Correlates
As a construct and measured by intelligence tests, intelligence is one of the most useful concepts used in psychology,
because it correlates with lots of relevant variables, like the
probability of suffering an accident, earning a higher salary, etc.
- Education
According to a 2018 metastudy
of educational effects on intelligence, education appears to be the
"most consistent, robust, and durable method" known for raising
intelligence.
- Myopia
A number of studies have shown a correlation between IQ and myopia.
Some suggest that the reason for the correlation is environmental,
whereby intelligent people are more likely to damage their eyesight with
prolonged reading, while others contend that a genetic link exists.
- Aging
There is evidence that aging causes decline in cognitive functions.
In one cross-sectional study, various cognitive functions measured
declines by about 0.8 in z-score from age 20 to age 50, the cognitive
functions included speed of processing, working memory and long term
memory.
Theories
Relevance of IQ tests
In psychology, human intelligence is commonly assessed by IQ
scores, determined by IQ tests. However, there are critics of IQ, who
do not dispute the stability of IQ test scores, or the fact that they
predict certain forms of achievement rather effectively. They do argue,
however, that to base a concept of intelligence on IQ test scores alone
is to ignore many important aspects of mental ability.
On the other hand, Linda S. Gottfredson (2006) has argued that the results of thousands of studies support the importance of IQ for school and job performance
(see also the work of Schmidt & Hunter, 2004). She says that IQ
also predicts or correlates with numerous other life outcomes. In
contrast, empirical support for non-g intelligences is lacking or very poor.
Theory of multiple intelligences
Howard Gardner's theory of multiple intelligences is based on studies not only of normal children and adults, but also of gifted individuals (including so-called "savants"), of persons who have suffered brain damage, of experts and virtuosos,
and of individuals from diverse cultures. Gardner breaks intelligence
down into at least a number of different components. In the first
edition of his book Frames of Mind (1983), he described seven distinct types of intelligence—logical-mathematical, linguistic, spatial, musical, kinesthetic, interpersonal, and intrapersonal.
In a second edition of this book, he added two more types of
intelligence—naturalist and existential intelligences. He argues that psychometric (IQ) tests address only linguistic and logical plus some aspects of spatial intelligence.
A major criticism of Gardner's theory is that it has never been tested,
or subjected to peer review, by Gardner or anyone else, and indeed that
it is unfalsifiable.
Others (e.g. Locke, 2005) have suggested that recognizing many specific
forms of intelligence (specific aptitude theory) implies a
political—rather than scientific—agenda, intended to appreciate the
uniqueness in all individuals, rather than recognizing potentially true
and meaningful differences in individual capacities. Schmidt and Hunter
(2004) suggest that the predictive validity of specific aptitudes over
and above that of general mental ability, or "g", has not received
empirical support. On the other hand, Jerome Bruner
agreed with Gardner that the intelligences were "useful fictions," and
went on to state that "his approach is so far beyond the data-crunching
of mental testers that it deserves to be cheered."
Howard Gardner describes his first seven intelligences as follows:
- Linguistic intelligence: People high in linguistic intelligence have an affinity for words, both spoken and written.
- Logical-mathematical intelligence: It implies logical and mathematical abilities.
- Spatial intelligence: The ability to form a mental model of a spatial world and to be able to maneuver and operate using that model.
- Musical intelligence: Those with musical Intelligence have excellent pitch, and may even be absolute pitch.
- Bodily-kinesthetic intelligence: The ability to solve problems or to fashion products using one's whole body, or parts of the body. Gifted people in this intelligence may be good dancers, athletes, surgeons, craftspeople, and others.
- Interpersonal intelligence: The ability to see things from the perspective of others, or to understand people in the sense of empathy. Strong interpersonal intelligence would be an asset in those who are teachers, politicians, clinicians, religious leaders, etc.
- Intrapersonal intelligence: It is a capacity to form an accurate, veridical model of oneself and to be able to use that model to operate effectively in life.
Triarchic theory of intelligence
Robert Sternberg proposed the triarchic theory of intelligence
to provide a more comprehensive description of intellectual competence
than traditional differential or cognitive theories of human ability.
