Does dyslexia exist?

© 2017 Informa UK Limited, trading as Taylor & Francis Group. The phonological theory of dyslexia makes it difficult to distinguish developmental dyslexia from social causes of reading failure, because, whatever their cause, all poor readers seem to have similar phonological problems. In order to understand why children with dyslexia fail, we need to understand the physiological mechanisms that underlie their failure to acquire phonological skills. An important cause is probably impaired development of the brain’s rapid temporal processing systems; these are required for sequencing accurately the order of the sounds and letters in a word. Such temporal, “transient”, processing is probably carried out in all parts of the brain primarily by a distinct set of “magnocellular” neurones, and the development of these has been found to be impaired in many people with dyslexia. Therefore measuring poor readers’ auditory and temporal processing skills should enable dyslexia to be reliably distinguished from other causes of phonological deficits.