Abstract/Summary

A developmental account of how bilinguals organise syntactic knowledge is crucial to understanding their mental representations. While adult studies suggest that syntactic representations can be shared across languages, evidence from child and adolescent heritage speakers remains limited and mixed. We conducted two syntactic priming experiments with adolescent heritage speakers of Polish in the UK (N = 35, mean age = 15;3) to test whether they would produce (1) relative clauses (RCs) instead of adjectival phrases for attributive relationships, and (2) possessor-second structures for possessive relationships with referential possessors, following cross-linguistic priming. A third experiment tested first-generation Polish-speaking adult immigrants in the UK (N = 32) on the same tasks. Adolescents were resistant to priming for RCs, whereas adults showed bidirectional priming. Both groups were primed to produce possessor-second structures only in Polish, where this is the canonical word order. Results indicate that increased proficiency and language experience facilitate priming for less frequent, complex structures like RCs, supporting shared syntax only in adults. For highly frequent constructions like possessives, where Polish and English differ in word order, priming occurred only when consistent with the language-specific preference. This underscores the role of frequency, canonicity, and complexity in shaping bilingual syntactic representations across development.