What is Dyslexia?
Dyslexics have unexpected problems learning to read and write compared with their general ability (IQ), but problems with arithmetic and reading musical notation are also common. Poor working memory - especially for sequencing visual or auditory-linguistic material - is a central characteristic, and difficulty with phonology (the sounds in words) is often regarded as a core feature, although these problems are found in any poor readers.
Associated features include problems in distinguishing left and right, poor direction sense, difficulties with time and tense, and subtle problems with both visual and auditory perception. The overlap with ADHD is around 30-50%, and with dyspraxia it appears to be even higher, although owing to the relative lack of attention that dyspraxia has received to date, fewer firm data are available.
There is a clear biological basis to dyslexia. Genetic studies suggest around 50% is inherited, prevalence across cultures is similar (and independent of socio-economic status and IQ), and more males than females are affected. Differences in brain structure in dyslexia include an unusual symmetry of language areas and microscopic differences in the arrangement and connection of neurons. The visual and auditory problems point to a mild disorder of 'magnocellular' systems, specialised for very rapid information processing.
