Spoken sentence comprehension in children with dyslexia and language impairment_ The roles of syntax and working memory

We examined spoken sentence comprehension in school-age children with developmental dyslexia or language impairment (LI), compared to age-matched and younger controls. Sentence–picture matching tasks were employed under three different working memory (WM) loads, two levels of syntactic difficulty, and two sentence lengths. Phonological short-term memory (STM) skills and their relation to sentence comprehension performance were also examined. When WM load was minimized, the LI group performed more poorly on the sentence comprehension task compared to the age-matched control group and the dyslexic group. Across groups, sentence comprehension performance generally decreased as the WM load increased, but this effect was somewhat more pronounced in the dyslexic group compared to the age-matched group. Moreover, both the LI and dyslexic groups showed poor phonological STM compared to the age-matched control group, and a significant correlation was observed between phonological STM and sentence comprehension performance under demanding WM loads. The results indicate subtle sentence processing difficulties in dyslexia that might be explained as resulting from these children’s phonological STM limitations. Children with developmental dyslexia fail to develop age appropriate reading skills despite normal-range nonverbal intelligence, adequate learning opportunities, and the absence of a frank neurological disorder (Snowling, 2000). Although dyslexia is by definition a reading disorder, there is a strong consensus that spoken language deficits also play a role in reading failure. Specifically, theories suggest that difficulties with phonological processing impair the ability to learn consistencies in the mapping between letters and sounds, which in turn, impacts the ability to efficiently read familiar and novel words (Bradley & Bryant, 1983; © Cambridge University Press 2009 0142-7164/10 $15.00 Applied Psycholinguistics 31:1 142 Robertson & Joanisse: Spoken sentence comprehension Stanovich & Siegel, 1994; Wagner, Torgesen, & Rashotte, 1994). Although there is much evidence in support of the strong relationship between phonological deficits and reading failure in children with dyslexia, less attention has been devoted to whether these children also have nonphonological language deficits. It has even been suggested that children with dyslexia have relatively normal nonphonological language skills, which they use to compensate for phonological deficits throughout reading development (Bishop & Snowling, 2004). However, language deficits outside the domain of phonology have been observed in children with dyslexia. McArthur, Hogben, Edwards, Heath, and Mengler (2000) found that in a sample of 110 children with dyslexia, over half of the children scored at least one standard deviation below the mean across tests of comprehension and production of syntax and vocabulary. There is also evidence that language skills in 2to 3-year-old children, such as the syntactic complexity and vocabulary size, are significant predictors of later reading accuracy and comprehension (Scarborough, 1990). These studies raise the possibility that children with dyslexia have nonphonological language problems in addition to phonological deficits. Consistent with this, dyslexia has been found to overlap moderately with specific language impairment (SLI; Catts, Adolf, Hogan, & Ellis Weismer, 2005; McArthur et al., 2000). SLI is a distinct disorder from dyslexia in which oral language is impaired, especially with respect to grammatical processing (Bishop, 1997). However, the limited number of direct comparisons made across these groups in the literature makes it difficult to assess whether nonphonological deficits in dyslexia are similar to those observed in children with SLI. Thus, the current study focused on the nature and extent of language deficits in dyslexia, especially with respect to spoken sentence comprehension. Rispens and Been (2007) examined sentence comprehension in SLI and dyslexic groups, and found that children with dyslexia were poorer than control children, but better than children with SLI. In the current study, we also compared sentence comprehension in children with dyslexia and language impairment (LI), and evaluated the extent to which sentence comprehension problems in either group are grounded in poor syntactic processing over limited verbal working memory (WM). THE RELATIONSHIPS BETWEEN READING, SYNTAX,