The triarchic theory describes three fundamental aspects of
intelligence. Analytic intelligence comprises the mental processes
through which intelligence is expressed. Creative intelligence is
necessary when an individual is confronted with a challenge that is
nearly, but not entirely, novel or when an individual is engaged in
automatizing the performance of a task. Practical intelligence is bound
in a sociocultural milieu and involves adaptation to, selection of, and
shaping of the environment to maximize fit in the context. The triarchic
theory does not argue against the validity of a general intelligence
factor; instead, the theory posits that general intelligence is part of
analytic intelligence, and only by considering all three aspects of
intelligence can the full range of intellectual functioning be fully
understood.
More recently, the triarchic theory has been updated and renamed as the Theory of Successful Intelligence by Sternberg. Intelligence is now defined as an individual's assessment of success in life by the individual's own (idiographic)
standards and within the individual's sociocultural context. Success is
achieved by using combinations of analytical, creative, and practical
intelligence. The three aspects of intelligence are referred to as
processing skills. The processing skills are applied to the pursuit of
success through what were the three elements of practical intelligence:
adapting to, shaping of, and selecting of one's environments. The
mechanisms that employ the processing skills to achieve success include
utilizing one's strengths and compensating or correcting for one's
weaknesses.
Sternberg's theories and research on intelligence remain contentious within the scientific community.
PASS theory of intelligence
Based on A. R. Luria's (1966) seminal work on the modularization of brain function, and supported by decades of neuroimaging research, the PASS Theory of Intelligence
proposes that cognition is organized in three systems and four
processes. The first process is the Planning, which involves executive
functions responsible for controlling and organizing behavior, selecting
and constructing strategies, and monitoring performance. The second is
the Attention process, which is responsible for maintaining arousal
levels and alertness, and ensuring focus on relevant stimuli. The next
two are called Simultaneous and Successive processing and they involve
encoding, transforming, and retaining information. Simultaneous
processing is engaged when the relationship between items and their
integration into whole units of information is required. Examples of
this include recognizing figures, such as a triangle within a circle vs.
a circle within a triangle, or the difference between 'he had a shower
before breakfast' and 'he had breakfast before a shower.' Successive
processing is required for organizing separate items in a sequence such
as remembering a sequence of words or actions exactly in the order in
which they had just been presented. These four processes are functions
of four areas of the brain. Planning is broadly located in the front
part of our brains, the frontal lobe. Attention and arousal are combined
functions of the frontal lobe and the lower parts of the cortex,
although the parietal lobes are also involved in attention as well.
Simultaneous processing and Successive processing occur in the posterior
region or the back of the brain. Simultaneous processing is broadly
associated with the occipital and the parietal lobes while Successive
processing is broadly associated with the frontal-temporal lobes. The
PASS (Planning/Attention/Simultaneous/Successive) theory is heavily
indebted to both Luria (1966, 1973), and studies in cognitive psychology involved in promoting a better look at intelligence.
Piaget's theory and Neo-Piagetian theories
In Piaget's theory of cognitive development
the focus is not on mental abilities but rather on a child's mental
models of the world. As a child develops, increasingly more accurate
models of the world are developed which enable the child to interact
with the world better. One example being object permanence where the child develops a model where objects continue to exist even when they cannot be seen, heard, or touched.
Piaget's theory described four main stages and many sub-stages in the development. These four main stages are:
- sensory motor stage (birth-2yrs);
- pre-operational stage (2yrs-7rs);
- concrete operational stage (7rs-11yrs); and
- formal operations stage (11yrs-16yrs).
Degree of progress through these stages are correlated, but not identical with psychometric IQ. Piaget conceptualizes intelligence as an activity more than a capacity.
One of Piaget's most famous studies focused purely on the
discriminative abilities of children between the ages of two and a half
years old, and four and a half years old. He began the study by taking
children of different ages and placing two lines of sweets, one with the
sweets in a line spread further apart, and one with the same number of
sweets in a line placed more closely together. He found that, "Children
between 2 years, 6 months old and 3 years, 2 months old correctly
discriminate the relative number of objects in two rows; between 3
years, 2 months and 4 years, 6 months they indicate a longer row with
fewer objects to have "more"; after 4 years, 6 months they again
discriminate correctly".
Initially younger children were not studied, because if at the age of
four years a child could not conserve quantity, then a younger child
presumably could not either. The results show however that children that
are younger than three years and two months have quantity conservation,
but as they get older they lose this quality, and do not recover it
until four and a half years old. This attribute may be lost temporarily
because of an overdependence on perceptual strategies, which correlates
more candy with a longer line of candy, or because of the inability for a
four-year-old to reverse situations.
