What Are Disabilities?

Individuals are not disabled—rather, some people have difficulties performing certain tasks, such as using a mouse or reading small print. When these limitations are serious enough to impact the person's performance, they are referred to as "disabilities." Anyone can experience the same difficulties because of illness or accident, environment (such as loud background noise), or hardware errors such as a missing mouse.

Disabilities can be divided into the following general categories:

• Visual impairments. This ranges from slightly reduced visual acuity to total blindness. Those with reduced visual acuity might only need images to be reasonably sized or specially enlarged, or they might need the high contrast between foreground and background. Users with more severe impairments might require output to be translated into audible cues, spoken text, or Braille.
• Hearing impairments. Some individuals do not notice beeps, distinguish different sounds, or recognize spoken words. These users might require that a computer prompt them in a different manner using a screen flash, an indicator lamp, or a display of messages as text.
• Movement impairments. Some users are unable to perform certain manual tasks, such as using a mouse or typing two keys at the same time. Others might have a tendency to hit multiple keys, "bounce" fingers off keys, or be unable to hold a printed book. Many users need keyboards and mouse functions to be adapted to their requirements, or they rely exclusively on a single input device.
• Cognitive impairments. Cognitive impairments take many forms, including short- and long-term memory loss, perceptual differences, and conditions such as Downs syndrome. Language impairments such as dyslexia or illiteracy are also very common. Even people learning the language used by their computer software as a second language can be considered to have a form of language impairment. Proper design can help increase accessibility for computer users with various cognitive and language impairments.
• Seizure disorders. People with some forms of epilepsy might experience minor or severe seizures when they see visual signals flash at certain rates or hear certain types of random or repetitive sounds.
• Speech impairments. Although difficulty speaking does not normally affect a person's ability to use a computer today, it can be a problem in using telecommunications and voice menus. Difficulty in speaking might affect normal computer usage more if voice recognition becomes a common form of input in the future.