Keeping track of who knows what in multiparty conversation despite severe memory impairment.

Language use has long been understood to be tailored to the intended addressee, a process termed audience design. Audience design is reflected in multiple aspects of language use, including adjustments based on the addressee's knowledge about the topic at hand. In group settings, audience design depends on representations of multiple individuals, each of whom may have different knowledge about the conversational topic. A central question, then, concerns how these representations are encoded and retrieved in multiparty conversation where successful conversation requires keeping track of who knows what. In the present research, we probe the biological memory systems that are involved in this process of multiparty audience design. We present the results of two experiments that compare language use in persons with bilateral hippocampal damage and severe declarative memory impairment (amnesia), and demographically matched neurotypical comparison participants. Participants played a game in which they discussed abstract images with one partner in conversation, and then discussed the images again with the same partner or with a new partner in a three-party conversation. Neurotypical participants' language use reflected newly formed representations of which partner was familiar with which images. Participants with amnesia showed evidence of partner-specific audience design in multiparty conversation but it was attenuated, especially when success required rapid alternations between representations of common ground. The findings suggest partial independence of the formation and use of partner-specific representations from the hippocampal-dependent declarative memory system and highlight the unique contributions of the declarative memory system to flexible and dynamic language use.