Bilingualism Enhances Metalinguistic Awareness in Autism: Extending the Two-Dimensional Grammaticality Judgment Task.

Bilingualism has been associated with enhanced metalinguistic awareness (MA), the ability to reflect upon language. However, findings remain mixed, and little is known about how proficiency in the most proficient (L1) and second-best language (L2) contribute to MA, especially in children with autism spectrum disorder (ASD), who often present heterogeneous cognitive and linguistic profiles. We tested 270 children aged 5-12 (90 autistic, 180 neurotypical) using a two-dimensional Grammaticality Judgment Task (GJT) requiring two components of MA: analyzed knowledge (understanding of grammatical rules) and cognitive control (suppressing irrelevant semantic cues). Bilingualism was examined both categorically (monolingual vs. bilingual) and continuously (L2 proficiency), using generalized linear mixed-effects models controlling for age, nonverbal IQ, and L1 proficiency. Among neurotypical children, no significant bilingual advantage was found. In contrast, bilingual autistic children significantly outperformed monolingual peers on items requiring cognitive control, and higher L2 proficiency was associated with better overall GJT performance. These findings advance understanding of how bilingualism relates to metalinguistic abilities in autism and suggest that it is not only non-detrimental but may confer specific metalinguistic benefits. The study underscores the importance of combining categorical and continuous approaches to bilingualism to better capture individual variability in neurodiverse populations.