In the English-speaking world, dyslexia is a familiar learning disorder. Most people are likely to have known someone who found reading and writing trickier than their peers.
In fact, more than one in 10 people that grew up with English as their first language are said to have dyslexia, with wide consensus pointing toward a person’s genetic history as the leading cause. One, it would appear, is either born dyslexic or not.
But there is also a phenomenon in which some people who speak both English and another language can be dyslexic in one, but not the other. The reason, it seems, is hidden in the characteristics of a language and its writing system.
“The English writing system is so irregular—print to sound or sound to print translation is not always one-to-one,” says Brunel University London’s Professor of Cognitive Neuroscience Taeko Wydell in a BBC radio documentary, “Dyslexia: Language and Childhood.”
“This irregularity or inconsistency makes it especially difficult for dyslexic individuals to master reading and writing in English,” she says.
So, for example, “mint,” “lint” and “hint” – all “int” words – are pronounced differently to the word “pint.”
And the words “through,” “though” and “tough” all sound different, despite looking on the page like they should sound similar. This makes English a so-called “opaque” language.
The only way one knows the individual pronunciations, is to learn and remember each exception, such as “pint” or “yacht,” individually.
“This kind of irregularity doesn’t happen in other languages such as Italian, Spanish or Finnish,” said Prof Wydell, pointing to so-called “transparent” languages where combinations of letters are always pronounced the same, with some rare exceptions.
As such, studies have shown Italian speakers are only half as likely to show signs of dyslexia than English speakers.
Levels of dyslexia can also be far lower in countries with a symbol-based writing system, such as Japanese or Chinese, because of how those writing systems are taught in schools.
When children learn to write Japanese Kanji or Chinese characters, they consistently repeat the order of strokes required to draw each character whilst speaking aloud the corresponding word.
This helps the motor sequence – the combination of small movements required to write each word or sound – get “wired in” to their brains.
“So when the child is asked to write later on, the child’s hands almost automatically write down the character from memory,” said Prof Wydell.
It’s therefore possible for people who learn to read and write in Chinese or Japanese to have no idea they have dyslexia until they later begin to learn English and are forced into reading and writing in a totally different way.
So low is the prevalence of diagnosed dyslexia in primary schools in Japan – as low as 1.4% when writing with syllabic Kana characters and 6.9% when writing with Kanji characters – that it wasn’t until 2006 that Prof Wydell published STRAW-I, the first and only standardized and systematic screening test for identifying dyslexia in Japanese primary school children.
The test has since been extended, with the new standardized test – STRAW-R – now being suitable for children up to 15 years old, significantly increasing the chance that young people in Japan will receive a timely diagnosis for dyslexia and be able to access to the right support throughout their schooling.
According to the International Dyslexia Association (IDA), dyslexia is a specific learning disability characterized by difficulties with accurate and/or fluent word recognition and spelling (Lyon et al., 2003). The IDA definition further proposes that these difficulties typically result from a deficit in the phonological component of language and are unexpected in relation to age and other cognitive and academic abilities.
The phonological difficulty most often associated with dyslexia is a deficit in phonological awareness, one’s sensitivity to, or explicit awareness of, the sound structure of language (Stanovich, 1988). It is generally argued that problems in phonological awareness make it difficult for children with dyslexia to learn how to apply the alphabetic principle to decode and spell printed words (Gillon, 2004).
Numerous studies have documented a deficit in phonological awareness in children with dyslexia or in children at risk for this disorder (Bradley & Bryant, 1983; Gallagher et al., 2000; Fletcher et al., 1994; H. Lyytinen et al., 2001).
The phonological processing problems associated with dyslexia also extend to areas other than phonological awareness. Specifically, children with dyslexia often demonstrate problems in phonological memory (Brady, Shankweiler, & Mann, 1983; Vellutino & Scanlon, 1982).
Among the phonological memory tasks with which children with dyslexia have difficulty is the nonword repetition task, in which participants must store and repeat a phonological sequence that could be a word in the language but is not. Research has shown that children with dyslexia consistently perform less well than control participants on nonword repetition tasks (Brady, Poggie, & Rapala, 1989; Catts, 1986; Hulme & Snowling, 1992; Kamhi & Catts, 1986; Snowling, 1981; van Daal & van der Leij, 1999; van der Bob & van der Pijl, 1997).
