General Intelligence

General Intelligence

Definition of Intelligence

The concept of intelligence can be found in the great texts of the Hindus and ancient Greeks. This is not very surprising since in almost any activity we can see things being done more or less intelligently. Most adults can correctly define “intelligence” in the lexical sense. It is defined in Merriam-Webster’s Dictionary (2017) as follows:

(1): the ability to learn or understand or to deal with new or trying situations: REASON; also: the skilled use of reason

(2): the ability to apply knowledge to manipulate one's environment or to think abstractly as measured by objective criteria (as tests)

Intelligence has been defined by prominent researchers in the field as:

Binet and Simon (1905): the ability to judge well, to understand well, to reason well.

Terman (1916): the capacity to form concepts and to grasp their significance.

Wechsler (1939): the aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with the environment.

Cattell (1940): the order of complexity of the relations that an individual is capable of handling.

Detailed definition of intelligence:

Life is essentially a relationship between a living organism and its environment, but it is a permanently threatened and unstable equilibrium. As long as the equilibrium between the organism and its environment is maintained, no further adaptation is required and the living process remains automatic. But when an obstacle, a hesitation or a choice occurs, this blind activity becomes insufficient and consciousness appears. Consciousness is not yet synonymous with intelligence; it is first a feeling or a need but not truly a thought-up relationship or the conscious awareness of a relationship.

To be intelligent is to understand, and to understand means to be aware of relationships. Judgment is what makes us aware of relationships. To be intelligent is also to be able to solve new problems or to deal with open-ended situations. In other words, it is about discovering relationships or being capable of invention. Thus, all intelligent action is characterized by the comprehension of relationships between the given elements and a finding out of what has to be done, given those relationships, to create new relationships, solve a difficulty or reach a desired goal. To study intelligence is therefore to study judgment and invention.

Logicians have defined judgment as the assertion of a relationship between two ideas. To say: "Dog is a mammal" is to establish a relationship between the idea of "dog" and the idea of "mammal". But this definition faultily assumes that those two ideas have already been distinguished one from another. In fact, the two ideas are not given right away as distinct. Given the judgment: "Milk is white," it is obvious that a child does not perceive milk on one side and the whiteness on the other. He grasps holistically the "white-milk" or the "milky whiteness". The discernment of the relationship implies, on the contrary, the discernment of the two terms between which dissociation must be established. Analytical thinking, which distinguishes, dissociates, is the first condition of judgment. But for the relationship to be perceived, the two terms must be consciously put together, united by the mind. This implies a synthetic activity of the brain capable of maintaining the two terms simultaneously present in consciousness.

The same two functions of analysis and synthesis are at work in the discovery of relationships (invention) but only more so. Our mind is usually a prisoner of old relationships which have a tendency to repeat themselves in thought. We have an inclination to use the same expressions, gestures or combinations of ideas. But the inventive mind is precisely opposed to such laziness. The discovery of new relationships implies that the mind is first capable of breaking old systems and of freeing itself from pre-established connections. This dissolving power of the brain is a necessary beginning to escape from obsessive routines and habits. The analytical part of our mind is always at the core of any invention or discovery. Yet, obviously, to demolish is not enough, to build is also required. For de Broglie: "Invention is the ability to discover relationships that are more or less hidden among ideas or difficulties." Indeed, in the ability to bring together seemingly remote elements lies a power of synthesis far beyond what is required for judgment.

Thus, the more mental schemes an individual can possess or handle, and the more differentiated and integrated the structure of these schemes, the more intelligent the individual.

Mental Growth and the IQ

In 1904, Alfred Binet and Théophile Simon were asked by the French Ministry of Education to create a practical and accurate method of assessing the children who could not profit from regular instruction. Binet chose to use a battery of tests, which made no pretense of measuring precisely any single faculty. Rather, it was aimed at evaluating the child general mental development with a heterogeneous group of tasks. Binet had noticed that children who had difficulties at school were very often late in other fields easily mastered by most pupils of the same age. It was their general development that was slow. Indeed, it was really not that they learned slowly as that they lagged behind in developmental readiness to grasp the concepts that were within easy reach of the majority of their age mates. Such children would eventually grasp these basic subjects fairly easily, but about a year or two later than their age mates. They were better thought of as “slow developers” than as “slow learners.”

