One end of the distribution of intelligence scores is defined by people with very low IQ. Mental retardation is a generalized disorder ascribed to peoplewho havean IQ below70, who have experienced deficits since childhood, and who havetroublewith basiclifeskills, such as dressing and feeding oneself and communicating with others (Switzky & Greenspan, 006). 1About 1% of the United States population, most of them males, fulfill the criteria for mental retardation, but some children who are diagnosed as mentally retarded lose the classification as they get older and better learn to function in society. A particular vulnerability of people with low IQ is that they may be taken advantage of by others, and this is an important aspect of the definition of mental retardation (Greenspan, Loughlin, & Black, 2001). 2 Mental retardation is divided into four categories: mild, moderate, severe, and profound. Severe and profound mental retardation is usually caused by genetic mutations or accidents during birth, whereas mild forms have both genetic a nd environmental influences.
One cause of mental retardation is Down syndrome, a chromosomal disorder leading to mental retardationcaused bythepresenceof all or part of an extra 21st chromosome. The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although its prevalence rises sharply in those born to older mothers. People with Down syndrome typically exhibit a distinctive pattern of physical features, including a flat nose, upwardly slanted eyes, a protruding tongue, and a short neck.
Societal attitudes toward individuals with mental retardation have changed over the past decades. We no longer use terms such as “moron,” “idiot,” or “imbecile” to describe these people, although these were the official psychological terms used to describe degrees of retardation in the past. Laws such as the Americans with Disabilities Act (ADA) have made it illegal to discriminate on the basis of mental and physical disability, and there has been a trend to bring the mentally retarded out of institutions and into our workplaces and schools. In 2002 the U.S. Supreme Court ruled that the execution of people with mental retardation is “cruel and unusual punishment,” thereby ending this practice (Atkins v. Virginia, 2002). 3