J.-C. Heudin (Ed.): VW 2000, LNAI 1834, pp. 99-106, 2000.
 Springer-Verlag Berlin Heidelberg 2000
Creating Emotive Responsive Characters
Within Virtual Worlds
Ken Perlin
Media Research Laboratory
NYU Department of Computer Science
perlin@nyu.edu
Abstract. Virtual Worlds can seem to come to life when they have virtual char-
acters in them. On the other hand, if these characters are not "believable" they
can actually damage the sense of presence and immersion for a human partici-
pant. This problem is not purely one of engineering or of artistic judgement,
but rather it calls for a combination of both. How do we combine technology
and artistic content effectively to create believable interactive virtual charac-
ters? We will look at several examples from our own research and try to ex-
trapolate some principles.
1 Introduction
Virtual worlds should be fun, engaging places, where participants' sense of humor,
adventure and playfulness (and therefore their sense of imagination) are allowed to
flourish [22]. One of the key components of such worlds are believable, engaging
interactive characters.
It has long been a goal of the animated agent community to bring embodied agent
technologies out of the research labs and into the hands of authors and designers who
may put them to practical use. Improv is a set of tools and techniques developed at
NYU which make it possible to create applications involving animated agents that
behave, interact and respond to user input in ways that convey mood and emotion.
These tools can be used without prior experience in computer programming, cogni-
tive science or ergonomic simulation, while still allowing creation of animated agents
who exhibit behavior which has the lifelike, somewhat unpredictable feel of human
behavior, yet remains consistent with a character's personality and defined goals.
The goal of this research has been to make improvisational animation accessible to
experts with minimal expertise in animation and dramatic performance, and to enable
researchers and educators to exploit these technologies without relying on expensive
production efforts. These are clearly two of the most important steps toward the wide-
scale acceptance and use of animated agents for education and training, social simu-
lation and collaborative environments.

100 Ken Perlin
In this paper we describe some of the experiments we have done to combine artis-
tic design with technological innovation toward this goal.
2 Goals
Our research goals in this area have focused on building and testing examples that can
run on the current World Wide Web and that demonstrate or embody interesting
ideas. Our experiments are mainly in the area of interactive character animation.
Other than the historical examples, all of the experiments shown are Java 1.0 com-
patible applets. This lowest-common-denominator platform was chosen because it
allows the broadest available flexibility in making on-line experiments simultane-
ously available to large numbers of users.
2.1 Animation Modeling
One question to ask is "how simple and intuitive can a system be, so that the
user/participant can be given authoring powers?"

Figure 1. How simple can we make it for people to design customized animated characters?
The figures above are from an interactive applet designed to investigate the ques-
tion "how simple can we make it for people to design customized animated charac-
ters?" The "character" on the left actually contains seven interactive zones. Dragging
the mouse within any of these zones causes certain regions of the body to change
shape so as to follow the mouse movement. Certain parts are coupled together, so that
dragging one always causes the other to change as well.
This interface was designed to be intuitive to the extent that even a small child
could design their own character. Experiments showed that this goal was achieved:
Children as small as four years old were successful in creating their own custom
character models, with no prior instruction.