Fonds de la Recherche Scientifique-FNRS, Belgium

The link between anomalous letter processing and developmental dyslexia has hitherto been unclear. The present study was aimed to (i) clarify the direction of causality between developmental dyslexia and deficient letter processing; and (ii) examine what are the processes involved in this putative deficit. Three groups of children - phonological dyslexics and two controls, one matched for chronological-age, the other for reading-level - performed a sequential same-different matching task, in which the inner target (either a letter or a pseudo-letter) was surrounded by a congruent (with the same global form) or incongruent geometric shape. For pseudo-letters, all groups showed congruence effects (CE: better performance when the target was surrounded by a congruent than incongruent shape). In contrast, for letters, only dyslexics exhibited a CE, thus differing not only from chronological-age but also from reading-level controls. The observation of CEs for both letters and pseudo-letters by dyslexic readers could thus depend on the adoption of the same processing mode for both materials or, alternatively, on the adoption of a deficient letter-specific procedure. We explored these two possibilities, specifically examining in dyslexics the association between the letter and the pseudo-letter CEs and the explanatory power of two latent variables (extracted from a Principal Component Analysis) on each of them, after partialling out the variance explained by age and nonverbal intelligence. The letter CE displayed by dyslexics was strongly related to their phonological recoding abilities even after partialling out working memory, whereas the reverse held true for the pseudo-letter CE. The present results suggest that deficient letter processing by dyslexics can be traced back to their phonological recoding deficit.