Page 101 - Designing Sociable Robots

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82 Chapter 7

of cross-cultural studies, Fernald suggests that much of this information is communicated
through the “melody” of infant-directed speech. In particular, there is evidence for at least
four distinctive prosodic contours, each of which communicates a different affective mean-
ing to the infant (approval, prohibition, comfort, and attention). Maternal exaggerations in
infant-directed speech seem to be particularly well-matched to the innate affective responses
of human infants (Mumme et al., 1996).
Inspired by this work, Kismet uses a recognizer to distinguish the four affective intents
for praise, prohibition, comfort, and attentional bids. Of course, not everything a human
says to Kismet will have an affective meaning, so neutral robot-directed speech is also
distinguished. These affective intents are well-matched to teaching a robot since praise
(positive reinforcement), prohibition (negative reinforcement), and directing attention could
be intuitively used by a human instructor to facilitate the robot’s learning process. Within
the AI community, a few researchers have already demonstrated how affective information
can be used to bias learning at both goal-directed and affective levels for robots (Velasquez,
1998) and synthetic characters (Yoon et al., 2000).
For Kismet, the output of the vocal classifier is interfaced with the emotion subsystem
(see chapter 8), where the information is appraised at an affective level and then used to
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directly modulate the robot’s own affective state. In this way, the affective meaning of the
utterance is communicated to the robot through a mechanism similar to the one Fernald
suggests. As with human infants, socially manipulating the robot’s affective system is a
powerful way to modulate the robot’s behavior and to elicit an appropriate response.
In the rest of this chapter, I discuss previous work in recognizing emotion and affective
intent in human speech. I discuss Fernald’s work in depth to highlight the important insights
it provides in terms of which cues are the most useful for recognizing affective intent, as well
as how it may be used by human infants to organize their behavior. I then outline a series of
design issues for integrating this competence into Kismet. I present a detailed description of
the approach implemented on Kismet and how it has been integrated into Kismet’s affective
circuitry. The performance of the system is evaluated with naive subjects as well as the
robot’s caregivers. I discuss the results, suggest future work, and summarize findings.

7.2 Affect and Meaning in Infant-Directed Speech

Developmental psycholinguists have studied the acoustic form of adult speech directed
to preverbal infants and have discovered an intriguing relation between voice pitch and
affective intent (Fernald, 1989; Papousek et al., 1985; Grieser & Kuhl, 1988). When mothers

1. Typically, “affect” refers to positive and negative qualities. For Kismet, arousal levels and the robot’s willingness
to approach or withdraw are also included when talking about Kismet’s affective state.