CHAPTER 13
Intelligence And
Cognitive
Functioning
The Nature of Intelligence
The Biological Origins of Intelligence
What is Intelligence?
• Intelligence is
– the ability to reason,
– to understand,
– to profit from experience.
• The measure of intelligence is typically expressed
as the intelligence quotient (IQ).
• Remember: IQ = score on test!
Intelligence = controversy
• Critical controversy to understanding of
intelligence:
– is intelligence is a single capability or a collection of several
independent abilities.
– Critical for both psychological AND biological understanding of
intelligence
• Intelligence theorists tend to fall into one of two
groups, lumpers or splitters.
– Lumpers: intelligence = single, unitary capability, which
is usually called the general factor, or simply g.
– Splitters: intelligence = composition of several mental
abilities that are more or less independent of each other.
The Biological
Origins of Intelligence
• Basically have to determine from individuals with
compromised intelligence
• Frontal lobe damage :
– impairs general intelligence more than performance on traditional IQ
tests,
– These tests emphasize crystallized intelligence (skills and information
learned earlier).
– Makes sense: Frontal areas involved in working memory and executive
control of problem solving
The Biological
Origins of Intelligence
• Brain size itself does not determine intelligence.
• What IS important? Ratio of the brain’s size to body size.
– Using ratio adjusts for the proportion of the brain to body size
– Adjusts brain area needed for managing the body
– Tells us how much is left over for intellectual functions.
– Ratio for humans is one of the highest.
• MRI Twin studies:
– Fraternal versus identical twins
– General intelligence correlated with both volume of gray matter and the
volume of white matter.
– Volume of gray matter in the frontal area appears to be particularly
important to general intelligence.
Rate of processing
important
• IQ scores also correlated with nerve conduction velocity
– Nerve conduction velocity: Speed with which nerve impulses transmitted
• Related to size of axon
• Degree of myelination, etc.
– Higher IQ correlated with faster nerve conduction velocity
– How examine? Speed of processing tasks on intelligence tests.
• People with higher IQ scores excel on tasks in which stimuli
presented for an extremely short interval and on tasks that require
choices.
– Both tasks: processing speed is important
– Assume that higher nerve conduction velocity contributes to the more
intelligent person’s superior performance.
– Thus: processing speed factors into IQ
Nerve conduction speed:
increased efficiency
• How make brain more efficient?
– greater efficiency through enhanced myelination of its neurons.
– Also insulates neurons form each other.
– reduces “crosstalk” that would interfere with accurate processing.
• Humans have a greater proportion of white matter (myelinated
processes) to gray matter than other animals
– appears IQ is related to the degree of myelination among individuals.
– Animals such as elephants, marine mammals, other nonhuman primates
also have high degree of myelination
– Sea aplysia has No myelination!
Working memory
• Increased nerve conduction velocity may particularly enhance efficiency of
working memory.
– Working memory correlated with white & gray matter volume,
– Similar to correlation of white/gray matter and general intelligence
– Indeed, working memory correlated with intelligence!
• Working memory:
– limited capacity: 7+/- 2
– Contents decay rapidly (>20 seconds).
• Individuals with rapid neuronal conduction can:
– complete manipulations more quickly
– transfer information to long-term memory faster
– All before decay occurs or short-term storage capacity is exceeded.
Issues with low nerve
conduction speed
• With low nerve conduction velocity:
– information in STM or working memory is lost
– person must restart the process
– Similar to when try to solve a problem and you not very alert
– You have to review information over and over because you can’t store it
– Takes LONGER to process similar amount of information.
• Interestingly, Higher IQ correlated with use of less brain
energy
– lower rate of glucose metabolism during a challenging task
– Remember is correlational, not causal
– Does support model
Factor analysis and
Intelligence
• Factor analysis approach to intelligence
– Statistical procedure
– useful in identifying possible components of intelligence,
– identified clusters of more specific abilities.
• Three capabilities have frequently emerged over the past 50
years as major components of intelligence:
– linguistic
– logical-mathematical
– Spatial
The Brain areas implicated
in Intelligence
• Linguistic
– left frontal
– Left temporal lobes.
– Language based
• Logical-mathematical
• Spatial ability depends on the interaction of somatosensory and visual
functions with parietal structures,
• Mostly right hemisphere.
• Spatial
– Mathematical ability in humans
– depends on two distinct areas of the brain:
• left frontal region
• both parietal lobes.
Inheritability of
intelligence
• Intelligence has a heritability of around 50%
– At least 50% of variance for intelligence due to inherited traits
– Suggests large contribution of environment, however
– Most important is likely the interaction between heredity and
environment
• Documented genetic influence on several of the functions that
contribute to intelligence:
– working memory,
– processing speed
– reaction time in making a choice.
Inheritability of
intelligence
• Genetic factors appear to be slightly more important than
environmental:
– Most differences among individuals accounted for by genetic factors.
– Estimated heritabilities in one twin study were
• 90% for brain volume
• 82% for gray matter
• 88% for white matter.
