 Dyslexia is thought to have two types of cause , one related to language processing and another to visual processing . It is considered a cognitive disorder , not a problem with intelligence . However , emotional problems often arise because of it . Some published definitions are purely descriptive , whereas others propose causes . The latter usually cover a variety of reading skills and deficits , and difficulties with distinct causes rather than a single condition . The National Institute of Neurological Disorders and Stroke definition describes dyslexia as " difficulty with spelling , phonological processing ( the manipulation of sounds ) , or rapid visual @-@ verbal responding " . The British Dyslexia Association definition describes dyslexia as " a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling " and is characterized by " difficulties in phonological awareness , verbal memory and verbal processing speed " . 
