Dyslexia – literally translated from Greek as ‘inadequate words or language’ – is a learning disability characterised by problems with reading, writing, spelling and speaking. The most common definition of dyslexia is the discrepancy definition, which suggests that dyslexics are those whose reading ability is below average for their age group, or IQ. The first case of dyslexia was reported in 1896 by Dr. Pringle-Morgan, who described an intelligent 14 year old boy who had an inability to read, as suffering from – as Pringle-Morgan believed – “word blindness” resulting from deficiencies in visual processing. Since Pringle-Morgan’s initial report, there have been many other explanations of dyslexia. This essay will attempt to evaluate
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This theory is based around research which indicates that dyslexic children performed below average on tasks related to word-onset awareness and rhyming (Bradley and Bryant, 1978) and tasks related to phonological awareness (Bruck and Treiman, 1990). Chiappe et al.’s research (2001) provided further support to the theory, when they demonstrated that children with dyslexia performed poorly on phoneme recognition tasks. Although there is support for the phonological deficit hypothesis, the theory fails to address the other symptoms of dyslexia not related to phonological processing, such as short term memory, clumsiness or handwriting. Furthermore, the theory fails to explain why some dyslexics do not perform poorly on tasks related to phonological processing. A further criticism of the theory is the research by Layton et al. (1998) which found no significant difference in later reading and writing between infants who received ‘phonological training’ – general tasks which increased children’s phonological awareness – and those who did not. It is also difficult to assess whether or not deficits within phonological processing are cause or effect of dyslexia.
The heritability of dyslexia is an interesting factor to consider, as it has been linked to the phonological deficit hypothesis. DeFries (1991) demonstrated that there is a 50 per cent chance of males developing dyslexia if his father is dyslexic, and a 40 per cent chance if his mother is dyslexic. From