- For "active intelligence" and its collection, see Intelligence (information gathering) and Espionage. For other uses, see Intelligence (disambiguation).
- "Intellect" redirects here. For other uses, see Intellect (disambiguation).
- "Human intelligence" redirects here. For human intelligence (HUMINT) in military and espionage contexts, see HUMINT.
|It has been suggested that some content from this article or section be split into a separate article titled Human Intelligence. (Discuss)|
Intelligence is an umbrella term describing a property of the mind including related abilities, such as the capacities for abstract thought, understanding, communication, reasoning, learning, learning from past experiences, planning, and problem solving.
Theories of intelligence are two-fold: (i) the “single intelligence” based upon the unilinear construct of “general intelligence”, and (ii) the construct of multiple intelligences. Influenced by his cousin Charles Darwin, Francis Galton was the first scientist to propose a theory of general intelligence; that intelligence is a true, biologically-based mental faculty that can be studied by measuring a person’s reaction times to cognitive tasks. Galton’s research in measuring the head sizes of British scientists and laymen led to the conclusion that head-size is unrelated to a person’s intelligence.
Alfred Binet, and the French school of intelligence, believed intelligence was a median average of dissimilar abilities, not a unitary entity with specific, identifiable properties.
- 1 Definitions
- 2 Human intelligence
- 2.1 Theories of human intelligence
- 2.2 Evolution of intelligence
- 2.3 Factors affecting intelligence
- 3 Animal and plant intelligence
- 4 Artificial intelligence
- 5 Intelligence in culture and arts
- 6 See also
- 7 References
- 8 Further reading
- 9 External links
Intelligence derives from the Latin verb intelligere; by that etymology, "understanding" (intelligence) is different from being "smart" (capable of adapting to the environment).[dubious ] Scientists have proposed two major definitions of intelligence:
(i) from Mainstream Science on Intelligence (1994), an editorial statement by fifty-two researchers:
A very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—"catching on," "making sense" of things, or "figuring out" what to do.
Individuals differ from one another in their ability to understand complex ideas, to adapt effectively to the environment, to learn from experience, to engage in various forms of reasoning, to overcome obstacles by taking thought. Although these individual differences can be substantial, they are never entirely consistent: a given person’s intellectual performance will vary on different occasions, in different domains, as judged by different criteria. Concepts of "intelligence" are attempts to clarify and organize this complex set of phenomena. Although considerable clarity has been achieved in some areas, no such conceptualization has yet answered all the important questions, and none commands universal assent. Indeed, when two dozen prominent theorists were recently asked to define intelligence, they gave two dozen, somewhat different, definitions.
|Alfred Binet||Judgment, otherwise called "good sense," "practical sense," "initiative," the faculty of adapting one's self to circumstances . . . auto-critique.|
|David Wechsler||The aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his environment.|
|Cyril Burt||Innate general cognitive ability|
|Howard Gardner||To my mind, a human intellectual competence must entail a set of skills of problem solving — enabling the individual to resolve genuine problems or difficulties that he or she encounters and, when appropriate, to create an effective product — and must also entail the potential for finding or creating problems — and thereby laying the groundwork for the acquisition of new knowledge.|
|Linda Gottfredson||The ability to deal with cognitive complexity.|
|Sternberg & Salter||Goal-directed adaptive behavior.|
|Reuven Feuerstein||The theory of Structural Cognitive Modifiability describes intelligence as "the unique propensity of human beings to change or modify the structure of their cognitive functioning to adapt to the changing demands of a life situation." |
Practical application — Furthermore, in clinical and therapeutic practice, such theoretic and academic definitions of intelligence might not apply to patients with borderline intellectual and adaptive functioning, whose treatments require comprehensive analysis of every diagnostic, testing, educational placement, and psychosocial factor. The eighth (2005) and ninth (2009) editions of the Kaplan & Sadock's Comprehensive Textbook of Psychiatry, by Frank John Ninivaggi, MD, address these matters.
