Page 134 - Designing Sociable Robots

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The Motivation System 115

• Perceptual State(s) The incoming percepts can contribute to the affective state on their
own (such as a looming stimulus, for instance), or in combination with other stimuli (such as
combining skin-tone with distance to perceive a distant person). An important assessment
is how intense the stimulus is. Stimuli that are closer to the robot, move faster, or are larger
in the field of view are more intense than stimuli that are further, slower, or smaller. This is
an important measure of the quality and threat of the stimulus.

Affective Appraisal
Within the appraisal phase, each releaser with activation above threshold is appraised in
affective terms by an associated somatic marker (SM) process. Recall from chapter 7 that
each active releaser is tagged by affective markers of three types: arousal (A), valence (V),
and stance (S). There are four types of appraisals considered:

• Intensity The intensity of the stimulus generally maps to arousal. Threatening or very
intense stimuli are tagged with high arousal. Absent or low intensity stimuli are tagged with
low arousal. Soothing speech has a calming influence on the robot, so it also serves to lower
arousal if initially high.

• Relevance The relevance of the stimulus (whether it addresses the current goals of the
robot) influences valence and stance. Stimuli that are relevant are “desirable” and are tagged
with positive valence and approaching stance. Stimuli that are not relevant are “undesirable”
and are tagged with negative arousal and withdrawing stance.

• Intrinsic Pleasantness Some stimuli are hardwired to influence the robot’s affective state
in a specific manner. Praising speech is tagged with positive valence and slightly high
arousal. Scolding speech is tagged with negative valence and low arousal (tending to elicit
sorrow). Attentional bids alert the robot and are tagged with medium arousal. Looming
stimuli startle the robot and are tagged with high arousal. Threatening stimuli elicit fear
and are tagged with high arousal, negative valence, and withdrawing stance.

• GoalDirectedness Eachbehaviorspecifies agoal,i.e.,aparticularrelation therobotwants
to maintain with the environment. Success in achieving a goal promotes joy and is tagged
with positive valence. Prolonged delay in achieving a goal results in frustration and
is tagged with negative valence and withdrawing stance. The stance component increases
slowly over time to transition from frustration to anger.
As initially discussed in chapter 4, because there are potentially many different kinds of
factors that modulate the robot’s affective state (e.g., behaviors, motivations, perceptions),
this tagging process converts the myriad of factors into a common currency that can be
combined to determine the net affective state. Further recall that the [A, V, S] trio is the
currency the emotion system uses to determine which emotional response should be active.