There are two main strategies for addressing the needs of users with disabilities:
accessibility and universal design. Although these two strategies are not mutually
exclusive, their objectives have slightly different focuses.
Accessibility strives to make an existing product usable for particular disability
groups. This may come in the form of retrofitting or assistive technologies
and may be specific to each type of disability. For example, television accessibility
needs to be approached differently for the visually impaired and for the hearing
impaired.
The aim of Universal Design is to design products that accommodate the broadest
range of users regardless of age or ability. This approach calls for design
that is usable for a broad range of end-users without alterations or accommodations
for accessibility.
Of course, nothing can be designed to be perfectly "universal." There will
always someone who cannot use a product. So both accessibility and universal
design will need to be kept in mind whenever a product is designed. Even when
something is built using universal design principals, designers should keep
in mind that retrofitting or assistive technologies may be used.
We have listed below computer related accessibility aids according to disability:
At least 1.5 million blind and visually impaired Americans use computers. The
most common aid for the visually impaired is a screen reader, a program that
reads out a computer display for the visually-impaired or for those who do not
have access to a monitor. The screen reader can read text that appears in a
standard way in dialog boxes, menus, icons, and text editing windows by attaching
to the operating system components that are used to display the text. The screen
reader may display information in Braille, use voice output, or use other audio
signals to indicate graphics on the screen. There are other tools that can be
useful in place of or in addition to a screen reader:
- text-to-speech system--software that takes written text and speaks it using
some kind of speech synthesizer. Text-to-speech systems are useful for the
visually impaired, and for situations where users are not able to view the
computer screen at all times, such as when they are driving.
- auditory feedback--sounds in response to user activity, such as a click
after a keypress, a whoosh accompanying opening and closing windows, or a
klunk when a file is deleted. Useful as redundant reinforcement of activities
and for those who are visually impaired.
- tactile interface--a user interface that uses touch for input and/or output,
such as a Braille reader.
- screen-enlargement utility--a system for zooming in on portions of the screen
to make it easier for the visually-impaired to view information on computer
monitors. Also called a screen magnifier.
For the most part, hearing loss does not seem to hinder computer use to a great
extent. With more websites including Flash and audio elements, sound could increasingly
become connected with important content and functional elements. Ways to make
software or websites accessible to the hearing impaired are to include:
- visible alerts that accompany any audio alerts.
- closed captions--a visual text view of audio that is in a sound byte or
video clip. Closed captions are an excellent provision for the hearing impaired,
for nonnative speakers who may find written language easier to understand
than spoken language, and for people who work in a noisy environment or a
work environment where noise would be unacceptable.
- speech-to-text system--a type of voice-recognition system--it converts spoken
language to text. Useful for text entry and command entry, especially for
the hearing impaired, people whose hands are busy with other tasks, and for
people with motor impairments.
Communication, for those with speech impairments or difficulty in spoken language,
whether through vocalization or articulation impairments or through neurological
language disorders, can actually be facilitated with computers.
The field of study examining this is called AAC--Augmentative and Alternative
Communication. Aphasias (language disorders) may be aided in a variety of ways
depending on the nature of the disorder. In extreme cases, a person with an
aphasia may find it impossible to communicate sentences in any amount of time
or in any medium, and in those cases, choice systems may help them communicate
a limited set of ideas without syntax.
When motor impairments are the source
of speech difficulties, assistive devices allow a person to use non-vocal means
to specify a phrase and may provide speech synthesis as output. Keyboards may
be sufficient devices for some, but when motor impairment is more broad, some
people may be able to enter single keystrokes only very slowly. A chart-retrieval
system allows a person to enter an entire message by selecting it from a set
of choices presented in a chart. Letter and message prediction systems anticipate
the most likely next letter, word, or phrase that someone will wish to enter
and make those easier to access.
Motor impairments are a loss or limitation of function in muscle control or
movement or a limitation in mobility. This may include hands that are too large
or small for a keyboard, shakiness, arthritis, paralysis, and limb loss, among
other difficulties. The wide variety of aids available include: software such
as Sticky Keys that make difficult keystrokes more accessible, voice recognition
systems, pointers controlled by mouth or head movements text entry systems to
help enter messages with fewer keystrokes. Some of the accessibility aids available
to address motor impairments are:
- head-mounted input devices and eye-tracking systems.
- mouth-stick--a device for the physically disabled that enables them to control
input through a stick they control with their mouth.
