Dyslexia background: part two

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For Part One see here:

Part OneAre

Theories of causation tell us much about how to assess dyslexic students. There are three main schools of thought, yet the theories can sit side by side as in the Kelly and Phillips Integrated Causal Model (2011). The theories deal with different parts of the brain but all seek to explain the phonological difficulty experienced by dyslexics. One of them, the cerebellar theory, also explains the additional difficulties related to sequencing, organisation and memory.

 

There is an undeniable genetic link, as dyslexia runs in families. Pennington and Gilger (1996) have claimed that where there is dyslexia in the family, there is an increased probability that the child will have it. Snowling (2008) points out that different environmental experiences will influence the genetic impact, both the severity and the outcome of the difficulty. We can also see this in the Morton and Frith Basic Causal Framework (1995).By talking with parents, the genetic link can be investigated. Sometimes, parents are diagnosed after their children.

 

The Phonological Deficit theory, the fact that dyslexic children struggle to link speech sounds to their written representation, has been popular. However, Nicolson and Fawcett suggest it is a symptom rather than a cause (2008). The theory does not explain the other difficulties shown by dyslexics: problems sequencing, forming handwriting and following instructions.

 

Nevertheless, speech is the foundation for written language and Snowling, (2000b) suggests that dyslexia is a speech-processing difficulty. To support this, abnormalities in the Perysylvian region of the brain, involved in phonological processing, result in impairments in phonological awareness. There are also studies, which show poor language skills predict poor reading, well before any reading instruction (Puolakanaho et al, 2007). It is important that we assess phonological ability as one of the main indicators of dyslexia. It is useful to look at how children acquire the skill of reading to inform how and what we assess. Phonological awareness is an important skill in learning to read, whether this is a pre-requisite or is brought about through the process of learning to read is debated in the field (Muter et. al., 2004).

 

Frith (1985) identified several stages of reading : logograohic (whole word), alphabetic (phoneme/grapheme correspondance) and orthographic (spelling patterns). This links with assessment of reading and spelling as these are the stages a successful reader goes through acquiring reading skills automatically. It helps to identify where the gaps are with dyslexic readers and gives a focus for intervention.

 

Wagner and Torgensen (1987) state the importance of several phonological skills in reading, including awareness, rapid automatised naming and verbal short-term memory. Therefore, knowledge of high frequency words, testing short-term memory e.g using a digit span test and knowledge of the alphabetic principle should also be part of any assessment. In addition, a learner’s ability to manipulate sounds, using phoneme and syllable deletion needs to be tested.

 

Coltheart’s dual route model of reading (2001) shows how some words are processed by a lexicon but non words cannot because they have no meaning, non words test the ability to link graphemes to their sound rather than relying on a memory of the word shape and/or it’s meaning. This further explains why non-words should feature in an assessment semantics and meaning come into this model, a learner’s comprehension should be assessed as well as their decoding ability.

 

A relatively recent study (Ramus, 2014), showed that it was a difficulty in retrieval i.e. access to phonological representations rather than the representations themselves, that dyslexics experience. Rapid automatised naming tests should expose this, an important indicator of dyslexia and one which differentiates it from a Specific Language Impairment (Bishop and Snowling, 2004).

 

Difficulties in phonology are explained by visual disturbances, or temporal processing difficulties in some studies. In the Magnocellular Theory, Evans (2001), Stein (2003, 2008), it is suggested that abnormalities in the Magnocellular (large) and Parvocellular (small) pathways in the brain are responsible for a visual disturbance resulting in reading difficulties. This has echoes of the original theory of ‘word-blindness’ (Hinshelwood, 1917). As well as problems with visual stimuli, the theory suggests that phonological difficulties are caused by an inability to detect rapidly changing auditory stimuli (Tallal 1993, 2007). As with the phonological theory, it doesn’t explain all of the difficulties which are associated with dyslexia.

 

A study by Galaburda et al (2006) suggested that early auditory problems (affecting phonological processing) can resolve themselves in some individuals. In terms of how the Magnocellular theory impacts on assessment and behaviours, what we can look for are tracking difficulties when reading eg losing place on the page, also sequencing sounds and syllables. Phonemes may get missed out of spelling and reading, because they can’t be distinguished and poor visual perception may cause letters to be transposed or swapped around (Kelly & Phillips, 2011). How competently a child copies work would also be telling (this will also test working memory). Deficits in auditory perception and memory storage might explain why certain letters are hard to distinguisheg. /b/,/t/,/k/,/d/ (Kelly and Phillips, 2011)

 

A study on visual motion processing deficits (Wilmer et al, 2004), revealed two types: a deficit in detecting coherent motion, resulting in low accuracy and a deficit in discriminating velocities, resulting in a slow performance. It is the first time these two deficits have been proven and they link to tracking difficulties, keeping the place on the page and accuracy. In the DST, reading is given a time limit as dyslexic readers have been found to be slow and effortful. These problems are linked by Nicolson & Fawcett (2008) to the cerebellar.

 

Sperling et al., (2005) found that noise levels affected the functioning of the pathways i.e. dyslexic children are less able to filter out background noise. By speaking to the child’s teacher, TA’s and parents, we can investigate whether they have auditory needs. Pammer and Vidyasagar (2005) suggest that both auditory and visual systems are compromised in dyslexics, arising from general impairment in the dorsal route for sensory impairment.

 

Whilst many dyslexics have difficulty with eye tracking, it could also be seen as a motor co-ordination or cerebellar difficulty. Since the discovery that the cerebellum has a function in reading, Nicholson and Fawcett have pursued their theory with renewed vigour (2008). In the 1990’s they challenged the phonological deficit theory by showing that dyslexics had other weaknesses which were unexplained: sequencing, handwriting, memory. Using balance, they showed that dyslexics couldn’t do two things at once: eg count and balance. The cerebellum’s role in motor skills is well established (ref?), this impacts on reading and especially writing, as dyslexics never reach the level of automaticity of their peers. Most dyslexics struggle with spelling in particular. It used to be argued that the cerebellum was not linked to the brain’s frontal lobes, which activate during reading, but new studies show it does indeed have the right connectivity (Fulbright et al 1999). Some would argue that problems with sequencing, multi-tasking and motor planning are indicators of dyspraxia. However, in support of the cerebellar theory, patients with cerebellar damage show dyslexic-type symptoms (Moretti et al, 2002).

 

The main argument hinges around automaticity, dyslexic children fail to acquire the automatic skills of reading and writing enjoyed by their peers. Postural/core stability will be affected if the cerebellum is implicated, therefore an assessment should test this, as poor postural stability would be a useful indicator. Within the DST was a balance tester, which tested stability by pushing into the child’s back. A discussion with the parents and/or teacher would also be useful on this area. Handwriting speed and accuracy is another aspect of the cerebellar theory, as is processing speed. Are letters well formed, legible with appropriate spacing? Has the learner always struggled with fine and gross motor control? eg fastening clothes and skipping. The cerebellar theory is attractive because it does account for several weaknesses that many dyslexics are known to possess. The cerebellum also controls eye movements so relates to the Magnocellular theory.

 

Theories abound and whilst there is much new research, there is still no consensus. Assessment should be made for the weaknesses we know dyslexics to display and timely intervention provided. The environment impacts massively on how the condition is manifested and may account for the different sub-types of dyslexia that are reported. It is crucial that intervention is tailored, based on a thorough assessment of the learner’s strengths and weaknesses. This will ultimately lead to a more effective outcome (Vellutino et. al 2004:31).

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