Page 239 - Designing Sociable Robots

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220 Chapter 12

toward that target. For cameras in other locations, accuracy of orientation would be limited
by the accuracy of the distance measurement.
Higher-level influences modulate the movement of the neck and eyes in a number of ways.
As already discussed, modifications to weights in the attention system translate to changes
of the locus of attention about which eye movements are organized. The overall posture of
the robot can be controlled in terms of a three-dimensional affective space (chapter 10).
The regime used to control the eyes and neck is available as a set of primitives to higher-
level modules. Regimes include low-commitment search, high-commitment engagement,
avoidance, sustained gaze, and deliberate gaze breaking. The primitive percepts generated
by this level include a characterization of the most salient regions of the image in terms
of the feature maps, an extended characterization of the tracked region in terms of the
results of post-attentive processing (eye detection, distance estimation), and signals related
to undesired conditions, such as a looming object, or an object moving at speeds the tracker
finds difficult to keep up with.

12.4 Visual Motor Skills

Recall from chapter 9, given the current task (as dictated by the behavior system), the motor
skills level is responsible for figuring out how to move the actuators to carry out the stated
goal. Often this requires coordination between multiple motor modalities (speech, body
posture, facial display, and gaze control).
The motor skills level interacts with both the behavior level above and the primitives level
below. Requests for visual skills (each implemented as a FSM) typically originate from the
behavior system. During turn-taking, for instance, the behavior system requests different
visual primitives depending upon when the robot is trying to relinquish the floor (tending to
make eye contact with the human) or to reacquire the floor (tending to avert gaze to break
eye contact). Another example is the searching behavior. Here, the search FSM alternates
ballistic orienting movements of the head and eyes to scan the scene with periods of gaze
fixation to lock on the desired salient stimulus. The phases of ballistic orientations with
fixations are appropriately timed to allow the perceptual flow of information to reach the
behavior releasers and stop the search behavior when the desired stimulus is found. If the
timing were too rapid, the searching behavior would never stop.

12.5 Visual Behavior

The behavior level is responsible for establishing the current task for the robot through
arbitrating among Kismet’s goal-achieving behaviors. By doing so, the observed behavior
should be relevant, appropriately persistent, and opportunistic. The details of how this is