UC San Diego

During language production, speakers modify various characteristics of their speech to match their linguistic partner’s speech. Although this linguistic alignment occurs for a wide range of dimensions, including speech rate, phonology, word choice, and gesture, the reasons why speakers align at all is poorly understood. Specifically, do speakers align to aid their listener’s comprehension, or to make their own language production easier? If alignment occurs for the listener’s benefit, then the speaker’s language processing system should track linguistic statistics produced by individual partners, allowing them to match their speech to the production of their current partner. Alternatively, if it occurs for the speaker’s benefit, alignment might be partner-independent, with speakers modulating their speech based solely on the overall statistics of their linguistic input.

This dissertation investigates the underlying cause of alignment by assessing whether linguistic alignment in the domain of syntax is partner-specific. In five experiments, speakers interacted with two partners who each systematically produced distinct syntactic structures. For example, one partner always produced prepositional dative sentences (e.g., “The student handed her dissertation to her committee.”) and the other partner always produced double object dative sentences (e.g., “The student handed her committee her dissertation.”). Thus, speakers received equal overall exposure to multiple syntactic structures, but each particular structure was spoken by only one of the partners.

Speakers did not show partner-specific alignment. However, they did show evidence of partner-independent syntactic learning: When the overall distribution of syntactic structures was biased – for example, when both partners produced only prepositional dative sentences – speakers did align to that bias. Additionally, preliminary evidence suggests that speakers aligned to match a specific partner’s production if – but only if – that partner has reduced proficiency (here, a non-native speaker).

Thus, at least in the syntactic domain, speakers modulate their speech to match the overall statistics of the linguistic context, but not to match the preferences of their current listener. These results suggest that linguistic alignment occurs for the speaker’s own benefit, because the linguistic features they recently heard are more accessible for their own production. However, alignment may be partner-specific when it is plausibly necessary for a listener’s successful comprehension, and thus, perhaps, alignment can be tuned for the listener’s benefit under extenuating linguistic circumstances.