Dyslexia Disorder Description

Dyslexia Disorder description

Dyslexia is a hereditary “neurodevelopmental disorder” that is recognised by slow and incorrect word recognition and inadequate reading/ spelling skills despite having the ability to learn (Peterson & Pennington, 2012). Dyslexia can be acquired, where a reading impairment occurs in individuals who had previously learnt how to read but have lost that ability due severe brain damage (Peterson & Pennington, 2012). The more common type however, seems to be developmental dyslexia, a reading impairment that occurs in often a child who has not learnt how to read normally in the first place (Coltheart & Jackson, 1998). According to the International Classification of Diseases (as cited in Silvia, Ueki, Oliveira, Boggio, & Macedo, 2016) developmental dyslexia is categorised as a specific reading disorder and is a well-known learning disability. Individuals with developmental dyslexia have a have a specific impairment in attaining reading skills that causes them to have difficulty with accurate and effortless word recognition and spelling (Silvia et al., 2016). Many children with developmental dyslexia have these impairments despite having intelligence, satisfactory instructions and no obvious neurological or sensory impairment (Snowling, 2008).

A study conducted by Stein (2001) found that 5-10% of children will fail to read to adequate standards regardless of their supportive environment. Dyslexia can be identified when individuals start to exhibit slow and influent reading, often making mistakes, such as mixing up letters and syllables incorrect word recognition (Ramus, Rosen, Dakin, Day, Castellote, White & Frith, 2003). Dyslexia can be identified in children through various reading tests to assess where their reading abilities lay compared to other children of the same age (Castles. A., personal communication, 2018). However, it is possible that some children might not have had the chance to learn reading. They are removed from the classification by providing them with supportive environment to learn to read and then comparing their reading skills after a short period of time to see if they have come up to range (Castles. A., personal communication, 2018). Reading involves many processes and therefore different kinds of dyslexia depending on which reading subskill has not developed (Castles. A., personal communication, 2018).

There are five main types of dyslexia. Surface dyslexia is when individuals have difficulty acquiring whole words (Castles. A., personal communication, 2018). Phonological dyslexia occur in individuals who have poor knowledge of letter-sound rules (Ramus et al., 2003). Individuals with Hyperlexia have accuracy in reading aloud of single words and nonwords normal for their age but their single word reading comprehension is inadequate (Castles. A., personal communication, 2018). Letter- identification is when single letters cannot be identified and letter- position dyslexia is when letters are identified accurately but their position within the word is not (Castles. A., personal communication, 2018). Case studyPatient R.E (Butterworth & Campbell, 1985)Patient R.E is a well-educated university graduate, who has a rare difficulty in reading and spelling nonwords (Butterworth & Campbell, 1985). R. E’s developmental dyslexia had been overlooked when she was a child and she went on graduating from university with her reading impairment being unnoticed. Due to her on-going illnesses, she was unable to attend school and was home schooled by her mother most of her life (Butterworth & Campbell, 1985). According to her mother, R.E. spoke well from an early age. However, on starting school, her reading failed to progress. Patient R.E was first noticed by Butterworth and Campbell (1985) when they observed that R.E could not read a new word aloud until she heard someone else say it.

