Page 164 - Designing Sociable Robots

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The Behavior System 145

exaggerated to increase readability). It holds its gaze on the person throughout this phase.
Due to noise in the visual system, however, the eyes tend to flit about the person’s face,
perhaps even leaving it briefly and then returning soon afterwards. This display signals
that the robot has finished speaking and is waiting for the human to say something. It
will time out after approximately 8 seconds if the person does not respond. At this point,
the robot reacquires its turn and issues another vocalization in an attempt to reinitiate the
dialogue.
• Attend to human’s speech Once the perceptual system acknowledges that the human has
started speaking, the robot’s ears perk. This subtle feedback cue signals that the robot is
listening to the person speak. The robot looks generally attentive to the person and continues
to maintain eye contact if possible.
• Reacquire speaking turn This phase is entered when the perceptual system acknowledges
that the person’s speech has ended. The robot signals that it is about to speak by leaning
back to a neutral posture and averting its gaze. The robot is likely to blink its eyes as it shifts
posture.

• Deliver speech Soon after the robot shifts its posture back to neutral, the robot vocalizes.
The utterances are short babbles, generated by the vocalization system (presented in chap-
ter 11). Sometimes more than one is issued. The eyes migrate back to the person’s face, to
their eyes if possible. Just before the robot is prepared to finish this phase, it is likely to
blink. The behavior transitions back to the relinquish turn phase and the cycle resumes.
The system is designed to maintain social exchanges with a person for about twenty
minutes; at this point the other drives typically begin to dominate the robot’s motivation.
When this occurs, the robot begins to behave in a fussy manner—the robot becomes more
distracted by other things around it, and it makes fussy faces more frequently. It is more
difficult to engage in proto-dialogue. Overall, it is a significant change in behavior. People
seem to sense the change readily and try to vary the interaction, often by introducing a toy.
The smile that appears on the robot’s face and the level of attention that it pays to the toy
are strong cues that the robot is now involved in satiating its stimulation-drive.

9.5 Overview of the Motor Systems

Whereasthebehaviorsystemisresponsiblefordecidingwhichtasktherobotshouldperform
at any time, the motor system is responsible for figuring out how to drive the motors in
order to carry out the task. In addition, whereas the motivation system is responsible for
establishing the affective state of the robot, the motor system is responsible for commanding
the actuators in order to convey that emotional state.