Categories of 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." Disabilities can be divided into the following general categories:

These categories describe groups of disabilities covering a broad range of people with widely different levels of need.

Visual impairments

Visual impairments range from slightly reduced visual acuity to total blindness. Millions of people have vision that is only slightly impaired. They find it difficult to read small print or black text on a gray background, or they experience eyestrain at the end of long computing sessions. These individuals usually do not consider themselves to have a disability.

People whose vision cannot be corrected to better than about 20/80 are described as having low vision. They probably require text to be larger than normal, and they often require a higher contrast between foreground text and the background. When people's vision cannot be corrected well enough to rely on visual information alone — that is, about 20/200 or higher — they are generally considered to be blind and require displayed information to be converted into spoken text or Braille.

Other types of visual impairments include reduced field of vision, a condition that limits a person's focus to only a small area at time, and color blindness, a condition that makes it difficult or impossible for a person to distinguish certain color combinations. Color blindness affects nearly 10% of males and 1% of females.

Hearing impairments

Some people cannot hear or distinguish different beeps, or recognize spoken words. They may require a program to prompt them in a different manner — for example, through a screen flash or spoken messages displayed as text. Other people can find themselves in this situation when working in a very noisy environment, working in a quiet environment (such as a library) where sound would disturb other people, or working on a machine with broken or missing speakers.

Mobility impairments

Some users are unable to perform certain manual tasks, such as using a mouse or typing two keys at the same time. Others may 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 and language 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 software design can help increase the number of people with mild cognitive and language impairments who can use computers.

Seizure disorders

People with some forms of epilepsy may 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 speaking may affect normal computer usage more if voice recognition becomes a common form of input in the future.