Testing the double-deficit hypothesis in an adult sample

Abstract

The double-deficit hypothesis of dyslexia posits that reading deficits are more severe in individuals with weaknesses in phonological awareness and rapid naming than in individuals with deficits in only one of these reading composite skills. In this study, the hypothesis was tested in an adult sample as a model of reading achievement. Participants were parents of children referred for evaluation of reading difficulties. Approximately half of all participants reported difficulty learning to read in childhood and a small subset demonstrated ongoing weaknesses in reading. Structural equation modeling results suggest that the double-deficit hypothesis is an accurate model for understanding adult reading achievement. Better reading achievement was associated with better phonological awareness and faster rapid automatized naming in adults. Posthoc analyses indicated that individuals with double deficits had significantly lower reading achievement than individuals with single deficits or no deficits.

Examination of the double-deficit hypothesis with adolescents and young adults with dyslexia

“…In comparison to the three extant studies in which adult participants were used and DDH subtype comparisons were made (Cirino et al, 2005;Miller et al, 2006;Vukovic et al, 2004), the current results are only partially consistent. Vukovic et al (2004) examined the DDH with college students diagnosed with reading disabilities and descriptively compared the NS-D subtype (n=11), PA-D subtype (n=4), and DD subtype (n=5) on word reading and reading comprehension measures.…”

“…These researchers did, however, find that the DD subtype was most impaired on pseudoword decoding accuracy and efficiency tasks in their sample of college students referred for learning problems. Miller et al (2006) investigated the DDH in a sample of parents of children with dyslexia, although it was not reported that the parents themselves had been diagnosed with dyslexia. Participants from the two single-deficit groups appear to have been aggregated into one group and then compared to the DD group, limiting comparison to the current study.…”

Students in higher education with reading and writing difficulties

“…They emphasise the importance of assessing adults' reading fluency, because it reveals persistent deficits. A reading comprehension study showed that phonological awareness accounted for less of the variance in reading comprehension accuracy (Miller et al 2006) than did listening comprehension, working memory, IQ, vocabulary or general knowledge, all of which were found to be more crucial. In this study, no single cognitive process was dominant in predicting reading comprehension; instead, a combination of several processes seemed to provide the best account of reading comprehension difficulties.…”

“…This and other challenges in phonological ability seem to be the core deficit in dyslexia (Elbro 2004;Goswami 2002;Høien and Lundberg 1999;Samuelsson, Herkner and Lundberg 2003;Vellutino et al 2004). Miller et al (2006) tested the double-deficit hypothesis of dyslexia on adults (N 0133). The hypothesis posits that dyslexia is more severe in adults who have problems with both rapid naming and phonological awareness than in those who have only one of these major problems.…”

“…Both of these skills are also good predictors of fluent reading in adulthood. Miller et al (2006) assume that adults have learned how to compensate. They emphasise the importance of assessing adults' reading fluency, because it reveals persistent deficits.…”