Developmental Dyslexia and the Phonological Deficit Hypothesis

Dehaene (in Reading in the Brain) reviews and finds support for the phonological deficit hypothesis of developmental dyslexia, which proposes that dyslexics have a basic deficit in processing the constituents of spoken words. This hypothesis can be seen as reflecting three associated claims: a) there is only one basic kind of dyslexia; b) all (or most) dyslexic children have phonological impairments, and c) these phonological impairments cause their dyslexia. We consider each of these claims, and the evidence presented by Dehaene, and conclude that questions remain about all three. Phonological deficits alone seem unlikely to be able to account for the complexity and heterogeneity of developmental dyslexia.