• General intelligence has higher heritability than more specific
abilities
– Less heritability for verbal and spatial abilities
– Book suggests this provides additional argument for a biological basis for
g factor or general intelligence factor
– Individual variations may influence specific intelligences
Intelligence = inherited?
• Conclusion that intelligence is highly heritable not
greeted with unquestioning acceptance
– 20-50% may be due to environmental effects
– This may be significant portion and greatly impact expression of
intelligence.
– May actually be a very critical portion
• Critics fear that inheritance of intelligence implies that
intelligence is inborn and unchangeable.
– Note true at all: genes do not fix behavior
– Genes set a range within which a person may vary
– Environment may impact degree of variance!
Twin studies:
Environmental or inherited?
• Argument: Does correlation of IQ among relatives = intelligence is
inherited.
– identical twins’ similarity in appearance/personality lead others to treat
them similarly
– true even when they are reared apart
– Similar treatment results in similar intellectual development.
• Researchers compared IQs of twins who had been either correctly or
incorrectly perceived by their parents as fraternal or identical.
– Hypothesis: If similar environmental treatment accounts for similarity then
parents’ perception of their twins’ classification should be more important
than twins’ actual genetic classification.
– Results: only the true genetic relationship influenced IQ similarity in the
twins, not the parents’ perception.
– Supports inheritability of intelligence
Controversy:
Ethnicity and intelligence
• Two questions:
– Are there IQ differences between ethnic groups ?
– Are these differences genetically based?.
• Task force appointed by the American Psychological
Association found:
– studied intelligence debate
– concluded that there is no direct evidence regarding the genetic
hypothesis of IQ differences between African-Americans and whites
– What evidence that does exist does not support the hypothesis.
– Probability of any individual being of “pure” racial genetic background
actually quite small; thus little likelihood of racial differences
So which is it?
Nature or Nurture?
• Most intelligence researchers agree that intelligence is the
result of the joint contributions of genes and environment.
– Intelligence is 100% hereditary
– Intelligence is 00% environmental
– Why!?! Both are necessary.
• More difficult than expected to identify just which
environmental conditions influence intelligence, other than
those that cause brain damage.
– Problem : environmental influences are many and individually weak.
– Second problem: environmental influences often hopelessly confounded
with genetic effects.
Deficiencies and Disorders
of Intelligence
• Intelligence and cognitive abilities do typically decline with
age
• BUT: The amount of loss has been overestimated.
• Why see these differences and declines?
– People often tested on meaningless tasks, like memorizing lists of
words.
– Older people not necessarily motivated to perform on this kind of task,
or out of practice compared to college students.
– When the elderly are tested on the content of meaningful material such
as television shows and conversations, the decline is moderate.
AGE Deficiencies and
Disorders of Intelligence
• Performance speed particularly vulnerable during aging
– This does turn out to be important
– Remember how slow processing speed slows down working memory and
everything else!.
• Working memory especially important to intellectual
capability.
– Studied of people ranging in age from 18 to 82
– Speed of processing accounted for all but 1% of age-related differences in
working memory.
• Some of the loss in performance is due to nonphysical
causes and is reversible.
– For example, older people often lack opportunity to use their skills.
– Use it or lose it!
Deficiencies and Disorders
of Intelligence
• Other loss in performance may have physical basis
– may be reduced if not reversed
– Unless due to syndrome such as dementia.
• Diet appears to be one factor.
– study of 6,000 people over the age of 65,
– Cognitive decline was 13% less in those who ate two or more fish meals per week,
compared to people who ate fish less than once per week.
– Elderly often have poor diets:
• Loneliness
• Loss of physical abilities
• income loss, etc.
• Also hypothesized that cognitive/sensory /motor decline partly due to
degradation of inhibitory activity at GABA receptors.
– Administration of GABA or a GABA agonist (muscimol) in visual cortex improved
selectivity of orientation-sensitive neurons in old monkeys but not in young ones.
Sex hormones affect
intelligence?
• Interestingly, sex hormones provide some protection against
cognitive effects of aging.
– In menopausal women, estrogen replacement therapy reduces the decline
in verbal and visual memory
– Estrogen correlated with lower risk of Alzheimer’s disease.
– Men who maintain testosterone production past the age of 50 have better
preserved visual and verbal memory and visuospatial functioning.
• Interestingly, testosterone improves only spatial memory.
– Additional memory improvement requires that testosterone be delivered
in form of dihydrotestosterone,
– This can then be converted to estrogen in the brain by a process called
aromatization.
– Remember bird songs!
– Suggests both estrogen and testosterone important
Bottom line for aging
• Use it or lose it!
– Staying active keeps neural circuits active
– Staying active enables brain to continue to make new connections
• General health important
– Healthy people show less cognitive decline
– Diet, exercise, general health contribute to brain health
• What you start with is important
– If have higher cognitive function, will maintain throughout life time
– Have more to work with, more to “lose”
• Most critical: using what you do have
– Maintaining what cognitive abilities you do have
– Making the most out of what abilities you have
– Taking care of your brain!