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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:

These impairments can present themselves with variable severity; they may be acquired from disease, trauma or may be congenital or degenerative in nature.

Accessibility is often abbreviated to 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 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 assistive hardware and software. In the UK this may be provided by an NHS specialist centre such as Access to Communication and Technology in Birmingham

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 webcam. 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.

Considerations for specific impairments

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 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 [1] and two accessible[2] web portals designed for people developing reading skills are [3] — try typing a letter with your keyboard for more — and [4] with enhanced graphics, unique style controls and improved interactivity (requires an SVG supported browser).

Visual impairment

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, colour 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.

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 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.

Hearing impairment

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).

Web accessibility

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.

Restrictive elements in computer software

These restrictive elements make utilization of a computer difficult for accessibility users[1]:

Collapsing menus

Software that incorporates collapsing menus has a facility that makes fundamental menu options not appear when the package menus are activated. Instead a downward facing arrow appears at the bottom of the menu. In order to access the missing menu options, it is necessary to activate the downward facing arrow. The menu will now change to include the missing options, and it is necessary to navigate the menu again to obtain the missing option. The problem reoccurs each time the menu is activated.


Problems with software incorporating this feature are:

  • The system requires more work for people who have difficulty in using the mouse or keyboard.
  • The downward facing arrow is difficult to activate with the mouse or the touchscreen.
  • The problem is recursive, requiring the procedure to be repeated each time the option is used.

Right click

A mouse with two buttons is required. Depression of the second mouse button provides an alternative function to a normal mouse click.


Problems with software incorporating this feature are:

The interface is not compatible with touchscreen based systems because touchscreen devices generally do not provide alternative finger recognition or right-click facilities.

Inclusion of a second mouse button causes confusion for left and right-handed users on shared computers.

Users unable to use a mouse cannot access the right-click functionality.

Double click

Double click is a facility that requires depression of the mouse button in rapid succession to obtain an alternative function to a normal mouse click.


Problems with software incorporating this feature are:

  • The system may not be usable by people with limited dexterity and have difficulty in using the mouse.
  • The double click functionality may not easily be achieved on some touchscreen devices

Middle click

Middle click is a facility that requires a three button mouse or emulation that requires pressing both mouse buttons simultaneously.


Problems with software incorporating this feature are:

The interface is not compatible with touchscreen based systems because touchscreens do not generally provide alternative finger recognition or middleclick facilities.

Users unable to use a mouse cannot access the middleclick functionality.

Accidental Click

An accidental click is caused when a mouse button is operated without the intention of the user. For example, a user may cause an accidental click, whilst trying to move the pointer across an area of the screen, or whilst trying to operate the scroll button.


A user may cause inadvertent or undesirable program operation as a result of an accidental click.

Mismatched copy and paste

Mismatched copy and paste is a facility built into some software, that causes a paste operation to be mismatched to the copy operation, due to the utilization of multiple copy and paste buffers, rather than a single consistent clipboard.


Problems with software incorporating this feature are:

The software becomes awkward to use, because a paste operation does not insert the text selected by the previous copy, and additional selection operations are required.


Mouseover is an event that occurs on some systems as the pointer is moved over a widget or particular section of the display screen.


This may cause an operational limitation in some software, because the user may be using a keyboard or touchscreen device, rather than a conventional pointing device, and may not be able to access the application functionality provided by a mouseover event.


A drag event can be achieved by:

  • Moving the mouse or pointing device with a button pressed
  • A finger or pointer being moved whilst in continuous contact with a touchscreen or tablet device.
  • A joystick being moved whilst the button is continually depressed
  • The aiming device being moved whilst the trigger is continually depressed


One of the problems with software incorporating this feature is that some users find interfaces requiring drag movements are difficult to use, particularly for accessibility users, or users with limited dexterity. On touchpads and touchscreens, it is particularly easy for a user to accidentally release something they are dragging.

Neighbouring widgets

Neighbouring widgets is a system design flaw in some graphical user interfaces caused by placement of widgets in close proximity to each other.


This causes a problem for users who lack precision targeting skills with the mouse pointing device, or users who produce a mouse jolt when they attempt to click a mouse button.

No dialogue copy facility

No Copy Dialogue is an operational restriction built into some systems that prevents the operator from copying the contents of a message box or dialogue box, for the purpose of copying the information into a document search tool.


This limitation causes may cause annoyance to some users, because they find themselves having to retype information that is already on the screen. This may be a considerable amount of additional operational work for an accessibility user.

No keyboard equivalents

This is a system design flaw, whereby some functionality provided by mouse navigation is not replicated by a keyboard equivalent.


The problem with software containing this flaw is that users with limited dexterity will not be able to make use of the required functionality.

Examples of this include the lack of a facilities in Microsoft Word to Switch Between Headers and Footers, or to resize boxes and tables using only the keyboard.

No joystick

Some windowing systems do not allow the joystick to be used to control the pointer or cursor.


This flaw makes the system difficult to operate by users with limited dexterity, because they cannot utilize the joystick for basic system operation.

Focus stealing

Focus stealing is a facility built into some graphical user interfaces and windowing management systems that allows an application that is not in focus to suddenly gain focus and steal user input intended for the previously focused application.

Scrolling menus

A scrolling menu facility makes some menu options not appear when the package menus are activated. Instead only a section of the menu is shown and upward and downward downward facing arrow appear at the top and bottom of the menus.


The problems with collapsible menus apply to scrolling menus as well. Also, people with learning difficulties may not recognize the menu, because the menu options may be in different positions, depending on the section of the menu that is currently showing.

Touchpad Click

Touchpad Click is a facility built into some systems that allows a mouse click event to be caused by an operator places their finger on touchpad.


Problems with systems that incorporate this facility include:

  • An unwanted system event may be caused by the accidental click operation

Laptop Computers

Some laptop computers are fitted with a touchpad which is the primary interface for controlling pointer movement, making them vulnerable to touchpad click when running systems that provide this facility.

Two handedness

Two handedness is a limitation within some software packages that requires the operator to make use of both hands simultaneously in order to operate the software. Software affected by this limitation may be inoperable by users with only one hand.

Microsoft Windows NT logon

The most famous example of a two handedness limitation is the Microsoft Windows NT login, because it requires pressing ctl+alt+del simultaneously (a combination intended to require two hands). Although it is actually possible to use one hand for this, it is difficult for users with limited dexterity, because this requires bending the wrist into an awkward position. The level of difficulty varies depending on the user's keyboard, because the position of the delete key varies between keyboard designs (particularly between laptops and desktops).

See also

External links

This audio file was created from a revision dated 2006-09-17, and does not reflect subsequent edits to the article. (Audio help)
More spoken articles

Accessibility features of Operating Systems

Web browser accessibility features

Software platform accessibility features


  1. ^ Table of User Interface Accessibility Restrictive Elements

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