Age of sign language acquisition has lifelong effect on syntactic preferences in sign language users

Acquisition of natural language has been shown to fundamentally impact both one’s ability to use the first language and the ability to learn subsequent languages later in life. Sign languages offer a unique perspective on this issue because Deaf signers receive access to signed input at varying ages. The majority acquires sign language in (early) childhood, but some learn sign language later—a situation that is drastically different from that of spoken language acquisition. To investigate the effect of age of sign language acquisition and its potential interplay with age in signers, we examined grammatical acceptability ratings and reaction time measures in a group of Deaf signers (age range = 28–58 years) with early (0–3 years) or later (4–7 years) acquisition of sign language in childhood. Behavioral responses to grammatical word order variations (subject–object–verb [SOV] vs. object–subject–verb [OSV]) were examined in sentences that included (1) simple sentences, (2) topicalized sentences, and (3) sentences involving manual classifier constructions, uniquely characteristic of sign languages. Overall, older participants responded more slowly. Age of acquisition had subtle effects on acceptability ratings, whereby the direction of the effect depended on the specific linguistic structure.