Role of embodiment and presence in human perception of robots' facial cues

Both robotic and virtual agents could one day be equipped with social abilities necessary for effective and natural interaction with human beings. Although virtual agents are relatively inexpensive and flexible, they lack the physical embodiment present in robotic agents. Surprisingly, the role of embodiment and physical presence for enriching human-robot-interaction is still unclear. This paper explores how these unique features of robotic agents influence three major elements of human-robot face-to-face communication, namely the perception of visual speech, facial expression, and eye-gaze. We used a quantitative approach to disentangle the role of embodiment from the physical presence of a social robot, called Ryan, with three different agents (robot, telepresent robot, and virtual agent), as well as with an actual human. We used a robot with a retro-projected face for this study, since the same animation from a virtual agent could be projected to this robotic face, thus allowing comparison of the virtual agent's animation behaviors with both telepresent and the physically present robotic agents. The results of our studies indicate that the eye gaze and certain facial expressions are perceived more accurately when the embodied agent is physically present than when it is displayed on a 2D screen either as a telepresent or a virtual agent. Conversely, we find no evidence that either the embodiment or the presence of the robot improves the perception of visual speech, regardless of syntactic or semantic cues. Comparison of our findings with previous studies also indicates that the role of embodiment and presence should not be generalized without considering the limitations of the embodied agents.