title: The double-deficit hypothesis: a comprehensive analysis of the evidence.
abstract: The double-deficit hypothesis of developmental dyslexia proposes that deficits in phonological processing and naming speed represent independent sources of dysfunction in dyslexia. The present article is a review of the evidence for the double-deficit hypothesis, including a discussion of recent findings related to the hypothesis. Studies in this area have been characterized by variability in methodology--how dyslexia is defined and identified, and how dyslexia subtypes are classified. Such variability sets limitations on the extent to which conclusions may be drawn with respect to the double-deficit hypothesis. Furthermore, the literature is complicated by the persistent finding that measures of phonological processing and naming speed are significantly correlated, resulting in a statistical artifact that makes it difficult to disentangle the influence of naming speed from that of phonological processing. Longitudinal and intervention studies of the double-deficit hypothesis are needed to accumulate evidence that investigates a naming speed deficit that is independent of a phonological deficit for readers with dyslexia. The existing evidence does not support a persistent core deficit in naming speed for readers with dyslexia.
authors.affiliation: Department of Educational Psychology, University of British Columbia, Vancouver.
authors.forename: Rose K
authors.initials: RK
authors.lastname: Vukovic
authors.forename: Linda S
authors.initials: LS
authors.lastname: Siegel
mesh_terms: D002648:Child; D004410:Dyslexia / Q000209:etiology*; D006801:Humans; D011582:Psychological Theory