Facial Expressions for Conversational Agents
University of Twente
PO Box 217
7500 AE, Enschede, NL
+31 53 4893745
In this paper, we argue that the choice of facial expressions
of conversational agents should be guided mainly by
interpersonal, and meta-communicative functions, and not
so much by the emotional state of the agent.
Facial expressions, conversational agents.
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
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
. 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: cslu.cse.ogi.edu/toolkit,
interface. digital. com, www. miralab. unige. ch, mrl. nyu.
edu / ~perlin/ facedemo). Often one can only work with the
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.