Dyslexia is a broad term defining a learning disability that impairs a person's fluency or accuracy in being able to read, speak, and spell and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, and/or rapid naming. Dyslexia is separate and 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. It is believed that dyslexia can affect between 5 to 10 percent of a given population although there have been no studies to indicate an accurate percentage.
There are three proposed cognitive subtypes of dyslexia: auditory, visual and attentional. Although dyslexia is not an intellectual disability, it is considered both a learning disability and a reading disability. Dyslexia and IQ are not interrelated, since reading and cognition develop independently in individuals who have dyslexia.
Accomplished adult dyslexics may be able to read with good comprehension, but they tend to read more slowly than non-dyslexics, and may perform more poorly at nonsense word reading (a measure of phonological awareness), and spelling.
