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Computer accessibility

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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.

Special-needs assessment

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.

Considerations for specific impairments

BBC News shown in 'desktop mode,' with Accessibility links at the top. The screenshot is taken from Windows Mobile.
A single switch assistive device that enables the user to access an on-screen computer keyboard.

Cognitive impairments and illiteracy

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.[1][2] 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.[3]

Visual impairment

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.

Motor and dexterity impairments

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). 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.[4]

Hearing impairment

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.

Software accessibility

Accessibility Application Programming Interfaces (APIs)

Software APIs exist to allow assistive technology products such as screen readers and screen magnifiers to work with mainstream software. The current or past APIs include:

Some of these APIs are being standardized in the ISO/IEC 13066 series of standards.[10][11]

Accessibility features in mainstream software

Accessibility software can also make input devices easier to access at the user level:

  • Keyboard shortcuts and MouseKeys allow the user to substitute keyboarding for mouse actions. Macro recorders can greatly extend the range and sophistication of keyboard shortcuts.
  • Sticky keys allows characters or commands to be typed without having to hold down a modifier key (Shift, Ctrl, Alt) while pressing a second key. Similarly, ClickLock[12] is a Microsoft Windows feature that remembers a mouse button is down so that items can be highlighted or dragged without holding the mouse button down while scrolling.
  • Customization of mouse or mouse alternatives' responsiveness to movement, double-clicking, and so forth.
  • ToggleKeys[13] is a feature of Microsoft Windows 95 onwards. A high sound is heard when the CAPS LOCK, SCROLL LOCK, or NUMBER LOCK key is switched on while a low sound is heard when any of those keys is switched off.
  • Customization of pointer appearance, such as size, color and shape.
  • Predictive text
  • Spell checkers and grammar checkers

Support for learning disabilities

Other approaches that may be particularly relevant to users with a learning disability include:

Web accessibility

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.

Open Accessibility Framework

The Open Accessibility Framework (OAF)[16] 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:

  1. Define what “accessible” means for the identified use of the platform. It must be clear what is meant by “accessible” as this will differ according to the modality and capabilities of each platform. Accessibility features may include tabbing navigation, theming, and an accessibility API.
  2. Provide accessible stock user interface elements. Pre-built “stock” user interface elements, used by application developers and authoring tools, must be implemented to make use of the accessibility features of a platform.
  3. Provide authoring tools that support accessibility. Application developers and content authors should be encouraged to implement tools that will improve the accessibility features of a platform. Using these tools can support accessible stock user interface elements, prompt for information required to properly implement an accessibility API, and identify accessibility evaluation and repair tools.

The “use” steps describe what is necessary in the computing environment in which these accessible applications will run. They are as follows:

  1. Provide platform supports. Computing platforms must properly implement the accessibility features that are specified in their accessibility definition. For example, the accessibility API definitions must be implemented correctly in the program code.
  2. Provide accessible application software. Accessible applications must be available for the platform and they must support the accessibility features of the platform. This may be achieved by simply engaging the accessible stock elements and authoring tools that support accessibility.
  3. Provide assistive technologies. Assistive technologies (e.g. screen readers, screen magnifiers, voice input, adapted keyboards) must actually be available for the platform so that the users can effectively interface with the technology.

The following examples show that the OAF can be applied to different types of platforms: desktop operating systems, web applications[17] and the mobile platform. A more complete list can be found in the Open Source Accessibility Repository by the Open Accessibility Everywhere Group (OAEG).[18]

  1. Accessibility APIs include the Assistive Technology Service Provider Interface and UI Automation on the desktop, WAI-ARIA in web applications, and the Blackberry Accessibility API[19] on the Blackberry operating system.
  2. Other APIs are keyboard access and theming in widget libraries like Java Swing for desktop applications, the jQuery UI and Fluid Infusion[20] for Web applications, and the Lightweight User Interface Toolkit (LWUIT) for mobile applications.
  3. Support for accessible development can be effective by using Glade (for the GTK+ toolkit),[21] the DIAS plugin for NetBeans IDE,[22] Xcode IDE for iOS applications.[23] Accessibility inspection tools like Accerciser (for AT-SPI)[24] and support for accessible authoring with the AccessODF plugin for LibreOffice and Apache OpenOffice[25] also fit into this step.
  4. Support for UI Automation on Microsoft Windows,[26][27] support for ATK and AT-SPI in Linux GNOME,[28] WAI-ARIA support in Firefox,[29][30] and the MIDP LWUIT mobile runtime[31] (or the MIDP LCDUI mobile runtime) that is available on mobile phones with Java are examples of APIs.
  5. The DAISY player AMIS on the Microsoft Windows desktop[32] and the AEGIS Contact Manager for phones with Java ME[33] are designed for accessibility.
  6. The GNOME Shell Magnifier and Orca on the GNOME desktop, GNOME's ATK (Accessibility Toolkit), the web-based screen reader WebAnywhere,[34] and the alternative text-entry system Dasher for Linux, iOS and Android[35][36] are examples of assistive technologies.

