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Like any computer user, users with disabilities vary in age,
computer experience, interests, and education. When barriers are
removed, the computer gives them a tool to compete with users without
disabilities on an equal basis. Users with disabilities may be engineers,
artists, scientists, designers, lawyers, administrative assistants,
and software engineers. The common thread among the people in these
diverse professions is that computers play an important role in
their daily work. The following sections discuss how to write interfaces for
users who have the following disabilities: Language, cognitive, and other
Physical Disabilities | |
Physical disabilities can be the result of congenital conditions,
accidents, or excessive muscular strain. Examples include spinal
cord injuries, degenerative nerve diseases, stroke, and typing-based
repetitive stress. The following design principles address creating applications
for those users with physical disabilities: Use new technology to aid in developing your application Adaptive hardware and software capable of optical character
recognition, word prediction, eye scanning, and synthesized speech
can give users with physical disabilities alternatives to keyboard
and mouse interaction. Provide keyboard access to all application features. While physical capabilities vary greatly, users all need keyboard
access to the controls, features, and information in applications.
Providing comprehensive keyboard access is essential to ensure that
the user who cannot use a mouse can productively use your application. Follow the key-mapping guidelines in this chapter
and throughout the style guide. Consistent use of these mappings provides applications that
are easier to use and increases the effectiveness of alternate input/output
technology, such as speech control and screen readers for blind
individuals.
For more information, see Chapter 6 “Selection” Appendix B “Keyboard Model and Key Bindings” and the Keyboard
(Device) reference page. Visual Disabilities | |
Effects of visual disabilities range from reduced visual acuity,
requiring reading glasses, to people who need large-size displays,
to the completely blind who require screen-reading software that
allows them to navigate and to hear what is on the screen. As with
physical disabilities, it is crucial that your application provide
complete keyboard access. The following design principles address creating applications
for those users with visual disabilities: Do
not hard code font sizes and type faces. Allow users to configure all of the fonts in your application,
including text in text-entry fields, menus, labels, and messages. Do not hard code your application colors. In addition to being difficult to interpret, some background
and text color combinations can result in text that is difficult
to read. Users should always have the capability to override default
colors so that they can choose the colors that work best for them. Never use color as the only source of information. Interpreting information that depends upon color (for example,
red=stop, green=go) is particularly difficult for those who are
color blind or unable to see differences among some colors. Do not hard code graphic attributes such as line,
border, and shadow thickness. Allow users to change the attributes of window controls for
sizing and separation. A window border, shadow, or separator that
is too thin or thick can be difficult to identify or may distort
the user's focus. Provide meaningful names for controls. If you use nonstandard (for example, custom) controls, or
standard controls without text (for example, push buttons or a palette
with graphics), then you must give each control a meaningful name.
Rather than calling an eraser graphic “control5,” for
example, call it “eraser.” Users who rely on screen
reading and character recognition devices will not understand the
control's purpose unless it has a meaningful name.
For more information, see “Visual Cues” and the Control,
Label,
and Text-Entry Field (Control)
reference pages. Hearing Disabilities | |
People with hearing disabilities cannot hear sound output
at typical volumes, if at all. In some cases, users can hear audible
cues only at certain frequencies or volumes. The following design principles address creating applications
for those with hearing disabilities: Do not overuse or rely exclusively
on audible cues. Never assume that a user can hear an auditory notice. Even
users who are not hearing impaired are often unable to use sound
because they are in a noisy office or using a portable computer
in an area where sound is prohibited. Sounds unaccompanied by visual notification, such as a beep
indicating that a print job has completed, are of no value to hearing-impaired
users or others who are not using sound. While such sounds can be
valuable, never create a design that works on the assumption that
they will be heard. Where appropriate, allow users to choose between
audible or visual cues. There are times when either an audible cue or a visual cue
is more appropriate. For example, hearing-impaired users and anybody
using a system in a public area would benefit from the option of
choosing to see rather than to hear a notice. Such notices can take
the form of a changing icon or a message in an information area
window. On the other hand, in the printer example it would be intrusive
for most users to see a warning window every time a printout is
ready. Therefore an audible cue is more appropriate. Allow users to configure the frequency and volume
of audible cues. Every user has different hearing abilities. Allowing the user
to change the frequency and volume of an audible cue helps to ensure
that the user will both hear the cue and distinguish it from other
audible cues.
For more information, see “Audible Cues”. Language, Cognitive, and
Other Disabilities | |
The wide range of disabilities is too broad to cover extensively.
However, users with language, cognitive, and other disabilities
can benefit from an application that: Allows flexible limits for task completion Minimizes the use of transitory signals Reduces the user's memory requirements
The guidelines outlined for physical, visual, and hearing
disabilities also typically benefit users with cognitive, language,
and other disabilities. |
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