Repeat After Us: Syntactic Alignment is Not Partner-Specific

Conversational partners match each other's speech, a process known as alignment. Such alignment can be partner-specific, when speakers match particular partners' production distributions, or partner-independent, when speakers match aggregated linguistic statistics across their input. However, partner-specificity has only been assessed in situations where it had clear communicative utility, and non-alignment might cause communicative difficulty. Here, we investigate whether speakers align partner-specifically even without a communicative need, and thus whether the mechanism driving alignment is sensitive to communicative and social factors of the linguistic context. In five experiments, participants interacted with two experimenters, each with unique and systematic syntactic preferences (e.g., Experimenter A only produced double object datives and Experimenter B only produced prepositional datives). Across multiple exposure conditions, participants engaged in partner-independent but not partner-specific alignment. Thus, when partner-specificity does not add communicative utility, speakers align to aggregate, partner-independent statistical distributions, supporting a communicatively-modulated mechanism underlying alignment.