Interpretation of compound nouns by adolescents with specific language impairment and autism spectrum disorders: an investigation of phenotypic overlap.

The study aimed to investigate (i) whether adolescents with Specific Language Impairment (SLI) and Autism plus Language Impairment (ALI) experience word-formation difficulties, and (ii) whether these two groups present with a similar language phenotype. The study investigated four groups using a 2 (language status) ×2 (autism status) design; adolescents with SLI (n = 14), ALI (n = 16), Autism Language-Typical (ALT; n = 14), and language matched controls (n = 17), with all groups presenting with typical non-verbal skills. Mean age was 14;10. Comprehension of conventional Noun-Noun lexical compounds (e.g., snowman), synthetic compounds (SCs, e.g., cat chaser), and novel root compounds (RCs, e.g., sheep socks), was assessed using a forced-choice picture selection task. The SLI and ALI participants frequently mis-parsed the SCs, interpreting the first noun as the agent. Those with poorer vocabularies and non-word repetition had greater difficulties. Reaction time (RT) profiles were flatter in the ASD groups, with similar RTs across different compounds. Language difficulties in the SLI and ALI groups extend to word-formation processes; for example, comprehension of SCs. This may reflect difficulties making analogies with stored lexical items. Overall the results support the hypothesis of a phenotypic overlap between SLI and ALI.