Summary: Putting It All Together - Foundations for Designing User-Centered Systems - page 376

age. The physical attributes of the user will affect how they use a particular
artifact, so you need to consider aspects such as whether they can reach the
controls, whether they can operate the levers, whether they can push buttons, and
so on.
The way that people use artifacts can also affect the well-being of the user.
Upper limb disorders, for example, can arise from having to carry out the same
task repeatedly over extended periods of time, and from the user failing to adopt
the correct posture.
Anthropometrics is an important consideration in interfaces where touch) plays
a central role. Probably the most obvious and widespread examples are smart-
phones and tablet computers. In addition, it is important when thinking about
keyboards: conventional keyboards are still widely used with most personal
computers, and many people use their thumbs to type on the keypads of some cell
phones, for example.
14.2.2 Behavior
The user's behavioral characteristics are mostly related to perception, and the most
important of these are vision and audition, as noted in Chap. 4 . Users will also
differ in terms of their perceptual capabilities. As people get older, for example,
their vision and hearing often diminish and there are people who have permanently
impaired vision or hearing.
When you are designing systems it is therefore important to realize that all users
will not always behave in exactly the same way. Their performance will vary
across a range of behavior which is approximately normally distributed, as shown
on the left in Fig. 14.1 . In those situations where the distribution cannot be two
tailed, such as where reaction times (which cannot be negative!) are being mea-
sured, performance more closely approximates a gamma distribution, as shown on
the right in Fig. 14.1 .
Understanding the way that people perceive things is important, because this
understanding can be used to create artifacts that more closely match the way that
users behave. Knowing about red-green color deficiency, for example, is impor-
tant because it will influence the way that colored items are used in an interface. At
a higher level, knowing the Gestalt laws that describe the way people perceive
groups of objects ( Chap. 4 ) can be used to help you work out the layout of objects
in an interface.
When it comes to designing audio outputs, knowing the way that hearing works
can help you determine what sort of sounds to use for alarms, for example. We
also know that people are poor at localizing sound, but it is easier to localize high
pitch sounds than low pitch ones, and that speech conveys more information than
sounds.
All users, from novices to experts, make errors and in some cases make the
same errors as noted in Chap. 10 . One of the main differences between novices and