Published online by Cambridge University Press: 13 July 2017
It has long been accepted in traditional animation that a character's expressions must be captured throughout the whole body as well as the face (Thomas & Johnston, 1995). Existing artificial agents express themselves using facial expressions, vocal intonation, body movements, and postures. Body language has been a focus of interest in research on embodied agents (virtual humans and social robots). It can be separated into four different areas that should be considered when animating virtual characters as well as social robots. (1) Postures: postures are specific positions that the body takes during a time-frame. Postures are an important modality during social interaction and play an important role as they can signal liking and affiliation (Lakin et al., 2003). Moreover, it has been established that postures are an effective medium to express emotion for humans (De Silva & Bianchi-Berthouze, 2004). Thus, virtual humans and social robots should be endowed with the capability to display adequate body postures. (2) Movement or gestures: throughout most of our daily interactions, gestures are used along with speech for effective communication (Cassell, 2000). For a review of the types of gestures that occur during interactions the reader can refer to Cassell (2000). Movements are also important for expressing emotions. Indeed, it has been shown that many emotions are differentiated by characteristic body movements and that these are effective clues for judging the emotional state of other people in the absence of facial and vocal clues (Atkinson et al., 2004). Body movements include the movements themselves as well as the manner in which they are performed, i.e. speed of movements, dynamics, and curvature – something captured by the traditional animation principles (Thomas & Johnston, 1995; Beck, 2012). Moreover, it should be noted that body movements occur in interaction with other elements, such as speech, facial expressions, gaze, all of which needs to be synchronised. (3) Proxemics: it is the distance between individuals during a social interaction. It is also indicative of emotional state. For example, angry people have a tendency to reduce the distance during social interaction, although this reduction would also be evident between intimate people.