The type of cognitive impairment can vary widely, from severe retardation to inability to remember, to the absence or impairment of specific cognitive functions (most particularly, language). Therefore, the types of functional limitations which can result also vary widely.
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, 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.
There are assistive devices for people with cognitive impairments. Simple cueing 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.
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 3% of Americans are mentally retarded. For most, the cause is unknown, although infections, Down 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 are considered educable, achieving 4th to 7th grade levels. They usually function well in the community and hold down semiskilled and unskilled jobs. People with moderate retardation (10%) have an IQ between 40 and 54 and are trainable in educational skills and independence. They can learn to recognize symbols and simple words, achieving approximately a 2nd grade level. They often live in group homes and work in sheltered workshops. People with severe or profound retardation represent just 5-10% of this population.
Language and Learning Disabilities
Aphasia, an impairment in the ability to interpret or formulate language symbols as a result of brain damage, is frequently caused by left cerebral vascular accident (stroke) or head injury. Specific learning disabilities are chronic conditions of presumed neurological origin which selectively interfere with the development, integration, and/or demonstration of verbal and/or nonverbal abilities. Many people with learning disabilities are highly intelligent aside from their specific learning disability. 1-8% of school-aged children and youth have specific learning disabilities.
Age-Related Disease
Alzheimer's disease is a degenerative disease that leads to progressive intellectual decline, confusion and disorientation. Dementia 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.
Seizure Disorders
A number of injuries or conditions can result in seizure disorders. Epilepsy is a chronic neurological disorder. It is reported that approximately 1 person in 15 has a seizure of some sort during his life, and between .5% and 1.5% of the general population have chronic, recurring seizures. A seizure consists of an explosive discharge of nervous tissue, which often starts in one area of the brain and spreads through the circuits of the brain like an electrical storm. The seizure discharge activates the circuits in which it is involved and the function of these circuits will determine the clinical pattern of the seizure. Except at those times when this electrical storm is sweeping through it, the brain is working perfectly well in the person with epilepsy. 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 lights, particularly in the 10 to 25 Hz range.
Multiple Impairments
It is 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.
Deaf-Blindness
Deaf-blindness is one commonly identified combination. Most of these individuals are neither profoundly deaf nor legally blind, but are both visual and hearing impaired to the extent that strategies for deafness or blindness alone won't work. People with developmental disabilities may have a combination of mental and physical impairments that result in substantial functional limitations in three or more areas of major life activity. Diabetes, which can cause blindness, also often causes loss of sensation in the fingers. This makes braille or raised lettering impossible to read. Cerebral palsy is often accompanied by visual impairments, by hearing and language disorders, or by cognitive impairments.
This article was previously published by the Trace Center as part of "Accessible Design of Consumer Products: Guidelines for the Design of Consumer Products to Increase Their Accessibility to People with Disabilities or Who are Aging," Gregg C. Vanderheiden and Katherine R. Vanderheiden, 1991. It was developed with major funding from the National Institute on Disability and Rehabilitation Research (NIDRR) in the U.S. Department of Education, under grant number G00850036. Note that the contents of this article do not necessarily represent the policy of the US Department of Education, and you should not assume endorsement by the Federal government.