Is Silence Golden in Human-Robot Dialogue?

The physical actions performed by any robot can be used to convey meaning to a user in human-robot interaction. For example, successfully performing an action following a request may be viewed as an acceptance, while performing the wrong action may be construed as a mis-understanding. Even hesitating to perform a requested physical action may be viewed as a signal of non-understanding. Thus, unlike in the more orthodox domain of non-situated dialogue, natural human-robot dialogue must account for physical actions as a natural and effective implicit communication channel. Though physical actions have not always been explicitly accounted for in dialogue act annotation schemes and models, e.g., vanilla DAMSL lacks a direct mechanism for such implicit communication (Allen and Core 1997), the nature of physical actions as a type of communicative act has been long recognized within the dialogue community (see for example Coulthard & Brazil (1979) for an early account). Indeed, the physical performance of an action can be regarded as a variant on multi-modal interaction (Pfleger, Alexandersson, and Becker 2003). However, while the analysis of physical actions as communicative acts is not new, it is less clear how dialogue planning policies for human-robot interaction should be influenced by the co-occurrence of physical tasks actions. Addressing this issue successfully inevitably depends on knowing whether users consider verbal communication acts alongside physical acts to be superficial or unnatural, and on whether explicit verbal acts can be beneficial given the limitations of imperfect communication. With these questions in mind, in the following we report on a recently conducted study with an implemented humanrobot dialogue system which was designed to assess the importance of compounded physical and verbal communicative acts in human-robot dialogue.