Dyslexia Diagnosis And Training Research Paper

1. The Definition Of Dyslexia

Since the landmark Isle of Wight studies, it has become conventional to distinguish children who have specific reading difficulties (dyslexia) from children who have reading difficulties in the context of more general learning problems (reading backwardness). A child is considered to have a specific problem with reading if their reading attainment is significantly below that predicted from their general cognitive ability on the basis of the correlation between reading and IQ in children of the same age (a discrepancy between expected and actual attainment). However, a limitation inherent in the ‘discrepancy-definition’ of dyslexia is its dependence on IQ because the verbal IQ of poor readers is likely to decline as a consequence of their limited reading experience. Thus, diagnosis using this definition of dyslexia runs the risk of missing true cases of dyslexia either in children whose verbal IQ is lowered, or in those who have overcome their reading problems but may have significant difficulty with spelling and written work.

2. Dyslexia As A Core Phonological Deficit

The most widely accepted current view of dyslexia is that it is part of the continuum of language disorders and reflects phonological (speech) processing difficulties (Share 1995). These include problems with phonological awareness, verbal short-term memory, naming especially in speeded tasks, phonological learning, speech perception and nonword repetition. Current theories suggest that dyslexic children have difficulties first in establishing, and later in accessing, adequate phonological representations. The strong evidence of phonological deficits in dyslexia has led to the definition of dyslexia as a core phonological deficit, irrespective of IQ (Stanovich and Siegel 1994). This definition makes sense in terms of what is known about normal reading acquisition; phonemic skills are critical to the development of the alphabetic principle that allows children to decode words they have not seen before. Dyslexic children typically have difficulty reading words that are not part of their sight vocabulary, such as non-words.

3. Subtypes Of Dyslexia

Most systematic studies of individual differences among dyslexics have revealed variations in their reading skills. As well as dyslexic children who have difficulties using phonological strategies for reading and spelling, it is possible to identify others who appear to have mastered alphabetic skills and can use these proficiently; at least when there are no time demands. Such children have been referred to as developmental ‘surface’ dyslexics. These children rely heavily upon phonological strategies for reading and spelling. Thus, they tend to pronounce irregular words as though they were regular (e.g., island—izland), they have particular difficulty distinguishing between homophones like pear-pair, and their spelling is usually phonetic.

A number of recent studies have suggested that individual differences in the reading skills of dyslexic readers might be explained by differences in the severity or developmental status of underlying phonological skills. Thus, children with phonological dyslexia appear to have a disorder of reading development whereas surface dyslexics are developmentally delayed in their acquisition of reading skills (Snowling 2000).

4. Dyslexia Across The Life-Span

A second advantage of the core phonological deficit hypothesis of dyslexia is that it accounts well for the changing profile of dyslexia across the life span. While reading problems are the key symptom of dyslexia in the early school years, adults with a childhood history of dyslexia often become fluent readers though few overcome their spelling problems. Adult dyslexics also have difficulty decoding words they have not seen before (i.e., nonwords) and with phonological awareness, speeded naming and verbal short-term memory tasks.

At the other end of the age spectrum, preschool children with a genetic risk of dyslexia show phonological difficulties in the context of slower than expected vocabulary development (Gallagher et al. 2000). Indeed, problems of phonological awareness, together with limitations of letter knowledge presage reading difficulties in high-risk children (Byrne et al. 1997, Lefly and Pennington 1996).

5. The Assessment Of Dyslexia

The convergence of evidence from studies of the normal development of reading and from dyslexia enables practitioners both to identify children at risk of dyslexia and to provide early intervention. Children who have a family history of dyslexia and children who have a history of speech-language difficulties appear to be at risk, although the nature of the speechlanguage impairment is an important factor in determining outcome. By school entry it is possible to identify with some certainty, children who will go on to have difficulties with reading by assessing their performance on tests of phonological awareness and letter knowledge. With young children in the age range of four to five, tests of syllable and rhyme awareness seem the most suitable, while from six years onwards, tests requiring awareness of spoken words at the level of the phoneme are the most sensitive.

In spite of the attractions of the core phonological definition of dyslexia, the whole-scale abandonment of general cognitive ability in the diagnosis of dyslexia would be hazardous. For children who have already failed to learn to read, the starting point of the assessment should involve an assessment of general cognitive ability. This form of assessment is important in diagnosing whether dyslexia accompanies a broader language disorder (Bishop 1997) or the syndrome of nonverbal learning disabilities (Rourke 1995). However, the assessment will be most useful if it proceeds to assess the phonological skills that underlie reading development and the reading strategies the child is currently using with a view to prescribing appropriate intervention (Snowling and Stackhouse 1996). From the point of view of diagnosis, a limitation of the core phonological definition of dyslexia is its focus on phonology and the development of decoding skills. Whilst there is a consensus that automatic decoding skills are critical to reading development, proficient reading is the product of both decoding and linguistic comprehension skills. Although dyslexic readers have basic level decoding difficulties, many have normal linguistic comprehension that can afford them a number of advantages; they tend to comprehend what they read relatively well and they can monitor their comprehension processes.

