Computer Accessibility

Computer accessibility is traditionally associated with access to interactive computer-based systems by people with physical, sensory or mental disabilities. However, there are several other user categories that confront substantial barries that may prevent them form access to, and use of, such systems, such as:

  • Elderly people, since aging very often results in limitations in vision, hearing, memory, of motor functions.
  • People with situational disabilities, due to the environment they operate in
    • For example, a person in a very noisy environment is situationally deaf, someone using a very small screen has deteriorated vision, and lack of enough or adequate space for using a mouse can create temporary "moter-impairments".
  • People with "technological disabilities", due to the devices / software they use.
    • For example, someone with an old / slow computer, a person connected to the Internet through the phone, someone using a PDA.

But, although there are several different user categories and possible contexts of use, alternative combinations of them may share many similarities and requirements. For example, a deaf person, someone working in a noisy environment, and a person using a computer that has no speakers attached have a "hearing disability", while a blind person, someone using a text-only browser and a person using a screen directly under bright sunlight have "visual impairments". So, most of the time, when designing for accessibility, a single solution is likely to accommodate multiple problems and situations.

People with disabilities

Worldwide, at least one person out of ten is disabled due to physical, mental or sensory impairments (i.e., more than 500 million people worldwide), while at least one out of four is adversely affected by disability (source: United Nations, World Programme of Action Concerning Disabled Persons). In addition, aging very often results in limitations in vision, hearing, memory, or motor functions, and world-wide there are around 600 million persons aged 60 years and over, a number that is estimated to double by the year 2025 and reach 2 billion by 2050 (source: World Health Organisation, Department of Chronic Diseases and Health Promotion). Unsurprisingly, the number of older people playing computer games also increases. In 2003, 41% of most frequent game players were over 35 years old (source: Entertainment Software Association).

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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.

Computer Accessibility Strategies


Disability-related accessibility problems are usually tackled through a combination of:

  • assistive technologies, i.e., devices that are suitable for, or compensate to some extent for a specific disability;
  • interaction techniques, that on the one hand are appropriate for the disabled person's interaction capabilities and needs and, on the other hand, can work with, and take advantage of, any available assistive technologies;
  • content annotation and adaptation, so that it can be rendered in a format that can be optimally perceived and used through the employed assistive technologies and interaction techniques.

The basic strategies for making computers accessible by each impairment category include:

  1. Visual impairments
    • Content annotation with semantic information.
    • Provision of the content through alternative modalities, such as audio and tactile (in the form of Braille).
    • Support for content enlargement, e.g., control of font size, zooming facilities.
    • Customization of color combinations to improve contrast and simplification of visual complexity (e.g., replacing background images with solid colours) to improve legibility.
    • Support of input through the keyboard, Braille devices and speech.
    • Ability to serially and hierarchically browse the content and interaction objects in a logical order.
  2. Motor or dexterity impairments
    • Support / provision of alternative input devices and techniques, such as switches, specialized keyboards, mice, trackballs and joysticks, scanning, visual keyboards and speech.
    • Speed and timing control and adjustment to suit different response times.
    • Ability to serially and hierarchically browse the content and interaction objects in a logical order.
  3. 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).
    • Visual representations of auditory information.
    • Augmentation of speech with sign language.
  4. Cognitive disabilities
    This is probably the hardest category since sometimes, depending on the type and level of disability, solutions must be provided at an individual basis. In general, all related solutions include:
    • Provision of alternative (simplified, illustrated) versions of the content.
    • Simplification of tasks, e.g., through step by step procedures and wizards.
    • Avoidance of blinking and flashing at particular rates that can cause photosensitive epileptic seizures in susceptible individuals.
  5. Speech impairments
    • Support of alternative input / communication methods when speech is required.
  6. Illeteracy
    • Content simplification.
    • Provision of textual content through illustrations, audio and video.

It should be noted that each impairment has different severity levels, possibly requiring different solutions, and that sometimes people have combinations of disabilities, thus raising compatibility issues between individual approaches.

Design for All and Universal Access

The term Design for All (or Universal Design - the terms are used interchangeably) is rooted in engineering disciplines, such as, for example, civil engineering and architecture. In the context of HCI, the term is defined as (Stephanidis et al. 1998): "the conscious and systematic effort to proactively apply principles, methods and tools, in order to develop IT&T products and services which are accessible and usable by all citizens, thus avoiding the need for a posteriori adaptations or specialised design".

Design for All promotes a design perspective that eliminates the need for "special features" and fosters individualisation and end-user acceptability. Design for all, in contrast to the common practice of designing a single solution for an illusionary "typical" or "average" user, suggests the development of products integrating numerous alternative solutions that allow them to adapt in order to suit the broatest possible end user population.

Universal Access (Stephanidis et al. 1998) is prerequisite for achieving Design for All and implies the global requirement for computer accessibility by individuals with different abilities, requirements and preferences, in a variety of disabilities, but with every aspect of diversity that may affect computer accessibility, such as:

  1. the target user population profile (including people with disabilities) and their individual and cultural differences;
  2. the scope and nature of tasks performed
  3. the technological platforms and associated devices (including assistive technology) through which information is accessed.


Stephanidis, C., Salvendy, G., Akoumianakis, D., Bevan, N., Brewer, J., Emiliani, P. L., Galetsas, A., Haataja, S., Iakovidis, I., Jacko, J., Jenkins, P., Karshmer, A., Korn, P., Marcus, A., Murphy, H., Stary, C., Vanderheiden, G., Weber, G., Ziegler, J., 1998. Towards an Information Society for All: An International R&D Agenda. International Journal of Human-Computer Interaction, vol. 10(2), pp 107-134.

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