Studies have also demonstrated that heritability for dyslexia is higher when the disorder is combined with a deficit in nonword repetition (Bishop, 2001; Bishop, Adams, & Norbury, 2004; Raskind, Hsu, Berninger, Thomson, & Wijsman, 2000). Finally, research suggests a link between deficits in phonological memory and phonological awareness in that both deficits may result from an inefficiency in the formation of phonological representations (Elbro, 1996; Metsala & Walley, 1998).
Other research indicates that the language problems in dyslexia may go beyond those in phonological processing. Studies show that children with dyslexia may also have problems in semantics, syntax, and discourse (Catts, Fey, Tomblin, & Zhang, 1999; McArthur, Hogben, Edwards, Health, & Mengler, 2000; Plaza, Cohen, & Chevrie-Muller, 2001).
For ease of reference, these problems are referred to in this article as oral language difficulties and do not include a phonological processing deficit. Some of these oral language difficulties could be the result of reading problems themselves. Poor readers do not read as much as good readers do, and as a result may not have the same language learning opportunities as do good readers.
However, a growing number of studies demonstrate that oral language difficulties are present in children at risk for dyslexia prior to school entry (Gallagher et al., 2000; P. Lyytinen et al., 2001; Scarborough, 1990, 1991). For example, Scarborough (1990, 1991) followed 20 children with a family risk of dyslexia from 30 months through second grade.
The at-risk children who later developed dyslexia showed syntactic deficits in terms of reduced mean length of utterance and restricted use of syntactic structures during the preschool years. Whereas these oral language difficulties were present, they were typically not severe enough for children to have been identified as having SLI (Scarborough & Dobrich, 1990).
This has also been the case for other studies that have documented oral language problems in children with a family risk for dyslexia (e.g., Gallagher et al., 2000).
Specific language impairment represents a disorder in the development of oral language (Leonard, 1998). It is specific in that children with SLI have nonverbal IQ scores within normal limits and no hearing or socioemotional deficits.
The oral language problems observed in SLI include problems in semantics, syntax, and discourse (Paul, 2001).
Particular attention has been given to deficits in morpho-syntax (Leonard, 1998). For example, children with SLI have been shown to have problems in the acquisition of tense marking, and this deficit has been posited by some as a psycholinguistic or clinical marker of SLI (Conti-Ramsden, Botting, & Faragher, 2001; Bedore & Leonard, 1998; Rice & Wexler, 1996).
Children with SLI have also been reported to have problems in phonological processing. These include deficits in phonological awareness (Briscoe, Bishop, &Norbury, 2001; Catts, 1993; Joffe, 1998; Nathan, Stackhouse, Goulandris, & Snowling, 2004; Snowling et al., 2000) and phonological memory (Bishop, North, & Donlan, 1996; Briscoe et al., 2001; Dollaghan & Campbell, 1998; Edwards & Lahey, 1998; Ellis Weismer et al., 2000; Gathercole & Baddeley, 1990; Kamhi & Catts, 1986).
In fact, considerable attention has been paid to a link between SLI and deficits in phonological memory. Specifically, Gathercole and Baddeley (1990) observed that children with SLI performed poorly on measures of phonological memory, especially nonword repetition.
On the basis of their results, they proposed that SLI involves a specific deficit in the phonological loop component of working memory, which causes difficulties in semantic and syntactic development. Furthermore, Bishop et al. (1996) proposed that difficulty in nonword repetition may be a good phenotypic marker for SLI (also see Conti- Ramsden et al., 2001).
Given the problems that children with SLI appear to have in phonological processing, it would be expected that these children would also have difficulties in word reading. Indeed, studies have shown that children with SLI often have problems in learning to recognize printed words (Bishop & Adams, 1990, Catts, 1993; Catts, Fey, Tomblin, & Zhang, 2002; McArthur et al., 2000; Snowling et al., 2000; Tallal, Allard, & Curtiss, 1988).
For example, Tallal et al. (1988) found that approximately 67% of children with SLI at 4 years of age showed low achievement in word recognition at age 8. Silva, Williams, and McGee (1987) also reported evidence of low word reading achievement in children with SLI, but at a lower prevalence rate (approximately 35%). In addition, McArthur et al. (2000) found in a series of three studies that approximately 50% of school-age children with SLI concurrently had a specific reading disability characteristic of dyslexia. Snowling et al. (2000) also reported high rates of dyslexia in children with SLI.
Relationship Between Dyslexia and SLI
Given the documented overlap between SLI and dyslexia, what is the best way to characterize the relationship between these disorders? Three possible models of this relationship are depicted in Figure 1. According to Model 1, dyslexia and SLI are different manifestations of the same underlying cognitive deficit (Kamhi & Catts, 1986;Tallal et al., 1997).
