DYSLEXIA

 

Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, processing speed, orthographic coding, auditory short-term memory, language skills/verbal comprehension, and/or rapid naming.

Dyslexia is 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 and 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 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.). Reading disability, or dyslexia, is the most common learning disability. 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.

Adult dyslexics can read with good comprehension, but they tend to read more slowly than non-dyslexics and perform more poorly at spelling and nonsense word reading, a measure of phonological awareness. Dyslexia and IQ are not interrelated as a result of cognition developing independent

Signs and symptoms

Some early symptoms that correlate with a later diagnosis of dyslexia include delays in speech, letter reversal or mirror writing, and being easily distracted by background noise. This pattern of early distractibility is partially explained by the co-occurrence of dyslexia and attention-deficit/hyperactivity disorder. Although each disorder occurs in approximately 5% of children, 25-40% of children with either dyslexia or ADHD meet criteria for the other disorder. At later ages symptoms can include a difficulty identifying or generating rhyming words, or counting syllables in words (phonological awareness)a difficulty segmenting words into individual sounds, or blending sounds to make words, a difficulty with word retrieval or naming problems (see anomic aphasia) commonly very poor spelling, which has been called dysorthographia or dysgraphia (orthographic coding), whole-word guesses, and tendencies to omit or add letters or words when writing and reading are considered classic signs. Other classic signs for teenagers and adults with dyslexia include trouble with summarizing a story, memorizing, reading aloud, and learning a foreign language. A common misconception about dyslexia is that dyslexic readers write words backwards or move letters around when reading – this only occurs in a very small population of dyslexic readers. Individuals with dyslexia are better identified by reading accuracy, fluency, and writing skills that do not seem to match their level of intelligence from prior observations.

Cause

Researchers have been trying to identify the biological basis of dyslexia since it was first identified by Oswald Berkhan in 1881 and the term dyslexia coined in 1887 by Rudolf Berlin. The theories of the etiology of dyslexia have and are evolving with each new generation of dyslexia researchers, and the more recent theories of dyslexia tend to enhance one or more of the older theories as understanding of the nature of dyslexia evolves.