6. Comorbidity And Compensation

Some of the variation among dyslexics seen at the behavioural level may be due to comorbidity between dyslexia and another disorder. A substantial body of research suggests that many dyslexic children have low level impairments of the transient visual system (Hogben 1997). Although there is no conclusive evidence that these are causally linked with dyslexic children’s reading impairments, such problems may affect the ability of children who have phonological difficulties to compensate. Similarly, some dyslexic children have motor impairments and others problems of attention control (Pennington et al. 1993).

Arguably, the course of reading development followed by a particular dyslexic child will be determined not only by the severity of their phonological processing problem, but also by their other cognitive skills (Snowling 2000). For dyslexic children who have good semantic skills and poor phonology, it is likely that their word recognition will improve in the face of decoding deficits because they rely heavily on context. In contrast, dyslexic children who have milder phonological difficulties or poorer general language skills will tend to show delayed development along normal lines. Furthermore, the environmental variables impinging upon the dyslexic child are critical to eventual outcome. Cross-linguistic studies are beginning to reveal that the manifestations of dyslexia depend on the orthography in which a child learns to read (Frith et al. 1998). More generally, print exposure, a measure of the extent to which a child reads, is an independent predictor of reading attainment.

7. Interventions For Dyslexia

There is now a considerable body of literature pointing to the benefits of phonological awareness training to subsequent literacy development (Toija 1999). Training in phonological skills is particularly effective when it is combined with highly structured reading tuition. However, it is also becoming clear that dyslexic children and children at risk of dyslexia respond relatively less well to these techniques than normally developing readers (Byrne et al. 1997). Indeed, initial phonological skill is one of the best predictors of responsiveness to intervention in such training regimes (Hatcher and Hulme 1999). For children who do not respond to such treatments, more intensive therapies may need to be designed and special school placement considered.

Bibliography:

1. Bishop D V M 1997 Uncommon Understanding. Psychology Press, Hove, UK
2. Byrne B, Fielding-Barnsley R, Ashley L, Larsen K 1997 Assessing the child’s contribution to reading acquisition: What we know and what we don’t know. In: Blachman B A (ed.) Cognitive and Linguistic Foundations of Reading Acquisition and Dyslexia. Lawrence Erlbaum Associates, Hillsdale, NJ
3. Frith U, Wimmer H, Landerl K 1998 Differences in phonological recoding in German and English speaking children. Scientific Studies of Reading 2: 31–54
4. Gallagher A, Frith U, Snowling M J 2000 Precursors of literacy delay among children at genetic risk of dyslexia. Journal of Child Psychology and Psychiatry 41: 203–13
5. Hatcher P J, Hulme C 1999 Phonemes, rhymes and intelligence as predictors of children’s responsiveness to remedial reading instruction: evidence from a longitudinal intervention study. Journal of Experimental Child Psychology 72: 130–53
6. Hogben J H 1997 How does a visual transient deficit affect reading? In: Hulme C, Snowling M (eds.) Dyslexia, Biology and Cognition. Whurr, London
7. Lefly D L, Pennington B F 1996 Longitudinal study of children at family risk for dyslexia: The first two years. In: Rice M L (ed.) Toward a Genetics of Language. Lawrence Erlbaum Associates, Mahwah, NJ, pp. 49–76
8. Pennington B F, Grossier D, Welsh M C 1993 Contrasting cognitive defects in attention deficit hyperactivity disorder vs. reading disability. Developmental Psychology 29: 511–23
9. Rourke B P 1995 Syndrome of Nonverbal Learning Disabilities. Guildford Press, New York
10. Seymour P H K 1986 A Cognitive Analysis of Dyslexia. Routledge, London
11. Share D L 1995 Phonological recoding and self-teaching: sine qua non of reading acquisition. Cognition 55: 151–218
12. Snowling M J 2000 Dyslexia. Blackwell, Oxford, UK
13. Snowling M J, Stackhouse J 1996 Dyslexia. Speech and Language: a Practitioners Handbook. Whurr Publishers, London
14. Stanovich K E, Siegel L S 1994 The phenotypic performance profile of children with reading disabilities: a regression-based test of the phonological-core variable-difference model. Journal of Educational Psychology 86: 24–53
15. Toija G A 1999 Phonological awareness intervention research: a critical review of the experimental methodology. Reading Research Quarterly 34: 28–52