Speed of Processing and Reading Disability: A Cross-Linguistic Investigation of Dyslexia and Borderline Intellectual Functioning Cognition

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.