Understanding accessibility challenges
When designing and developing software applications and Web
pages that you want to make accessible to people with disabilities,
there are four general types of impairments you need to consider:
- Visual
- Hearing
- Mobility
- Cognitive or learning
Visual impairments
Application users who are blind require text equivalents for all
graphic images and videos available to the sighted user. The text
needs to convey content that is conceptually equivalent to the information
provided in graphical form, so that assistive technologies such
as screen and braille readers can make the information fully accessible.
All user interface (UI) elements must have text or menu equivalents,
and blind users need keyboard equivalents for entering input that
a sighted user would enter with a mouse.
To accommodate users who are color blind, you should avoid
using color as the sole means of conveying information. Using fill
patterns in addition to colors in graphs and other images is one
strategy for supplementing information conveyed by color. Auditory
cues can serve as an alternative way of presenting warnings or other
content signaled by color only.
By enabling high contrast support, you can allow color-blind
users and users with low vision to adjust default system colors
and fonts to make areas of a window or Web page easier to distinguish.
Users with low vision also use hardware or software magnifiers to
enlarge the pixels on a display, and they depend on alternate text
to get some of the information presented in images.
Hearing impairments
Users who are deaf or hard of hearing require visual representations
of auditory information. You might need to provide alternate visual
cues in your application for audible warnings, for example. Blinking
text is one alternative, though the blink rate must be within a
certain range to avoid causing problems for users with seizure disorders.
Audio tracks require transcripts, and videos might require closed
captioning.
Technology to assist with hearing impairments includes voice
recognition products that can convert auditory information to text
or sign language. Important also are TTY/TDD modems that
connect computers with telephones and convert typed ASCII text output
to Baudot code, which is what deaf individuals commonly use to communicate
over the telephone.
Limited mobility
Users with limited mobility often have difficulty handling
hardware and media, but input is typically their biggest challenge.
Depending on the disability, mobility-impaired users might need
to use voice recognition or an on-screen keyboard with an electronic
switch, tracking ball, or joy stick. They might enter input at a
slower pace, which means that timers and response times should be adjustable.
Systems with built-in intelligence can provide cues to cut down
the amount of input required. For Windows applications, the FilterKeys
feature is available to slow the keyboard repeat rate, and the Windows
StickyKeys feature allows users to enter multiple keystrokes such
as Ctrl/Alt/Delete as key sequences.
Cognitive impairments
Reading difficulties,
an inability to process visual or auditory information, problems
with text input, and short-term memory problems can all affect a user’s
access to the content of software and Web applications. Use of clear, simple language,
enforcement of consistent design, and presentation of the same information
in redundant format, such as both audio and video, can all help
users with cognitive impairments to access information. Providing adjustable
response times is important to those whose comprehension is slower than
normal. Making content available to screen readers to reinforce
visual representation is another strategy for aiding comprehension
of people with cognitive impairments.
General suggestions
For Web display, it is important to use elements for all markup
instead of manipulating text features such as font size directly.
Visual appearance should not be the only indicator of function for
text elements. Element markup allows assistive technologies such
as screen readers to announce text elements such as headings by
their function.
Good design for accessibility benefits not only those with
disabilities, but users in general. By enforcing a consistent interface
design, using simple language, ensuring ease of navigation, and
providing the same information in a variety of ways, you can make
your applications more usable for everyone.
For more information
For general information about making Web sites accessible,
see the World Wide Web Consortium Web site
and the Utah State University WebAim Web site
.
For information on how your users can adjust various browsers
for better legibility, and for ways to accommodate vision impairments
in general, see the Lighthouse International Web site
.