The 30 tests on the 1905 scale ranged from very simple sensory tasks to complex verbal abstractions. The items were arranged by approximate level of difficulty instead of content. A rough standardization had been done with 50 normal children ranging from three to eleven years of age and several subnormal children as well. The notion of mental age originated directly from Binet's observation that, as they grow up, children can learn increasingly difficult concepts and ideas and do increasingly difficult things. This allowed Binet and Simon to order their tests according to the age level at which they were typically passed.

Wilhelm Stern soon decided to express mental development as a ratio computed from the mental age (obtained from Binet's tests) that he then divided by the chronological age of the child. He obtained a number he called the MQ for Mental Quotient. Lewis Terman suggested multiplying the Mental Quotient by 100 to remove decimals and he created the Intelligence Quotient or IQ, which has survived to our days:

IQ = (Mental Age) / (Chronological Age) x 100

Psychologists at the beginning of the 20th century discovered two things about the IQ that really impressed them: first, the IQs of children of the same age were normally distributed or bell shaped, like height for instance or most other physical measures. Second, mental growth was almost linear and therefore the IQ was quite constant: a child who was three years late at the age of 8 (IQ = 5/8 x 100 = 62.5) turned out to be six years late at the age of 16.

Because mental growth plateaus at around 20 years of age, it was obvious that adults could not be assessed by the same formula; so psychologists decided to measure intelligence for the adult population as a whole after roughly age 20. They simply kept the questions used for the oldest teens and slightly changed them for adults. (Psychologists also kept the name of IQ to avoid artificially distinguishing the intelligence of children from that of adults.) Similarly, the distribution of adult scores was quite bell shaped, as had already been observed for all children of a given age.

Today, the Stanford-Binet Fifth Edition (SB-5, 2003) is perhaps the most prestigious of all individual intelligence tests (along with the Wechsler scales). A major goal of the fifth edition was to tap the extremes in intelligence – the major historical strength of the Binet that had been fundamentally lost in the fourth edition. The standardization sample consisted of 4800 subjects ranging from age 2 to 85+. The SB-5 consists of 10 subtests designed to assess ability in different fields: the examinee's IQ is his/her standing on the composite performance on the different cognitive skills sampled. By sampling broadly from a wide range of cognitive tasks, factors specific to any particular subtest diminish in importance.

As Binet used to say: "The tests do not really matter provided they are numerous."

Spearman and the g factor

Charles Spearman was puzzled by his discovery: "Mental abilities of nearly all kinds are positively linked in the sense that if we are good at one thing, we are also likely to be good at others." If a person has a good vocabulary, there is a better than even chance that he has a good memory and that arithmetic is not a problem. Similarly, if a person is good at arithmetic, he probably has a better than average vocabulary or memory. These associations are not always true, but they are true on average and it is said that all our abilities are intercorrelated.

Spearman proposed the simplest possible explanation for this universal fact. Intelligence would consist of two kinds of factors: a single general factor, the g factor (or g for short) that would explain all the observed correlations, and numerous specific factors, s1, s2... that would account for the differences across tests. Suddenly, it became clear why the IQ was such a good measure of mental growth and of general mental functioning: the IQ is an average where the specific factors are unrelated across tasks – they cancel each other out. The g factor (or general intelligence) can thus stand out. Spearman was fascinated, would some specific tests be more "g loaded" than others and if yes, what would those tasks be? Only insight into the nature of such tasks would let him know whether he had found something trivial or worthwhile.

To understand better what Spearman did and what the g factor is, the following analogy with school may be useful. We are all familiar with schools/universities and with the concept of the “bright” student vs. the “not so bright” student. The GPA (Grade Point Average or overall mean) is calculated everywhere in the world to evaluate students on a single dimension: scholastic success. Schools and universities can be harsh or lenient but school subjects are always intercorrelated and a general factor of school success – the GPA – does exist. This general factor is correlated with absolutely all school subjects. Spearman, once he discovered the g factor, was like a school principal curious about which subjects would be the best summary of his entire curriculum (or that would be most correlated with the GPA). The only difference being that Spearman's "curriculum" was the entire range of human skills and abilities and that his "GPA" was the IQ.

