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assumes that the designer either understands motor output fairly well, or that the
details of motor output do not matter. When the interface is either simple, or has
been poorly designed, it will be relatively easy to make judgments about where it
can be improved. For more complex interfaces, where there are realistic design
trade-offs that need to be made, it will be more difficult to make these judgments
accurately and for a wide range of users.
12.8 Summary
The Cognitive Dimensions and the Gulfs of Evaluation and Execution both pro-
vide a less formal and much lighter weight approach than task analyses and user
modeling techniques. They provide useful heuristics about interface design, and a
way to describe interface trade-offs, but they cannot always be used to compute the
quality of alternative designs.
The Cognitive Dimensions provide a way to discuss particular aspects of
interface design. They are not a complete method, but do provide a useful way to
carry out an early sanity check on a particular interface design. It is useful to have
such techniques that can be used early on and with little effort.
The Gulfs of Evaluation and Execution remind us how users interact with a
system. Nearly all users have some common tasks related to interaction, including
evaluating the system state and executing actions. Bridging these gaps (Gulfs) will
mean creating the system to support these two fundamental aspects of task per-
formance. Thinking about the Gulfs can yield practical suggestions for improving
designs, such as making things more visible but avoiding clutter.
12.9 Other Resources
There are many resources related to Blackwell and Green's Cognitive Dimensions
available at their web site. These include papers, reports, and tools.
http://www.cl.cam.ac.uk/*afb21/CognitiveDimensions/
Don Norman's book The Design of Everyday Things (originally published as
ThePsychologyof Everyday Things) includes several examples of the Gulfs of
Evaluation and Execution arising out of poor design. These include a fridge
freezer, doors on buildings, and a slide projector where how to evaluate or how to
use the devices were not clear. He also discusses how the designs could be
improved to reduce or eliminate the Gulfs:
Norman, D. A. (1988). The psychology of everyday things. NY: Basic Books. (2013 ed.,
The design of everyday things).
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