Page 168 - Designing Sociable Robots

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The Behavior System 149

primitives is called a skill, and each skill is implemented as a finite state machine (FSM).
Each motor skill encodes knowledge of how to move from one motor state to the next,
where each sequence is designed to bring the robot closer to the current goal. The motor
skills level must arbitrate among the many different FSMs, selecting the one to become
active based on the active goal. This decision process is straightforward since there is an
FSM tailored for each task of the behavior system.
Many skills can be thought of as fixed action patterns (FAPs) as conceptualized by
early ethologists (Tinbergen, 1951; Lorenz, 1973). Each FAP consists of two components,
the action component and the taxis (or orienting) component. For Kismet, FAPs often
correspond to communicative gestures where the action component corresponds to the
facial gesture, and the taxis component (to whom the gesture is directed) is controlled by
gaze. People seem to intuitively understand that when Kismet makes eye contact with them,
they are the locus of Kismet’s attention and the robot’s behavior is organized about them.
This places the person in a state of action readiness where they are poised to respond to
Kismet’s gestures.
A classic example of a motor skill is Kismet’s calling FAP (see figure 9.8). When the
current task is to bring a person into a good interaction distance, the motor skill system
activates the calling FSM. The taxis component of the FAP issues a hold gaze request
to the oculo-motor system. This serves to maintain the robot’s gaze on the person. In the
first state (1) of the gesture component, Kismet leans its body toward the person (a request
to the body posture motor system). This strengthens the person’s perception that the robot
has taken a particular interest in them. The ears also begin to waggle exuberantly (creating
a significant amount of motion and noise) which further attracts the person’s attention to

attend
(2)
Last
State, X
call wait
(1) (3)

wake home
up flee

sleep

Figure 9.8
The calling motor skill. The states 1, 2, and 3 are described in the text. The remaining states encode knowledge of
how to transition from any previously active motor skill state to the call state.