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Child using a symbol-based tablet. Many people who wear contacts or glasses might not consider themselves disabled. Yet, just under half of all Americans require some type of assistive aid to see more clearly. Because glasses and contacts correct most common visual impairments such as nearsightedness (myopia), farsightedness (hyperopia), and age-related degradation (presbyopia) so easily, we tend to forget that, without assistive technology, these conditions could be debilitating.
Other disabilities are less common, and they remain a mystery to many people. Much of this arises because we may not have had the opportunity to know someone who has a disability. We may be confused or frightened by some of the effects of the disability, or we may be unsure about how to interact with the person who has the disability.
Disabilities can be caused by genetics, traumatic injuries, age, illnesses, diseases, environmental factors, and as side effects from some medications. We are all likely to develop disabilities at some point in our lives. Understanding a bit about different types of disabilities can help you better understand how to design accessible Web sites. Here is a brief introduction to some.
Blindness is a disability that affects a person's eyesight. A person is generally considered "legally" blind when his or her best corrected visual acuity is 20/200 or less. This means that what this person sees at 20 feet can be seen by a person with 20/20 vision at 200 feet. A person is also considered blind if his or her visual field is 20 degrees or less. A person with an unobstructed visual field can see 180 degrees from each eye.
Most people who are blind don't just see blackness. They can often perceive some light to dark contrasts. People who have some vision but who cannot achieve clear vision by wearing corrective lenses are considered to have low vision. Color blindness is another visual condition that can affect people's lives because they are unable to distinguish some colors, such as reds from greens, or yellows from blues.
People who are blind benefit from assistive technologies such as refreshable Braille displays that provide a tactile output of the information presented on the computer screen, and screen readers which audibly read information presented on the screen. People with low vision benefit from closed-circuit televisions (CCTVs) which can magnify printed material such as books and letters, and from computer screen magnifiers. Voice recognition systems and software are also helpful to people with visual disabilities.
Deafness is a disability that affects a person's ability to hear. Deafness is not an all-or-nothing condition. Some individuals are completely deaf, and others have varying degrees of functional hearing loss. Degrees of hearing loss are often categorized as mild, moderate, severe, and profound. Those who refer to themselves as Deaf usually have either severe or profound hearing loss.
Many Deaf people communicate using sign language, which may be their primary language. As a result, English or another language may be their second language. Learning a language by writing or through translation, without being able to hear how its words are spoken, can be quite difficult. As with any language translation, some phrases or words may not translate directly, or they may be misinterpreted.
People who have lesser degrees of hearing loss are commonly referred to as hard of hearing. They generally use their residual hearing and speech to communicate because they can understand some speech sounds with or without a hearing aid.
Deaf people benefit from assistive technologies such as a Telecommunications Device for the Deaf (TTY or TDD), which is a device with a keyboard that sends and receives typed messages over a telephone line. Some are also equipped with answering machines. Television and Web video captioning is a vital necessity for comprehension of auditory-based material.
A motor disability arises from a condition that limits basic physical activities, such as walking, reaching, dexterity or speech. A motor disability can arise from a spinal cord injury such as quadriplegia, amputation of a limb, or other joint or nerve damage. Diseases and genetic disorders also cause motor disabilities, such as cerebral palsy, muscular dystrophy, multiple sclerosis, spina bifida, Lou Gehrig's disease, arthritis, Parkinson's disease, Tourette syndrome, and others.
The Web can be a lifeline for people with motor disabilities because they are often isolated. For many, mobility is cumbersome or very restricted. Some motor disabilities can have physical effects such as tremors, flailing, stuttering, slurred or impaired speech, drooling, spasms, muscle stiffness, muscle slowness, twitches, tics, etc., and this may cause them to be embarassed or suffer from ridicule when they are in public. This is unfortunate because these effects are entirely involuntary.
People with motor disabilities benefit from a variety of specialized input and keyboard devices, along with voice recognition systems. These devices can include head wands, mouth sticks, trackballs, single-hand keyboards, keyboards with oversized keys, eye-tracking devices, and touch screens.
Cognitive disabilities arise from a change in the biology or physiology of the brain, such as a change in chemical or neurotransmitter activity, blood or oxygen flow, or cellular structure. There is a wide variety of cognitive disabilities, and oftentimes the effects are specific to each individual. Effects can range from being only mildly disruptive to one's life, or they can be completely debilitating.
A cognitive disability can stem from a traumatic brain injury caused by an event such as a motor vehicle accident, a fall, or a gunshot wound. Or, it can involve a learning disorder such as dyslexia or attention deficit hyperactivity disorder (ADHD). Cognitive disabilities also include genetic disorders such as autism or Down's syndrome, and age-related disorders such as dementia or Alzheimer's disease. A person with a cognitive disability may have difficulty with attention, memory, judgement, organization, perception, emotions, personality, or learning.
Designing accessible Web content to meet the needs of people with cognitive disorders can be complicated, and some material and designs will always be too complex for certain audiences. However, most will benefit from content that is presented simply and clearly, with predictable, non-distracting results such as consistent navigation and well-structured documents.
People with cognitive disabilities benefit from assistive technologies such as programmable keyboards through which letters, words and phrases can be entered by pressing custom keys. Conceptual, image-based keyboards and touch-screen applications are very helpful as well.
