Dyslexia is characterized by difficulty with learning to read fluently and with accurate comprehension despite normal intelligence. This includes difficulty with phonological awareness, phonological decoding, processing speed, orthographic coding, auditory short-term memory, language skills/verbal comprehension, and/or rapid naming. Developmental reading disorder (DRD) is the most common learning disability. Dyslexia is the most recognized of reading disorders, however not all reading disorders are linked to dyslexia. Adult dyslexics can read with good comprehension, although they tend to read more slowly than non-dyslexics and perform more poorly at spellingand nonsense word reading, a measure of phonological awareness.
Some see dyslexia as distinct from reading difficulties resulting from other causes, such as a non-neurological deficiency with vision or hearing, or from poor or inadequate 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 and co-occurring learning disabilities (e.g. attention-deficit/hyperactivity disorder, math disability, etc.). Although it is considered to be a receptive language-based learning disability in the research literature, dyslexia also affects one’s expressive language skills. Researchers at MIT found that people with dyslexia exhibited impaired voice-recognition abilities. It is believed the prevalence of dyslexia is around 5-10 percent of a given population although there have been no studies to indicate an accurate percentage.