The double-deficit hypothesis for the developmental dyslexias.

Abstract

The authors propose an alternative conceptualization of the developmental dyslexias, the double-deficit hypothesis (i.e., phonological deficits and processes underlying naming-speed deficits represent 2 separable sources of reading dysfunction). Data from cross-sectional, longitudinal, and cross-linguistic studies are reviewed supporting the presence of 2 singledeficit subtypes with more limited reading impairments and 1 double-deficit subtype with more pervasive and severe impairments. Naming-speed and phonological-awareness variables contribute uniquely to different aspects of reading according to this conception, with a model of visual letter naming illustrating both the multicomponential nature of naming speed and why naming speed should not be subsumed under phonological processes. Two hypotheses concerning relationships between naming-speed processes and reading are considered. The implications of processing speed as a second core deficit in dyslexia are described for diagnosis and intervention. A major tenet of the best developed theory of reading disabilities is that a core deficit in phonological processes impedes the acquisition of word recognition skills, which, in turn, impedes the acquisition of fluent reading (Bradley &

Enhancement of brain event-related potentials to speech sounds is associated with compensated reading skills in dyslexic children with familial risk for dyslexia

“…Furthermore, language and language-based deficits can be divided into semantic and syntactic deficits (like vocabulary deficits) and phonological deficits, but a double-deficit hypothesis has also been introduced. The double-deficit hypothesis suggests the existence of three subtypes of reading disability: phonological deficits (like phonological awareness and letter-sound decoding), a rapid naming deficit that disrupts orthographic processing and reading speed, or both of the aforementioned types of deficits (Bowers & Wolf, 1993;Wolf & Bowers, 1999;Wolf et al, 2000). Rapid automatized naming (RAN) is a task of naming a series of familiar items as quickly as possible (Denckla & Rudel, 1976).…”

Genetic and environmental effects of serial naming and phonological awareness on early reading outcomes.

“…More recently, others have suggested that in addition to phonology, naming speed constitutes an independent and additive source of variance in early reading skills (e.g., Wolf & Bowers, 1999). In a recent meta-analysis, Swanson, Trainin, Necoechea, and Hammill (2003) examined the association between phonological awareness, rapid automatized naming (RAN), reading, and related abilities in a set of 49 independent samples.…”

Lexical access and phonological decoding in adult dyslexic subtypes.

“…Adult dyslexic individuals have also shown impairments in phonological awareness and rapid naming (Felton, Naylor, & Wood, 1990), and it is likely that these variables reflect genuine impairments, as opposed to some form of developmental delay. It can also be argued that phonological awareness and rapid naming represent distinctly different cognitive components underlying reading (Wolf & Bowers, 1999, giving rise to different subtypes of adult dyslexia.Although the heterogeneity of dyslexic populations has supported the separation of dyslexic subtypes, in many cases the evidence has been purely empirical and has lacked theoretical grounding. One theoretical approach comes from models of word recognition.…”