- blow-suck tube--an input device for users with limited mobility; a blow-suck
tube is placed in the mouth and blown through. It can be used in conjunction
with a tongue-activated joystick to move a pointer around and make selections.
- tongue-activated joystick--an input device for users with limited mobility;
a tongue-activated joystick is placed in the mouth and manipulated with the
tongue. It can be used in conjunction with a blow-suck tube to move a pointer
around and make selections.
- chording--an input mechanism which requires pushing more than one button
simultaneously in different patterns to represent different letters or commands.
"Chording keyboards" allow rapid entry of letters and words which can allow
faster typing than conventional keyboards and permits one-handed operation
of keyboards. "Chording mice" are mice with multiple buttons where clicking
with more than one button is equivalent to having an additional mouse button.
Chording is a powerful tool for some users, but chording is more difficult
to learn and should never be required of users. In particular, many people
with arthritic conditions or other motor impairments may find chording extremely
difficult (though note that one-handed operation may be extremely helpful
to users without the use of one hand).
- speech-to-text system--a type of voice-recognition system - it converts
spoken language to text. Useful for text entry and command entry, especially
for people whose hands are busy with other tasks and for people with motor
impairments.
- "Sticky Keys"--a method of typing where modifier keys, such as Shift, Control,
Command, and Alt/Option, will "stick" down and apply to the next keystroke,
so that only one key needs to be pressed at a time. This is extremely useful
for people who have motor impairments that make it difficult to press combinations
of keys. * This feature is part of Apple's EasyAccess system.
- "Slow Keys"--a keyboard feature that prevents keystrokes from registering
until a key has been held down for a certain period of time. This is extremely
useful for people with motor impairments that make it difficult to target
keys accurately or that cause unpredictable motion. * This feature is part
of Apple's EasyAccess system.
- scanning--for the physically disabled, the ability to move through a set
of options (usually automatically) and to select one of the options. This
enables an interface with only one input: "select now". With this interface,
a user can select objects on a screen, menu items, speech output, or a wide
variety of other commands.
Cognitive impairments are any limitations in the ability to think or reason
that affect a person's capacity to perform a task. Cognitive impairments can
be congenital or the result of a head injury, stroke, or disease. Head injuries
in particular can result in very localized damage, producing highly-specific
problems. Many cognitive impairments are quite common, such as attention difficulties
and dyslexia.
Because cognitive impairments span such a wide range of problems, there are
really no broad solutions in interface design that help everyone, though general
usability recommendations that help reduce cognitive load for everyone will
often provide some benefit, in particular: minimize the load on working memory,
simplify tasks, organize interfaces to minimize error, be forgiving and allow
users to undo mistakes. Cognitive impairments are often less observable and
well-defined than other types of impairments, so it is helpful to consult a
doctor or learning specialist to help clarify the exact nature of the impairment.
- reminder systems-- a system for alerting a user to important items on a
schedule, after a timeout, or when a critical event happens. Used, for instance,
in a medical setting to remind clinicians of necessary tests or interventions.
Useful especially to people with memory impairments.
RSI (Repetitive Stress Injury), also called Cumulative Trauma Disorder (CTD),
can result from many activities (such as assembly line work), and interacting
with computers is only one manifestation. Repetitive stress injuries can also
result from excessive repeated movement with little variation, such as typing
and using a mouse. Damage occurs to soft body tissues, such as tendons and nerves.
Carpal Tunnel Syndrome (CTS), a problem with swelling or inflammation around
the median nerve in the wrist, causing pain or numbness, is one of the most
commonly known of the RSIs. Poor wrist support
and posture during extensive typing is considered a contributing factor. Some
ways to prevent it include improved posture, wrist supports, and taking regular
breaks to stretch and rest.
- RSI can be avoided by using a good posture, varying tasks, and taking frequent
breaks to stretch and relax.
Color blindness is an inability to distinguish certain color combinations. About
8% of males and 0.5% of females are colorblind in some fashion, so it is common
enough to be a highly-significant factor in design. Red-green color blindness
is most common, followed by yellow-blue color blindness.
To avoid problems for users with color blindness, make sure that color is never
the sole way of distinguishing objects. Never expect users to be able to name
colors or recognize a color by name. Use differences in brightness to make colored
regions distinct, and test your interfaces in grayscale to confirm that they
are still usable.
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