Listeners expect grammatical variation across dialects

Dialect variation is universally attested among languages, yet the cognitive processes underlying listeners' adaptations to different dialects, particularly in morphosyntactic variation, remain underexplored. This paper investigates how monodialectal speakers of Dominant American English (DAE) and bidialectal speakers of DAE and African American Language (AAL) represent and adapt to their interlocutor’s dialect based on their linguistic experience. In Experiment 1, participants rated written sentences to indicate the likelihood that a speaker of a given dialect would say them. All participants demonstrated knowledge of AAL’s regularized subject-verb agreement rules, rating sentences like "They was happy" as more likely than "He were happy." However, bidialectal participants showed greater differentiation between the sentences than monodialectal participants. This finding suggests that listeners do not simply relax grammatical expectations when exposed to linguistic diversity; rather, they form specific expectations of a dialect's grammatical rules. In Experiment 2, we tested whether these expectations influence perception in ambiguous contexts. Participants transcribed sentences spoken by either a DAE or an AAL speaker, where subject-verb agreement was acoustically ambiguous ("She sit[s] still"). Participants were more likely to transcribe regularized subject-verb agreement ("She sit still") when listening to an AAL speaker compared to a DAE speaker, regardless of their group. Bidialectal participants were generally more likely to transcribe regularized subject-verb agreement overall. These results suggest that listeners form mental models of others' grammars and use these models to guide comprehension, with the precision of these models depending on their linguistic experience.