By the end of this experiment several results were found. First, younger
children have a discriminative ability that shows the logical capacity
for cognitive operations exists earlier than acknowledged. This study
also reveals that young children can be equipped with certain qualities
for cognitive operations, depending on how logical the structure of the
task is. Research also shows that children develop explicit
understanding at age 5 and as a result, the child will count the sweets
to decide which has more. Finally the study found that overall quantity
conservation is not a basic characteristic of humans' native
inheritance.
Piaget's theory has been criticized for the age of appearance of a
new model of the world, such as object permanence, being dependent on
how the testing is done (see the article on object permanence).
More generally, the theory may be very difficult to test empirically
because of the difficulty of proving or disproving that a mental model
is the explanation for the results of the testing.
Neo-Piagetian theories of cognitive development
expand Piaget's theory in various ways such as also considering
psychometric-like factors such as processing speed and working memory,
"hypercognitive" factors like self-monitoring, more stages, and more
consideration on how progress may vary in different domains such as
spatial or social.
Parieto-frontal integration theory of intelligence
Based on a review of 37 neuroimaging studies, Jung and Haier (2007) proposed that the biological basis of intelligence stems from how well the frontal and parietal regions of the brain communicate and exchange information with each other. Subsequent neuroimaging and lesion studies report general consensus with the theory.
A review of the neuroscience and intelligence literature concludes that
the parieto-frontal integration theory is the best available
explanation for human intelligence differences.
Investment theory
Based on the Cattell–Horn–Carroll theory,
the tests of intelligence most often used in the relevant studies
include measures of fluid ability (Gf) and crystallized ability (Gc);
that differ in their trajectory of development in individuals. The 'investment theory' by Cattell states that the individual differences
observed in the procurement of skills and knowledge (Gc) are partially
attributed to the 'investment' of Gf, thus suggesting the involvement of
fluid intelligence in every aspect of the learning process.
It is essential to highlight that the investment theory suggests that
personality traits affect 'actual' ability, and not scores on an IQ test.
In association, Hebb's theory of intelligence suggested a bifurcation
as well, Intelligence A (physiological), that could be seen as a
semblance of fluid intelligence and Intelligence B (experiential), similar to crystallized intelligence.
Intelligence compensation theory (ICT)
The intelligence compensation theory (a term first coined by Wood and Englert, 2009)
states that individuals who are comparatively less intelligent work
harder, more methodically, become more resolute and thorough (more
conscientious) in order to achieve goals, to compensate for their 'lack
of intelligence' whereas more intelligent individuals do not require
traits/behaviours associated with the personality factor conscientiousness to progress as they can rely on the strength of their cognitive abilities as opposed to structure or effort.
The theory suggests the existence of a causal relationship between
intelligence and conscientiousness, such that the development of the
personality trait conscientiousness is influenced by intelligence. This
assumption is deemed plausible as it is unlikely that the reverse causal
relationship could occur; implying that the negative correlation would be higher between fluid intelligence (Gf) and conscientiousness. The justification being the timeline of development of Gf, Gc and personality, as crystallized intelligence
would not have developed completely when personality traits develop.
Subsequently, during school-going ages, more conscientious children
would be expected to gain more crystallized intelligence (knowledge)
through education, as they would be more efficient, thorough,
hard-working and dutiful.
This theory has recently been contradicted by evidence, that identifies compensatory sample selection.
Thus, attributing the previous findings to the bias in selecting
samples with individuals above a certain threshold of achievement.
Bandura's theory of self-efficacy and cognition
The
view of cognitive ability has evolved over the years, and it is no
longer viewed as a fixed property held by an individual. Instead, the
current perspective describes it as a general capacity, comprising not
only cognitive, but motivational, social and behavioural aspects as
well. These facets work together to perform numerous tasks. An essential
skill often overlooked is that of managing emotions, and aversive
experiences that can compromise one's quality of thought and activity.
The link between intelligence and success has been bridged by crediting
individual differences in self-efficacy.
Bandura's theory identifies the difference between possessing skills
and being able to apply them in challenging situations. Thus, the theory
suggests that individuals with the same level of knowledge and skill
may perform badly, averagely or excellently based on differences in
self-efficacy.
