| Summary: | Children with Autism Spectrum Disorders (ASD) have deficits in communication and delays in language development, but there have been few studies of their vocabulary. This study compared longitudinal parent report data from the MCDI collected for 49 children with ASD over three years with data from the MCDI norms. It focused on three aspects of lexical development: (1) change in lexical composition as evident in percentage of predicates/nominals; (2) order of emergence for predicate types and (3) predictive value of lexical variables for later grammatical development. ASD Groups were matched to typically developing group norms on total MCDI scores for each comparison. Subsequent analysis indicated: (1) no differences in the percentages of predicates/nominals for the two groups at 3 time points; and, (2) virtually identical orders of emergence for different predicate types with the exception of three meaning type categories—quantitative predicates, cognitive/affective predicates and predicates involving causal acts to change experiential states. Cognitive/affective predicates were found to come in somewhat later in ASD groups while quantitative predicates and predicates involving changes in experiential states came in earlier in ASD groups. This study also found (3) that lexical variables, especially number of predicates, strongly predicted grammatical complexity one year later, a process common in typical language development. The study concludes that lexical development in ASD follows the normal course, albeit later and more slowly. It also suggests that communication deficits in this population are rooted in challenges with social acts rather than from an inability to match meanings to words.
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