Page 127 - Designing Sociable Robots

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108 Chapter 8

the emotion processes. Since the robot’s expressions reflect its affective state, the drives
indirectly control the affective cues the robot displays to people. Last, they provide a func-
tional context that organizes behavior and perception. This is of particular importance for
emotive appraisals.
The design of Kismet’s homeostatic regulation subsystem is heavily inspired by etholog-
ical views of the analogous process in animals (McFarland & Bosser, 1993). It is, however,
a simplified and idealized model of those discovered in living systems. One distinguishing
feature of a drive is its temporally cyclic behavior. That is, given no stimulation, a drive
will tend to increase in intensity unless it is satiated. This is analogous to an animal’s degree
of hunger or level of fatigue, both following a cyclical pattern.
Another distinguishing feature is its homeostatic nature. Each acts to maintain a level of
intensity within a bounded range (neither too much nor too little). Its change in intensity
reflects the ongoing needs of the robot and the urgency for tending to them. There is a
desired operational point for each drive and acceptable bounds of operation around that
point. I call this range the homeostatic regime. As long as a drive is within the homeostatic
regime, the robot’s needs are being adequately met. For Kismet, maintaining its drives
within their homeostatic regime is a never-ending process. At any point in time, the robot’s
behavior is organized about satiating one of its drives.
Each drive is modeled as a separate process, shown in figure 8.1. Each has a tem-
poral input to implement its cyclic behavior. The activation energy A drive of each drive
−max +max
ranges between [A , A ], where the magnitude of the A drive represents its intensity.
drive drive

“degree of
urgency”
Time A drive
-max +max
A drive A drive
Satiatory drive
Stimulus
0
Overwhelmed Homeostatic Under-stimulated
regime regime regime
consum.
behavior

Valence: negative positive negative
contact
desired
stimulus Arousal: high medium low
Figure 8.1
The homeostatic model of a drive process.