dyslexia

dyslexia , in psychology, a developmental disability in reading or spelling, generally becoming evident in early schooling. To a dyslexic, letters and words may appear reversed, e.g., d seen as b or was seen as saw. Many dyslexics never learn to read or write effectively, although they tend to show above average intelligence in other areas. With the aid of computerized brain scans such as positron emission tomography (PET), recent studies have offered strong evidence that dyslexia is located in the brain. Damage to the brain can cause a reading disability similar to dyslexia, known as acquired dyslexia or alexia.

DYSLEXIA, also alexia. A language disorder that primarily affects the ability to read and that can result in such written errors as ‘saw’ for was and ‘dit’ for bit. It may be developmental, occurring in young children with no clear cause, or acquired, occurring in previously literate adults as a result of brain damage. There are several types of acquired dyslexia, in which adults find themselves unable to read at all, or find difficulty with certain types of word, but most public attention has focused on children, where there has been considerable controversy over the nature of the problem. There are many children who, after only a short time at school, fail at the task of reading, writing, and spelling, despite normal intelligence, instruction, and opportunity to learn. Surveys of incidence vary greatly in their results, with the mean percentage of non-retarded children with reading difficulties often reaching 5%, and sometimes much larger. Boys outnumber girls in a ratio of at least 3 to 1.

The question of causation has prompted great controversy. Candidate causes have included medical, psychological, and social factors, including problems of visual perception, memory, eye movement, verbal processing, and hemispheric dominance. The two traditional camps are those who favour a medical explanation (such as unstable eye dominance), and those who consider that social and psychological factors (such as a poor short-term memory) are critical. No single explanation fits the various symptoms. Individual case studies show that there is a variety of dyslexic syndromes, reflecting several possible causes, and requiring careful behavioural assessment and individual methods of teaching.

dyslexia Impairment in reading ability. Dyslexia is usually diagnosed when difficulty in learning to read is clearly not due to inadequate intelligence, brain damage, or emotional problems. Its specific causes are disputed, but is probably due to a neurological disorder. Symptoms may include difficulty with writing, especially in spelling correctly.