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 websites accessible, see the World Wide Web Consortium website at http://www.w3.org/ and the Utah State University WebAim website at http://www.webaim.org.

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 website at http://www.lighthouse.org/.