chi-subtle - Facial Expressions for Conversational Agents...

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Facial Expressions for Conversational Agents Dirk Heylen University of Twente PO Box 217 7500 AE, Enschede, NL +31 53 4893745 ABSTRACT In this paper, we argue that the choice of facial expressions of conversational agents should be guided mainly by parameters in the dialogue context: the ideational, interpersonal, and meta-communicative functions, and not so much by the emotional state of the agent. Keywords Facial expressions, conversational agents. INTRODUCTION It is perhaps questionable whether the facial expressions of synthetic characters should be modeled to any realistic detail on the example of that of their human creators. For instance, Blumberg’s work at MIT on Synthetic Characters takes inspiration from the Disney guidelines for animating characters which involves taking the real humans as a basis but modifying the behavior by exaggeration and simplification (Kline and Blumberg, 1999). However, even in this case the human face serves partly as a model for the synthetic behavior. For other purposes the human model may even be more relevant. Suppose then, that we want to make synthetic characters that resemble real humans as much as possible. What behavior should they display? Or in other words, how do humans act with their face? In this paper, we take another look at the literature on human facial expressions to come up with a list of guidelines for implementing synthetic faces. We will focus on the use of synthetic faces in a conversational setting. There is a core repertoire of facial displays that appears in most work on synthetic faces. Often, this core constitutes almost the whole of the repertoire of facial displays. It is familiar to anyone who has been concerned with this topic. The displays are based on the work of Ekman on the universal expressions of what he claims to be the six basic emotions anger , disgust , fear , happiness , sadness , and surprise . Sometimes the repertoire is extended with variations on the emotions by allowing differences in intensity or blends of displays. Symptomatic of this dominance of attention to basic expressions are the predefined displays that appear in facial animation software or toolkits (see, for example:, interface. digital. com, www. miralab. unige. ch, mrl. nyu. edu / ~perlin/ facedemo). Often one can only work with the predefined displays. A number of non-emotional expressions, mostly conversational signals have been worked on by researchers on conversational agents. For instance, the topic of gaze and eye-movements has been investigated by quite a few authors examining the function in discourse, the affective meanings, etcetera (Cassell et al. (1994), Cassell et al. (1999), Chopra-Khullar, N.I. Badler (1999), Colburn et al.
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chi-subtle - Facial Expressions for Conversational Agents...

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