Theories of human intelligence
A popular theory of intelligence is based on psychometric testing, i.e. intelligence quotient (IQ) tests; however, some researchers’ dissatisfaction with traditional IQ tests prompted their developing alternative theories of intelligence suggesting that intelligence results from independent capabilities that uniquely contribute to human intellectual performance.
Despite the variety of concepts of intelligence, the approach to understanding intelligence with the most supporters and published research over the longest period of time is based on psychometrics testing. Such intelligence quotient (IQ) tests include the Stanford-Binet, Raven's Progressive Matrices, the Wechsler Adult Intelligence Scale and the Kaufman Assessment Battery for Children.
Charles Spearman is generally credited with defining general intelligence, which he reported in his 1904 American Journal of Psychology article titled "General Intelligence," Objectively Determined and Measured. Based on the results of a series of studies collected in Hampshire, England, Spearman concluded that there was a common function (or group of functions) across intellectual activities including what he called intelligence (i.e., school rank, which Spearman thought of as “present efficiency” in school courses; the difference between school rank and age, which was conceptualized as “native capacity;” teacher ratings; and peer ratings provided by the two oldest students, which was termed “common sense”) and sensory discriminations (i.e., discrimination of pitch, brightness, and weight). This common function became known as “g” or general intelligence.
To objectively determine and measure general intelligence, Spearman invented the first technique of factor analysis (the method of Tetrad Differences) as a mathematical proof of the Two-Factor Theory. The factor analytic results indicated that every variable measured a common function to varying degrees, which led Spearman to develop the somewhat misleadingly named Two-Factor Theory of Intelligence. The Two-Factor Theory of Intelligence holds that every test can be divided into a “g” factor and an “s” factor. The g-factor measures the “general” factor or common function among ability tests. The s-factor measures the “specific” factor unique to a particular ability test. Based on a more modern interpretation of his work, Spearman’s g factor represents the fact that any set of cognitive ability tests, no matter how different, tend to all correlate positively.
L. L. Thurstone extended and generalized Spearman’s method of factor analysis into what is called the Centroid method and which became the basis for modern factor analysis. Thurstone demonstrated that Spearman’s one common factor method (Spearman’s method yielded only a single factor) was a special case of his multiple factor analysis. Thurstone’s research led him to propose a model of intelligence that included seven orthogonal (unrelated) factors (i.e., verbal comprehension, word fluency, number facility, spatial visualization, associative memory, perceptual speed and reasoning) referred to as the Primary Mental Abilities.
In a critical review of the adult testing literature, Raymond B. Cattell found that a considerable percentage of intelligence tests that purported to measure adult intellectual functioning had all of the trappings of using college students in their development. To account for differences between children/adolescents and adults, which past theory did not address, Cattell proposed two types of cognitive abilities in a revision of Spearman’s concept of general intelligence. Fluid intelligence (Gf) was hypothesized as the ability to discriminate and perceive relations (e.g., analogical and syllogistic reasoning), and crystallized intelligence (Gc) was hypothesized as the ability to discriminate relations that had been established originally through Gf, but no longer required the identification of the relation (commonly assessed using information or vocabulary tests). In addition, fluid intelligence was hypothesized to increase until adolescence and then to slowly decline, and crystallized intelligence increases gradually and stays relatively stable across most of adulthood until it declines in late adulthood.
With his student John L. Horn, Cattell indicated that Gf and Gc were only two among several factors manifest in intelligence tests scores under the umbrella of what became known as Gf/Gc Theory. General visualization (Gv; visual acuity, depth perception), general fluency (F, facility in recalling words), general speediness (Gs; performance on speeded, simple tasks) were among several cognitive ability factors added to Gf/Gc Theory.
