Dyslexia is a developmental disorder marked by difficulty in learning to read despite adequate intelligence, conventional instruction, and sociocultural opportunity. It appears to occur in 5 to 10 percent of the general population, and affects boys 3 to 6 times as frequently as girls. Research suggests that it results from various causes and that a number of subtypes of dyslexia probably exist with different origins and associated symptoms. Contrary to earlier theories, very few individuals with dyslexia appear to have a visual-perceptual problemÑthat is, the problem does not lie in perceiving words correctly. Recent research indicates that dyslexia is instead usually related to some kind of language impairment and is often associated with verbal memory problems. In particular, reading difficulty appears to be based on poor linguistic awareness and phonological analysis. That is, dyslexics have trouble analyzing spoken or written words into smaller units of sound, or phonemes.
The underlying causes of dyslexia are presumed to involve some kind of neurological dysfunction. Some theories have suggested that the two hemispheres of the brain have developed in an unusual manner. Evidence exists for both genetic and environmental causes of such dysfunction. Dyslexia can run in families, and it has also been related to problems arising during birth.
There are three main kinds of approaches to dealing with dyslexia. The developmental approach, based on the belief that dyslexic children may have slower brain development, simply intensifies conventional methods of instruction. The corrective approach emphasizes the dyslexic individual's assets and interests. The remedial approach focuses on deficiencies. Studies suggest that reading skills can be improved to some degree, but they also indicate that problems tend to persist into adulthood. The prognosis for improvement is usually best for individuals with high overall intelligence, less severe reading problems, and no neurological impairment.