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Children who have both autism and intellectual disability may understand fewer words than their speaking skills suggest, which is not the case for typically developing children or those with intellectual disability alone. The results were published 21 February in the Journal of Autism and Developmental Disorders1.
Researchers aiming to understand the role of language in autism typically study children with high-functioning autism, or those with a high intelligence quotient. This is because intellectual disability can also lead to language impairment, which can confound the association between language and autism.
To better understand the interaction between autism, intellectual disability and language, researchers in the new study compared the language ability of 36 children with both autism and intellectual disability, 26 children with intellectual disability only and 34 typically developing controls. Children were matched on the basis of mental age, independent of language ability. The mean age for children with autism was about 7 years; those with intellectual disability were about 6.5 years old and controls were about 3 years old.
The researchers used a number of measures to rate expressive language, or speaking ability, and receptive language, the ability to understand the speech of others, in each of the children. These measures included both direct tests and parental-report questionnaires.
Overall, children with autism and intellectual disability have lower scores in receptive language than do those with intellectual disability alone, who themselves score lower than controls. There is no statistically significant difference in expressive language between children with autism and intellectual disability compared with children with intellectual disability alone; but, again, both groups score lower than controls.
This suggests that, overall, children with autism have stronger expressive than receptive language skills, whereas this trend is reversed in the other two groups. Specifically, about 34 percent of children with autism and intellectual disability have better expressive compared with receptive language, the study found. By contrast, 54 percent of children with intellectual disability only and 44 percent of controls have better receptive than expressive language.
The researchers also looked at whether the children’s ability to engage the attention of others, called joint attention, and their understanding of symbols was related to their language ability. These two factors account for 81 percent of the variation in receptive language scores and 72 percent of the variation in expressive language scores among the children with autism, the study found. For example, children with autism who have more difficulty with joint attention have lower language scores than those with better joint attention ability.
The discrepancy between expressive and receptive language should be taken into account when designing interventions for children with autism, the researchers say.
1: Maljaars J. et al. J. Autism Dev. Disord. Epub ahead of print (2012) PubMed