Disabilities affecting computer accessibility

There are several types of disabilities that can affect computer accessibility. Although there is no single universally accepted classification, an indicative list of impairments includes the following:

Visual impairments: blindness, low vision and color blindness.
- Blind people rely on hearing and touch to use computers.
- People with low vision may be able to read text and distinguish forms, objects and pictures under specific conditions (e.g., very large fonts, high contrast, particular lighting conditions) but usually also rely on other senses, such as hearing and touch.
- People with color blindness have inability to discriminate differences in colors, mainly between red and green.
Motor or dexterity impairments: total absence of limbs or digits, paralysis, lack of fine control, instability or pain in the use of fingers, hands, wrists, or arms.
- Individuals with motor impairments mainly face difficulties in using standard input devices, i.e., the keyboard and the mouse.
Hearing disabilities: they may range from total deafness (i.e., the person is not able to hear at all), to slight loss of hearing (the person can sense sounds and speech, but finds it hard to identify their content).
- Deaf people communicate using sign and written language, while hard of hearing individuals may rely on lip-reading and hearing-aids.
Cognitive disabilities: this is a very broad category, which roughly includes difficulties in the performance of mental tasks. These can range from limited and focused problems affecting a very specific cognitive function (e.g., the ability to understand math), to severe cases (e.g., brain damage) where the individual is unable to take care of daily living activities.
- The most common types of cognitive disabilities are: mental retardation, language and learning disabilities (e.g., dyslexia), head injury and stroke, Alzheimer's disease (i.e., memory retention problems) and dementia.
Speech impairments: Speech impairments are quite rare and sometimes are combined with other disabilities but they do not indicate limited intelligence.
- Individuals with speech impairments may have articulation problems (e.g., stuttering), be unable to speak loudly or clearly, or even to speak at all. Obviously, they have problems in using speech recognition systems. Depending on the severity of their case, they may use communication aids, to substitute speech.
Illeteracy: Illeteracy is the lack of ability to read and write in any language.
- Although illeteracy is not a physical disability, it creates considerable barriers to computer accessibility and is often treated in the overall context of computer accessibility.

Age-related disabilities are frequently referred to as a separate category, but all related problems fall within the above categories.