In this model, a phonological processing deficit is responsible for both disorders. The different manifestations (SLI vs. dyslexia), however, result from variations in the severity of the phonological processing deficit. If the deficit is severe, children will show problems in word reading as well as difficulties in oral language (i.e., SLI).
If, on the other hand, the deficit is less severe, children will demonstrate problems in word reading and show limited or no problems in oral language (i.e., dyslexia).
If Model 1 is correct, there should be a great deal of overlap between SLI and dyslexia. Children with SLI and those with dyslexia should have problems on tasks involving phonological processing and word reading; however, these problems should be more severe in children with SLI.
Model 2 indicates that dyslexia and SLI are partially similar but distinct disorders. A model such as this was proposed by Bishop and Snowling (2004) in a recent review of the literature. According to Model 2, both disorders are similar in that they are characterized by a phonological processing deficit that underlies word-reading problems.
Unlike Model 1, the severity of the phonological deficit is equal, on average, in dyslexia and SLI. The disorders, however, are different in that SLI involves an additional cognitive deficit or deficits, which operates independently of the phonological processing deficit and causes problems in the development of oral language.
If this model is accurate, it would be expected that there would be considerable overlap between dyslexia and SLI in that both disorders would have similar problems in phonological processing and word reading.
However, the disorders would be distinct in that children with SLI would have difficulties in oral language, and those with dyslexia would show normal or at least low normal development in this area.
Model 3 depicts a third possible relationship between dyslexia and SLI. According to this model, dyslexia and SLI are distinct developmental disorders with different cognitive deficits and behavioral manifestations. As shown in this model, a phonological processing deficit is the core deficit in dyslexia and is responsible for the word reading problems of children with this condition.
Children with SLI, on the other hand, have a different deficit(s) at the core of their disability that causes problems in the development of oral language. Unlike Model 2, in which the overlap results from both disorders showing a deficit in phonological processing, the overlap in Model 3 is due to comorbidity (Caron & Rutter, 1991).
That is, although the disorders are distinct, they are related and sometimes occur together in the same individual. If this view is correct, it would be expected that greater-than-chance overlap should be found between SLI and dyslexia. However, numerous cases should be observed of children with SLI who do not have word reading problems (and a phonological processing deficit) and children with dyslexia who do not have a history of oral language difficulties.
In this article we report the results of two studies that sought to determine which of the above models best characterizes the relationship between dyslexia and SLI.1 In Study 1, we used a large longitudinal database to study the overlap between these developmental disorders.
This database included measurements of oral language (and IQ) in kindergarten, second, fourth, and eighth grades and assessments of word recognition in second, fourth, and eighth grades. In our analyses, we examined the percentage of children with SLI in kindergarten who had dyslexia in second, fourth, and eighth grades.
Conversely, we also determined the percentage of children identified as having dyslexia in second, fourth, or eighth grades who showed SLI in kindergarten.
In both of the above cases, SLI was identified during kindergarten. The decision to identify SLI at this point was based on several factors. First, because SLI is characterized by problems in the development of oral language, it has traditionally been diagnosed during the preschool years (Leonard, 1998; Rice & Wexler, 1996).
Second, it is preschool problems in oral language that have often been argued to be an early manifestation of dyslexia (Scarborough, 2005; Snowling et al., 2003; Tallal et al., 1997). Third, and perhaps most important, by identifying SLI in kindergarten, prior to formal reading instruction, we reduce the possibility that the oral language impairments associated with SLI are the result of dyslexia rather than an early manifestation of the disorder.
As noted above, children with dyslexia read less often and thus are not as able to take advantage of the language learning opportunities that accompany reading experience (Stanovich, 1986). This may in turn lead to the development of language problems during the school years (Share & Silva, 1987). Thus, by identifying oral language impairments in kindergarten, one can reduce the impact of poor reading on this diagnosis.
reference link : https://www.researchgate.net/publication/7299404
More information: Taeko N. Wydell. Developmental Dyslexia in Japanese, Developmental Dyslexia across Languages and Writing Systems (2019). DOI: 10.1017/9781108553377.009
Taeko N.. Cross-Cultural/Linguistic Differences in the Prevalence of Developmental Dyslexia and the Hypothesis of Granularity and Transparency, Dyslexia – A Comprehensive and International Approach (2012). DOI: 10.5772/31499