Let's shake hands! On the coordination of gestures of humanoids

Hand gestures are important means of expressivity for humanoids. In this paper by humanoid we understand user-controlled or autonomous virtual humans (VHs) or conversational agents (ECAs) [4] as well as human-like robots [18]. We cover both cases of human-humanoid and humanoid-humanoid interaction. The semantics, the morphology, the variations in performance of gestures reflecting cultural, affective and other characteristics of the speaker [8]. as well as general gesture movement laws [6] have been addressed Our focus in this paper is the issue of coordination of hand gestures to external signals. One type of coordination, alignment of speech-accompanying gestures to the speech, has been studied extensively, and different design principles have been formulated and implemented for specific applications with virtual humans [11, 13, 25]. In these cases, the phonological synchrony rule [15] have been taken as basis, usually resulting in gestures timed to the speech – even if it is generated by TTS. An exception is [24], where in assembly tasks, where a physical manipulation may be accomplished in a shorter or longer time, the speech is aligned to the manipulative hand gestures. Another domain where two-handed gestures play a role is sign language [9]. Also, mechanisms for fast planning for deictic gestures have been proposed [14]. Our ongoing research extends these works in the following aspects: • We propose a coordination scheme which is more general, allowing to take into consideration external events such as tempo indication or perceived state information about the interlocutor of the ECA. • We allow the declaration of coordination requirements on a low level of granularity, looking at different stages of gestures. Such a refined approach makes it possible to perform experiments on e.g. expressivity and style, and to include timing strategies as a means to fine-tune the gesturing behavior of a humanoid. • Our main interest is in reactive scheduling and planning of gestures with reference to an environment influencing the timing of the gestures. • We are using the (still under development) BML language for the formulation of scheduling requirements. As BML is meant to become a general-purpose markup language [3], our testing and extension of its constructs contributes to the development of this unifying language.