I. Introduction
An experimental apparatus that is indistinguishable from a human being, at least superficially, has the potential to contribute greatly to an understanding of face-to-face interaction in the social and neurosciences. Such a device could be a perfect actor in controlled experiments, permitting scientists to vary precisely the parameters under study. It could also serve as a testbed for cognitive theories, including theories about how the brain acts as a control system in mediating whole-bodied communication. The device would also have the advantage of having the physical presence that simulated characters lack. Unfortunately, no such device yet exists, nor will one any time soon; nevertheless, robots are being built that with each new generation more closely simulate human beings in appearance, facial expression, and gesture [11][9][10]. They are capable of eliciting some of the kinds of responses that people direct toward each other but not toward mechanical-looking robots.