Biomedical Engineering Reference
In-Depth Information
2006; Braga, 2006; Querrec, Buche, Maffre
and Chevaillier, 2004), simulation of inhabited
environment for security, adequacy analysis and
evaluation or historical studies (Papagiannakis,
Schertenleib, O'Kennedy, Arevalo-Poizat, Mag-
nenat-Thalmann, Stoddart and Thalmann, 2005),
product or service demonstration (Kopp, Jung,
Lessmann and Wachsmuth, 2003), ergonomics
(Colombo and Cugini , 2006; Xu, Sun and Pan,
2006), are some of many others possible uses for
Intelligent Virtual Environments (IVE).
The key issue about virtual environments is
immersion
, or, as it is usually said, the suspension
of disbelief. The system developer's first concern
tends to be related to graphical and sound issues,
since senses are very important to involvement in
a virtual world. However, when related to dynamic
and complex environments, the believability of
the virtual world elements behavior becomes
paramount, especially if it includes life simulation.
There are many levels of activity to be simulated,
and modeling depends heavily on which is the
main concern of the application. For instance, if
we are simulating a garden just for aesthetic ap-
preciation, there is no point in simulating complex
interactions occurring between plants, and plants
and other organisms of the world. It is different,
though, if the same world is being simulated for
ecological analysis.
This problem becomes more complex when
virtual humans or humanoids are to be simu-
lated. To show believability, the behavior must
express an internal life, some kind of goal-driven
attitude, even when it is erratic as in drunk or
crazy people. But on what basis is it possible to
accomplish this?
Virtual environment inhabitants are usually
developed as agents with some varying levels of
autonomy, which encapsulate specific context-
sensitive knowledge to accomplish their role in
the system application. What may be considered
“behavior” goes from just body movements to
complex interactions with the environment,
depending on the character role. It is expected
that when the underlying mechanism of behavior
production is more similar to the actual function-
ing in the real world, more the resulting virtual
behavior will be believable. That tends to be
particularly true when complex and rich virtual
worlds are being created. If a VE is simple, it
may suffice just to imitate the real behavior. But
if the virtual world is complex, and relies on
emergence to produce behavior, just to emulate
it may be too risky.
The present chapter focuses on virtual charac-
ter behavior as believable sequence of actions of
humanlike virtual entities, and not on character
computer animation, or virtual biomechanical
body movements. Some approaches are discussed,
and a motivation-driven architecture is proposed
based on assumptions derived from cognitive
science.
The first part of the chapter focuses on vari-
ous forms of modeling the relationship between
characters and their environment in order to
produce believable behavior. The second part
discusses different approaches for modeling
character behavior, and suggests the convenience
of integrating the underlying mechanisms in a
single high-level structure, the artificial mind.
The third part presents a proposed motivation-
driven architecture for artificial minds. Finally,
conclusions are presented and future trends are
discussed.
CHARACTER INTELLIGENCE AND
vIRTUAL ENvIRONMENT
As already pointed out, immersion is a key issue
when virtual environments are considered. Of
course, when they are populated, the “suspension
of disbelief” requirement is extended to their
inhabitants. Believable lifelike virtual characters
have to behave as if internal forces are driving
them. They have to show autonomy and some
kind of environment awareness. How can this
be accomplished? Two approaches are possible:
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