Page 116 - Designing Sociable Robots

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The Auditory System 97

face will first exhibit an aroused and interested expression, then the orienting response
ensues. By staging the response in this manner, the caregiver gets immediate expressive
feedback that the robot understood her intent. For Kismet, this feedback can come in a
combination of facial expression and posture (chapter 10), or tone of voice (chapter 11).
The robot’s facial expression also sets up the human’s expectation of what behavior will
soon follow. As a result, the human observing the robot can see its behavior, in addition
to having an understanding of why the robot is behaving in that manner. As I have argued
previously, readability is an important issue for social interaction with humans.

Socio-Emotional Context Improves Interpretation
Most affective speech recognizers are not integrated into robots equipped with emotion
systems that are also embedded in a social environment. As a result, they have to classify
each utterance in isolation. For Kismet, however, the surrounding social context can be
exploited to help reduce false categorizations, or at least to reduce the number of “bad”
misclassifications (such as mixing up prohibitions for approvals).
Some of this contextual filtering is performed by the transition dynamics of the emotion
processes. These processes cannot instantaneously become active or inactive. Decay rates
and competition for activation with other emotion processes give the currently active
process a base level of persistence before it becomes inactive. Hence, for a sequence of
approvals where the activation of the robot’s joy process is very high, an isolated prohibition
will not be sufficient to immediately switch the robot to a negatively valenced state.
If the caregiver intends to communicate disapproval, reiteration of the prohibition will
continue to increase the contribution of negative valence to the emotion system. This serves
to inhibit the positively valenced emotion processes and to excite the negatively valenced
emotion processes. Expressive feedback from the robot is sufficient for the caregiver to
recognize when the intent of the vocalization has been communicated properly and strongly
enough. The smooth transition dynamics of the emotion system enhances the naturalness
of the robot’s behavior since a person would expect to have to “build up” to a dramatic
shift in affective state from positive to negative, as opposed to being able to flip the robot’s
“emotional” state like a switch.
The affective state of the robot can also be used to help disambiguate the intent behind
utterances with very similar prosodic contours. A good example of this is the difference
betweenutterancesintendedtosootheversusutterancesintendedtoencourage.Theprosodic
patterns of these vocalizations are quite similar, but the intent varies with the social context.
The communicative function of soothing vocalizations is to comfort a distressed robot—
there is no point in comforting the robot if it is not in a distressed state. Hence, the affective
assessment phase somatically tags these types of utterances as soothing when the robot is
distressed, and as encouraging otherwise (slightly arousing, slightly positive).