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The Physical Robot 57

instruments it has to interact with the caregiver. Examples of these vocalizations can be
heard by watching the “Readable Expressions” demonstration on the included CD-ROM.

5.3 Overview of the Perceptual System

Human infants discriminate readily between social stimuli (faces, voices, etc.) and salient
non-social stimuli (brightly colored objects, loud noises, large motion, etc.). For Kismet, the
perceptual system is designed to discriminate a subset of both social and non-social stimuli
from visual images as well as auditory streams. The specific percepts within each category
(social versus non-social) are targeted for social exchanges. Specifically, the social stimuli
are geared toward detecting the affective state of the caregiver, whether or not the caregiver
is paying attention to the robot, and other people-related percepts that are important during
face-to-face exchanges such as the prosody of the caregiver’s vocalizations. The non-social
percepts are selected for their ability to command the attention of the robot. These are useful
duringsocialexchangeswhenthecaregiverwantstodirecttherobot’sattentiontoeventsout-
side pure face-to-face exchange. In this way, the caregiver can focus the interaction on things
and events in the world, such as centering an interaction around playing with a specific toy.
Our discussion of the perceptual limitations of infants in chapter 3 has important impli-
cations for how to design Kismet’s perceptual system. Clearly the ultimate, most versatile
and complete perceptual system is not necessary. A perceptual system that rivals the per-
formance and sophistication of the adult is not necessary either. As argued in chapter 3,
this is not appropriate and would actually hinder development by overwhelming the robot
with more perceptual information than the robot’s synthetic nervous system could possibly
handle or learn from. It is also inappropriate to place the robot in an overly simplified en-
vironment where it would ultimately learn and predict everything about that environment.
There would be no impetus for continued growth. Instead, the perceptual system should
start out as simple as possible, but rich enough to distinguish important social cues and
interaction scenarios that are typical of caregiver-infant interactions. In the meantime, the
caregiver must do her part to simplify the robot’s perceptual task by slowing down and
exaggerating her behavior in appropriate ways. She should repeat her behavior until she
feels it has been adequately perceived by the robot, so the robot does not need to get the
perception exactly right upon its first appearance. The challenge is to specify a perceptual
system that can detect the right kinds of information at the right resolution.
A relatively broad and well-integrated real-time perceptual system is critical for Kismet’s
success in the infant-caregiver scenario. The real-time constraint imposes some fairly strin-
gent restrictions in the algorithms used. As a result, these algorithms tend to be simple and
of low resolution so that they can run quickly. One might characterize Kismet’s perceptual