Subtleties of facial expressions in embodied agents

Our goal is to develop a believable embodied agent able to dialogue with a user. In particular, we aim at making an agent that can also combine facial expressions in a complex and subtle way, just like a human agent does. We first review a taxonomy of communicative functions that our agent is able to express non-verbally; but we point out that, due to the complexity of communication, in some cases different information can be provided at once by different parts and actions of an agent's face. In this paper we are interested in assessing and treating what happens, at the meaning and signal levels of behaviour, when different communicative functions have to be displayed at the same time and necessarily have to make use of the same expressive resources. In some of these cases the complexity of the agent's communication can give rise to conflicts between the parts or movements of the face. In this paper, we propose a way to manage the possible conflicts between different modalities of communication through the tool of belief networks, and we show how this tool allows us to combine facial expressions of different communicative functions and to display complex and subtle expressions. Copyright (C) 2002 John Wiley Sons, Ltd.