First, it is important to understand that there are many different types and severities of impairment which lead to disabilities. Some types of impairment are:
Within each of these major types, there are many variations and degrees of impairment. Each of these may present different barriers and need to be addressed with different strategies.
The following pages provide a brief overview of the major types of impairments, along with a brief discussion of the implications of these impairments on computer use.
PLEASE NOTE: It is not up to the application software developer/ manufacturer to directly meet all of these needs. The next section will discuss the role of application program manufacturers versus the role of others in providing accessibility. It is important, however, for everyone to understand the basic problems faced by people with different types or degrees of impairment and their resulting disabilities.
Visual impairment represents a continuum, from very poor vision, to people who can see light but no shapes, to people who have no perception of light at all. However, for general discussion it is useful to think of this population as representing two broad groups: those with low vision and those who are legally blind. The National Society for the Prevention of Blindness estimates that there are 11 million people in the U.S. who have visual impairments. This includes both people with low vision and those who are blind.
Low vision is defined as vision that is between 20/40 and 20/200 after correction. (20/200 means that something at 20 feet would be just as visible as something at 200 feet would be to someone with normal 20/20 vision) There are 9-10 million people with low vision. Some of these can read print if it is large and held close (or viewed through a magnifier). Others can only use their sight to detect large shapes, colors or contrasts. There are approximately 1.2 million people with severe visual impairments who are not legally blind.
A person is termed legally blind when their visual acuity (sharpness of vision) is 20/200 or worse after correction, or when their field of vision is less than 20 degrees. There are approximately half a million people in the U.S. who are legally blind.
Blindness can be present at birth, acquired through illness or accident, or associated with aging (glaucoma, cataracts, macular degeneration, optic nerve atrophy, diabetic retinopathy). According to the American Foundation for the Blind, almost 1 person in every 1,000 under age 45 has a visual impairment of some type, while 1 in every 13 individuals older than 65 has a visual impairment which cannot be corrected with glasses. With current demographic trends toward a larger proportion of elderly, the prevalence of visual impairments will certainly increase.
Functional limitations of people with visual impairments include increased sensitivity to glare, viewing the world as through a yellowed lens, no central vision, no peripheral vision, loss of visual acuity or focus, poor night vision, reduced color distinction ability or a general hazing of all vision. Those who are legally blind may still retain some perception of shape and contrast or of light vs. dark (the ability to locate a light source), or they may be totally blind (having no awareness of environmental light).
As would be expected, people with visual impairments have the greatest problem with information displayed on the screen. However, mandatory use of a mouse or other pointing device requiring eye-hand coordination is also a problem. Special programs exist to provide individuals with the ability to magnify the screen image. There are also programs which allow the individual to have the content of the screen read aloud. However, application programs sometimes do things in ways that make it difficult or impossible for these special programs to work well or at all. Individuals with low vision may also miss messages which pop-up at different points on the screen, since their attention is usually focused on only a small area of the screen at any time.
Written operating instructions and other documentation may also be inaccessible if they are not provided in electronic or alternate form (e.g., audio tape or braille) and even then people may have difficulty accessing graphic or pictorial information included in documentation. Because many people with visual impairments still have some visual capability, many of them can read with the assistance of magnifiers, bright lighting (for printed text), and glare reducers. Many are helped immensely by use of larger lettering, sans-serif typefaces, and high contrast coloring.
Key coping strategies for those who are blind or have severe visual impairments include the use of braille, large raised lettering or raised line drawings, braille and audio tape. Note, however, that braille is preferred by only about 10% of people who are blind (normally those blind from early in life). Those who use braille, however, usually have strong preferences for it, especially for shorter documents. Raised lettering must be large and is therefore better for providing simple labels on raised line drawings than for extensive text.
Hearing impairments are among the most prevalent chronic disabilities in the U.S. More than 15 million people have some form of hearing impairment. Almost two million are deaf.
Hearing impairments are classified into degrees based on the average hearing level for various frequencies (pitches) by decibels (volume) required to hear, and also by the ability to understand speech. Loudness of normal conversation is usually 40-60 decibels. A person is considered deaf when sound must reach at least 90 decibels (5-10 times louder than normal speech) to be heard, and even amplified speech cannot be understood, even with a hearing aid.
Hearing impairments can be found in all age groups, but loss of hearing acuity is part of the natural aging process. Of those aged 65 to 74, 23% have hearing impairments, while almost 40% over age 75 have hearing impairments. The number of individuals with hearing impairments will increase with the increasing age of the population and the increase in the severity of noise exposure.
