Information Technology Reference
In-Depth Information
interfaces employ a psychologist's knowledge of how people relate to ob-
jects in the real world in the belief that people can carry that knowledge
across to the manipulation of virtual
5
objects that represent computational
entities and processes. The term “direct manipulation” was coined by Ben
Shneiderman of the University of Maryland, who listed these key criteria:
1. Continuous representation of the object of interest.
2. Physical actions or labeled button presses instead of complex syntax.
3. Rapid incremental reversible operations whose impact on the object
of interest is immediately visible (Shneiderman 1982).
Shneiderman (1982) reported that direct-manipulation interfaces can
“generate a glowing enthusiasm among users that is in marked contrast
with the more common reaction of grudging acceptance or outright hos-
tility.” In a cognitive analysis of how direct manipulation works, Edwin
Hutchins, James Hollan, and Don Norman suggest that direct manipulation
as defi ned may provide only a partial explanation of such positive feel-
ings. They posit a companion effect, labeled direct engagement: A feeling
that occurs “when a user experiences direct interaction with the objects in
a domain” (Hutchins et al. 1986). They add the requirements that input ex-
pressions must be able to make use of previous output expressions, that
the system must create the illusion of instantaneous response (except where
inappropriate to the domain), and that the interface must be unobtrusive.
It seems likely that direct manipulation and direct engagement are
head and tail of the same coin (or two handfuls of the same elephant): one
focusing on the qualities of action and the other focusing on subjective re-
sponse. The basic issue is what is required to produce the feeling of taking
action within a representational world, stripped of the “meta-context” of
the interface as a discrete concern. Hutchins et al. sum it up this way: “Al-
though we believe this feeling of direct engagement to be of critical impor-
tance, in fact, we know little about the actual requirements for producing
it” (Hutchins et al. 1986).
5. The adjective “virtual” describes things—worlds, phenomena, etc.—that look and feel like
reality, but which lack the traditional physical substance. A virtual object, for instance, may be
one that has no real-world equivalent, but the persuasiveness of its representation allows us to
respond to it as if it were real.
