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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.
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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!