Hearing impairment may be sensorineural or conductive. Sensorineural involves damage to the nerves used in hearing (i.e., the problem is in transfer from ear to brain). Causes include aging, exposure to noise, trauma, infection, tumors and other disease. Conductive hearing loss is caused by damage to the ear canal and mechanical parts of the inner ear. Causes include birth defects, trauma, foreign bodies or tumors.
The functional limitations faced by people with hearing impairment fall into four categories.
First, individuals may not be able to hear auditory information if it is not presented loudly enough as compared to the background noise. The ability to control volume or to plug headphones or other devices into a headphone jack are the primary strategies for dealing with this problem.
Second, individuals who are deaf or who have more severe hearing impairments will not receive any information which is presented only in auditory form. Beeps which are accompanied by an on-screen visual indication prevent this problem. They also avoid the problem of the sound output being too quiet, since the auditory information is also provided visually. With newer systems which include voice output, presentation of the text on-screen or the ability to turn on captions may be necessary.
Third, as voice input becomes more prevalent, it too will present a problem for many deaf individuals. While many have some residual speech, which they work to maintain, those who are deaf from birth or a very early age often are unable to learn to speak or have very poor speech. Thus, alternatives to voice input will be necessary for these individuals to access products which require voice input.
Fourth, many individuals who are deaf communicate primarily through ASL (American Sign Language). It should be noted, however, that this is a completely different language from English. Thus, deaf people who primarily use ASL may understand English only as a second language (and may therefore not be as proficient with English as native speakers).
Because individuals who are deaf cannot hear and sometimes cannot speak, they have difficulty using telephone support services. Special telecommunication devices for the deaf (TDDs) have been developed, however, which allow individuals to communicate over the phone using text and a modem. In order for these users to access phone-in support services, software companies would need to have TDD-equipped support personnel. Individuals who are deaf are also be unable to take advantage of support systems that use touch-tone input and recorded voice output.
Physical impairments vary greatly. They include paralysis (complete or partial), severe weakness, interference with control, missing limbs, and speech impairment. Causes include cerebral palsy, spinal cord injury, traumatic head injury (includes stroke), injuries or diseases resulting in amputation, or various diseases such as arthritis, ALS (Lou Gehrig's Disease), multiple sclerosis or muscular dystrophy.
Cerebral Palsy (CP). CP is defined as damage to the motor areas of the brain prior to brain maturity (in most cases, this occurs before, during or shortly after birth). There are 400,000-700,000 individuals in the U.S. with CP. The most common types are spastic, where the muscles are tense and contracted and voluntary movement is very difficult, and athetoid, where there is constant, uncontrolled motion. Most cases are combinations of the two types.
Spinal Cord Injury. Spinal cord injury can result in paralysis or paresis (weakening). The extent of paralysis/paresis and the parts of the body effected are determined by how high or low on the spine the damage occurs and the type of damage to the cord. Quadriplegia involves all four limbs and is caused by injury to the cervical (upper) region of the spine; paraplegia involves only the lower extremities. There are 150,000 to 175,000 people with spinal cord injuries in the U.S.
Head Injury and Stroke. The term "head injury" is used to describe a huge array of injuries, including concussion, brain stem injury, closed head injury, cerebral hemorrhage, depressed skull fracture, foreign object (e.g., bullet), anoxia, and post-operative infections. Like spinal cord injuries, head injury and also stroke often results in paralysis and paresis, but there can be a variety of other effects as well. Currently about 1,000,000 Americans (1 in 250) suffer from effects of head injuries, and over 2,000,000 people in the U.S. have suffered strokes. However, many of these do not have permanent or severe disabilities.
Arthritis. Arthritis is defined as pain in joints, usually reducing range of motion and causing weakness. Rheumatoid arthritis is a chronic syndrome. Osteoarthritis is a degenerative joint disease. About 1% of the U.S. population (or 2.4 million people) are affected by arthritis.
ALS (Lou Gehrig's Disease). ALS is a fatal degenerative disease of the central nervous system characterized by slowly progressive paralysis of the voluntary muscles. The major symptom is progressive muscle weakness involving the limbs, trunk, breathing muscles, throat and tongue, leading to partial paralysis and severe speech difficulties. This is not a rare disease. About 2 out of 125,000 people will develop ALS each year. It strikes mostly those between age 40 and 70, and men twice as often as women.
Multiple Sclerosis (MS). MS is defined as a progressive disease of the central nervous system characterized by the destruction of the insulating material covering nerve fibers. The problems these individuals experience include poor muscle control, weakness and fatigue, difficulty walking, talking, seeing, sensing or grasping objects. It is estimated that about 300,000 in the U.S. suffer from this disease.
Muscular Dystrophy (MD). MD is a hereditary, progressive condition resulting in muscular weakness and loss of control, contractions and difficulty in walking and breathing. About 10,000 new cases are reported per year.
