Information Technology Reference
In-Depth Information
Tr a n s i t i o n s
The second requirement of narrative comprehensibility is that the user be able
to tell
why
the agent is doing what it is doing. In behavior-based terms, every
time an agent selects a particular behavior, it should express to the user the
reason it is changing from the old behavior to the new one. This is difficult
to do in most behavior-based systems because behaviors are designed and run
independently; when a behavior is chosen, it has no idea who it succeeds, let
alone why.
In the Expressivator, behavioral
transitions
are used to express the agent's
reasoning. Transitions are special behaviors which act to 'glue' two signifying
behaviors together. When a transition notices that it is time to switch between
two signifiers, it takes over from the old signifier. Instead of switching abruptly
to the new signifier, it takes a moment to express to the user the reason for the
behavioral change.
Transitions are implemented in two parts, each of which is a full-fledged
behavior: (1)
transition triggers
, that determine when it is appropriate to switch
to another behavior for a particular reason, and (2)
transition demons
,thatim-
plement the transition sequence that expresses that reason to the user. Tran-
sition triggers run in the background, generally checking which behaviors are
running (e.g. exploring the world), and combining this information with sen-
sory input about current conditions (e.g. the Overseer is approaching). When
its conditions are fulfilled, the transition trigger adds a special token to mem-
ory, noting the behavior which should terminate, the behavior which should
replace it, and a label which represents the reason for the replacement (e.g.
afraid_of_overseer
).
Transition demons monitor memory, waiting for a transition for a partic-
ular reason to be triggered. They then choose an appropriate behavioral ex-
pression for the reason for change, according to the current likely user inter-
pretation and conditions in the virtual environment. Expressing the reasoning
behind behavioral change often requires changes to subsequent behaviors; for
example, if the Patient starts doing some odious task because it is forced to by
the Overseer, it should include some annoyed glances at the Overseer as part
of the task-fulfilling behavior. Transitions are able to express these kinds of
interbehavioral influences using the meta-level controls described below.
