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72 Chapter 6

looks around. To compensate for this, the measure is subject to rapid habituation. This has
the side-effect that a slowly approaching object will not be detected—which is perfectly
acceptable for a loom response where the robot quickly withdraws from a sudden and
rapidly approaching object.
Threat detection A nearby object (as computed above) along with large but concen-
trated movement in the wide FoV is treated as a threat by Kismet. The amount of motion
corresponds to the amount of activation of the motion map. Since the motion map may
also become very active during ego-motion, this response is disabled for the brief inter-
vals during which Kismet’s head is in motion. As an additional filtering stage, the ratio of
activation in the peripheral part of the image versus the central part is computed to help
reduce the number of spurious threat responses due to ego-motion. This filter thus looks
for concentrated activation in a localized region of the motion map, whereas self-induced
motion causes activation to smear evenly over the map.

6.3 Results and Evaluation

The overall attention system runs at 20 Hz on several 400 MHz processors. In this section,
I evaluate its behavior with respect to directing Kismet’s attention to task-relevant stimuli. I
also examine how easy it is people to direct the robot’s attention to a specific target stimulus,
and to determine when they have been successful in doing so.

Effect of Gain Adjustment on Saliency
In section 6.1, I described how the active behavior can manipulate the relative contributions
of the bottom-up processes to benefit goal achievement. Figure 6.7 illustrates how the skin
tone, motion, and color gains are adjusted as a function of drive intensity, the active behavior,
and the nature and quality of the perceptual stimulus.
As shown in figure 6.7, when the social-drive is activated by face stimuli (middle),
the skin-tone gain is influenced by the seek-people and avoid-people behaviors. The
effectsonthegainsareshownontheleftsideofthetopplot.Whenthestimulation-drive
is activated by color stimuli (bottom), the color gain is influenced by the seek-toys
and avoid-toys behaviors. This is shown to the right of the top plot. Seeking people
results in enhancing the face gain and avoiding people results in suppressing the face gain.
The color gain is adjusted in a similar fashion when toy-oriented behaviors are active
(enhancement when seeking out, suppression during avoidance). The middle plot shows
how the social-drive and the quality of social stimuli determine which people-oriented
behavior is activated. The bottom plot shows how the stimulation-drive and the quality
of toy stimuli determine which toy-oriented behavior is active. All parameters shown in
these plots were recorded during the same four-minute period.