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David Geary
There are two methods for studying general
intelligence (g) in psychology:
Psychometric Tradition- The study of individual
differences on paper-and-pencil ability tests,
standardized achievement, and IQ tests. It is one of
the longest and most successful research
 Individual differences in IQ tests as well as other
measures of g are strong predictors of individual
differences in achievement in school, the ability to learn in
non-school settings, and productivity at work.
Cognitive Tradition- Involves the study of processes
underlying performance on the test of g and tests of
more specific cognitive abilities, including working
memory and attentional control.
Psychometrics and Mental Abilities
Francis Galton (late 1800’s)- Darwin’s
half cousin
 Francis Galton did a systematic study of
hereditary talent, including mental abilities.
 Galton was interested in whether intellectual
ability ran in families.
 Galton (1865) concluded “that hereditary
influence is as clearly marked in mental
aptitudes as in general intellectual power.”
Psychometrics and Mental Abilities
Spearman (1904) administered a series of sensory and
perceptual sensitivity and discrimination tasks, like
discriminating one musical pitch from another, to
elementary students, high school students, and adults.
 Teachers and peers also rated the students in-school
intelligence and commonsense. Scores on standardized
exams in classics, French, English, and Mathematics
were also available for high school students.
 All scores across scales were positively correlated.
Spearman concluded that all types of intellectual activity
have one fundamental function in common, but specific
elements of the activity differ.
Psychometrics and Mental Abilities
Factor Analysis- Statistical method for clustering
sources of variability across mental and other
Thurstone (1938) used the newly developed factor
analysis to find that performance on paper-andpencil ability tests tended to cluster into a set of
primary abilities.
Verbal Comprehension
Numerical Facility
Spatial Abilities
Perceptual Speed
 These primary abilities represent core domains of human
intellectual competency.
 Performance across these measures was correlated.
Psychometrics and Mental Abilities
Spearman and Thurstone’s work
revealed that human intellectual abilities
could be hierarchically organized.
Spatial Abilities
Psychometrics and Mental Abilities
Cattell and Horn- argued that the single
general ability proposed by Spearman
(1904) should be subdivided into two
equally important and distinct abilities
 Crystallized intelligence (gC)
○ Crystallized intelligence is the result of experience,
schooling, and acculturation. It refers to over
learned skills and knowledge.
 Fluid intelligence (gF)
○ Fluid intelligence represents biologically based
ability, such as the ability to acquire skills and
○ Visualization, perceptual speed, and fluency skills
Intelligence Tests
Spearman’s early work and work of other
experimental psychologists contributed to the
work on the development of standardized
intelligence tests, such as IQ tests.
Binet and Simon- developed the first practical
IQ test.
 Goal- develop an objective measure of children’s
readiness for school and to determine whether they
were mentally delayed and not likely to benefit from
 Result- a battery of tests ranging from simple motor
and perceptual tasks to tests of working memory,
judgment, and reasoning.
IQ Testing
Current IQ tests used:
 Stanford-Binet Intelligence Scale
 Wechsler Scale
 Raven’s Progressive Matrices Test
Performance on IQ scales is highly stable
from year to year
 Scoring:
Normal, bell curve distribution
Average Score = 100
Mental Giftedness = 125 or 130
Mental Retardation = 70 or below
Spearman’s law of diminishing returns
For low IQ groups, low performance on one type of test is
strongly predictive of low performance on a different type
of test. As intelligence increases, the strength of this
relation diminishes.
Test Scores
Cognitive and Brain Correlates of
With the development of computers and
conceptual advances, experimental
psychologists were able to study processes
that contributed to cognitive abilities.
 Speed of Scanning visual information held in
short term memory
 Speed of retrieving basic facts from long term
semantic memory
 Speed of executing and coordinating the
operations involved in analogical and other
forms of reasoning
Speed of Processing:
Does the speed of executing elementary
processes relate to performance of g?
