Page 128 - Designing Sociable Robots

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The Motivation System 109

For a given A drive intensity, a large positive magnitude corresponds to under-stimulation
by the environment, whereas a large negative magnitude corresponds to over-stimulation
by the environment. In general, each A drive is partitioned into three regimes: an under-
stimulated regime, an overwhelmed regime, and the homeostatic regime. A drive remains
in its homeostatic regime when it is encountering its satiatory stimulus and that stimulus
is of appropriate intensity. In the absence of the satiatory stimulus (or if the intensity is too
low), the drive tends toward the under-stimulated regime. Alternatively, if the satiatory
stimulus is too intense, the drive tends toward the overwhelmed regime. To remain in
balance, it is not sufficient that the satiatory stimulus be present; it must also be of a good
quality.
In the current implementation there are three drives. They are:

• Social
• Stimulation
• Fatigue
The social drive The social-drive motivates the robot to be in the presence of people
and to be stimulated by people. This is important for biasing the robot to learn in a social
context. On the under-stimulated extreme, the robot is “lonely”; it is predisposed to act in
ways to establish face-to-face contact with people. If left unsatiated, this drive will continue
to intensify toward the under-stimulated end of the spectrum. On the overwhelmed extreme,
the robot is “asocial”; it is predisposed to act in ways to avoid face-to-face contact. The robot
tends toward the overwhelmed end of the spectrum when a person is over-stimulating the
robot. This may occur when a person is moving too much or is too close to the robot’s eyes.
The stimulation drive The stimulation-drive motivates the robot to be stimulated,
where the stimulation is generated externally by the environment, typically by engaging
the robot with a colorful toy. This drive provides Kismet with an innate bias to interact
with objects. This encourages the caregiver to draw the robot’s attention to toys and events
around the robot. On the under-stimulated end of this spectrum, the robot is “bored.” This
occurs if Kismet has been unstimulated over a period of time. On the overwhelmed part
of the spectrum, the robot is “over-stimulated.” This occurs when the robot receives more
stimulation than its perceptual processes can handle well. In this case, the robot is biased to
reduce its interaction with the environment, perhaps by closing its eyes or turning its head
away from the stimulus. This drive is important for social learning as it encourages the
caregiver to challenge the robot with new interactions.

The fatigue drive The fatigue-drive is unlike the others in that its purpose is to allow
the robot to shut out the external world instead of trying to regulate its interaction with
it. While the robot is “awake,” it receives repeated stimulation from the environment or