Page 230 - Designing Sociable Robots

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12 Social Constraints on Animate Vision

The control of animate vision for a social robot poses challenges beyond issues of stability
and accuracy, as well as advantages beyond computational efficiency and perceptual robust-
ness (Ballard, 1989). Kismet’s human-like eye movements have high communicative value
to the people that interact with it. Hence the challenge of interacting with humans constrains
how Kismet appears physically, how it moves, how it perceives the world, and how its be-
haviors are organized. This chapter describes Kismet’s integrated visual-motor system. The
system must negotiate between the physical constraints of the robot, the perceptual needs of
the robot’s behavioral and motivational systems, and the social implications of motor acts.
It presents those systems responsible for generating Kismet’s compelling visual behavior.
From a social perspective, human eye movements have a high communicative value (as
illustrated in figure 12.1). For example, gaze direction is a good indicator of the locus
of visual attention. I have discussed this at length in chapter 6. The dynamic aspects of
eye movement, such as staring versus glancing, also convey information. Eye movements
are particularly potent during social interactions, such as conversational turn-taking, where
making and breaking eye contact plays an important role in regulating the exchange. We
model the eye movements of our robots after humans, so that they may have similar
communicative value.
From a functional perspective, the human system is so good at providing a stable percept
of the world that we have no intuitive appreciation of the physical constraints under which
it operates. Fortunately, there is a wealth of data and proposed models for how the human
visual system is organized (Kandel et al., 2000). This data provides not only a modular
decomposition but also mechanisms for evaluating the performance of the complete system.

12.1 Human Visual Behavior

Kismet’s visual-motor control is modeled after the human oculo-motor system. By doing
so, my colleagues and I hope to harness both the computational efficiency and perceptual
robustness advantages of an animate vision system, as well as the communicative power
of human eye movements. In this section I briefly survey the key aspects of the human
visual system used as a guideline to design Kismet’s visual apparatus and eye movement
primitives.

Foveate vision Humans have foveate vision. The fovea (the center of the retina) has a
much higher density of photoreceptors than the periphery. This means that to see an object
clearly, humans must move their eyes such that the image of the object falls on the fovea. The
advantage of this receptor layout is that humans enjoy both a wide peripheral field of view
as well as high acuity vision. The wide field of view is useful for directing visual attention
to interesting features in the environment that may warrant further detailed analysis. This

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