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In human-computer interaction, computer accessibility (also known as Accessible computing) refers to the accessibility of a computer system to all people, regardless of disability or severity of impairment. It is largely a software concern; when software, hardware, or a combination of hardware and software, is used to enable use of a computer by a person with a disability or impairment, this is known as Assistive Technology.
There are numerous types of impairment that impact computer use. These include:
Accessibility is often abbreviated a11y, where the number 11 refers to the number of letters omitted. This parallels the abbreviations of internationalization and localization as i18n and l10n respectively.
People wishing to overcome an impairment in order to be able to use a computer comfortably and productively may need a "special needs assessment" by an assistive technology consultant (such as an occupational therapist or clinical scientist) to help them identify and configure appropriate assertive hardware and software.
Where a disabled person is unable to leave their own home, it may be possible to assess them remotely using remote desktop software and a web cam. The assessor logs on to the client's computer via a broadband Internet connection. The assessor then remotely makes accessibility adjustments to the client's computer where necessary and is also able to observe how they use their computer.
The biggest challenge in computer accessibility is to make resources accessible to people with cognitive disabilities - particularly those with poor communication skills - and those without reading skills.
Their further development relies on public domain icons being available. Many people with a learning disability learn and rely on proprietary symbols. They thus become tied to particular products. The copyright owners are generally unwilling to release them on the web.
Other examples include Web accessibility a set of guidelines  and two accessible web portals designed for people developing reading skills are peepo.com  &m dash; try typing a letter with your keyboard for more &m dash; and peepo.co.UK  with enhanced graphics, unique style controls and improved interactivity (requires an SVG supported browser).
Another significant challenge in computer accessibility is to make software usable by people with visual impairment, since computer interfaces often solicit input visually and provide visual feedback in response. For individuals with mild to medium vision impairment, it is helpful to use large fonts, high DPI displays, high-contrast themes and icons supplemented with auditory feedback and screen magnifying software.
In the case of severe vision impairment such as blindness, screen reader software that provides feedback via text to speech or a refreshable braille display is a necessary accommodation for interaction with a computer.
About 8% of people, mostly males, suffer from some form of colour-blindness. In a well-designed user interface, color should not be the only way of distinguishing between different pieces of information. However, the only colour combinations that matter are those that people with a deficiency might confuse, which generally means red and green and blue and green.
Some people may not be able to use a conventional input device, such as the mouse or the keyboard. Therefore it is important for software functions to be accessible using both devices; ideally, software uses a generic input API that permits the use even of highly specialized devices unheard of at the time of software development. Keyboard shortcuts and mouse gestures are ways to achieve this. More specialized solutions like on-screen software keyboards and alternate input devices like switches, joysticks and trackballs are also available. Speech recognition technology is also a compelling and suitable alternative to conventional keyboard and mouse input as it simply requires a commonly available audio headset.
The astrophysicist Stephen Hawking is a famous example of a person suffering from motor disability. He uses a switch, combined with special software, that allows him to control his wheelchair-mounted computer using his remaining small movement ability. This performs as a normal computer, allowing him to research and produce his written work, and as an Augmentative and Alternative Communication and environmental control device.
While sound user interfaces have a secondary role in common desktop computing, usually limited to system sounds as feedback, software producers take into account people who can't hear, either for personal disability, noisy environments, silence requirements or lack of sound hardware. Such system sounds like beeps can be substituted or supplemented with visual notifications and captioned text (akin to closed captions).
Accessibility software can also make input devices easier to use at the user level:
Other approaches that may be particularly relevant to users with a learning disability include:
Enabling access to Web content for all users is the concern of the Web accessibility movement. Websites can be designed to be more accessible by their conformance to certain design principles.
Screen readers are of limited use when reading text from websites designed without consideration to accessibility; this can be due to the differences between spoken and written language and the complexity of text, but it is mainly due to poor page design practices. The tendency to indicate semantic meaning using methods that are purely presentational (e.g. larger or smaller font sizes, using different font colors, or images or multimedia to provide information) restricts meaningful access to some users. Therefore designing sites in accordance with Web accessibility principles helps enable meaningful access for all users.
For example, web designers can ensure that navigation and content is as plain and simple as appropriate and long texts should provide summaries.
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