Methodology II: Cognitive Dimensions and the Gulfs - Foundations for Designing User-Centered Systems - page 337

perform their tasks to achieve their goals. You should also try to anticipate potential
problems, and understand how your users will use problem solving to resolve them.
By doing so you should be able to identify redundancies that you can build into the
system to allow (and help) users to work around the problem until it can be fixed.
12.5.1 The Gulfs of Evaluation and Execution
In Norman's seven stages of action he explicitly talks about the need to map between
psychological and physical concepts. Often there is not a direct correspondence
between the two. If we think about behavior in terms of Neisser's ( 1976 ) perceive-
decide-act cycle we can identify two areas where the mapping occurs.
When the user perceives the state of the system (or more generally, the envi-
ronment) this will be in terms of physical concepts (usually variables and values)
that the user will have to translate into a form that is compatible with their mental
model of how the system operates. Norman describes the gap between the physical
concepts and the psychological concepts as the Gulf of Evaluation (see Fig. 12.2 ).
The user will normally have to do some (cognitive) work to bridge this Gulf. If the
user cannot interpret the effects in terms of the original goals and intentions, this
may mean that they have to resort to problem solving to determine whether the
effects of their actions indicate that the goal has been achieved.
When the user formulates a goal, this usually leads to the intention to perform
some actions to attain that goal. The user then has to translate these psychological
concepts into physical concepts, which are usually actions that can be executed on
the system (or, more generally, the environment). Norman describes the gap
between the (psychological) goals and intentions and the physical actions as the
Gulf of Execution (see Fig. 12.2 ). If the user cannot readily work out how to
translate the goals and intentions into the available actions that can be performed
on the system, they may end up not knowing what to do, or how to do it. In such
cases they will often have to resort to problem solving to determine what actions to
take and how to execute them.
When designing systems you should normally try to minimize the size of the
Gulfs of execution and evaluation. Often it may not be possible to eliminate them
completely, but you should try to make it obvious what the user needs to do to
bridge the Gulfs.
12.5.2 The Gulfs in Practice
A couple of examples should help to illustrate the two Gulfs more clearly, and show
how serious the effect of large Gulfs can be. In the Kegworth air crash (see Appendix)
and in many other air disasters a large Gulf of Evaluation can be identified. The true
state of the aircraft was not very clear from the instruments in the cockpit, and there