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Micro-timing of backchannels in human-robot interaction

Timing is important for all aspects of human-human and human-machine interaction. For example, collaborative action in various tasks becomes successful through well coordinated sequences of actions. Of course, dialogues, as a particular form of joint action, benefit from timing as well. It helps to avoid overlapping speech and long pauses, which makes the participants feel more positive about the conversation as well as the conversation partner [36, 7]. Our research has so far been conducted in the context of embodied conversational agents, where timing has been identified a crucial issue early-on for gesture [33], with applications also in HRI [31], and in the conversational agents domain. It more recently focused on backchanneling [11]. These investigations should also be relevant for making humanrobot interaction more natural and pleasant. There is already a vast body of literature on the importance of timing, and on strategies for timing gestures and verbal utterances. If timing is viewed as a single level phenomenon, then quality of interaction can be viewed as increasing more or less linearly with timing accuracy. However, we propose the existence of at least two distinct levels of timing that are sensitive to different influences, and are processed cognitively in different ways. We call the lowest level of timing, which we assume to be based on entrainment, micro-timing as compared to macro-timing, which takes place on coarser time scales and is likely to involve more conscious, strategic processing. We propose that to achieve a high quality of interaction, one should pay attention to timing on both levels. Here we are particularly interested in one aspect of timing in dialogue: The timing of backchannels. Backchannels are brief signals produced by the listener in an asymmetric dialogue to signal attention and encourage the speaker to go on. Head nodding is one of the most unobtrusive forms of backchannels. Brief utterances like ’um’, ’ok’, or