 Hunt et al (1975) found that speed of
accessing letter names, word names,
and other bits of language from long
term memory was related to
performance on a paper-and-pencil
measure of verbal ability.
speed of access
score on test
Speed of Processing:
Reaction Time
Geary and Widaman found that variables
representing the speed of executing two basic
processes (arithmetic fact retrieval and
carrying from one column to the next) were
strongly related to performance on paper- andpencil tests of Thurstone’s numerical facility,
but were unrelated to performance on tests of
spatial abilities.
The faster individuals execute elementary
cognitive processes in specific domains, the
higher they score on paper-and-pencil ability
tests in these same domains supports
hierarchical models of intelligence.
Speed of Processing:
General Intelligence
Keating and Bobbitt- found that children who had average
scores on IQ tests were slower at accessing letter names
from long term memory than children with above average
 Jenson- found that faster speed of cognitive processing is
related to higher scores on measures of g
 Individuals who are consistently fast in executing these
processes have the highest scores on IQ tests, even after
extensive practice.
Deary, Der, and Ford- administered IQ tests and simple
and complex reaction time tasks to a sample of 900 adults
from Scotland.
 They found a relation between speed and IQ
 The relation was stronger for the complex task. The more g at
disposal of the individual, the better they perform.
Speed of Processing: Mechanisms
Horn (1988) found that speed of processing was
related to speed of identifying basic pieces of
information or patterns under conditions that require
focused attention and speed of making decisions
Jensen (1998) said that speed of making these
identifications and decisions might be related to
nerve conduction velocity.
 Nerve conduction velocity (NCV) is a test of the speed of
electrical signals through a nerve.
P.A. Vernon and Mori (1992) found that faster
peripheral nerve conduction velocities, like
measuring speed of reflexes from wrist to elbow,
were associated with higher IQ scores and faster
reaction times on cognitive tasks.
Speed of Processing:
Inspection Time
The methods involved in reaction time
tasks necessarily involve a motor
component, like pressing response keys
 Time needed for motor response is
incorporated into the overall reaction
 Inspection time is not influenced by
motor responses.
Measuring Inspection Time
Participant is told to focus on X, they are then shown
the stimulus for a given amount of time, and asked to
determine if left line or right line is shorter by
pressing response key.
Researcher is measuring the amount of time the
stimulus must be viewed in order to answer correctly.
Short inspection time is associated with high IQ
Electrophysiological studies
In electrophysiological studies, individual
differences in IQ are related, in part, to
individual differences in the sensitivity with
which sensory and perceptual systems identify
information patterns in the external world and
represent them in short term memory.
More intelligent people identify and respond to
subtle variations in external information more
quickly than less intelligent people.
Inspection time taps into these individual
Working Memory
Working memory- the ability to maintain attentional control and
prevent irrelevant information from diverting attention from the
task at hand.
 Research on the relation between performance on laboratory
working memory tasks and performance on IQ tests and other
measures of g have focused on Cattell’s and Horn’s fluid
intelligence, gF.
 Performance on measures of fluid intelligence should be
strongly associated with individual differences in working
 Embertson- conducted one of the few studies that separated
working memory capacity and the processes involved in making
controlled, explicit inferences. This study suggests that many
measures of working memory capacity are actually assessing
multiple skills, specifically the ability to hold and manipulate
information in working memory, draw inferences about relations
among these pieces of information, and then apply these
inferences during the act of controlled problem solving.
Brain Regions
Bigger brain=higher IQ
Higher fluid intelligence scores:
Larger total brain volume
Larger dorsolateral prefrontal cortex
More white matter in prefrontal cortex
Dorsolateral Prefrontal Cortex
Involved in maintaining the task goal in the mind, guiding the sequencing of the multiple
problem-solving steps, and suppressing the potential interfering effects of distractions
It was active when young adults solved reasoning and related working memory
problems. These same regions were active when older adults solved the same
reasoning problems but older adults did not perform as well because the activation
of several task-irrelevant brain regions that were suppressed in younger adults.
Damage to the prefrontal cortex can severely disrupt fluid intelligence but not
crystallized intelligence. It also affects the person's ability to use their crystallized
knowledge in novel conditions.
A consistent but modest relation has been found between brain size and IQ scores
has been found.
