The association of cognitive abilities with language disorder in 8-year-old children: A population-based clinical sample.

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Despite accumulated evidence that language development depends on basic cognitive processes, the balance in contributions of verbal and non-verbal cognitive skills to language abilities is still underexplored. Little is known about which cognitive measures best predict the degree of severity in children with language disorder (LD). To examine the association between verbal and non-verbal cognitive abilities with language abilities in typically developing and language impaired 8-year-old children, as well as which cognitive abilities are most effective in distinguishing LD severity levels. Children (N = 509) from the Language-8 Study, which oversampled probable cases of children with LD from a population-based cohort in Norway, were assessed at 8 years. Language skills were assessed using the Norwegian Clinical Evaluation of Language Fundamentals-4 (CELF-4). Children's verbal and non-verbal cognitive abilities were assessed via standardized cognitive measures. An exploratory factor analysis (EFA) was first conducted to uncover the underlying factor structure of the cognitive variables. Using a hierarchical multiple regression analysis, we then examined to what extent the non-verbal cognition factor explained language abilities above and beyond verbal cognition factors. Lastly, multinomial logistic regression was used to examine which cognitive measures best predicted the degree of severity in the children with LD. The EFA resulted in three factors (Verbal Cognition, Processing Speed and Memory, and Non-Verbal Cognition). The hierarchical multiple regression analysis revealed that all three cognitive factors contributed significantly to individual variation in language abilities. Non-Verbal Cognition explained 5.4% variance in language abilities above and beyond that accounted for by Verbal Cognition and Processing Speed and Memory. Results from the multinomial logistic regression analysis indicated that cognitive subtests, including Familiar Sequences, WASI Vocabulary and WASI Similarities, not only distinguished LD from typically developing children, but were also efficient in distinguishing severity of LD symptoms. This study confirms concurrent links between language and non-verbal cognitive skills above and beyond the contribution of verbal cognitive skills. The results provide further evidence that children with LD experience both language and cognitive problems in mid-childhood. Our findings suggest implications for LD intervention and diagnosis. The findings support the importance of measuring both verbal and non-verbal cognitive skills when making an LD diagnosis, and point to the potential of targeting underlying cognitive skills as one strategy to support language abilities. What is already known on the subject Language development is dependent on basic cognitive processes. These include both verbal and non-verbal cognitive abilities. Children with LD often experience both language and cognitive problems. There is evidence that performance on cognitive tests may be associated with the degree of severity of LD. What this paper adds to existing knowledge The current results from a large population-based cohort establish that a number of verbal and non-verbal cognitive abilities are tightly linked to variation in language abilities and the degree of severity of LD. Our study confirms concurrent links between language and non-verbal cognitive abilities above and beyond the contribution of verbal cognitive abilities. We also identify specific verbal and non-verbal cognitive tests that distinguish between typical children and children with LD, as well as LD severity. What are the potential or actual clinical implications of this work? Our findings support the importance of measuring both verbal and non-verbal cognitive skills when making an LD diagnosis. Our findings also point to the potential of targeting underlying cognitive skills as one strategy to support language abilities. We suggest that future intervention studies focus on the impact of non-verbal cognitive skills on language development in children with LD.