Factors influencing bilingual expressive vocabulary size in children with autism spectrum disorders

•Some children with ASD develop second language (L2) expressive vocabularies.•Recent direct exposure to a L2 strongly correlated with L2 vocabulary size.•Children's dominant language abilities made a contribution to L2 vocabulary size.•Social impairments did not differ between groups with different L2 outcomes.•Cognitive impairments did not prevent children from developing L2 vocabularies.

This study explored bilingual exposure, language, social impairment and cognitive factors that could influence second language (L2) expressive vocabulary size as measured on the MacArthur–Bates Communicative Development Inventories (various languages) in 33 children (mean age = 60 months) diagnosed with ASD. In the 23 children with L2 vocabularies, recent language exposure estimates accounted for 69% of the variation in L2 vocabulary size, and the VABS-II expressive scale score explained an additional 13% of the difference. The complete sample was then subgrouped into three levels of L2 vocabulary size to compare children with no L2 vocabularies (NON-B, n = 10), low L2 word counts (LOW-B, n = 11) and high L2 counts (HIGH-B, n = 12), as determined by a median split procedure. The HIGH-B group had significantly larger L1 vocabularies than both the LOW-B (p = .045) and the NON-B (p = .003) groups, and higher VABS-II expressive scale scores than both the LOW-B (p = .008) and the NON-B (p = .012) groups. Social impairment did not significantly differ across groups and cognitive impairment did not preclude the development of L2 vocabularies. Expressive bilingualism in this population appears related to high levels of recent direct L2 exposure in combination with stronger dominant language abilities.