Methodology II: Cognitive Dimensions and the Gulfs - Foundations for Designing User-Centered Systems - page 340

Table 12.3 Design principles derived from Norman's analysis to make the Gulfs narrower
where appropriate
1. Use both the knowledge in the world and the knowledge in the head. Provide information in the
environment to help the user determine the system state and to perform actions, such as
explicit displays of system state, and affordances on the system controls
2. Simplify the structure of tasks. Require less of the user by automating subtasks, or using
displays to describe information without being asked, or provide common actions more
directly. However, do not reduce this below their natural level of abstraction
3. Make the relevant objects and feedback on actions visible. Bridge the Gulf of Evaluation.
Make the state of the system easier to interpret
4. Make the available actions visible. Bridge the Gulf of Execution. Make the actions the user can
(and should) perform easier to see and to do
5. Get the mappings correct from objects to actions. Make the actions that the user can apply
natural
6. Exploit the power of constraints, both natural and artificial, to support bridging each Gulf.
Make interpretations of the state and of possible actions easier by removing actions that are
not possible in the current state and reducing the complexity of the display for objects that are
not active or available
7. Design for error. Users will make errors, so you should expect them and be aware of their
effects. Where errors cannot be prevented, try to mitigate their effects. Help the user see errors
and provide support for correcting them
8. When all else fails, standardize. If the user does not know what to do, allow them to apply their
knowledge of existing standards and interfaces
be more deliberate (closer to Rasmussen's rule-based level of behavior). Making
interaction harder can be useful for safety critical systems (e.g., nuclear power,
aviation, and so on), security critical systems, and more generally as a way of
preventing inappropriate, costly, and illegal actions in any interface. If you want to
make the Gulfs wider, you should apply the inverse of these principles; some are
noted in Table 12.4 . Figure 12.3 , for example, shows a picture of an electrical
outlet designed, one can only presume, to be difficult for travelers to use.
At this point it should be clear to you that you are not simply designing to make
the system fit the user in isolation. At the same time, you need to consider how to
mold the task environment to fit the user. In other words, you need to fit the
environment to the tasks, goals, knowledge, and expectations of the user.
12.7 Limitations of the Gulfs
While Norman's approach has been very useful as a metaphor and approach for
improving interface design over the years, it has some limitations that should be
noted. The most obvious limitation is that it is intentionally simplistic. The sug-
gestions that it makes are context independent. The sizes of the Gulfs are not
measurable, and this makes it difficult to apply this approach to choose between
alternative designs.