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158 Chapter 5 Understanding how interfaces affect users

Figure 5.1 0 User interacting with Silas the dog in (a) physical world (b) virtual world, and 1
(c) close-up of Silas.

and have company. He responds to events in the environment; for example, he be-
comes aggressive if a hamster enters his patch.
A person can interact with Silas by making various gestures that are detected by a
computer-vision system. For example, the person can pretend to throw a stick, which
is recognized as an action that Silas responds to. An image of the person is also pro-
jected onto a large screen so that he can be seen in relation to Silas (see Figure 5.10).
Depending on his mood, Silas will run after the stick and return it (e.g., when he is
happy and playful) or cower and refuse to fetch it (e.g., when he is hungry or sad).

2. Animated agents

These are similar to synthetic characters except they tend to be designed to play a
collaborating role at the interface. Typically, they appear at the side of the screen
as tutors, wizards and helpers intended to help users perform a task. This might be
designing a presentation, writing an essay or learning about a topic. Most of the
characters are designed to be cartoon-like rather than resemble human beings.
An example of an animated agent is Herman the Bug, who was developed by In-
tellimedia at North Carolina State University to teach children from kindergarten to
high school about biology (Lester et al., 1997). Herman is a talkative, quirky insect
that flies around the screen and dives into plant structures as it provides problem-
solving advice to students (See Figure 5.11 on Color Plate 7). When providing its ex-
planations it performs a range of activities including walking, flying, shrinking,
expanding, swimming, bungee jumping, acrobatics, and teleporting. Its behavior in-
cludes 30 animated segments, 160 canned audio clips, and a number of songs. Herman
offers advice on how to perform tasks and also tries to motivate students to do them.

3. Emotional agents
These are designed with a predefined personality and set of emotions that are ma-
nipulated by users. The aim is to allow people to change the moods or emotions of
agents and see what effect it has on their behavior. Various mood changers are pro-