Problems faced by individuals with physical impairments include poor muscle control, weakness and fatigue, difficulty talking, seeing, sensing or grasping (due to pain or weakness), difficulty reaching things, and difficulty doing complex or compound manipulations (push and turn). Individuals with spinal cord injuries may be unable to use their limbs and may use "mouthsticks" for most manipulations.
Individuals with movement impairments may have difficulty with programs which require a response in a specified period of time, especially if it is short. Individuals with impaired movement or who must use a mouthstick or headstick have difficulty in using pointing devices. Programs which require the use of a mouse or pointing devices and have no option for keyboard control of the program present problems. Individuals who can use only one hand or who use a headstick or mouthstick to operate the keyboard have difficulty pressing two keys at the same time.
This category contains a wide range of impairments including impairments of thinking, memory, language, learning and perception. Causes include birth defects, head injuries, stroke, diseases and aging-related conditions. Some commonly known types and causes of cognitive/language impairment are:
Mental Retardation. A person is considered mentally retarded if they have an IQ below 70 (average IQ is 100) and if they have difficulty functioning independently. An estimated 1% of Americans (2.4 million) are mentally retarded. For most, the cause is unknown, although infections, Down's Syndrome, premature birth, birth trauma, or lack of oxygen may all cause retardation. Those considered mildly retarded (80-85%) have an IQ between 55 and 69 and achieve 4th to 7th grade levels. They usually function well in the community and can hold down semi-skilled and unskilled jobs.
Language and Learning Disabilities. This is a general term referring to a wide range of disorders manifested by significant difficulties in listening, speaking, reading, writing, reasoning, and calculating/integrating perceptual/cognitive information. These disorders are presumed to be due to central nervous system dysfunction. It is estimated that over 43% of children in special education programs in the U.S. (1.9 million) have some type of language and learning disability.
Head Injury and Stroke. This group includes individuals with closed and open head injuries as well as those suffering strokes. These injuries usually result in physical impairments, cognitive impairments or both. There are approximately 400,000 to 600,000 people with head injuries and approximately 2 million people who have suffered a stroke.
Alzheimer's Disease. This is a degenerative disease that leads to progressive intellectual decline, confusion and disorientation. 5% of Americans over 65 have Alzheimer's; 20% of those above 80 have it.
Dementia. This is a brain disease that results in the progressive loss of mental functions, often beginning with memory, learning, attention and judgment deficits. The underlying cause is obstruction of blood flow to the brain. Some kinds of dementia are curable, while others are not. 5% of the population over 65 has severe dementia, with 10% having mild or moderate impairment. 30% of those over 85 are affected.
Cognitive impairments are varied, but may be categorized as memory, perception, problem-solving, and conceptualizing disabilities. Memory problems include difficulty getting information from short-term storage (20-40 seconds, 5-10 items), long term and remote memory. This includes difficulty recognizing and retrieving information. Perception problems include difficulty taking in, attending to, and discriminating sensory information. Difficulties in problem solving include recognizing the problem, identifying, choosing and implementing solutions, and evaluation of outcome. Conceptual difficulties can include problems in sequencing, generalizing previously learned information, categorizing, cause and effect, abstract concepts, comprehension and skill development. Language impairments can cause difficulty in comprehension and/or expression of written and/or spoken language. Problems can occur both in the use of software and in understanding manuals written at too high a technical/comprehension level.
Approximately 1 million U.S. workers (age 18-69) report impaired abilities to read, reason and/or understand spoken or written information as a result of a chronic disabling condition.
There are few assistive devices for people with cognitive impairments. Simple cuing aids or memory aids are sometimes used. As a rule, these individuals benefit from use of simple displays, low language loading, use of patterns, simple, obvious sequences and cued sequences.
A number of injuries or conditions can result in seizure disorders. Seizures can vary from momentary loss of attention to grand mal seizures which result in the severe loss of motor control and awareness.
Seizures can be triggered in people with photosensitive epilepsy by rapidly flashing light, particularly in the 10-25 hz range. This can be caused by screen refresh or by rapidly flashing different images on the screen. The brighter the flash, and the larger the portion of the screen involved, the more significant the visual stimulation. Somewhere between 1 in 25,000 and 1 in 10,000 people in the US have seizure disorders.
It is all too common to find that whatever caused a single type of impairment also caused others. This is particularly true where disease or trauma is severe, or in the case of impairments caused by aging.
Diabetes, which can cause blindness, also often causes loss of
sensation in the fingers. Unfortunately, this makes braille or
raised lettering impossible to read. Cerebral palsy is accompanied
by visual impairments in 40% of cases, by hearing and language
disorders in 20% of cases, and by cognitive impairments in 60%
of cases. Individuals who have hearing impairments caused by aging
also often have visual impairments.