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children use language and can learn self…help skills； and their training involves teaching of skills
that will enable them to have a degree of independence in the munity。 Many of them learn to tell
time； to count money； and to find their way around in the environment。
Severe Mental Retardation。 Severely delayed/disabled children have an IQ of 20 to 35。 They can
learn some language and self…help skills。 Most of these children are institutionalized。 About 8
percent of people with an IQ below 70 are severely delayed/disabled。
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CHAPTER 10： INTELLIGENCE AND INTELLIGENCE ASSESSMENT
Profound Mental Retardation。 These children have an IQ of less than 20； and require supervision
and nursing care all their lives。 About 1 percent of delayed/disabled children are profoundly
retarded。
It is probably more meaningful to classify the developmentally delayed or disabled individual
according to the cause of their retardation。
Genetic causes。 Down syndrome is the result of a genetic aberration （it is not a hereditary problem）
that results in three chromosomes at the 21st position rather than two。 It is the most mon
genetic cause of retardation； and occurs in approximately one of every 1；000 live births。 The
incidence of this disorder has decreased as a function of the ability to detect it through
amniocentesis and chorionic villi sampling。 The next most mon genetic cause of retardation is
phenylketonuria （PKU）； a metabolic disease carried by a recessive gene。 It can be detected shortly
after birth and controlled。 There are a number of other relatively rare genetic causes of mental
retardation； including Tay…Sachs disease； Klinefelter’s syndrome； and Niemann…Pick disease。
Intrauterine infection or trauma。 Infections contracted by the mother can cause mental retardation。
These causes include encephalitis； rubella； and syphilis。 Brain damage to the fetus can also result
from malnutrition and dietary deficiencies； poisoning by lead or carbon monoxide； or drug use by
the mother； especially alcohol； during the mother’s pregnancy。 Recent evidence supports a
correlation between use of crack cocaine and fetal injury。
The birth process。 Premature children sometimes have an immature nervous system； and anoxia
（oxygen deprivation） or head injury during birth can damage the brain and cause mental
retardation。 All of these causes together probably account for no more than 30 percent of all cases of
developmental delay/disability； and all have identifiable physical causes。 In many cases； these
children have physical deficiencies and deformities in addition to their retardation。 It is striking to
note how many of such cases could be prevented or avoided； given appropriate prenatal care of the
mother； and the mother’s knowledge and acceptance of her responsibility to protect her unborn
child。
Cultural—familial causes。 The majority of cases of retardation fall into this category。 Children in
this category are usually mildly delayed or disabled。 Usually； they do not have other physical
handicaps and generally do not look any different from normal children。
Cultural—familial retardation is most likely to occur among the children of the poor； often in
families that have struggled against poverty for several generations。 There are often several
developmentally delayed or disabled individuals among the relatives； and sometimes one or both of
the parents is or are delayed or disabled。 In cultural—familial retardation； it is difficult to separate
the effects of heredity and environment； because neither is favorable。 Many psychologists currently
think that heredity sets an upper limit； and that environment determines how closely an individual
will approach his or her maximum intellectual capacity。 For example； in the case of a child with
cultural…familial retardation； the genes may set a limit of 80 or 90； or higher； but because of lack of
language and cognitive stimulation； his or her test score could be 60 or 65。
The study of the Hollow Children is highly instructive。 There was a group of people of English and
Scots…Irish descent who settled and lived as a little subculture near the Atlantic coast in Virginia for
many years。 The land they lived on was subsequently granted to German immigrants and the Scots…
Irish were forced to move into hollows in the Blue Ridge Mountains。 They formed a number of small
munities that varied in degree of isolation from civilization。 In 1932； an investigator named
Sherman studied these people； reasoning that the citizens of the various Hollows munities had
a mon gene pool； and he was interested in whether isolation from civilization had affected the
intellectual ability of the children。 Isolation meant things like no road in and out； no post office； no
newspapers or magazines； and； of course； since the study was done in the early 1930s； there was no
radio or TV。 In Colvin Hollow； the most isolated of the munities； school had been in session for
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PSYCHOLOGY AND LIFE
a total of 16 months during the years between 1918 and 1930； and there were only three literate
adults in the munity。 To test the children’s intelligence； Sherman used the Stanford…Binet and
other tests that are not so language dependent。
The results showed that the more isolated the munity； the lower the IQ scores of the children。
The average of the test scores in the least isolated munity was close to the population mean；
while the average of the scores of the children in the most isolated munities was below 70。
Sherman tested children from 6 to 16 years of age； and one of his notable findings was that IQ
scores declined with age。 In the more isolated munities； the IQs of the 6… to 8…year…olds averaged
about 80。 The scores of the 14… to 16…year…olds averaged about 50。
There are a number of other studies that confirm the negative effect an impoverished environment
can have on intellectual development。 It is a challenge to a society to dedicate resources for the
prevention of cultural—familial retardation。 Because of President Johnson’s “war on poverty；”
funds for Operation Head Start were made available in the mid…1960s。 A problem arose because
although money was available； the educators lacked the background research to develop a clear
idea concerning how one goes about giving a child a “head start。” Some years later； the program
was pronounced a failure and used as a rationale for reducing funds for early childhood education。
In reality； the program was not an unqualified failure。 In some places； it was quite successful； and
provided a wealth of data concerning methods and techniques。 If we made another concentrated
effort； maybe it would be very successful。 We are often very shortsighted； unwilling to spend a
dollar today to save hundreds of dollars in the future。 Perhaps we would serve ourselves and our
children better； if we realized that no amount of money saved in the future can obviate the fact that
our children are our future。
Single versus Multiple Intelligence
Is intelligence a single； inborn ability that is relatively unaffected by the environment； as