Human intelligence

Human intelligence is the intellectual capability of humans, which is marked by complex cognitive feats and high levels of motivation and self-awareness. Using their intelligence, humans are able to learn, form concepts, understand, and apply logic and reason. Human intelligence is also thought to encompass their capacities to recognize patterns, plan, innovate, solve problems, make decisions, retain information, and use language to communicate.
There are conflicting ideas about how intelligence should be conceptualized and measured. In psychometrics, human intelligence is commonly assessed by intelligence quotient tests, although the validity of these tests is disputed. Several subcategories of intelligence, such as emotional intelligence and social intelligence, have been proposed, and there remains significant debate as to whether these represent distinct forms of intelligence.
There is also ongoing debate regarding how an individual's level of intelligence is formed, ranging from the idea that intelligence is fixed at birth to the idea that it is malleable and can change depending on a person's mindset and efforts.

History

Psychologists such as Thomas Suddendorf argue we can learn about human intelligence by studying close relatives like primates. We can also get insights into the evolution of human brain by comparing the human brain with that of other organisms which in turn can offer insights into evolution of human intelligence.

Correlates

As a construct and as measured by [|intelligence tests], intelligence is one of the most useful concepts in psychology, because it correlates with many relevant variables, for instance the probability of suffering an accident, or the amount of one's salary. Other examples include:
; 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.
; Personality: A landmark set of meta-analyses synthesizing thousands of studies including millions of people from over 50 countries found that many personality traits are intricately related to cognitive abilities. Neuroticism-related traits display the most negative relations, whereas traits like activity, industriousness, compassion, and openness are positively related to various abilities.
; Myopia: A number of studies have shown a correlation between IQ and myopia. Some suggest that the reason for the correlation is environmental: either people with a higher IQ are more likely to damage their eyesight with prolonged reading, or people who read more are more likely to attain a higher IQ; others contend that a genetic link exists.
; Aging: There is evidence that aging causes a 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.
; Genes: A number of single-nucleotide polymorphisms in human DNA are correlated with higher IQ scores.

Theories

Relevance of IQ tests

In psychology, human intelligence is commonly assessed by IQ scores that are determined by IQ tests. In general, higher IQ scores are associated with better outcomes in life. However, while IQ test scores show a high degree of inter-test reliability, and predict certain forms of achievement effectively, their construct validity as a holistic measure of human intelligence is considered dubious. While IQ tests are generally understood to measure some forms of intelligence, they may fail to serve as an accurate measure of broader definitions of human intelligence inclusive of creativity and social intelligence. According to psychologist Wayne Weiten, "IQ tests are valid measures of the kind of intelligence necessary to do well in academic work. But if the purpose is to assess intelligence in a broader sense, the validity of IQ tests is questionable."

Theory of multiple intelligences

's theory of multiple intelligences is based on studies of normal children and adults, of gifted individuals, of persons who have suffered brain damage, of experts and virtuosos, and of individuals from diverse cultures. Gardner breaks intelligence down into components. In the first edition of his book Frames of Mind, he described seven distinct types of intelligence: logical-mathematical, linguistic, spatial, musical, kinesthetic, interpersonal, and intrapersonal. In a second edition, he added two more types of intelligence: naturalist and existential intelligences. He argues that psychometric tests address only linguistic and logical plus some aspects of spatial intelligence. A 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 suggest that recognizing many specific forms of intelligence 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 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."

Triarchic theory of intelligence

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 to 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 understood.
Sternberg updated the triarchic theory and renamed it to the Theory of Successful Intelligence. He now defines intelligence as an individual's assessment of success in life by the individual's own 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 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 the following four processes:

Planning involves executive functions responsible for controlling and organizing behavior, selecting and constructing strategies, and monitoring performance.
Attention is responsible for maintaining arousal levels and alertness, and ensuring focus on relevant stimuli.
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 theory is heavily indebted both to Luria and to 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, the child creates increasingly more accurate models of the world which enable the child to interact with the world more effectively. One example is object permanence with which the child develops a model in which 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:

Progress through these stages is correlated with, but not identical to psychometric IQ. Piaget conceptualizes intelligence as an activity more than as 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.
This experiment demonstrated several results. First, younger children have a discriminative ability that shows the logical capacity for cognitive operations exists earlier than previously acknowledged. Also, 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 five 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 on the grounds that the age of appearance of a new model of the world, such as object permanence, is dependent on how the testing is done. 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.