To comprehend the nature of g was not easy, the tests or items with a high g loading (highly correlated with the IQ) were not similar at all at first glance, and neither were those with a low g loading (low correlation with the IQ). "All sorts of vehicles could carry g." The great discovery of Spearman, which has been refined ever since, was that the tests or items were loaded on g in direct proportion to the level of mental complexity involved to solve them ! The best measures of g are still those where one must compare and choose, analyze and synthesize, induce and deduce purposefully or discover structures and infer properly. In other words, judgment and invention (see detailed definition of intelligence above) are the two exact synonyms of the g factor.

Let's summarize: Binet invented the notion of mental age to describe the global level of children's cognitive development. This approach led to the notion of IQ, a kind of super-average of all our mental aptitudes. Spearman extracted the quintessence of the IQ, the g factor, by identifying the items loading it the most. The g factor turned out to be more, qualitatively, than the mere sum of the different elements involved in the original IQ tests: g was the ability to manage complexity, the essence of intelligence itself.

Intelligence at War and in the Workplace

Given the American pragmatism and efficiency, intelligence tests quickly crossed the ocean where the slow pace of development in testing picked up dramatically when the US entered World War One. Colonel Yerkes (originally from Harvard) helped design two group tests whose influence would be difficult to overestimate: the Army Alpha and the Army Beta. The Army Alpha was a mostly verbal group test of intelligence for average and superior recruits, whereas the Army Beta was a nonverbal group test of intelligence for illiterates and non-English-speaking recruits.

Shortly after the Army Alpha and Beta were released for general use, C.C. Brigham, a disciple of Colonel Yerkes, became the secretary of the College Entrance Examination Board (CEEB), which became the College Board and the Educational Testing Service (ETS) in 1948. The CEEB had been established in 1899 to avoid duplication in the testing of applicants to American colleges. In 1926, C.C. Brigham created the SAT (Scholastic Aptitude Test), which is now the most widespread of any intelligence test ever used (it is a college admissions test taken by millions of students each year). Arthur Kroll, an ETS official who has worked on the SAT, estimates that the correlation between the SAT verbal score and the full IQ is .60 to .80. Thus, in spite of several recent name changes, the SAT remains mostly what it was 90 years ago, a strongly g-loaded test of intelligence akin to the Army Alpha. For the record, the SAT was massively used in 1945 and 1946 to help millions of US soldiers return to civil life and countless jobs were granted based on SAT scores.

It is probably not true that mental testing contributed much to the outcome of WWI but what cannot be denied is the paramount contribution of mental testing to the successful drafting of millions of men and women in the US and British armed forces during World War II. Without mental tests, quick and efficient allocation of human resources would have been impossible. Second World War testing showed that over 90% of recruits with an IQ of 140 or more became commissioned officers, while less than half of those with an IQ of 110 succeeded. If intelligence testing is the major achievement of psychology in the 20th century, both world wars made it what it is today.

The scores on intelligence tests predict who will succeed and who will fail in the professions or in the army and such tests are quick, inexpensive and easy to interpret. According to Gregory:

"An ongoing debate within Industrial/Organizational psychology is whether employment testing is best accomplished with highly specific ability tests or with measures of general cognitive ability. The weight of the evidence supports the conclusion that a general factor of intelligence (the so-called g factor) is usually a better predictor of training and job success than are scores on specific cognitive measures – even when several specific cognitive measures are used in combination. Of course, this conclusion runs counter to common sense and anecdotal evidence… The reason that g usually works better than specific cognitive factors in predicting job performance is that most jobs are factorially complex in their requirements, stereotypes notwithstanding. For example, the successful engineer must explain his or her ideas to others and so needs verbal ability as well as spatial and numerical skills. Since measures of general cognitive ability tap many specific cognitive skills, a general test often predicts performance in complex jobs better than measures of specific skill."

