Causes and Treatments for Dyslexia: Overview of Theories

Causes and Treatments for Dyslexia: Overview of Theories A common definition of dyslexia states it is a specific difficulty in gaining literacy skills that occurs in people who otherwise appear to be developing normally (Snowling, 1987). It is thought to occur in between 3% and 10% of the population (Habib, 2000). Methods of treating and managing dyslexia have been largely influenced by theories about its aetiology. Three different types of explanations are examined here: the behavioural, the cognitive and the biological. Each of these suggests a contrasting approach to treatment. The cognitive approach to dyslexia can be seen in the phonological theory. This has one of the longest pedigrees amongst explanations for dyslexia and it suggests a deficit in working memory (Bradley Bryant, 1978). Specifically, this theory suggests that part of the short-term memory the phonological loop has a deficit causing dyslexics to have difficulties representing, storing and retrieving the sounds of speech. In order to learn to read, the theory argues, it is necessary to make connections between phonemes (the units of sounds that make up words) and graphemes (the units of letters that make up words). Problems in making this connection will tend to result in reading deficits. This cognitive explanation clearly suggests that strengthening the link between graphemes and phonemes will help those with dyslexia (Lyytinen, Erskine, Aro Richardson, 2007). Consequently there are a huge range of different interventions focussed on encouraging the learning of these connections. Ehri et al. (2001), reviewing these approaches, found they generally fall into three categories of interventions. The first are designed to break down the sounds in a word after it has been learnt. The second category are designed to help build up a word from its component sounds. The third take a more whole-language approach. When compared to other forms of intervention those based on phonics instruction, according to this meta-analysis, provide the best outcome for children. Despite this, other interventions are frequently recommended for those with dyslexia these stem from different explanations. One example of a more biological, rather than cognitive approach to dyslexia suggests the source of reading difficulties in this condition is related to deficiencies in the visual system (Lovegrove, Bowling, Badcock Blackwood, 1980). Specifically, this theory is based on findings about two particular visual pathways in the brain: the magnocellular and parvocellular. It is thought that it is the magnocellular pathway that is deficient (Stein Walsh, 1997). This is then thought to cause a variety of visual problems such as unstable eye fixations, poor vergence and visual crowding. It has been argued by Whiteley Smith (2001) that around half of those with dyslexia suffer from eye strain and distortion of text. A treatment for dyslexia suggested by the magnocellular theory is the use of coloured lenses. Irlen (1997) argues that the use of blue filters slows down the functioning of the faster parvocellular pathway, thereby stabilising the speed more in line with the slower magnocellular pathway. Early research such as that carried out by Jeaanes et al. (1997) found these overlays were preferred by children, although later research suggested this was a result of the placebo effect. Attempts to correct for these methodological problems have proved difficult with, for example, Robinson Foreman (1999) finding little support for the coloured lens approach specifically helping those with dyslexia. Along with cognitive and biological explanations for dyslexia have come those which focus on primarily behavioural causes. These can include a wide variety of different sources such as generally poor teaching, a poor relationship with a teacher or a home life that is disturbed (Morton Frith, 1995). Ridsdale (2004) has pointed out the connection between dyslexia and low self-esteem, behavioural difficulties, withdrawal and depression. Behavioural approaches to treatment, then, can aim to raise self esteem which can include changing goal orientations, giving praise, increasing the levels at which others provide support and so on. Metacognitive approaches help to provide ways of thinking about thinking this means teaching those with dyslexia to be able to monitor their thinking processes. Some of these behavioural interventions have been evaluated. Steinhausen and Metzke (2001), for example, found that peer group support could help those with behavioural difficulties. In conclusion, there a variety of cognitive, biological and behavioural explanations for dyslexia, each of which has different associated treatment or management options. In general each of the explanations explains some of the evidence from dyslexia but none of them explain all of it. This suggests that either theories are as yet incomplete, or there are methodological problems with the evaluations or there are different types of dyslexia to be explained. In practical terms, however, support and treatment for those with dyslexia often uses a multi-modal approach on the basis this is more likely to prove beneficial. References Bradley, L., Bryant, P. E. (1978) Difficulties in auditory organisation as a possible cause of reading backwardness. Nature, 271, 746-7. Ehri, L. C., Nunes, S. R., Willows, D. M., Schuster, B. V., Yaghoub-Zadeh, Z., Shanahan, T. (2001). Phonemic Awareness Instruction Helps Children Learn to Read: Evidence from the National Reading Panels Meta-Analysis. 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