Dyslexia is a developmental disorder in the acquisition of reading skills, in children of otherwise normal intelligence, which cannot be explained on the basis of educational deprivation or sensory impairment. The child may have fluent speech and good communicative skills, yet has difficulty in mastering the formal written code employed for reading.

Historical perspectives

At the end of the nineteenth century, the term ‘word blindness’ was coined, first to refer to acquired disorders of reading resulting from brain damage, and then to refer to reading disabilities which occur developmentally. The angular gyrus was damaged in many cases of acquired word blindness and there was speculation that a congenital aplasia of the angular gyrus might underlie problems in learning to read. Early discussions of congenital word blindness can be found in Hinshelwood (1917).

Labelling

Throughout the twentieth century, there has been disagreement regarding the labelling of the disorder. This continues today, with the term ‘developmental dyslexia’ being accepted in most academic and medical settings but not in educational circles, where the terms ‘specific reading disability’, ‘specific reading difficulty’ and ‘specific learning difficulty’ are employed.

Incidence

Lewis and colleagues (1994) tested the population of 9- and 10-year-olds in a single education authority district in England, finding 6.2% with specific reading disabilities. It remains unclear whether these children represent a distinct group from the main distribution, or the lower tail of a normal distribution. Lewis et al. (1994) also reported a male to female ratio of 3.2:1, though Smith et al. (1991) suggest a lower ratio of 1.7:1–1.3:1.