American Sign Language basic clause comprehension strategies used by late first-language learners: Plausibility, animacy, and linguistic structure.

Few studies to date have explored the role of early language experience on syntactic development during the early stages of language acquisition. Understanding the language outcomes of deaf individuals with severely delayed first language (L1) onset can provide valuable insights into the nature of the critical period for early syntactic development. The current study examines the use of linguistic versus extra-linguistic (plausibility, animacy) cues at the basic clausal level by deaf late first language (L1) signers of American Sign Language (ASL). Nine late L1 signers of ASL completed a sentence-picture matching task involving sentences that varied in linguistic structure, plausibility, and noun animacy. Overall, late L1 signers tended to rely on linguistic cues in noun-attribute and spatial classifier sentences even when the sentence meanings were implausible. In contrast, when faced with implausible and irreversible transitive sentences, they showed resilient but fragile use of word order, with overall high accuracy except when animacy conflicted with word order. These comprehension patterns resemble those of young children with an immersive early language environment, who often rely on a mix of linguistic and extra-linguistic cues before robustly relying on linguistic rules. Together, these findings suggest that late L1 signers exhibit a graded representation of basic syntactic structures, emphasizing the critical role of early language exposure in fostering the robust development of basic clausal structures.