Page 141 - Designing Sociable Robots

breazeal-79017 book March 18, 2002 14:5

122 Chapter 8

Sleep Behavior
2500
Anger
2000 Tired
Activation Level 1500

1000
500

0
0 50 100 150 200 250
Time (seconds)
3500
3000 Fatigue drive
Sleep behavior
2500
Activation Level 2000
NonFace stimulus
1500
1000
500
0
0 50 100 150 200 250
Time (seconds)
Figure 8.6
Experimental results for long-term interactions of the fatigue-drive and the sleep behavior. The
fatigue-drive continues to increase until it reaches an activation level that potentiates the sleep behavior.
If there is no other stimulation, this will allow the robot to activate the sleep behavior.

waving stimulus stops for the remainder of the run. Because of the prolonged loss of the
desired stimulus, the robot is under-stimulated and an expression of sadness reappears on
the robot’s face.
Figure 8.6 illustrates the influence of the fatigue-drive on the robot’s motivational and
behavioral state when interacting with a caregiver. Over time, the fatigue-drive increases
toward the under-stimulated end of the spectrum. As the robot’s level of “fatigue” increases,
the robot displays stronger signs of being tired. At time step t = 95, the fatigue-drive
moves above the threshold value of 1600, which is sufficient to activate the sleep behavior
when no other interactions are occurring. The robot remains “asleep” until all drives are
restored to their homeostatic ranges. Once this occurs, the activation level of the sleep
behavior decays until the behavior is no longer active and the robot “wakes up” in an calm
state.