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English and Italian children with dyslexia were compared with children with reading difficulties associated with low-IQ on tests of simple and choice RT, and in number and symbol scanning tasks. On all four speed-of-processing tasks, children with low-IQ responded more slowly than children with dyslexia and age-controls. In the choice RT task, the performance of children with low-IQ was also less accurate than that of children of normal IQ, consistent with theories linking processing speed limitations with low-IQ. These findings support the hypothesis that dyslexia is a specific cognitive deficit that can arise in the context of normal IQ and normal speed of processing. The same cognitive phenotype was observed in readers of a deep (English) and a shallow (Italian) orthography.

Original publication




Journal article



Publication Date





999 - 1017


Adolescent, Child, Cross-Cultural Comparison, Dyslexia, Female, Humans, Intellectual Disability, Male, Phenotype, Reaction Time, Recognition (Psychology), Severity of Illness Index