Butterworth and Campbell (1985) then conducted an examination on patient R.E, investigating some parts of reading and writing, to determine exactly where the impairment occurred. The study states that “R.E.’s neuropsychological cerebral organization is normal.” (Butterworth and Campbell, 1985, p.440). It was observed that R.E performs at above average levels on standard tests of reading, spelling and cognitive ability. However, she performs inadequately on tasks that need knowledge of phonemic structure, like “nonword reading, rhyme judgement and homophone matching” (Butterworth & Campbell, 1985, p. 446). Butterworth and Campbell (1985, p.442) found that R.E can read aloud, correctly and without hesitancy, unusual and irregularly spelled words such as “placebo and idyll”. In this test, out of the 45 irregularly spelt words R.E was able to accurately read aloud and provide correct definitions for 33 of them. On the basis of this, R.E can be classified as a good reader. Secondly R.E was asked to read aloud words from a list of 30, three letter nonwords. From these words, she was unable to provide the correct pronunciation for nine of them and her reading of each word was very slow and hesitant (Butterworth & Campbell, 1985). R.E was then asked to read a list of longer nonwords, in which out of 20 she was only able to adequately read aloud three of them. She claimed to have found this task very tiring and gave up many times (Butterworth & Campbell, 1985). This study suggested that R.E. shows a particular deficit in the capability to recall and manipulate phonemic information, which is essential to pronounce most nonwords stimuli (Butterworth & Campbell, 1985).

The study concludes that R.E has deficits related to phonological decoding impairments, shown by her low scores on the phonological awareness tasks (Butterworth & Campbell, 1985). Cognitive theoryThe phonological theory suggests that people with dyslexia have a specific deficit in the, “storage or recovery and representation of speech sounds”, known as phonemes (Peterson & Pennington, 2012, p.4). According to the phonological theory of dyslexia, individuals lack the capability to attend to and manipulate letter sounds which is crucial for various oral language tasks such as nonword reading (Ramus et al., 2003). The theory suggests that, it is the process of phonological coding that determines accurate and fluent reading and word recognition, therefore a deficit in this process leads to poor performance in phonemic awareness tasks (Silvia et al., 2016). To read an alphabetic system, it is necessary to learn the “grapheme- phoneme correspondence” which is the relationship between the letters and the sound it creates (Ramus, 2001, p.2). The theory suggests that dyslexic individuals have deficits in representing those sounds in their brain and recalling them, hence there is an impairment with the organisation of phoneme-grapheme mappings in dyslexic brains (Ramus, 2001). For example, to read nonwords accurately the reader must be able to recall the sounds and map them onto letters and assemble a pronunciation for that word, however, individuals with dyslexia lack this ability (Wimmer, 1996).

Evidence The most significant indication of phonological dyslexia the inability to read nonwords. This is due to the fact that nonword reading is more highly dependent on phonological processes compared to reading of words (Ramus, 2001). The discovery that there are dyslexic patients such as patient R.E, that can read words accurately but not nonwords supports the phonological theory of dyslexia. Observations of patients like R.E, who have low scores in phonological awareness tasks, and have difficulty in retaining speech in short-term memory supports the theory that dyslexic individuals have a phonological deficit (Butterworth & Campbell, 1985). The finding that R.E has an unusual difficulty in reading and spelling nonwords provides evidence that she must have a deficit in the ability to store and recall phonemes (Butterworth & Campbell, 1985).

Many other individual case studies and group studies have also found evidence to support the phonological theory of dyslexia. Stothard, Snowling & Hulme (1996) studied the case of LF, a normal child with average intelligence, who had significant difficulties with phonological tasks. It was observed that even though LF’s reading and spelling skills were proficient, her nonword reading was impaired (Stothard et al., 1996). They proposed that LF has severe phonological impairments, shown by her poor performance on phonological tasks. Snowling, Stackhouse and Rack (1996) investigated seven developmental dyslexics who were observed to have problematic nonword reading numerous spelling errors. Based on poor their performance on phonological awareness and short-term memory tests, Snowling et al. (1986) also concluded that all of the subjects studied can be seen to have phonological deficits. These studies suggest that the subjects lack the phonological representations that are needed in order to learn to read fluently and therefore provide evidence that provides support for the phonological theory (Butterworth & Campbell, 1985; Stothard et al., 1996; Snowling et al. 1986). However, a study conducted by Stein (2001) suggest that dyslexics have difficulties in learning to read due to magnocellular pathways involved in vision and hearing being impaired. This study however, includes limitations such as the measurement of visual attention using linguistic stimuli and has faced major criticism for being unable to replicate the findings (Stein, 2001; Ramus, 2001).

