Discussion: Dyslexia a milder form of specific language impairment?
Dyslexia and Specific language impairment (SLI) are two of the most commonly occurring learning disorders among children (Pennington and Bishop, 2009). SLI and dyslexia have similar a prevalence in modern day society and is estimated to affect 3 – 10% of children (Tomblin, 1997). Broadly speaking dyslexia has generally been viewed as a disorder that includes a deficit in printed word recognition whereas SLI is more to do with oral language deficits (Ramus, Marshall, Rosen and Van der Lely, 2010). Research investigating both of these disorders over many years has been vast but has traditionally been carried out by separate professionals and disciplines. Typically SLI research was conducted by speech/language pathologists and clinical linguists and dyslexia studies were mainly carried out by educational psychologists (Fraser, Goswami, and Ramsden, 2010). Although dyslexia and SLI have often been treated and classified as distinct disorders in the past, the recent reclassification of dyslexia in the 1970’s as a language disorder has bought attention to the striking similarities (Bishop and Snowling, 2004). This has resulted in the general consensus regarding the nature of the relationship between these disorders as “...different manifestations of the same underlying problem differing only in severity or developmental stage” (Bishop and Snowling, 2004). However there are various research findings and theories that offer persuasive arguments and evidence suggesting opposing and conflicting views about the relationship of dyslexia and SLI. This essay aims to determine whether dyslexia can be considered as a mild form of SLI. This will be achieved by reviewing a range of factors on varying levels, firstly by comparing the definitions of each disorder drawing on any overlap or similarities that indicate supportive or opposing evidence. Secondly, evaluation of current literature and prominent findings that advocate and oppose the notion of dyslexia being a milder form of SLI will be carried out. Thirdly, causational aspects: etiology and neurobiology (biology and environment), cognition and behaviour of dyslexia and SLI will be investigated with consideration to commonalities and disparities. Finally, this essay will review the most renowned models and hypotheses that pertain to the relationship between these two disorders. An argument will be made throughout the essay and a conclusion will be drawn from the evidence presented as to whether dyslexia can be considered as a milder form of SLI. Firstly, examining the definitions of dyslexia and SLI results in an inconclusive conclusion. Both dyslexia and SLI can be defined in various ways due to the varying levels of severity and subcategories of each disorder. For the purpose of this essay the definitions that will be used are the definitions that appeared most frequently cited among the literature reviewed. These definitions are specific yet broad enough to encompass the range of different levels and subcategories. Leonard (1998) describes SLI as oral language that is impaired and lagging behind other areas of development for no apparent reason. Snowling (2000) defines dyslexia as having poor literacy skills despite adequate intelligence and opportunity to learn. The diagnosis criteria in both disorders are similar in that they both specify that no other impairment should be present that could account for these deficits (i.e. hearing problems) patients must display an otherwise normal IQ level and display no signs of any other handicaps or disadvantages that may affect the learning process (Newbury et al, 2011). Both dyslexia and SLI have similar aspects with diagnosis and overlapping exclusion criteria’s, however, the definitions are distinctly different in that they both specify impairments in different aspects of development, literacy skills in dyslexia and oral skills in SLI. It could be argued that due to...
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