J. P. Guilford sought to more fully explore the scope of the adult intellect by providing the concept of intelligence with a strong, comprehensive theoretical backing. The Structure-of-Intellect model (SI model) was designed as a cross classification system with intersections in the model providing the basis for abilities similar to Mendeleev’s periodic table in chemistry. The three-dimensional cube—shaped model includes five content categories (the way in which information is presented on a test; visual, auditory, symbolic, semantic, and behavioral), six operation categories (what is done on a test; evaluation, convergent production, divergent production, memory retention, memory recording, and cognition), and six product categories (the form in which information is processed on a test; units, classes, relations, systems, transformations, and implications). The intersection of three categories provides a frame of reference for generating one or more new hypothetical factors of intelligence.
John B. Carroll re-analyzed 461 datasets in the single most comprehensive study of cognitive abilities. This analysis led him to propose the Three Stratum Theory, which is a hierarchical model of intellectual functioning. The strata represent three different levels of generality over the domain of cognitive abilities. At the bottom is the first stratum, which is represented by narrow abilities that are highly specialized (e.g., induction, spelling ability). The second stratum is represented by broad abilities that include moderate specializations in various domains. Carroll identified eight second-stratum factors: fluid intelligence, crystallized intelligence, general memory and learning, broad visual perception, broad auditory perception, broad retrieval ability, broad cognitive speediness, and processing speed (reaction time decision speed). Carroll has noted the similarity of his second stratum abilities and the Gf/Gc factors, although the Three-Stratum Theory does not incorporate the developmental trajectories associated with Gf/Gc Theory. Carroll accepted Spearman’s concept of general intelligence, for the most part, as a representation of the uppermost third stratum.
More recently, an amalgamation the Gf-Gc theory of Cattell and Horn with Carroll's Three-Stratum theory has led to the Cattell-Horn-Carroll (CHC) theory of cognitive abilities. CHC researchers have produced numerous studies that have influenced diagnostic issues and test development.
Intelligence tests are widely used in educational, business, and military settings due to their efficacy in predicting behavior. g is highly 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 g is the single best predictor of successful job performance.
IQ tests were originally designed to identify mentally "defective" children. The inventors of the IQ did not necessarily believe they were measuring fixed intelligence. Despite this, critics argue that intelligence tests have been used to support nativistic theories which view intelligence as a qualitative object with a relatively fixed quantity.
Critics of the psychometrics point out that intelligence is often more complex and broader in conception than what is measured by IQ tests. Furthermore, skeptics argue that even though tests of mental abilities are correlated, people still have unique strengths and weaknesses in specific areas. Consequently they argue that psychometric theorists over-emphasize g, despite the fact that g was defined so as to encompass all inter-correlated capabilities and skills.
Researchers in the field of human intelligence have encountered a considerable amount of public concern and criticism — much more than scientists in other areas normally receive. A number of critics have challenged the relevance of psychometric intelligence in the context of everyday life. There have also been controversies over genetic factors in intelligence, particularly questions regarding the relationship between race and intelligence and sex and intelligence. Another controversy in the field is how to interpret the increases in test scores that have occurred over time, the so-called Flynn effect.
Stephen Jay Gould was one of the most vocal critics of intelligence testing. In his book The Mismeasure of Man Gould argued that intelligence could not be quantified to a single numerical entity. He also challenged the hereditarian viewpoint on intelligence. Many of Gould's criticisms were aimed at Arthur Jensen, who responded that his work had been misrepresented. Gould also investigated the methods of nineteenth century craniometry. Jensen stated that drawing conclusions from early intelligence research is like condemning the auto industry by criticizing the performance of the Model T.
Howard Gardner's theory of multiple intelligences is based on studies not only of normal children and adults but also by studies of gifted individuals (including so-called "savants"), of persons who have suffered brain damage, of experts and virtuosos, and of individuals from diverse cultures. This led Gardner to break intelligence down into at least eight different components: logical, linguistic, spatial, musical, kinesthetic, interpersonal, intrapersonal in 1983 and naturalist intelligences added in 1999. He argues that psychometric tests address only linguistic and logical plus some aspects of spatial intelligence.
A major criticism of Gardners theory is that it has never been tested, or subjected to peer review, by Gardner or anyone else, and indeed that it is unfalsifiable.
