Specific reading disability (dyslexia): what have we learned in the past four decades?
Version of Record online: 9 JAN 2004
Journal of Child Psychology and Psychiatry
Volume 45, Issue 1, pages 2–40, January 2004
How to Cite
Vellutino, F. R., Fletcher, J. M., Snowling, M. J. and Scanlon, D. M. (2004), Specific reading disability (dyslexia): what have we learned in the past four decades?. Journal of Child Psychology and Psychiatry, 45: 2–40. doi: 10.1046/j.0021-9630.2003.00305.x
- Issue online: 9 JAN 2004
- Version of Record online: 9 JAN 2004
- Manuscript accepted 18 August 2003
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 reading-related 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.