Who Needs Emotions? The Brain Meets the Robot

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ter 5 (Rolls). Hence, the affective contributions of the drives do not directly
evoke emotive responses, but they do bias the robot’s net affective state. In
this sense, the drives contribute to the robot’s “mood” over time, which makes
the corresponding emotive responses easier to elicit.
Drives shape the internal agenda of the robot (in concert with perceptual
and emotive factors) and play an important role in determining which
behavior to next engage. To keep its activation level within the homeostatic
regime, each drive can preferentially spread activation to behaviors at the
top level of the behavior hierarchy that help to restore that drive (described
in detail in the following section).
Behaviors, in turn, encode specific task-achieving goals that serve to
maintain the robot’s internal state (as defined by the state of the drives and
“emotions”). To remain in balance (near the center of the spectrum), it is
not sufficient that the satiatory stimulus merely be present; it must also be
of good quality. For instance, in the absence of the satiatory stimulus (or if
the intensity is too low), a drive increases in intensity to the positive end of
the spectrum and preferentially biases the activation of those behaviors that
seek out that stimulus. In addition, the affective contribution of the drive
(negative valence and low arousal) contributes to a net affective state that
makes it easier for the sorrow emotive response to become active. Sorrow
represents a different strategy to help the robot come into contact with a
desired stimulus by signaling to people that it needs attention.
Alternatively, if the satiatory stimulus is too intense (e.g., a visual stimulus
moving too fast or too close to the robot’s face), a drive tends toward the
extreme negative end of the spectrum. In this circumstance, the drive biases
the activation of avoidance behaviors to limit the robot’s exposure to
the intense stimulus. Also, the affective contribution of the drive (negative
valence, high arousal) contributes to a net affective state that makes it easier
for Kismet’s fear response to become active. Once active, the fearful expression
on Kismet’s face signals people to back off a bit.
Hence, the drives work in concert with behaviors and contribute to an
affective state that helps Kismet keep its level of interaction with the world
and people in balance, neither too much nor too little.
Behavior Arbitration as Decision Making
Within the behavior system, the behavior processes are organized into loosely
layered, heterogeneous hierarchies of behavior groups (see Fig. 10.4), much
in the spirit of those ethological models proposed by Tinbergen (1951) and
Lorenz (1973). Implicit in this model is that a decision is being made among
several alternatives at every level of the hierarchy, of which one is chosen.