A key role of cognition is to allow for one to predict events and
in turn devise methods to deal with these events effectively. These
skills are dependent on processing of stimuli that is unclear and
ambiguous. To learn the relevant concepts, individuals must be able to
rely on the reserve of knowledge to identify, develop and execute
options. They must be able to apply the learning acquired from previous
experiences. Thus, a stable sense of self-efficacy is essential to stay
focused on tasks in the face of challenging situations.
To summarize, Bandura's theory of self-efficacy and intelligence
suggests that individuals with a relatively low sense of self-efficacy
in any field will avoid challenges. This effect is heightened when they
perceive the situations as personal threats. When failure occurs, they recover from it more slowly than others, and credit it to an insufficient aptitude.
On the other hand, persons with high levels of self-efficacy hold a task-diagnostic aim that leads to effective performance.
Process, personality, intelligence and knowledge theory (PPIK)
Predicted growth curves for Intelligence as process, crystallized intelligence, occupational knowledge and avocational knowledge based on Ackerman's PPIK Theory.
Developed by Ackerman, the PPIK (process, personality, intelligence
and knowledge) theory further developes the approach on intelligence as
proposed by Cattell, the Investment theory and Hebb, suggesting a distinction between intelligence as knowledge and intelligence as process (two concepts that are comparable and related to Gc and Gf
respectively, but broader and closer to Hebb's notions of "Intelligence
A" and "Intelligence B") and integrating these factors with elements
such as personality, motivation and interests.
Ackerman describes the difficulty of distinguishing process from
knowledge, as content cannot be entirely eliminated from any ability
test. Personality traits have not shown to be significantly correlated with the intelligence as process aspect except in the context of psychopathology. One exception to this generalization has been the finding of sex differences in cognitive abilities, specifically abilities in mathematical and spatial form.
On the other hand, the intelligence as knowledge factor has been associated with personality traits of Openness and Typical Intellectual Engagement, which also strongly correlate with verbal abilities (associated with crystallized intelligence).
Improving
Because intelligence appears to be at least partly dependent on brain
structure and the genes shaping brain development, it has been proposed
that genetic engineering could be used to enhance the intelligence, a process sometimes called biological uplift in science fiction. Experiments on mice have demonstrated superior ability in learning and memory in various behavioral tasks.
IQ leads to greater success in education, but independently education raises IQ scores.
A 2017 meta-analysis suggests education increases IQ by 1-5 points per
year of education, or at least increases IQ test taking ability.
Attempts to raise IQ with brain training have led to increases on aspects related with the training tasks – for instance working memory – but it is yet unclear if these increases generalise to increased intelligence per se.
A 2008 research paper claimed that practicing a dual n-back task can increase fluid intelligence (Gf), as measured in several different standard tests. This finding received some attention from popular media, including an article in Wired.
However, a subsequent criticism of the paper's methodology questioned
the experiment's validity and took issue with the lack of uniformity in
the tests used to evaluate the control and test groups. For example, the progressive nature of Raven's Advanced Progressive Matrices
(APM) test may have been compromised by modifications of time
restrictions (i.e., 10 minutes were allowed to complete a normally
45-minute test).
Substances which actually or purportedly improve intelligence or other mental functions are called nootropics.
A meta analysis shows omega 3 fatty acids improves cognitive
performance among those with cognitive deficits, but not among healthy
subjects.
A meta-regression shows omega 3 fatty acids improve the moods of
patients with major depression (major depression is associated with
mental deficits). However, exercise, not just performance-enhancing drugs, enhances cognition for healthy and non healthy subjects as well.
On the philosophical front, conscious efforts to influence intelligence raise ethical issues. Neuroethics
considers the ethical, legal and social implications of neuroscience,
and deals with issues such as the difference between treating a human neurological disease and enhancing the human brain, and how wealth impacts access to neurotechnology. Neuroethical issues interact with the ethics of human genetic engineering.
Transhumanist theorists study the possibilities and consequences of developing and using techniques to enhance human abilities and aptitudes.
Eugenics is a social philosophy which advocates the improvement of human hereditary traits through various forms of intervention.
Eugenics has variously been regarded as meritorious or deplorable in
different periods of history, falling greatly into disrepute after the
defeat of Nazi Germany in World War II.