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 the Theory of Successful Intelligence by Sternberg. Intelligence is 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.
Jean Piaget  was the founder of the developmental approach to the study of intelligence. According to his theory of cognitive development, intelligence is the basic mechanism of ensuring equilibrium in the relations between the person and the environment. This is achieved through the actions of the developing person on the world. At any moment in development, the environment is assimilated in the schemes of action that are already available and these schemes are transformed or accommodated to the peculiarities of the objects of the environment, if they are not completely appropriate. Thus, the development of intelligence is a continuous process of assimilations and accommodations that lead to increasing expansion of the field of application of schemes, increasing coordination between them, increasing interiorization, and increasing abstraction. Piaget described four main periods or stages in the development towards completely equilibrated thought and problem solving. In the sensorimotor stage (0–2 years), thought is based on perceptions and external actions and their coordination. In the preoperational stage, sensorimotor schemes are internalized and thought occurs mentally rather than externally, through the manipulation of representations and symbols that stand for sensorimotor schemes and objects.
At the beginning, however, mental schemes are not coordinated. As a result, systematic logical reasoning is not possible (that, for example, A = C, if A = B and B = C). When mental schemes are coordinated, thinking enters the concrete operational stage. In this period, thinking is logical, but limited to the concrete aspects of the world. That is, children can grasp several important aspects of the world, such as the conservation of number, matter, length, weight, volume, etc. despite external transformation. Gradually, concrete operational schemes are coordinated with each other and cognitive development enters the final formal operational stage. In this period reality is subsumed to possibilities and reasoning becomes formal. As a result, abstract scientific concepts such as the concept of inertia, energy, algebra, and proportionality can be grasped and scientific experiments can be designed. All in all, for Piaget intelligence is not the same at different ages. It changes qualitatively, thereby allowing access to different levels of organization of the world. Researched showed that Piagetian intelligence is correlated but it is not identical with psychometric intelligence and IQ.
The neo-Piagetian theories of cognitive development  advanced by Case, Demetriou, Halford, and Pascual-Leone, attempted to integrate Piaget's theory with cognitive and differential theories of cognitive organization and development. Their aim was to better account for the cognitive factors of development and for intra-individual and inter-individual differences in cognitive development. They suggested that development along Piaget's stages is due to increasing processing efficiency which is defined in terms of speed of processing and working memory capacity. Moreover, Demetriou's theory ascribes an important role to hypercognitive processes of self-recording, self-monitoring, and self-regulation and it recognizes the operation of several relatively autonomous domains of thought.
Overall, this approach suggests that there indeed is a general intelligence factor. This factor is geared on general processing efficiency functions that enable humans to represent and process information, that processing involves general inferential processes that are gradually constructed, and self-awareness and reflection are instrumental in this construction. The general understanding and problem solving ability associated with this factor changes qualitatively with age and this change is related to the succession of Piagetian stages. At the same time, individual differences in the state of the general efficiency factors may cause differences in the rate of intellectual development of different individuals and this differences may be reflected in psychometric measures of cognitive ability, such as the IQ tests. Moreover differences between individuals may come from differences in their predispositions or facility related to different domains of knowledge and problem solving.
Daniel Goleman and several other researchers have developed the concept of emotional intelligence and claim it is at least as "important" as traditionally proposed components of intelligence. These theories grew from observations of human development and of brain injury victims who demonstrate an acute loss of a particular cognitive function — e.g. the ability to think numerically, or the ability to understand written language — without showing any loss in other cognitive areas.
Many researchers[who?] believe that emotional intelligence is a composite of general intelligence and agreeableness, one of the five dimensions of personality in the five-factor model of personality. In this model, an emotionally intelligent person would score higher than average in both dimensions, and vice versa. Moreover, an emotionally intelligent person cannot score high on only one of the two traits. For example, an individual with low general mental ability and high agreeableness would be impaired in his ability to produce emotionally intelligent behavior despite his intentions, while an individual with high general mental ability and low agreeableness would be perfectly capable of being emotionally intelligent, but not inclined to do so.
