Impaired Letter-String Processing in Developmental Dyslexia: What Visual-to-Phonology Code Mapping Disorder?

• Published in: Dyslexia (Chichester, England) England), 2012-05, Vol.18 (2), p.77-93
• Main Authors: Valdois, Sylviane, Lassus-Sangosse, Delphine, Lobier, Muriel
• Format: Article
• Language: English
• Subjects: Adolescent; Alphabets; Analysis of Variance; Attention; Attention Deficit Disorder with Hyperactivity; Attention Deficit Disorder with Hyperactivity - diagnosis; Attention Deficit Disorder with Hyperactivity - etiology; Attention Span; Case-Control Studies; Child; Child, Preschool; Children; Color; Color Perception; Developmental disabilities; Dyslexia; Dyslexia - complications; Evidence; Experiments; Familiarity; Female; Foreign Countries; France (Grenoble); French; Humans; Language Processing; letter-string processing; Life Sciences; Male; Mapping; Neurodevelopmental disorders; Neurons and Cognition; Neuropsychological Tests; Numbers; Pattern Recognition, Visual; Phonetics; Phonology; Reading; Reading disabilities; Statistics as Topic; Stimuli; visual attention span; Visual Perception; Visual Perception - physiology; visual processing; visual-to-phonological code mapping
• ISSN: 1076-9242; 1099-0909
• DOI: 10.1002/dys.1437

Poor parallel letter‐string processing in developmental dyslexia was taken as evidence of poor visual attention (VA) span, that is, a limitation of visual attentional resources that affects multi‐character processing. However, the use of letter stimuli in oral report tasks was challenged on its capacity to highlight a VA span disorder. In particular, report of poor letter/digit‐string processing but preserved symbol‐string processing was viewed as evidence of poor visual‐to‐phonology code mapping, in line with the phonological theory of developmental dyslexia. We assessed here the visual‐to‐phonological‐code mapping disorder hypothesis. In Experiment 1, letter‐string, digit‐string and colour‐string processing was assessed to disentangle a phonological versus visual familiarity account of the letter/digit versus symbol dissociation. Against a visual‐to‐phonological‐code mapping disorder but in support of a familiarity account, results showed poor letter/digit‐string processing but preserved colour‐string processing in dyslexic children. In Experiment 2, two tasks of letter‐string report were used, one of which was performed simultaneously to a high‐taxing phonological task. Results show that dyslexic children are similarly impaired in letter‐string report whether a concurrent phonological task is simultaneously performed or not. Taken together, these results provide strong evidence against a phonological account of poor letter‐string processing in developmental dyslexia. Copyright © 2012 John Wiley & Sons, Ltd. Key Messages Poor letter/digit‐string processing in dyslexia can follow from either a phonological or a visual attention span disorder. The dissociation between letter/digit versus symbol‐string processing was viewed as supporting the phonological account. Using three nameable stimuli types, Experiment 1 shows poor letter/digit‐string processing but preserved colour‐string processing in developmental dyslexia. Experiment 2 shows that the dyslexic's low performance in letter‐string processing is not affected by a concurrent phonological task. These findings speak against a phonological interpretation of the disorder. The observed dissociation may well reflect a visual familiarity effect.