Selection method	Validity	Cost
Intelligence test	High	Low
Biographical questionnaires	High	Low
Integrity tests	High	Low
Comprehensive test batteries	High	High
Assessment centers	High	High
Aptitude and ability tests	Moderate	Low
Personality and interests tests	Moderate	Moderate
Panel Interviews	Moderate	High
CV ratings	Low	Low
Educational records	Low	Low
Reference check	Low	Moderate
One-to-one interviews	Low	Moderate

A measuring device cannot be valid unless it is reliable, but the opposite does not hold true. Reliability is a necessary but insufficient condition for validity. Reliability has to do with the consistency or reproducibility of what is measured. Being highly valid, intelligence tests are also highly reliable (e.g., they provide consistent and stable results).

g-tests provide the best basis for personnel selection in most occupations. Rivaled maybe only by the work sample, g-tests have a validity coefficient of .55 averaged over many tests and many samples.

In sum, the g factor is a better predictor of adult occupational status and income than any other known combination of variables (it is also a strong predictor of life expectancy).

The Biological Basis of Intelligence

The first point to make is that intelligence tests are merely samples of what people know and can do. Tests are never samples of innate intelligence or culture-free knowledge. The meaning of a test may differ among cultural groups, which will affect the validity of comparisons. Today, few would dispute the claim that human intelligence – in its most common scientific and lay definitions – reflects a biological property of the brain.

The brain waves that scientists can detect follow a common pattern when an individual reacts to a sudden stimulus such as a flash of light or a loud noise. Most effective has been a type of EEG study known as the averaged evoked potential (AEP) which records what happens in the cortex during transmission of a message.

Eysenck (1994) did some work on the phenomenon and discovered that during the transmission of a message through the cortex (from the dendrites of one cell through the intermediary of the synapse to the axons of other cells) errors might occur that alter the EEG picture (the more errors, the lower the IQ). Thus he defined human intelligence as "Error free transmission through the cortex".

The AEP curves (following auditory stimulation) of the high IQ subjects are more detailed (less smooth) than those of the low IQ subjects because the evoked potentials are more alike (less error prone) before being averaged.

Today, the most promising biological approach to general intelligence is to consider what is known about the structure of the human brain. Indeed, the most striking feature of our brain is its unmatched proportion of association areas, not the quality of the neural impulse.

The parieto-frontal integration theory (P-FIT) by Jung and Haier (2007) considers intelligence to relate to how well the parietal and the frontal brain regions integrate to form complex behaviors. The P-FIT was based on a review of 37 neuroimaging studies with a total of 1,557 participants – the review included the very best neuroimaging techniques with high spatial resolution to examine the structural and functional correlates of intelligence.

The P-FIT theory is of paramount importance because it shows the links between the parietal cortex and the frontal/prefrontal cortex which are the most associative of all the association areas of the brain: the parietal cortex is for sensory integration and abstraction, whereas frontal areas are for reasoning and problem solving. Hence smarter brains have a stronger power of association and communication – they are capable of managing more complex information.

The P-FIT was recently reinforced by Aron Barbey (2012) who investigated the neural substrates of the general factor of intelligence (g) and executive function in 182 patients with focal brain damage using voxel-based lesion–symptom mapping. “The observed findings support an integrative framework for understanding the architecture of general intelligence and executive function, supporting their reliance upon a shared fronto-parietal network for the integration and control of cognitive representations.”

In brief, the more developed the association areas of an individual and the more connected they are, the smarter the individual (it is worth noticing that Einstein had exceptionally large parietal lobes as well as a fourth ridge in his mid-frontal lobes).

Challenges to General Intelligence

A very weak challenge to general intelligence is Gardner's theory of "multiple intelligences". First of all, it must be said that Gardner's theory is not new. Psychometricians have long established that intelligence consists of a lot of aptitudes, and Gardner is in fact developing a theory of the "multiple aptitudes". Guilford once proposed a theory with 120 aptitudes, and then he suggested 150. There is virtually no limit to the number of aptitudes we can come up with: chewing gum can be considered an aptitude, or biking, or watching TV, or… Indeed, Gardner's approach can be highly confusing. Consider the following syllogism: "My computer can beat me at chess. Playing chess is a form of intelligence. Therefore my computer is smarter than me…"

Intelligence is not a collection of various aptitudes but the integration of various aptitudes into a coherent whole. Humans are smarter than computers because they can switch from chess to music and see the connections between those fields, something that computers are completely unable to do. Idiot-savants may have very high aptitudes in one field but have very low IQs; this is why they are considered "idiots". Intelligence is at least as much in the links between our various aptitudes as in these aptitudes themselves and it is a serious mistake to reduce intelligence to the aptitudes that support it.

