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mental retardation

mental retardation, below average level of intellectual functioning, usually defined by an IQ of below 70 to 75, combined with limitations in the skills necessary for daily living. Daily living skills include such things as communication, the ability to care for oneself, and the ability to work. The definition of mental retardation has evolved over the years. Prior categorizations of mental retardation, defined solely by IQ, have largely been abandoned in favor of an approach that looks at how much support the retarded person needs in various areas of his or her life at any given time. Such support can range from intermittent help in such things as finding housing or a job, to pervasive, daily, lifelong help in all areas.


There are several hundred possible causes of mental retardation. They include genetic conditions (e.g., Down syndrome, fragile X syndrome); prenatal problems (e.g., fetal alcohol syndrome, rubella, malnutrition); problems apparent at birth (e.g., low birth weight and prematurity); and problems that occur after birth (e.g., injuries and childhood diseases like measles that can lead to meningitis and encephalitis). The most commonly identified causes of mental retardation are Down syndrome, fragile X syndrome, and fetal alcohol syndrome. In many cases the cause is never known.


Most mentally retarded children are capable of learning new things, both in and out of a formal school setting, but they may learn at a slower pace than other children. Schools are responsible for providing an appropriate education for retarded children. Many teachers and parents feel that the practice of mainstreaming, or inclusion, which places such children in standard classrooms for at least part of the day, helps them to feel more a part of society and helps others to better understand their special needs and capabilities.


Many cases of mental retardation are now prevented by improved health care. Vaccines against rubella and measles prevent an estimated 3,000 cases of mental retardation in the United States yearly. Vaccination against Haemophilus influenzae b (Hib), a cause of childhood meningitis, is expected to prevent 3,000 more. Prevention of Rh disease (see Rh factor), screening and treatment for phenylketonuria, and emphasis on prenatal care and the dangers of poor nutrition or alcohol consumption during pregnancy have also resulted in a decrease in cases of mental retardation in the United States. Mental retardation rates in poor nations, however, are rising.


The treatment of mentally retarded people has always reflected the changes in society. They have been officially referred to as idiots and as the feebleminded. The introduction of the IQ test was followed by a classification system that used such terms as moron (IQ of 51–70), imbecile (26–50), and idiot (0–25); later these terms were softened and classifications redefined somewhat to mild (IQ of 55–70), moderate (40–54), severe (25–39), and profound (0–24) retardation. The term mentally retarded itself, although still commonly used, has been replaced in some settings by the term developmentally disabled.

Mentally retarded people have been subjected to unnecessary institutionalization and, as a result of the eugenics movement, involuntary sterilization. The deinstitutionalization movement of the 1970s reflected a concern for the civil rights of mentally retarded. Very few of the mentally retarded are now institutionalized; most now live independently, with their families, or in group homes. The emphasis on education and self-sufficiency seen in the late 20th cent. mirrors a similar movement in the 1840s.


See M. Adams, Mental Retardation and Its Social Dimensions (1971); A. Clarke et al., ed., Mental Retardation: The Changing Outlook (1985); E. Zigler, Understanding Mental Retardation (1986); American Association on Mental Retardation, Mental Retardation: Definition, Classification, and Systems of Support (1992).

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(ree-tar-day -shŏn) The difference in the Moon's rising time between successive nights.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in biology, the late formation and delayed development of an organ in offspring as compared with ancestors. Retardation depends on the beginning of the functioning of an organ and consequently on the environmental conditions in which the development of the individual organism (ontogeny) occurs.



(1) In linguistics, a variation of the phenomenon of phonetic analogy consisting of a change in the form of a word (lexeme) under the influence of the phonetic form of another lexeme that precedes it in context. Retardation is characteristic of numbers, for example, Tadzhik shonzdakh (“sixteen”), instead of the expected shazdakh, by analogy with ponzdakh (“fifteen”). The same phenomenon operating in the reverse direction is known as anticipation, for example, Russian deviat’ (“nine”), instead of neviat’, under the influence of desiat’ (“ten”).

(2) In poetics, a compositional technique of holding back the development of the plot; it is accomplished by such means as lyric digressions, descriptions of landscapes or interiors, and the repetition of episodes of the same type.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


Slow mental or physical functioning.
The amount of delay in time or phase angle introduced by the resistivity of the surface over which the radio wave in radio navigation is passing.
The amount of time by which corresponding tidal phases grow later day by day, averaging approximately 50 minutes.
In interference microscopy, the difference in optical path between the light passing through the specimen and the light bypassing the specimen. Also known as optical-path difference.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


Reduction in the rate of hardening or setting; an increase in the time required to reach initial and final set or to develop early strength of fresh concrete, mortar, plaster, or grout.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
Detailed analyses of several molecular regulators yielded data consistent with the hypothesis that alcohol- induced fetal growth retardation occurs, for the most part, as a result of impaired placental development and transport of nutrients resulting primarily from disruption of the maternal GH-IGF system (Shankar et al.
A prospective study of 218 high-risk infants born in 1978 found fetal growth retardation is the primary risk factor for learning deficits later in life.
The meta-analysis suggests that confounding facts -- such as other drugs, alcohol and smoking -- may account for the fetal growth retardation or prematurity commonly ascribed to cocaine, the researchers assert in the October TERATOLOGY.
However recent studies found out that the placenta was mostly normal or larger with no fetal growth retardation in late onset preeclampsia but was hypoplastic and associated with fetal growth retardation when preeclampsia was early onset, suggesting probably early onset preeclampsia is a placental disorder whereas late onset is a maternal disorder.
Cardiac and obstetric complications are common, including New York Heart Association functional class deterioration, atrial fibrillation, gestational hypertension, premature rupture of the membranes, and fetal growth retardation.
Inadequately treated depression also poses prenatal and neonatal risks, including increased rates of fetal growth retardation, preterm delivery, operative delivery, and mental retardation, as well as decreased Apgar scores and altered mother-infant bonding, he said.
The current Institute of Medicine (IOM) guidelines on weight gain--which recommend a gain of 25-35 pounds for normal-weight women with a singleton pregnancy--are too high and are based on historical concerns about the effects of famine on fetal growth retardation.
Fetal growth retardation ranks third after prematurity and malformations as a cause of perinatal deaths.