PASS theory has been offered as an alternative to general intelligence, and is based on a description of neuropsychological processes. These authors suggested that a unidimensional model with just intelligence fails to assist researchers and clinicians who study learning disabilities, disorders of attention, mental retardation, and interventions designed for special populations who face those challenges. The PASS model covers four kinds of competencies that are associated with areas of the brain. (1) The planning processes involve decision making, problem solving, and performing activities and requires goal setting and self-monitoring. (2) The attention/arousal component involves selectively attending to a particular stimulus, ignoring distractions, and maintaining vigilance. (3) Simultaneous processing involves the integration of stimuli into a group and requires the observation of relationships. (4) Successive processing involves the integration of stimuli into serial order. The planning and attention/arousal components comes from structures located in the frontal lobe, and the simultaneous and successive processes come from structures located in the posterior region of the cortex.
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IQ proponents have claimed that IQ's predictive validity has been demonstrated, for example in predicting non-academic outcomes such as job performance (see IQ), and that the various multiple intelligence theories have little or no such support. Meanwhile, it has been claimed that the relevance and existence of multiple intelligences have not been borne out when tested. A set of ability tests that do not correlate together would support the claim that multiple intelligences are independent of each other.
Evolution of intelligence
Our hominid and human ancestors evolved large and complex brains exhibiting an ever-increasing intelligence through a long and mostly unknown evolutionary process. This process was either driven by the direct adaptive benefits of intelligence, or − alternatively − driven by its indirect benefits within the context of sexual selection as a reliable signal of genetic resistance against pathogens.
Factors affecting intelligence
Intelligence is an ill-defined, difficult to quantify concept. Accordingly, the IQ tests used to measure intelligence provide only approximations of the posited 'real' intelligence. In addition, a number of theoretically unrelated properties are known to correlate with IQ such as race, gender and height but since correlation does not imply causation the true relationship between these factors is uncertain. Factors affecting IQ may be divided into biological and environmental.
Other biological factors correlating with IQ include ratio of brain weight to body weight and the volume and location of gray matter tissue in the brain.
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 of animals, a process sometimes called biological uplift in science fiction. Experiments on mice have demonstrated superior ability in learning and memory in various behavioural tasks.
Evidence suggests that family environmental factors may have an effect upon childhood IQ, accounting for up to a quarter of the variance. Other variance in IQ results from environmental influences not shared by siblings who grow up in the same home. Another important influence on IQ that was often neglected in earlier human genetic studies is the "maternal effect" of the prenatal environment of the mother's womb. In the context of follow-up research on the nature versus nurture debate, it is still unclear whether the "nature" component is more important than the "nurture" component in explaining IQ variance in the general population.
There are indications that in middle age intelligence is influenced by life style choices (e.g., long working hours).
Cultural factors also play a role in intelligence. For example, on a sorting task to measure intelligence, Westerners tend to take a taxonomic approach while the Kpelle people take a more functional approach. For example, instead of grouping food and tools into separate categories, a Kpelle participant stated "the knife goes with the orange because it cuts it"
Since intelligence is susceptible to modification through the manipulation of environment, the ability to influence intelligence raises ethical issues. Transhumanist theorists study the possibilities and consequences of developing and using techniques to enhance human abilities and aptitudes, and individuals ameliorating what they regard as undesirable and unnecessary aspects of the human condition; eugenics is a social philosophy which advocates the improvement of human hereditary traits through various forms of intervention. The perception of eugenics has varied throughout history, from a social responsibility required of society, to an immoral, racist stance.
Neuroethics considers the ethical, legal and social implications of neuroscience, and deals with issues such as 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.
