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decided would be on that subject). Alan gave me the opportunity. “Inter-
face” was every other word in the conversations of the bright young MIT
wizards that populated the lab. I dimly perceived that there must be more
to it than ease of use, and so I signed up for a weekly interface seminar that
one of the psychologists on staff was conducting.
The interface seminar group began by looking at how the concept was typi-
cally understood by people in the computer fi eld. Figure 1.1 shows a sche-
matic model of the interface. The shaded rectangle in the middle represents
the interface, and it was seen to include what appears on the screen, hard-
ware input/output devices, and their drivers.
Compelling as its simplicity might make it, this model was immedi-
ately dismissed by everyone in the group. In order for an interface to work,
the person has to have some idea about what the computer expects and can
handle, and the computer has to incorporate some information about what
the person's goals and behaviors are likely to be. These two phenomena—a
person's mental model of the computer and the computer's “understand-
ing” of the person—are just as much a part of the interface as its physical
and sensory manifestations (see Figure 1.2).
But in order to use an interface correctly, a person must also have an
idea of what the computer is “expecting” her to do. If you are going to
admit that what the two parties “think” about each other is part of what's
going on, you will have to agree that what the two parties think about what
the other is thinking about them must perforce be included in the model
(see Figure 1.3). This elaboration has dizzying ramifi cations.
Figure 1.1.
The pre-cognitive-science view of the interface
