We summarize some of the most important findings from research evaluating the hypothesized causes of specific reading disability (dyslexia) over the past four decades. After outlining components of reading ability, we discuss manifest causes of reading difficulties, in terms of deficiencies in component reading skills that might lead to such difficulties. The evidence suggests that inadequate facility in word identification due, in most cases, to more basic deficits in alphabetic coding is the basic cause of difficulties in learning to read. We next discuss hypothesized deficiencies in readingrelated cognitive abilities as underlying causes of deficiencies in component reading skills. The evidence in these areas suggests that, in most cases, phonological skills deficiencies associated with phonological coding deficits are the probable causes of the disorder rather than visual, semantic, or syntactic deficits, although reading difficulties in some children may be associated with general language deficits. Hypothesized deficits in general learning abilities (e.g., attention, association learning, cross-modal transfer etc.) and low-level sensory deficits have weak validity as causal factors in specific reading disability. These inferences are, by and large, supported by research evaluating the biological foundations of dyslexia. Finally, evidence is presented in support of the idea that many poor readers are impaired because of inadequate instruction or other experiential factors. This does not mean that biological factors are not relevant, because the brain and environment interact to produce the neural networks that support reading acquisition. We conclude with a discussion of the clinical implications of the research findings, focusing on the need for enhanced instruction.

http://www.dr-hatfield.com/educ538/docs/Vellutino,+etal+2004.pdf

Specific reading disability (dyslexia): what have we learned in the past four decades?

The authors report a systematic meta-analytic review of the relationships among 3 of the most widely studied measures of children's phonological skills (phonemic awareness, rime awareness, and verbal short-term memory) and children's word reading skills The review included both extreme group studies and correlational studies with unselected samples (235 studies were included, and 995 effect sizes were calculated) Results from extreme group comparisons indicated that children with dyslexia show a large deficit on phonemic awareness in relation to typically developing children of the same age (pooled effect size estimate: -137) and children matched on reading level (pooled effect size estimate: -057) There were significantly smaller group deficits on both rime awareness and verbal short-term memory (pooled effect size estimates: rime skills in relation to age-matched controls, -093, and reading-level controls, -037; verbal short-term memory skills in relation to age-matched controls, -071, and reading-level controls, -009) Analyses of studies of unselected samples showed that phonemic awareness was the strongest correlate of individual differences in word reading ability and that this effect remained reliable after controlling for variations in both verbal short-term memory and rime awareness These findings support the pivotal role of phonemic awareness as a predictor of individual differences in reading development We discuss whether such a relationship is a causal one and the implications of research in this area for current approaches to the teaching of reading and interventions for children with reading difficulties

https://psycnet.apa.org/journals/bul/138/2/322.pdf

Phonological skills and their role in learning to read: A meta-analytic review.

This study used a nonreferred sample of twins to contrast the performance of individuals with reading disability (RD; n = 93), attention-deficit/hyperactivity disorder (ADHD; n = 52), RD and ADHD (n = 48), and neither RD nor ADHD (n = 121) on measures of phoneme awareness (PA) and executive functioning (EF). Exploratory factor analysis of the EF measures yielded underlying factors of working memory, inhibition, and set shifting. Results revealed that ADHD was associated with inhibition deficits, whereas RD was associated with significant deficits on measures of PA and verbal working memory. The RD + ADHD group was most impaired on virtually all measures, providing evidence against the phenocopy hypothesis as an explanation for comorbidity between RD and ADHD.

A comparison of the cognitive deficits in reading disability and attention-deficit/hyperactivity disorder.

Background: An inhibition deficit, including poor interference control, has been implicated as one of the core deficits in AD/HD. Interference control is clinically measured by the Stroop Colour-Word Task. The aim of this meta-analysis was to investigate the strength of an interference deficit in AD/HD as measured by the Stroop Colour-Word Task and to assess the role of moderating variables that could explain the results. These moderating variables included: methods of calculating the interference score, comorbid reading and psychiatric disorders, AD/HD-subtypes, gender, age, intellectual functioning, medication, and sample size. Methods: Seventeen independent studies were located including 1395 children, adolescents, and young adults, in the age range of 6‐27 years. A meta-analysis was conducted to assess the effect sizes for the scores on the word and the colour card as well as the interference score. Results: Children with AD/HD performed more poorly on all three dependent variables. The effect sizes for word reading (d ¼ .49) and colour naming (d ¼ .58) were larger and more homogeneous than the effect size for the interference score (d ¼ .35). The method used to calculate the interference score strongly influenced the findings for this measure. When interference control was calculated as the difference between the score on the colour card minus the score on the colour-word card, no differences were found between AD/HD groups and normal control groups. Discussion: The Stroop Colour-Word Task, in standard form, does not provide strong evidence for a deficit in interference control in AD/HD. However, the Stroop Colour-Word Task may not be a valid measure of interference control in AD/HD and alternative methodologies may be needed to test this aspect of the inhibitory deficit model in AD/HD. Keywords: AD/HD, Stroop Colour-Word Task, interference control, rapid naming, metaanalysis. Abbreviations: AD/HD: Attention Deficit/Hyperactivity Disorder; C: Colour; CD: Conduct Disorder; CW: Colour-Word; ODD: Oppositional Defiant Disorder; W: Word.

/pdf/the-stroop-revisited-a-meta-analysis-of-interference-control-3ibfktrwz5.pdf

The Stroop revisited: a meta-analysis of interference control in AD/HD

Developmental dyslexia is not just a literacy problem. Dyslexics' reading and spelling difficulties are but two of a much larger number of differences between dyslexic and normal readers. The condition is a wide-ranging, genetically based, neurodevelopmental syndrome. Reading requires fast and accurate processing of transient visual and auditory stimuli, functions for which large neurones, known as magnocellular, are specialized. We review the evidence that many dyslexics have impaired function of the visual magnocellular system, which correlates with their reading impairment, whereas good readers have high magnocellular sensitivity. We discuss possible mechanisms for this relationship. Although there is no such clearly defined magnocellular pathway in the auditory system as there is for vision, there is an analogous set of large auditory neurones which are specialized for following changes in the frequency or amplitude of sounds. We review evidence that the sensitivity of this auditory transient system is reduced in many dyslexics and that this reduction correlates with, hence may cause, their impaired phonological ability. As for the visual magnocellular system we show that auditory transient sensitivity predicts phonological and reading ability not only in dyslexics but also in good readers. Thus the magnocellular hypothesis postulates that dyslexics have lower sensitivity to dynamic visual and auditory stimuli as a result of slightly impaired development of large neurones and that this may explain not only their visual problems when attempting to read, but also their phonological deficit. Copyright © 1999 John Wiley & Sons, Ltd.

Impaired neuronal timing in developmental dyslexia—the magnocellular hypothesis

Most individuals interested in reading disability favor the view that disordered language processing is the main cause of children's reading problems and that visual problems are seldom, if ever, responsible. Nevertheless, in a preliminary study (Eden, Stein, & Wood, 1993) we showed that visuospatial and oculomotor tests can be used to differentiate children with reading disabilities from nondisabled children. In the present study we investigated a larger sample of children to see if these findings held true. Using 93 children from the Bowman Gray Learning Disability Project (mean age = 11.3 years; 54 boys, 39 girls), we compared the phonological and visuospatial abilities of nondisabled children (children whose reading at fifth grade rated a Woodcock-Johnson reading standardized score between 85 and 115), and children with reading disability (whose reading standardized score was below 85 on the Woodcock-Johnson). In addition to performing poorly on verbal tests, the children with reading disability were ...

Maria H. Wood

Papers

Verbal and Visual Problems in Reading Disability