Anterior Cingulate Cortex
Activated when goal achievement requires dealing with a novelty or conflict (e.g.
choosing between two alternatives)
General Fluid
General Crystallized
Performance Characteristics
Controlled problem solving:
Reasoning, inferring, and
Knowledge Base:
Facts, procedures, and heuristics
Cognitive Mechanisms
Working Memory:
Attentional and inhibitory control;
speed of processing; and, shortterm memory
Long-Term Memory:
Quantity of organization of
information and speed of
information access
Brain Mechanisms
Dorsolateral prefrontal cortex;
anterior cingulate cortex and other
attentional systems and
neurophysiological processes
supporting short-term memory
Brain regions involved in the
storage(e.g. , the hippocampus) of
evolved or learned information
Intelligent Individuals
More intelligent individuals require less practice to shift the processing
demands of a task from the explicit system to the implicit system
High intelligence=more efficient use of the brain systems, less glucose
used by neurons
More able to cope with novel, complex, and dynamic circumstances
that require problem solving, reasoning, making inferences, forming
abstractions, and engaging the explicit system.
Identify and apprehend bits of social and ecological information more
easily and quickly than do other people, and their perceptual systems
process this information so it is activated in short-term memory more
quickly and with greater accuracy than in other people.
Able to represent more information in working memory
Have an enhanced ability to consciously manipulate this information.
gF is associated a strong long-term memory system combined with an
interest in seeking novel experiences. The result is the acquisition of a
large store of crystallized knowledge over a lifetime.
Know more facts, procedures for problem solving, and more heuristics.
Brain Mechanisms of Intelligent Individuals
The same brain systems that underlie working memory should be
engaged when people solve items on IQ tests, and these same
systems should differ comparing groups of people with higher and
lower IQ scores.
High scores on measures of gF are associated with activation of the
dorsolateral prefrontal cortex and several brain regions dealing with
attentional control, including the anterior cingulate cortex and regions of
the parietal cortex.
Intelligent people are more able to inhibit irrelevant information from
intruding into conscious awareness.
They have a larger dorsolateral prefrontal cortex and more white
matter, or axons, in this brain region. More white matter indicates more
neuronal connections within the prefrontal cortex and a prefrontal
cortex that is richly integrated with posterior and subcortical brain
The ability to learn over a lifetime is related to gF, personality
characteristics that influence the seeking of knowledge, and the brain
systems that support the representation and access to information
stored in LTM
Heredity of Intelligence
Galton (1869)- demonstrated that accomplishments
in politics, literature, science, music, poetry, etc often
run in families
 concluded that the traits that result in exceptional talent or
"genius", are largely hereditary.
Behavior genetic study of individual differences in
behavior, personality, and cognition focuses on both
hereditary and environmental influences.
 As environmental conditions vary within the population of
interest, the potential for environmental influences on the
trait will necessarily increase.
 Environments can influence gene expression, and
individuals with different genotypes sometimes seek
different environments.
Heredity of Intelligence
Bouchard and McGue- closely related family
members were more similar in their IQ scores than
were distantly related family members.
 Results indicate that about 50% of the individual
differences in intelligence were related to genetic
 Genetic influences on intelligence are moderate during
the preschool years and increase in importance as the
individual moves into adulthood.
 During early childhood, parents provide many of the
environmental influences. As individuals mature, they are
better able to seek and benefit from experiences such as
continued formal and informal educational experiences
that can result in improvements in performance on some
subscales on some IQ tests.
Heredity of Intelligence
DeFries et al (1979)- parents and their biological children
resembled one another for several specific cognitive
abilities, especially language-related and spatial abilities.
 Plomin et al- In a 16 year study of similarity between
adopted children and their adoptive parents found that as
children matured, they became increasingly similar to
their biological parents and less similar to their adoptive
parents for measures of g and for measures of verbal
abilities, spatial abilities, and short-term memory.
 The correlation between performance on IQ tests and
measures of specific cognitive abilities appeared to be
related to shared genes. There is substantial overlap
between the genetic influences on g and the genetic
influences for specific cognitive abilities.
