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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 type or severity of impairment. The term "accessibility" is most often used in reference to specialized hardware or software, or a combination of both, designed to enable use of a computer by a person with a disability or impairment. Specific technologies may be referred to as assistive technology.
There are many disabilities or impairments that can be a barrier to effective computer use. These impairments, which can be acquired from disease, trauma, or may be congenital, include but are not limited to:
Accessibility is often abbreviated as the numeronym 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 use a computer comfortably and productively may require a "special needs assessment" by an assistive technology consultant (such as an occupational therapist, a rehabilitation engineering technologist, or an educational technologist) to help them identify and configure appropriate assistive technologies to meet individual needs. Even those who are unable to leave their own home or who live far from assessment providers may be assessed (and assisted) remotely using remote desktop software and a web cam. For example, the assessor logs on to the client's computer via a broadband Internet connection, observes the users computer skills, and then remotely makes accessibility adjustments to the client's computer where necessary.
The biggest challenge in computer accessibility is to make resources accessible to people with cognitive disabilities - particularly those with poor communication and reading skills. As an example, people with learning disabilities may rely on proprietary symbols and thus identify particular products via the product's symbols or icons. Unfortunately copyright laws can limit icon or symbol release to web-based programs and websites by owners who are unwilling to release them to the public.
In these situations, an alternative approach for users who want to access public computer based terminals in libraries, ATMs, and information kiosks is for the user to present a token to the computer terminal, such as a smart card, that has configuration information to adjust the computer speed, text size, etcetera to their particular needs. The concept is encompassed by the CEN EN 1332-4 Identification Card Systems - Man-Machine Interface. This development of this standard has been supported in Europe by SNAPI and has been successfully incorporated into the Local Authority Smartcards Standards e-Organisation (LASSeO) specifications.
Since computer interfaces often solicit visual input and provide visual feedback, another significant challenge in computer accessibility involves making software usable by people with visual impairments. 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 suffer from some form of color-blindness. The main color combinations that might be confused by people with visual deficiency include red/green and blue/green. However, in a well-designed user interface, color will not be the primary way to distinguish between different pieces of information.
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 will use a generic input API that permits the use even of highly specialized devices unheard of at the time of software's initial development. Keyboard shortcuts and mouse gestures are ways to achieve this access, as are more specialized solutions, including on-screen software keyboards and alternate input devices (switches, joysticks and trackballs). Users may enable a bounce key feature, allowing the keyboard to ignore repeated presses of the same key. 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's use of assistive technology is an example of a person with severe motor and physical limitations who uses technology to support activities of daily living. He uses a switch, combined with special software, that allows him to control his wheelchair-mounted computer using his limited and small movement ability. This personalized system allows him to remain mobile, do research, produce his written work. Mr. Hawking also uses augmentative and alternative communication technology to speak and an environmental control device to access equipment independently.
A small amount of modern research indicates that utilizing a standard computer mouse device improves fine-motor skills.
While sound user interfaces have a secondary role in common desktop computing, these interfaces are usually limited to using system sounds such as feedback. Some software producers take into account people who can't hear due to hearing impairments, silence requirements or lack of sound producing software. System sounds like beeps can be substituted or supplemented with visual notifications and captioned text (akin to closed captioning). Closed captions are a very popular means of relaying information for the Deaf and hearing impaired communities.
Accessibility software can also make input devices easier to access 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, which strives to create accessible websites via conformance to certain design principles. For example, screen readers are of limited use when reading text from websites designed without consideration to accessibility. Sometimes these limitations are due to the differences between spoken and written language and the complexity of text, but it is often caused by 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, embedded 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.
The Open Accessibility Framework (OAF) provides an outline of the steps that must be in place in order for any computing platform to be considered accessible. These steps are analogous to those necessary to make a physical or built environment accessible. The OAF divides the required steps into two categories: creation and use.
The "creation" steps describe the precursors and building blocks required for technology developers to create accessible applications and products. They are as follows:
The "use" steps describe what is necessary in the computing environment in which these accessible applications will run. They are as follows:
The following examples show that the OAF can be applied to different types of platforms: desktop operating systems, web applications and the mobile platform. A more complete list can be found in the Open Source Accessibility Repository by the Open Accessibility Everywhere Group (OAEG).
The goal of the listed tools is to embed accessibility into various mainstream technologies.
ISO 9241-171: Ergonomics of human-system interaction - Guidance on software accessibility
Compiled from independent standards experts, this document is the most comprehensive and technical standard for designing accessible features for software, covering all disabilities and all aspects of software. It provides examples of two priority levels ('Required' and 'Recommended') and offers a handy checklist designed to help with recording software testing results.
The only trouble is that because of its complexity and technical nature, and with upwards of 150 individual statements, ISO 9241-172 is difficult to interpret and apply. Luckily, not every statement is relevant to every situation, therefore it may be advisable to identify a subset of statements that are tailored to the particular software environment, making the use of this document much more achievable.
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