Page 156 - Designing Sociable Robots

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The Behavior System 137

Specificity of Releasers

Behaviors that are located deeper within the hierarchy are more specific. As a result, both
the antecedent conditions that release the behavior, as well as the goal relations that signal
success, become more specific. This establishes a hierarchy of releasers, progressing in
detail from broad and general to more specific. The broadest releasers simply establish the
type of stimulus (people versus toys) and its presence or absence. Deeper in the hierarchy,
many of the releasers are the same as those that are passed to the affective tagging process in
the emotion system. Hence, these releasers are not just simple combinations of perceptual
features. They are contextualized according to the motivational and behavioral state of
the robot (see chapter 8). They are analogous to simple cognitions in emotional appraisal
theories because they specifically relate the perceptual features to the “well-being” and
goals of the robot.
Adjustment Parameters

Each behavior follows this general model. Several parameters are used to specify the dis-
tinguishing properties of each behavior. This amount of flexibility allows rich behaviors to
be specified and interesting behavioral dynamics to be established.
Activation within a group One important parameter is the releaser used to elicit the
behavior. This plays an important role in determining when the behavior becomes active.
For instance, the absence of a desired toy stimulus is the correct condition to activate the
seek-toy behavior. However, as discussed previously, it is not a simple one-to-one mapping
from stimulus to response. Motivational factors also influence a behavior’s relevance.
Deactivation within a group Another important parameter is the goal-signaling releaser.
This determines when an appetitive behavior has achieved its goal and can be deactivated.
The consummatory behaviors remain active upon success until a motivational switch occurs
that biases the robot to tend to a different need. For instance, during the seek-toy behavior
(an appetitive behavior), the behavior is successful when the found-toy releaser fires. This
releaser is a combination of toy-present with the context provided by the seek-toy
behavior. It fires for the short period of time between the decay of the seek-toy behavior
and the activation of engage-toy (the consummatory behavior).
Temporal dynamics within a group The timing of activating and deactivating behav-
iors within a group is very important. The human and the robot establish a tightly coupled
dynamic when in face-to-face interaction. Both are continuously adapting their behavior
to the other, and the manner in which they adapt their behavior is often in direct response
to the last action the partner just performed. To keep the flow of interaction smooth, the