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Chapter 9

Psychology 2320A/B Chapter Notes - Chapter 9: Phenylalanine, Caffeine, Muscle Tone

Course Code
Elizabeth Hayden

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Chapter 9: Intellectual Disability (Mental Retardation)
Intellectual disability and mental retardation used interchangeably
Intellectual disability (ID) characterized by significant limitations in both intellectual functioning and adaptive
behaviour that begin before age 18
Mental retardation appears on Axis II in the DSM-IV-TR because it is considered a stable condition rather than a
clinical disorder
Intelligence and Intellectual Disability
The Eugenics Scare
o Eugenics was first defined by Sir Francis Galton as “the science which deals with all influences that
improve the inborn qualities of a race
o Public/professional emphasis shifted away from the needs of persons with mental retardation toward a
consideration of the needs of society thus, society was to be protected from the presumable harm
that would be done by the presence of these persons
o Consequently, the appearance, belief, and behaviour of persons with mental retardation were
considered evidence of their lack of moral fiber, a belief that led to the diagnostic term moron, used to
explain and describe their differences
Defining and Measuring Children’s Intelligence and Adaptive Behaviour
o General intellectual functioning defined by an intelligence quotient (IQ or equivalent) that is based on
assessment with one or more of the standardized, individually administered intelligence tests, such as
the WISC-IV, SB5 and KABC-II
These tests assess various verbal and visual-spatial skills in the child and mathematical concepts,
which together are presumed to constitute the general construct known as intelligence
IQ scores (with mean of 100 and standard deviation of 15) are derived from a standardized table
based on a person’s age and test score
Because intelligence is defined along a normal distribution, approx. 95% of the population has
scores within 2 standard deviations of the mean (i.e. between 70 and 130)
Subaverage intellectual functioning is defined as an IQ of about 70 or below
o Definition of mental retardation includes not only subaverage intellectual functioning, but also
subaverage level of adaptive functioning refers to how effectively individuals cope with ordinary life
demands, and how capable they are of living independently and abiding by community standards
The Controversial IQ
o IQ generally is stable from childhood through adulthood
One exception to this rule is during early infancy, when considerable fluctuation can still occur
o But can change for some individuals between childhood and adolescence differences I noutcome vary
widely in relation to opportunities for each child to learn and develop
Features of Intellectual Disabilities
Clinical description
o DSM-IV-TR diagnostic criteria consists of three core features:
Individuals must have “significant subaverage intellectual functioning” – individual must have IQ
of 70 or below, which falls 2 standard deviations below the average and therefore include rougly
2 3%
Requires “concurrent deficits/impairments in adaptive functioning” – refers to the ability to
perform daily activities
A person must also show significant limitations in at least two areas of adaptive
behaviour such as communication, self-care, social/interpersonal skills or functional
academic or work skills
Child’s below-average intellectual and adaptive abilities must be evident prior to age 18
Acknowledges that mental retardation is a developmental disorder that is evident
during childhood and adolescence
Age criterion rules out persons who may show mental deficiencies caused by adult-
onset degenerative diseases such as Alzheimer’s disease or head trauma
Degrees of impairment

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o Because of wide variation in cognitive functioning and impairment, DSM-IV-TR designates retardation as
mild, moderate, severe or profound based primarily on IQ scores
o Persons with mild mental retardation (IQ level 55 70) constitute the largest group, estimated to be as
many as 85% of persons with the disorder
Often show small delays in development during preschool years, but not identified until
academic or behavior problems emerge during early elementary
Typically develop social/communication skills during the preschool years, with delays in
expressive language, minimal or no sensorimotor impairment and engage with peers readily
With appropriate support, usually live successfully independently or in supervised settings
o Persons with moderate mental retardation (IQ level 40 54) constitute about 10% of those with ID
More intellectually and adaptively impaired than someone with mild mental retardation, and
usually are identified during the preschool years when delays in early developmental milestones
are shown
Communicate through a combination of single words and gestures, and show self-care and
motor skills similar to an average 2-3 year old by the time they enter school
Benefit from various types of training such as vocational training, and training in social and
communicational skills
Some may require only a few supportive services whereas others may continue to require some
help throughout life
o Those with severe mental retardation (IQ level 25 39) constitute approx. 3% to 4% of persons with ID
Most suffer one or more organic causes of retardation, such as genetic deficits, and are
identified at a very young age because they have substantial delays in development and visible
physical features/anomalies
In addition to intellectual impairment, may have problems with physical mobility or other
health-related problems such as respiratory, heart or physical complications
Most require special assistance throughout their lives
Acquire little or no communicative speech during early childhood, and by age 12, they may use
some two to three-word phrases
Between 13-15, academic and adaptive abilities are similar to those of an average 4 to 6 year old
o Persons with profound mental retardation (IQ level below 20 25) constitute approx. 1 2% of those
with ID
Identified typically in infancy because of marked delays in development and biological anomalies
such as asymmetrical facial features
Show considerable impairments in sensorimotor functioning in early childhood, and are only
able to learn the rudiments of communication skills; require intensive training to learn basic
eating, grooming, and dressing behaviors
Require lifelong care and assistance and have severe co-occurring medical conditions such as
heart defects or epilepsy
Level of needed supports
o DSM-IV-TR has been criticized because it emphasizes the degree of impairment
o American Association on Intellectual and Developmental Disabilities (AAIDD) focuses on levels of needed
support and assistance
Emphasizes resources and strategies necessary to promote the overall adjustment and well-
being of a person with ID
Some AAIDD categories include employment activities, home living activities, health and safety
activities, social activities, behavioural activities, etc.
Race, sex, and SES prevalence
o Between 1-3% of the entire population
o About twice as many males as females among those with mild mental retardation, with this sex ratio
decreasing to 1.5:1.0 among those with more severe forms
o More prevalent among children of lower SES and children from minority groups (mild form)
o Children with more severe levels are identified equally in different racial/economic groups
Developmental Course and Adult Outcomes
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