Cognition: Mental Representations, Problem Solving, and Decision Making - Foundations for Designing User-Centered Systems - page 173

support this type of analysis can help users. If a disk is full, the user will want to
create a less full disk. What are the large files that can be deleted, or what are the
files that are rarely used or that were temporary? Displays of this information
provide the way for users to understand and apply operators to solve their problem.
Metaphors for design exploit this process by prompting an appropriate mental
model of the device. However, one needs to be careful. This type of problem
solving fails when the mental model is wrong. Novice writers, for example, look at
papers and notice that the paper is not long enough, and simply attempt to add
more pages (this is not how good papers or textbooks are written).
6.3.3.2 Avoids Apparent Backtracking
Early work on problem solving found that problem solvers do not like to move
away from the goal. This is sometimes called backtracking. This was found with
problems like the Missionaries and Cannibals problem and the Goat, Cabbage, and
Wolf problem, but occurs in many problems, and can include, for example,
installing software that has to be then uninstalled to move on. These problems are
shown in Table 6.2 . In these problems you have to make some moves that appear
to take you away from the goal. In each of these problems this means carrying
something that you have already taken across the river back to the starting side.
Problem solvers have particular difficulty finding and doing this move, pre-
sumably because it looks like going away from the goal. These changes can be
differentiated from simple undoing progress from a dead end.
So, if you are building a system, you should be careful how you represent the
goal and the state of the system. If an action is required that might look like it's
going away from the goal, you might support the user by providing a display that
shows that the move is in the right direction, or you might emphasize it in other
ways or with other instructional materials. Or, if you are trying to make a game
more difficult, you might require backtracking.
6.3.3.3 Functional Fixedness, Einstellung, and Insight Problems
Sometimes the ways we view objects and problems is biased by previous expe-
rience. This leads to viewing objects and how to view problems not being done as
well as they could be. Functional fixedness and Einstellung are two examples of
this type of effect.
Functional fixedness is where a person becomes fixated on a particular use of an
object. Figure 6.8 provides an example. In this task, solving it requires not fixating
on a common usage of the objects, and using them in a very reasonable but harder
to think of way.
Einstellung is related to Functional Fixedness but refers to the situation where a
person gets fixated on a strategy to solve a problem. The most famous example is
solving a puzzle using water jugs (Luchins 1942 ). In this task, people were given a