Dyslexia, also known as alexia or developmental reading disorder, is a specific learning difficulty that mainly affects the development of literacy and language-related skills. It is likely to be present at birth and to be life-long in its effects. It is characterised by difficulties with phonological processing, rapid naming, working memory, processing speed, and the automatic development of skills that may not match up to an individual’s other cognitive abilities.

Dyslexia is the most common learning difficulty. Some see dyslexia as distinct from reading difficulties resulting from other causes, such as a non-neurological deficiency with hearing or vision, or poor reading instruction. There are three proposed cognitive subtypes of dyslexia (auditory, visual and attentional), although individual cases of dyslexia are better explained by specific underlying neuropsychological deficits (e.g. attention deficit hyperactivity disorder, a visual processing disorder / visual stress) and co-occurring learning difficulties (e.g. dyscalculia and dysgraphia). Although it is considered to be a receptive (afferent) language-based learning disability, dyslexia also affects one’s expressive (efferent) language skills.