All disciplines would probably agree that dyslexia is evidenced by persons of otherwise normal intellectual capacity who have not learned to read despite exposure to adequate instruction.
According to The British Dyslexia Association, word 'Dyslexia' comes from the Greek language and means 'difficulty with words'. The British Dyslexia Association defines Dyslexia as, "a combination of abilities and difficulties that affect the learning process in one or more of reading, spelling and writing. It is a persistent condition. Accompanying weaknesses may be identified in areas of speed of processing, short term memory, organization, sequencing, and spoken language and motor skills"(British Dyslexia Association, Online Journal).
Dyslexia causes difficulties in quite specific areas of learning. It usually affects reading, writing and spelling, but can also influence mathematical skills. The condition is hard to define precisely because dyslexia often overlaps with other types of specific learning difficulties which can also affect spoken language and motor skills (Mattis, 1978).
Although dyslexia can manifest itself in many ways, there may be a single cause: a phonological deficit. ...
Visual difficulties: Dyslexic people may be unable to process fast-incoming sensory information adequately. This could explain visual difficulties such as unstable binocular vision and unsteady fixation when reading. It might result in visual confusion of letter order, which can lead to poor memory of the visual form of words. Again, this may be a symptom of a deeper cause.
Temporal or timing difficulties: Phonological, visual, or motor difficulties may all be indicative of an underlying temporal or timing difficulty, rather than alternative explanations for dyslexia. These timing difficulties may also have their origin in brain structure.
Automaticity: Some tasks may be less 'automatic' for dyslexic individuals and may take up more of their concentration and attention than is the case for non-dyslexic individuals. Lack of automaticity in basic skills such as literacy and numeracy could mean that dyslexic people are more likely to experience processing overload when they are required to carry out new or complex tasks. They may need far more practice at any skill before they achieve automaticity. This condition is linked with differences in the structure of the cerebellum.
Working memory: Working memory is used to hold new information in the mind for a short time before it is rejected or transferred into long-term memory. Some theorists regard inefficient working memory as being a key underlying factor in dyslexia.
'Difference' model: A lot of research focuses on the deficits associated with dyslexia. It may be more beneficial to refer to cognitive differences, as opposed to deficits, as some of these differences may enable dyslexic individuals to have particular strengths, such