 There is also evidence for unique genetic influences on
competencies in the areas of language, spatial cognition, and
short term memory.
Heredity of Intelligence
Unique Environment
Shared Environment
Old Age
Developmental Change
Heredity of Intelligence
Pederson et al (1992) found the same pattern for a sample of
older adult twins and reported higher heritability estimates for
some language and spatial measures than is typically found in
younger samples, suggesting that genetic influences on specific
cognitive abilities might show the same developmental increase
found with measures of g.
 Petrill (2002) - Intra-individual differences in specific abilities
appear to be largely due to unique environmental influences
once the influence of g is controlled.
 The genetic influences that result in faster speed of processing,
quicker inspection times, and greater consistency in speed of
processing are the same genetic influences that contribute to
high measured intelligence, especially fluid intelligence.
 The relation between working memory and fluid intelligence is
mediated, in part, by a set of genes that are related to
performance on both types of measures.
Heredity of Intelligence
Baare' and his colleagues used imaging techniques to
determine the overall brain volume and corresponding volumes
of gray(neurons) and white(axons) matter for twins and sibling
young adults.
 Genetic influences explained 90% of the individual differences in total
brain volume and 82% and 87% of the individual differences in volume of
gray and white matter, respectively.
 The remaining differences were due to unique environmental effects;
there were no significant shared environmental effects.
P. Thompson et al (2001)- constructed three-dimensional maps
of the entire brain for sets of monozygotic and dizygotic twins
and were able to estimate the degree of anatomical similarity of
the entire cortex for these twin pairs.
 In monozygotic twins, Broca's area and Wernicke's areas, which are
both associated with language functions; the parietal-occipital
association cortices; and several prefrontal regions, including part of the
dorsolateral prefrontal cortex are indistinguishable from one another
The environmental effects are composed of
influences shared by family members, such
as the wealth of the family, and influences
that are unique to each individual. The
specific types of experiences that influence
such abilities are not well understood.
 There are several environments that can
effect an individual’s intelligence
 Prenatal environment
 Family environment
 Intervention programs
Prenatal environment
Prenatal environment- maternal nutrition or alcohol use may
influence the prenatal environment in ways that can affect early
brain development and, through this, intelligence.
 B.Devlin, Daniels, and Roeder (1997)- estimated that maternal
effects including prenatal environment, could account for as much
as 20% of the similarity in the IQ scores of pairs of monoxygotic
twins and 5% of the similarity among other siblings.
Fetal Alcohol syndrome- Maternal alcohol use during pregnancy
is associated with brain malformations and lower IQ scores in
their children.
 Only a minority of fetuses exposed to alcohol develop FAS, and it is
unclear whether prenatal exposure to moderate levels of alcohol
and other damaging chemicals have long-term influences on
 Streissguth et al. found that maternal consumption of three or more
drinks per day was associated with an estimated loss of five IQ
points., but Greene et al found that it may result in a loss of 2 or less
IQ points.
Family Environment
Adopted children with intelligent adoptive parents score higher
on IQ tests than do adopted children with less intelligent
adoptive parents, but the relation strength is small.
 Virtual twins are formed when parents adopt a child and have a
biological child of about the same age.
These children grow up in the same household with the same parents,
go to the same school, and likely have many of the same friends.
 The IQ scores of virtual twins, at least in childhood, are moderately
 Families that provide an intellectually stimulating environment allow all of
their children to develop their full intellectual potential.
The beneficial effects of such family contexts are not detected in behavior
genetic studies because these studies focus on individual differences, and
in optimal environments individual differences are more strongly related to
genetic variability than to variability across families.
The strongest environmental influences on individual differences in general
intelligence are experiences unique to each individual. Unique experiences
can influence the development and expression of intellectual activities.
Openness to experience is a personality trait that influences general
Early Intervention programs
Many interventions have been developed to improve the
cognitive and social competencies of children living in
poverty or other difficult circumstances.
 Head Start
These types of interventions appear to result in a number
of beneficial outcomes, including improved academic
 Many of these interventions are initially associated with
modest, and sometimes substantial, improvements in IQ
scores, but most of these gains fade with time.
