Cognition: Mental Representations, Problem Solving, and Decision Making - Foundations for Designing User-Centered Systems - page 166

Fig. 6.3 Diagram of the Philadelphia airport concourse where the user's mental model does not
support finding Gates A2 and A4
Fig. 6.4 Setting the speed for writing a CD. Which is best? Slow and careful, or faster but
slightly more likely to throw an error? Taken from Toast 10 Titanium
Therefore, when you design a system you need to have an accurate mental
model of how people will use it. This requires understanding how people will use
it, the tasks they will perform using the system, and their normal working context.
The developer's mental model of the system is often different from the user's
mental model of the system (this topic is intended to help designers build a better
mental model of users in their own heads). Systems should describe things using
conventions that are consonant with the users' mental models, for example, or be
prepared to change either the users' mental models or the designer's. Making the
system compliant with the user's mental model will almost certainly help reduce
the time it takes to perform tasks, reduce learning time, and improve the accept-
ability of the system.
An important area of consideration for you and your users' mental model is
processing speed and the complexity of the task. Computer programs and algo-
rithms have a time to process an object that may be based on the number of objects
(e.g., simply filing objects, or coloring them), or it may be based on their