The goal of the listed tools is to embed accessibility into various mainstream technologies.[37]

Standards and Regulations

International Standards

ISO 9241-171

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.[citation needed]

See also


  1. CEN: Personal identification, electronic signature and cards and their related systems and operations - Structure.
  2. "Draft EN 1332-4 Identification Card Systems - Man-Machine Interface - Part 4 : Coding of user requirements for people with special needs". 2009-11-20. Retrieved 2013-07-28.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. LASSeO: Feasibility Studies - Final Report. August 2011.
  4. Bohannon, John (December 19, 2013). "Click here to improve your motor skills". Science. Retrieved 23 December 2013.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. Oracle: Java Accessibility
  6. Oracle: Java SE Desktop Accessibility (page containing a link to the Java Access Bridge).
  7. ISO: ISO/IEC PRF TR 13066-6: Information technology -- Interoperability with Assistive Technology (AT) -- Part 6: Java accessibility application programming interface (API).
  8. ISO: ISO/IEC PDTR 13066-4: Information Technology - Interoperability with Assistive Technology (AT) -- Part 4: Linux/UNIX graphical environments accessibility API.
  9. ISO: ISO/IEC TR 13066-3:2012: Information technology -- Interoperability with assistive technology (AT) -- Part 3: IAccessible2 accessibility application programming interface (API).
  10. Richard Hodgkinson: 7th Report on International ICT Accessibility Standards Proposed, Being Developed and Recently Published. 3 October 2008.
  11. Richard Hodgkinson: 10th Report on International ICT Accessibility Standards Proposed, Being Developed and Recently Published. 26 June 2009.
  12. Microsoft: Using ClickLock
  13. Microsoft: To turn on ToggleKeys. Windows XP Professional Product Documentation.
  14. Bates, Roger; Jones, Melanie (2003). "Using Computer Software To Develop Switch Skills". 2003 [Technology and Persons with Disabilities] Conference Proceedings. Retrieved 2007-02-08.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  15. Hawes, Paul; Blenkhorn, Paul (2002). "Bridging the Gap between Aspiration and Capability for Aphasic and Brain Injured People". 2002 [Technology and Persons with Disabilities] Conference Proceedings. Retrieved 2007-02-08.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  16. AEGIS Consortium: AEGIS OAF and high-level architecture. Accessed 2013-01-17.
  17. AEGIS Consortium: AEGIS Architecture Definition. Accessed 2013-01-17.
  18. Open Accessibility Everywhere Group (OAEG): Open Source Accessibility Repository. Accessed 2013-01-17.
  19. Research in Motion (RIM): Package net.rim.device.api.ui.accessibility. BlackBerry JDE 6.0.0 API Reference. Accessed 2013-01-17.
  20. Fluid Infusion. Accessed 2013-01-17.
  21. Glade - A User Interface Designer. Accessed 2013-01-17.
  22. DIAS Netbeans IDE plugin & Standalone. Accessed 2013-01-17.
  23. Apple Inc.: Xcode 4. Accessed 2013-01-17.
  24. Accerciser.
  25. AccessODF. Accessed 2013-01-17.
  26. Microsoft Developer Network: Accessibility (.NET Framework 4.5). Accessed 2013-01-17.
  27. Microsoft Windows Dev Center: UI Automation (Windows). Accessed 2013-01-17.
  28. GNOME Dev Center: Introducing ATK, AT-SPI, GAIL and GTK+. Accessed 2013-01-17.
  29. Access Mozilla. Accessed 2013-01-17.
  30. Access Firefox: Firefox Accessibility Features. Accessed 2013-01-17.
  31. AEGIS Consortium: LWUIT - Mobile Accessibility. Accessed 2013-01-21.
  32. DAISY Consortium: AMIS: DAISY 2.02 & DAISY 3 Playback Software. Accessed 2013-01-17.
  33. AEGIS Contact Manager. Accessed 2013-01-17.
  34. WebInSight: WebAnywhere: A Screen reader on the go. Accessed 2013-01-17.
  35. Inference Group (University of Cambridge): Mobile Dasher. Accessed 2013-01-17.
  36. Dasher for iOS on iTunes. Accessed 2013-01-17.
  37. Iosif Klironomos, Julio Abascal, Ilse Bierhoff: D3.1 Report with background material needed to support the SDDP-2 Meeting: An Introduction to the Key Issues Relating to Accessible User Interfaces. Accessed 2013-01-17.

External links


it:Accessibilità (informatica)