 The gain in IQ was highest for the group of children
adopted into professional homes and lowest for those
adopted into working class homes.
 It was also higher for children with a higher pre-adoption
IQ. The brighter children gained more from their
The evolved function of brain and cognition is to
process information patterns and guide associated
behavioral responses that have tended to covary
with survival and reproduction outcomes during the
species' evolutionary history.
These patterns vary along a continuum from
invariant to variant.
Invariant patterns Basic shape of the human body
 Should result in the evolution of modular systems.
Variant patterns can be understood on at least two
1. within the constraints of modular systems, such as
individual differences in body shape.
2. At a more macro level, as in the behavioral
dynamics of predator-prey and social relationships.
Modular Systems
The evolved modular systems associated with invariant
information patterns, along with learning during the
individual's lifetime, can be mapped onto Cattell and
Horn's crystallized intelligence.
 The ability to learn during a lifetime should be dependent,
in part, on the extent to which modular systems are plastic
and thus adaptable to novel conditions.
 The result is the potential for acquisition of evolutionarily
novel competencies, such as reading.
 Adapting to novelty and dealing with complex and varied
information is the primary condition that Cattell and Horn
found to be associated with fluid intelligence, and thus
fluid intelligence can be linked to the selection pressures
that create novelty and complexity, but at the macro level.
Selection Pressures
Three types of selection pressures
 Climatic
○ Refers to the effects of the environment and long
term weather patterns impacting a species.
 Ecological
○ Refers to the ability to extract resources from the
environment and, at the same time, avoid being
extracted by other species
 Social
○ The achievement of ecological dominance shifts
selection pressures to social competition.
○ Group-level competition and dynamics often
require sustained attention and other features of
executive control.
Selection Pressures and evolution of the mind
A combination of ecological and social factors likely contributed to the
evolution of the human brain and mind.
Patterns of cooperation and competition among individuals and
coalitions of individuals were the most potent of these pressures, at
least during more recent human evolutionary history.
3 selection criteria include:
 generating recurrent and somewhat unpredictable patterns of change
during the life span
○ generates conditions that provide a plausible explanation for the
evolution of fluid intelligence. Social dynamics generate recurrent and
somewhat unpredictable conditions that would favor the evolution of
brain and cognitive mechanisms that enable the ability to anticipate
these conditions, inhibit heuristic-based responses, and generate
novel behavioral solutions.
 they favor the evolution of self-awareness
○ related to the evolution of autonoetic mental models, of which gF is
only one component.
 they have the potential for generating a within-species co-evolutionary
arms race.
○ explains the rapid expansion in EQ, and presumably gF
Mental Models and Fluid
The empirical and theoretical research on general intelligence and gF
has identified many of the core features that support the use of
autonoetic mental models, which evolved as a result of the social and
ecological pressures described previously.
Autonoetic mental model
The individual is able to mentally generate a problem space that includes
representation of the "perfect world". In the perfect world, the person is in control of
the social, biological, and physical resources that have tended to covary with the
survival and reproductive prospects during human evolution. The behavior of others
and the flow of resources align with the individual's best interest.
The real world operates differently, but the goal is to generate strategies that will
reduce the difference between the real world and the perfect world.
The ability to use these simulations is dependent on working memory,
attentional control, and the underlying brain systems.
Geary believes that evolution of gF was due to social and ecological
pressures that are independent of the current uses of standardized
intelligence tests in modern society.
The evolved function of gF is to cope with change and novelty in social
and ecological conditions.
Modulariy and Crystallized
J.B. Carroll 1993- concluded that most of the
psychometric tests that index gC involve
language directly or indirectly, cultural
knowledge, and spatial and visual abilities.
Legree 1995- found that measures that
assessed knowledge of social conventions
and social judgments were related to
psychometric g, a combination of gF and gC.
Geary believes that the inherent knowledge
represented in the modular systems defines
one class of crystallized intelligence. The other
class of gC is represented by knowledge
learned during the individual's lifetime.