Animal and plant intelligence
Although humans have been the primary focus of intelligence researchers, scientists have also attempted to investigate animal intelligence, or more broadly, animal cognition. These researchers are interested in studying both mental ability in a particular species, and comparing abilities between species. They study various measures of problem solving, as well as mathematical and language abilities. Some challenges in this area are defining intelligence so that it means the same thing across species (eg. comparing intelligence between literate humans and illiterate animals), and then operationalizing a measure that accurately compares mental ability across different species and contexts.
Wolfgang Köhler's pioneering research on the intelligence of apes is a classic example of research in this area. Stanley Coren's book, The Intelligence of Dogs[unreliable source?] is a notable popular book on the topic. Nonhuman animals particularly noted and studied for their intelligence include chimpanzees, bonobos (notably the language-using Kanzi) and other great apes, dolphins, elephants and to some extent parrots and ravens. Controversy exists over the extent to which these judgments of intelligence are accurate.
Cephalopod intelligence also provides important comparative study. Cephalopods appear to exhibit characteristics of significant intelligence, yet their nervous systems differ radically from those of most other notably intelligent life-forms (mammals and birds).
It has been argued that plants should also be classified as being intelligent based on their ability to sense the environment and adjust their morphology, physiology and phenotype accordingly.
Artificial intelligence (or AI) is both the intelligence of machines and the branch of computer science which aims to create it, through "the study and design of intelligent agents" or "rational agents", where an intelligent agent is a system that perceives its environment and takes actions which maximize its chances of success. Achievements in artificial intelligence include constrained and well-defined problems such as games, crossword-solving and optical character recognition. General intelligence or strong AI has not yet been achieved and is a long-term goal of AI research.
Intelligence in culture and arts
The concept of intelligence has been treated in many works:
- Active intellect
- Artificial Intelligence
- Downing effect
- Educational psychology
- Evolution of human intelligence
- Fertility and intelligence
- Flynn effect
- History of the race and intelligence controversy
- Individual differences psychology
- Intellectual giftedness
- Intelligence quotient
- Passive intellect
- Race and intelligence
- Religiosity and intelligence
- Situational intelligence
- Systems intelligence
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(Books listed in chronological order of publication)
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- Khalfa, Jean, ed. (1996). What Is Intelligence?. Darwin College Lectures. Cambridge: Cambridge University Press. ISBN 9780521566858. Lay summary (4 July 2010).
- Sternberg, ed. (2000). Handbook of Intelligence. Cambridge: Cambridge University Press. ISBN 9780521596480. Lay summary (29 June 2010).
|last1=in Authors list (help);
- Richardson, Ken (2000). The Making of Intelligence. New York (NY): Columbia University Press. ISBN 978-0-231-12005-0. Lay summary (28 June 2010).
- Bock, Gregory; Goode, Jamie; Webb, Kate, eds. (2000). The Nature of Intelligence. Novartis Foundation Symposium 233. Chichester: Wiley. doi:10.1002/0470870850. ISBN 978-0471494348. Retrieved 16 July 2010.
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- Sternberg, ed. (2004). International Handbook of Intelligence. Cambridge: Cambridge University Press. ISBN 9780521004022. Lay summary (29 June 2010).
|last1=in Authors list (help);
- Flynn, James R. (2009). What Is Intelligence: Beyond the Flynn Effect (expanded paperback ed.). Cambridge: Cambridge University Press. ISBN 978-0-521-74147-7. Lay summary (18 July 2010).
- Stanovich, Keith (2009). What Intelligence Tests Miss: The Psychology of Rational Thought. New Haven (CT): Yale University Press. ISBN 9780300123852. Lay summary (9 August 2010).
- Garlick, Dennis (2010). Intelligence and the Brain: Solving the Mystery of Why People Differ in IQ and How a Child Can Be a Genius. Burbank (CA): Aesop Press. ISBN 9780615319216. Lay summary (23 August 2010).
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- APA Task Force Examines the Knowns and Unknowns of Intelligence - American Psychological Association, Press release
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- History of Influences in the Development of Intelligence Theory and Testing - Developed by Jonathan Plucker at Indiana University
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