Critically evaluate the claim that 'dyslexia is a specific form of language impairment that affects the way in which the brain encodes the phonological features of spoken words'
Critically evaluate the claim that ‘dyslexia is a specific form of language impairment that affects the way in which the brain encodes the phonological features of spoken words’
The term dyslexia is widely but inconsistently used in relation to reading difficulties (Mcshane 1991). A definition of this condition was proposed by the World Neurology Federation in 1968 ‘a disorder manifested in by difficulties in learning to read despite conventional instruction, adequate intelligence, and socio-cultural opportunity. It is dependant upon fundamental cognitive disabilities which are frequently of constitutional origin’ however this definition has since fallen out of use as of a number of flaws.
The definition by Snowling (the title) derives from the cognitive theory of phonological processing difficulties. This theory suggests that phonological deficit is the single cause of dyslexia. Phonological processing is the means by which an individual processes sounds within all words. With dyslexic individuals there may be difficulty in identifying, reproducing and sequencing sounds contained in a word. This theory also suggests there complications with rhyme, sound blending and non-word repetition (portrayed in Snowling et al longitudinal study of JM). Phonological storage and retrieval are a fundamental part of processing incoming verbal information and important to other short term memory tasks. With dyslexic individuals, in childhood literacy skills are below average, even if these skills become average with age, phonological deficits continue throughout life, (Brunswick et al 1999). This hypothesis proposes that dyslexic individuals have poorly specified phonological representations (Snowling 2000). The phonological deficit theory seems to be the consensus for some time. At the present there are some different view becoming apparent. Although some acknowledge the theory they see phonological difficulties as a symptom of dyslexia, relating the cause to brain structure. Some evidence for the phonological theory is derived from memory tests. In studies by Hulme et al (1984), Johnstone et al(1987) and more recently Snowling et al (1997) is was found that memory impairments with word recall were found in dyslexic individuals. This impairment is suggested to be because dyslexic individuals are less efficient than normal readers when required to recruit phonetic memory codes (Snowling 2000), in other words they have impaired interpretations of the phonological structure of words. There is difficulty retaining verbal items because of the deficit which restricts the number of items retained and also the performance on working memory tasks. These studies correlate with another theory of dyslexia, the working memory hypothesis, based on the Working Memory model. (Baddeley & Hitch) This model has four components, audio, visual, procedural and semantic memory. Deficits in any of these components are suggested to be an underlying factor in dyslexia, any weaknesses in these channels will put pressure on the others (Mortimer 2003), so this does involve phonological deficit to an extent but not as a single cause. Stanovich suggests that visual processing deficits can occur together with phonological deficits in some dyslexic individuals.