Measuring
Score distribution chart for sample of 905 children tested on 1916 Stanford-Binet Test
The approach to understanding intelligence with the most supporters
and published research over the longest period of time is based on psychometric testing. It is also by far the most widely used in practical settings. Intelligence quotient (IQ) tests include the Stanford-Binet, Raven's Progressive Matrices, the Wechsler Adult Intelligence Scale and the Kaufman Assessment Battery for Children.
There are also psychometric tests that are not intended to measure
intelligence itself but some closely related construct such as
scholastic aptitude. In the United States examples include the SSAT, the SAT, the ACT, the GRE, the MCAT, the LSAT, and the GMAT.
Regardless of the method used, almost any test that requires examinees
to reason and has a wide range of question difficulty will produce
intelligence scores that are approximately normally distributed in the general population.
Intelligence tests are widely used in educational, business, and military settings because of their efficacy in predicting behavior. IQ and g
(discussed in the next section) are correlated with many important
social outcomes—individuals with low IQs are more likely to be divorced,
have a child out of marriage, be incarcerated, and need long-term
welfare support, while individuals with high IQs are associated with
more years of education, higher status jobs and higher income. Intelligence is significantly correlated with successful training and performance outcomes, and IQ/g is the single best predictor of successful job performance.
General intelligence factor or g
There are many different kinds of IQ tests using a wide variety of
test tasks. Some tests consist of a single type of task, others rely on a
broad collection of tasks with different contents (visual-spatial,
verbal, numerical) and asking for different cognitive processes (e.g.,
reasoning, memory, rapid decisions, visual comparisons, spatial imagery,
reading, and retrieval of general knowledge). The psychologist Charles Spearman early in the 20th century carried out the first formal factor analysis of correlations between various test tasks. He found a trend for all such tests to correlate positively with each other, which is called a positive manifold. Spearman found that a single common factor explained the positive correlations among tests. Spearman named it g for "general intelligence factor".
He interpreted it as the core of human intelligence that, to a larger
or smaller degree, influences success in all cognitive tasks and thereby
creates the positive manifold. This interpretation of g as a
common cause of test performance is still dominant in psychometrics.
(Although, an alternative interpretation was recently advanced by van
der Maas and colleagues. Their mutualism model
assumes that intelligence depends on several independent mechanisms,
none of which influences performance on all cognitive tests. These
mechanisms support each other so that efficient operation of one of them
makes efficient operation of the others more likely, thereby creating
the positive manifold.)
IQ tasks and tests can be ranked by how highly they load on the g factor. Tests with high g-loadings
are those that correlate highly with most other tests. One
comprehensive study investigating the correlations between a large
collection of tests and tasks has found that the Raven's Progressive Matrices have a particularly high correlation with most other tests and tasks. The Raven's
is a test of inductive reasoning with abstract visual material. It
consists of a series of problems, sorted approximately by increasing
difficulty. Each problem presents a 3 x 3 matrix of abstract designs
with one empty cell; the matrix is constructed according to a rule, and
the person must find out the rule to determine which of 8 alternatives
fits into the empty cell. Because of its high correlation with other
tests, the Raven's Progressive Matrices are generally acknowledged as a
good indicator of general intelligence. This is problematic, however,
because there are substantial gender differences on the Raven's, which are not found when g is measured directly by computing the general factor from a broad collection of tests.
General collective intelligence factor or c
A recent scientific understanding of collective intelligence, defined
as a group's general ability to perform a wide range of tasks,
expands the areas of human intelligence research applying similar
methods and concepts to groups. Definition, operationalization and
methods are similar to the psychometric approach of general individual
intelligence where an individual's performance on a given set of
cognitive tasks is used to measure intelligence indicated by the general intelligence factor g extracted via factor analysis. In the same vein, collective intelligence research aims to discover a ‘c factor’ explaining between-group differences in performance as well as structural and group compositional causes for it.
Historical psychometric theories
Several different theories of intelligence have historically been important for psychometrics. Often they emphasized more factors than a single one like in g factor.
Cattell–Horn–Carroll theory
Many of the broad, recent IQ tests have been greatly influenced by the Cattell–Horn–Carroll theory.
