Speakers adapt gestures to addressees' knowledge: Implications for models of co-speech gesture.

Are gesturing and speaking shaped by similar communicative constraints? In an experiment, we teased apart communicative from cognitive constraints upon multiple dimensions of speech-accompanying gestures in spontaneous dialogue. Typically, speakers attenuate old, repeated or predictable information but not new information. Our study distinguished what was new or old for speakers from what was new or old for (and shared with) addressees. In 20 groups of 3 naive participants, speakers retold the same Road Runner cartoon story twice to one addressee and once to another. We compared the distribution of gesture types, and the gestures’ size and iconic precision across retellings. Speakers gestured less frequently in stories retold to Old Addressees than New Addressees. Moreover, the gestures they produced in stories retold to Old Addressees were smaller and less precise than those retold to New Addressees, although these were attenuated over time as well. Consistent with our previous findings about speaking, gesturing is guided by both speaker-based (cognitive) and addressee-based (communicative) constraints that affect both planning and motoric execution. We discuss the implications for models of co-speech gesture production