Page 126 - Designing Sociable Robots

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The Motivation System 107

influenceincallingforthnurturingbehaviorsofadults.Darwinarguedthatemotivesignaling
functions were selected for during the course of evolution because of their communicative
efficacy. For members of a social species, the outcome of a particular act usually depends
partly on the reactions of the significant others in the encounter. As argued by Scherer, the
projection of how the others will react to these different possible courses of action largely
determines the creature’s behavioral choice. The signaling of emotion communicates the
creature’s evaluative reaction to a stimulus event (or act) and thus narrows the possible
range of behavioral intentions that are likely to be inferred by observers.

Overview of the Motivation System
Kismet’s motivations establish its nature by defining its “needs” and influencing how and
when it acts to satisfy them. The nature of Kismet is to socially engage people and ultimately
to learn from them. Kismet’s drive and emotion processes are designed such that the
robot is in homeostatic balance, and an alert and mildly positive affective state, when it
is interacting well with people and when the interactions are neither overwhelming nor
under-stimulating (Breazeal, 1998). This corresponds to an environment that affords high
learning potential as the interactions slightly challenge the robot yet also allow Kismet to
perform well.
Kismet’s motivation system consists of two related subsystems, one which implements
drives and a second which implements emotions. There are several processes in the
emotion system that model different arousal states (such as interest, calm, or boredom).
These do not correspond to the basic emotions, such as the six proposed by Ekman (anger,
disgust, fear, joy, sorrow, and surprise). Nonetheless, they have a corresponding expression
and a few have an associated behavioral response. For the purposes here, I will treat these
arousal states as emotions in this system. Each subsystem serves a regulatory function
for the robot (albeit in different ways) to maintain the robot’s “well-being.” Each drive
is modeled as an idealized homeostatic regulation process that maintains a set of critical
parameterswithinaboundedrange.Thereisonedriveassignedtoeachparameter.Kismet’s
emotions are idealized models of basic emotions, where each serves a particular function
(often social), each arises in a particular context, and each motivates Kismet to respond
in an adaptive manner. They tend to operate on shorter, more immediate, and specific
circumstances than the drives (which operate over longer time scales).

8.2 The Homeostatic Regulation System

Kismet’s drives serve four purposes. First, they indirectly influence the attention system.
Second, they influence behavior selection by preferentially passing activation to some be-
haviors over others. Third, they influence the affective state by passing activation energy to