It is argued to reflect much of what is known about intelligence from
research. A hierarchy of factors for human intelligence is used. g
is at the top. Under it there are 10 broad abilities that in turn are
subdivided into 70 narrow abilities. The broad abilities are:
- Fluid intelligence (Gf): includes the broad ability to reason, form concepts, and solve problems using unfamiliar information or novel procedures.
- Crystallized intelligence (Gc): includes the breadth and depth of a person's acquired knowledge, the ability to communicate one's knowledge, and the ability to reason using previously learned experiences or procedures.
- Quantitative reasoning (Gq): the ability to comprehend quantitative concepts and relationships and to manipulate numerical symbols.
- Reading & writing ability (Grw): includes basic reading and writing skills.
- Short-term memory (Gsm): is the ability to apprehend and hold information in immediate awareness and then use it within a few seconds.
- Long-term storage and retrieval (Glr): is the ability to store information and fluently retrieve it later in the process of thinking.
- Visual processing (Gv): is the ability to perceive, analyze, synthesize, and think with visual patterns, including the ability to store and recall visual representations.
- Auditory processing (Ga): is the ability to analyze, synthesize, and discriminate auditory stimuli, including the ability to process and discriminate speech sounds that may be presented under distorted conditions.
- Processing speed (Gs): is the ability to perform automatic cognitive tasks, particularly when measured under pressure to maintain focused attention.
- Decision/reaction time/speed (Gt): reflect the immediacy with which an individual can react to stimuli or a task (typically measured in seconds or fractions of seconds; not to be confused with Gs, which typically is measured in intervals of 2–3 minutes).
Modern tests do not necessarily measure of all of these broad
abilities. For example, Gq and Grw may be seen as measures of school
achievement and not IQ. Gt may be difficult to measure without special equipment.
g was earlier often subdivided into only Gf and Gc which
were thought to correspond to the nonverbal or performance subtests and
verbal subtests in earlier versions of the popular Wechsler IQ test.
More recent research has shown the situation to be more complex.
Controversies
While
not necessarily a dispute about the psychometric approach itself, there
are several controversies regarding the results from psychometric
research.
One criticism has been against the early research such as craniometry.
A reply has been that drawing conclusions from early intelligence
research is like condemning the auto industry by criticizing the
performance of the Model T.
Several critics, such as Stephen Jay Gould, have been critical of g, seeing it as a statistical artifact, and that IQ tests instead measure a number of unrelated abilities. The American Psychological Association's report "Intelligence: Knowns and Unknowns" stated that IQ tests do correlate and that the view that g is a statistical artifact is a minority one.
Intelligence across cultures
Psychologists have shown that the definition of human intelligence is unique to the culture that one is studying. Robert Sternberg
is among the researchers who have discussed how one's culture affects
the person's interpretation of intelligence, and he further believes
that to define intelligence in only one way without considering
different meanings in cultural contexts may cast an investigative and
unintentionally egocentric view on the world. To negate this,
psychologists offer the following definitions of intelligence:
- Successful intelligence is the skills and knowledge needed for success in life, according to one's own definition of success, within one's sociocultural context.
- Analytical intelligence is the result of intelligence's components applied to fairly abstract but familiar kinds of problems.
- Creative intelligence is the result of intelligence's components applied to relatively novel tasks and situations.
- Practical intelligence is the result of intelligence's components applied to experience for purposes of adaption, shaping and selection.
Although typically identified by its western definition, multiple
studies support the idea that human intelligence carries different
meanings across cultures around the world. In many Eastern cultures,
intelligence is mainly related with one's social roles and
responsibilities. A Chinese conception of intelligence would define it
as the ability to empathize with and understand others — although this
is by no means the only way that intelligence is defined in China.
In several African communities, intelligence is shown similarly through a
social lens. However, rather than through social roles, as in many
Eastern cultures, it is exemplified through social responsibilities. For
example, in the language of Chi-Chewa, which is spoken by some ten
million people across central Africa,
the equivalent term for intelligence implies not only cleverness but
also the ability to take on responsibility. Furthermore, within American
culture there are a variety of interpretations of intelligence present
as well. One of the most common views on intelligence within American
societies defines it as a combination of problem-solving skills, deductive reasoning skills, and Intelligence quotient (IQ), while other American societies point out that intelligent people should have a social conscience, accept others for who they are, and be able to give advice or wisdom.
