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5.6 Virtual characters: agents 159

vided at the interface in the form of sliders and icons. The effect of requesting an
animated agent to become very happy, sad, or grumpy is seen through changes to
their behavior, For example, if a user moves a slider to a "scared" position on an
emotional scale, the agent starts behaving scared, hiding behind objects and mak-
ing frightened facial expressions.
The Woggles are one of the earliest forms of emotional agents (Bates, 1994). A
group of agents was designed to appear on the screen that played games with one
another, such as hide and seek. They were designed as different colored bouncy
balls with cute facial expressions. Users could change their moods (e.g., from happy
to sad) by moving various sliders, which in turn changed their movement (e.g., they
bounced less), facial expression (e.g., they no longer smiled), and how willing they
were to play with the other Woggles (See Figure 5.12 on Color Plate 7).

4. Embodied conversational interface agents
Much of the research on embodied conversational interface agents has been con-
cerned with how to emulate human conversation. This has included modeling vari-
ous conversational mechanisms such as:
recognizing and responding to verbal and non-verbal input
generating verbal and non-verbal output
coping with breakdowns, turn-taking and other conversational mechanisms
giving signals that indicate the state of the conversation as well as contribut-
ing new suggestions for the dialog (Cassell, 2000, p.72)

In many ways, this approach is the most anthropomorphic in its aims of all the
agent research and development.
Rea is an embodied real-estate agent with a humanlike body that she uses in
humanlike ways during a conversation (Cassell, 2000). In particular, she uses eye
gaze, body posture, hand gestures, and facial expressions while talking (See Figure
5.13 on Color Plate 8). Although the dialog appears relatively simple, it involves a
sophisticated underlying set of conversational mechanisms and gesture-recognition
techniques. An example of an actual interaction with Rea is:
Mike approaches the screen and Rea turns to face him and says:
"Hello. How can I help you?"
Mike: "I'm looking to buy a place near MIT."
Rea nods, indicating she is following.
Rea: "I have a house to show you" (picture of a house appears on the screen).
"It is in Somerville."
Mike: "Tell me about it."
Rea looks up and away while she plans what to say.
Rea: "It's big."
Rea makes an expansive gesture with her hands.