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

Abstract

We summarize some of the most important findings from research evaluating the hypothesized causes of specific reading disability (ÔdyslexiaÕ) 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.

Neurocognitive Development and Predictors of L1 and L2 Literacy Skills in Dyslexia: A Longitudinal Study of Children 5–11 Years Old

“…For many years the theory of impaired phonological skills has had a dominant position, and has also been seen as a causal explanation of dyslexia (Vellutino et al ., 2004). But the theory has also been questioned, mainly because it has been given a definitional status without being clearly defined (see e.g.…”

The notion of ‘phonology’ in dyslexia research: cognitivism—and beyond

“…The main argument for the theory of phonological awareness is the high correlation between awareness of sound segments and reading performance (Vellutino et al, 2004). This finding has been replicated so often that it is considered to reflect a causal relationship.…”

“…If we take a look at the state of the art in dyslexia research, we find that Vellutino et al (2004) highlight the causal relationship between phonological awareness and the ability to read and write. Their notion of causality is, however, constrained by what we have claimed to be poor definitions of basic terms.…”

“…(Taylor, 1991, p. 28) The belief in the existence of an underlying system along these lines is firm in dyslexia research: 'We earlier defined phonological coding as the ability to use speech codes to represent information in the form of words and parts of words.' (Vellutino, Fletcher, Snowling, & Scanlon, 2004). However, as we are not alone in thinking, this approach is unfortunate if the focus is to be kept on empirical science:…”

“…Written language is only 'linguistic' in the sense that it is dependent on spoken language skills. (Liberman et al, 1989;Vellutino, 1979;Vellutino et al, 2004). Throughout Vellutino's book on dyslexia (1979), the notion of 'linguistic' is reserved for speech.…”