Conclusion

In conclusion, previous studies of dyslexic individuals such as R.E and LF, provide evidence that dyslexia is caused by the inability to map representations of speech sounds onto letters (Butterworth & Campbell, 1985; Stothard et al., 1996). Most of the existing literature provide evidence and support towards the phonological theory of dyslexia, while accepting that there is possible interaction with other neurocognitive factors (Butterworth & Campbell, 1985; Stothard et al., 1996; Snowling et al. 1986; Ramus et al., 2003). However, the present literature does contain its limitations. Many of the studies were conducted on a small sample size, lack replication, and age and gender bias was present (Ramus et al., 2003; Carroll & Snowling, 2004). Recent studies suggest that, a single phonological deficit is insufficient to cause dyslexia, as there seem to be few rare cases of children with other language disorders, that have normal reading despite these deficits (Peterson & Pennington, 2012). Future research should further, investigate the how visual problems are associated with reading and how the phonological deficit interacts with other linguistic, visual, auditory and environmental, factors to cause a reading impairment.

References:

1. Campbell, R., & Butterworth, B. (1985). Phonological Dyslexia and Dysgraphia in a Highly Literate subject: A Developmental Case with Associated Deficits of Phonemic Processing and Awareness. The Quarterly Journal of Experimental Psychology Section A, 37(3), 435–475. https://doi.org/10.1080/14640748508400944
2. Carroll, J. M., & Snowling, M. J. (2004). Language and phonological skills in children at high risk of reading difficulties. Journal of Child Psychology and Psychiatry, 45(3), 631–640. https://doi.org/10.1111/j.1469-7610.2004.00252.x
3. Coltheart, M., & Jackson, N. E. (1998). Defining Dyslexia. Child Psychology and Psychiatry Review, 3(1), 12–16. https://doi.org/10.1017/S1360641797001378
4. Peterson, R. L., & Pennington, B. F. (2012). Developmental dyslexia. The Lancet, 379, 1997–2007. https://doi.org/10.1016/S0140-6736(12)60198-6
5. Ramus, F. (2001). Dyslexia: Talk of two theories. Nature. https://doi.org/10.1038/35086683
6. Ramus, F., Rosen, S., Dakin, S. C., Day, B. L., Castellote, J. M., White, S., & Frith, U. (2003). Theories of developmental dyslexia: Insights from a multiple case study of dyslexic adults. Brain, 126(4), 841–865. https://doi.org/10.1093/brain/awg076
7. Silva, P. B., Ueki, K., Oliveira, D. G., Boggio, P. S., & Macedo, E. C. (2016). Early stages of sensory processing, but not semantic integration, are altered in dyslexic adults. Frontiers in Psychology, 7(APR). https://doi.org/10.3389/fpsyg.2016.00430
8. Snowling, M. J. (2008). Specific disorders and broader phenotypes: The case of dyslexia. Quarterly Journal of Experimental Psychology, 61(1), 142–156. https://doi.org/10.1080/17470210701508830
9. Snowling, M., Stackhouse, J., & Rack, J. (1986). Phonological dyslexia and dysgraphia—a developmental analysis. Cognitive Neuropsychology, 3(3), 309-339.
10. Stein, J. (2001). The Magnocellular Theory of Developmental Dyslexia. Dyslexia, 7(1), 12–36. https://doi.org/10.1002/dys.186

11. 11. Stothard, S. E., Snowling, M. J., & Hulme, C. (1996). Deficits in Phonology but Not Dyslexic? Cognitive Neuropsychology, 13(5), 641–672. https://doi.org/10.1080/026432996381872

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12. 12. Wimmer, H. (1996). The nonword reading deficit in developmental dyslexia: Evidence from children learning to read German. Journal of Experimental Child Psychology, 61(1), 80–90. https://doi.org/10.1006/jecp.1996.0004