Average raw scores on various IQ tests have been rising regularly and substantially in many populations all over the world. This secular increase in IQ is known as the Flynn Effect. Using the IQ values of 1997, Neisser estimated that the average IQ of the United States in 1932, according to the first Stanford–Binet Intelligence Scales standardization sample, was 80. He states that "Hardly any of them would have scored 'very superior', but nearly one-quarter would have appeared to be 'deficient.'"

The graph below indicates the point gains on different tests over 50 years:

green = Raven Progressive Matrices

blue = Wechsler Similarities

red = Wechsler Total IQ

mauve = Wechsler Comprehension

dark grey = Wechsler Information, Vocabulary, and Arithmetic

Trahan et al. (2014) found that the effect was about 2.93 points per decade, based on both Stanford–Binet and Wechsler tests; they also found no evidence the effect was diminishing. Thus, the theory that IQ is a kind of inborn “ceiling” to our possible development doesn’t seem to agree with the facts. Intelligence is not something fixed and stable. Yes, thinking can be taught and improved. Intellectual development is not a fatal process in which the basic assimilative faculties are more or less fixed at birth. Because the elementary laws of intellectual development are not well understood, IQ tracking or segregation cannot be justified. Recent pedagogical advances make it more and more possible to facilitate the development of intellectual skills in everyone and at any time.

Many people believe that they were not born smart. This myth is popular because it shifts responsibility for failure away from an individual and onto the genetic blueprint from which the brain was constructed. Students who get poor grades can excuse their marks by thinking: "I wasn't born smart enough to cope with studying!" Incompetent teachers can justify poor grades by complaining: "How can we teach kids who were born to fail?"

If the Flynn effect proves anything, intelligence is something we acquire from experience rather than an inborn ability. This does not mean that inheritance has no role to play in establishing levels of intellectual ability. Few would argue against the fact that the upper limits of human intellectual capacity are to a great extent determined by the physical structure of the brain (as explained in the previous section). It is also fair to assume that these upper limits will vary from one individual to the next.

My contention is, however, that these genetically determined upper limits are of no practical significance to the person seeking to increase mental ability substantially. There are many reasons for supposing that we never come anywhere near these limits and that man's ability to reason, to remember, and to learn expands as the need arises. Our brains are not significantly different, in biological terms, from the brains of our Bronze Age forebears, yet they are capable of exploring space, constructing computers, and comprehending complex abstract scientific concepts. The harder your brain is obliged to work, the greater will be its capacity for work. The more efficiently you allow your brain to function, the greater will be its ability to function with speed, accuracy, and confidence, no matter what the intellectual challenge.

Of key importance in imposing restrictions on this functioning, however, is the manner in which an individual comes to view his or her intellect. This is why the myth of inborn mental inferiority is so damaging. Believe it, and you place your brain behind bars to serve out a life sentence of inadequacy. Change those beliefs, and you can free it to work better than you might ever have considered possible.

Although I believe that many people restrict their horizons and others’ unnecessarily, and I encourage you to expand yours, I do not profess that you can accomplish anything you set your mind on, so long as you believe you can. All of us have our restrictions and limitations. Taking charge of your cognitive development does not imply that you can achieve anything imaginable. It implies, instead, taking advantage of the opportunities you have.

Look at it this way. Suppose that the total amount of terrain over which you might travel at will equals a million acres. Due to various constraints you cannot overcome – no-trespassing areas, as it were – the possibilities are reduced to 10,000 acres. You are certainly blocked off from a lot of terrain. That's a pity, but why complain, when at present you only utilize 100 acres, or 1 percent of your possibilities? Stop bemoaning the limitations, and start exploring the possibilities.

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