Measuring conventionalization in the manual modality

Gestures produced by users of spoken languages differ from signs produced by users of sign languages in that gestures are more typically ad hoc and idiosyncratic, while signs are more typically conventionalized and shared within a language community. To measure how gestures may change over time as a result of the process of conventionalization, we used a social coordination game to elicit repeated silent gestures from hearing non-signers, and used Microsoft Kinect to unobtrusively track the movement of their bodies as they gestured. Our approach follows from a tradition of laboratory experiments designed to study language evolution and draws upon insights from sign language research on language emergence. Working with silent gesture, we were able to simulate and quantify hallmarks of conventionalization that have been described for sign languages, in the laboratory. With Kinect, we measured a reduction in the size of the articulatory space and a decrease in the distance traveled by the articulators, while communicative success increased between participants over time. This approach opens the door for more direct future comparisons between ad hoc gestures produced in the lab and natural sign languages in the world.