Intelligence Definition Psychology

Human Intelligence is the cognitive ability to gain knowledge from previous experiences, adapt to different situations, grasp and apply abstract ideas, and utilize the knowledge gained to manipulate one's surroundings.

A large portion of the enthusiasm among investigators working in intelligence is due to their efforts to figure out the definition of intelligence. Different scientists have highlighted distinct aspects of intelligence in their definitions. For instance, at the 1921 symposium, American psychology experts Lewis Terman and Edward L. Thorndike were at odds over the concept of intelligence. Terman insisted on the ability to be abstract, while Thorndike focused on learning and delivering satisfactory responses to inquiries. However, in recent years, psychologists have generalized that adapting to an environment is essential to comprehending the concept of intelligence and what it can do.

The process of changes could be observed in many different contexts: A student at school is taught the information that he must know to be successful in class, or a doctor taking care of a patient suffering from unfamiliar signs and symptoms discovers the source of the condition; a painter reworks an artwork to give an even more consistent perception. In the majority of cases, adaptation is the process of changing yourself to be able to deal better with your surroundings. However, it may be a matter of changing the surroundings or creating a completely different one.

Effective adaptation relies on various cognition-related processes like the perception of learning, memory, thinking, reasoning, and problem-solving. The most important aspect of the definition of intelligence is that it's not a mental or cognitive procedure in itself but a combination of various actions that are purposefully focused on achieving effective adaption. Therefore, the medical professional who discovers a new condition adapts by observing material regarding the illness from medical journals, absorbing the content while retaining the essential elements required to diagnose the patient, then using reason to resolve the issue by applying that data to the specific needs of the patients. Intelligence as a whole is now viewed not as one thing but instead as a successful gathering of many talents. It hasn't always been apparent to those who study the field; the majority of the background of the subject centers around the characteristics and capabilities which make up intelligence.

Theories of Intelligence

Intelligence theories, like the majority of scientific theories, have developed through a succession of models. Some of the most powerful models have been the psychometric theories, also referred to as psychometrics, that focus on the mechanisms by which the brain functions; cognitive and contextualism; an integrated approach to study interactions between the surrounding mind and the environment; and biological science that examines the neural basis of intelligence.

Psychometric Theories

Psychometric theories generally seek to comprehend the structure of intelligence. What shape is it in, and what are the parts that make it up, if they exist? These theories are generally built upon and confirmed by evidence gathered from tests of mental capabilities, which include analogies (e.g., water is to the plant just as food is to _____) and classifications (e.g., which word doesn't belong with other words? Robin, sparrow, blue jay, and chicken) and series closures (e.g., What number will be the next coming series? 3, 6, 10, 15, 21, _).

Psychometric theories stem from the concept of intelligence as a combination of capabilities measured through psychological tests. It is possible to quantify this model. For example, the performance of tests based on numbers could represent an unweighted combination of numbers, reasoning, and memory skills for a more complex sequence. Mathematical models enable weaknesses in one particular area to be compensated with a high level of proficiency in the other area of ability. So, higher levels of reasoning ability could compensate for any weakness in the ability to count.

The British psychologist Charles E. Spearman (1863-1945) developed one of the first psychometric theories. He published his first important article on intelligence in 1904. It was a revelation that may seem obvious today: people who performed very well on one test of mental ability tend to perform better on the other tests, while those who did poorly on one tend to do poorly on other tests. To determine the root causes of these differences in performance, Spearman created factor analysis. It is a statistical method that analyzes the patterns of different test scores. He found that only two types of variables underlie the individual variations in test scores. The second and most important aspect, he called "the general factor," also known as the "general factor," or g, pervades the ability to perform any task which requires intelligence.

Whatever the job or the task is, it requires intelligence; the task will need an amount of g. Another factor is associated with a particular test. If, for instance, an individual takes a test in reasoning with arithmetic, their success on the test will require an element that is universal to every test (g) and an additional element that is linked to one particular mental operation, such as for mathematical reasoning. What exactly is g? Since the act of giving a name to something isn't the same as knowing what it actually is. Spearman was unsure what the primary aspect was but proposed the idea in 1927 that it could be something similar to "mental energy."

There was an American psychologist L.L. Thurstone. He did not agree with Spearman's theories and argued that there were seven aspects that he identified as "primary mental abilities." According to these seven capabilities were, stated by Thurstone, the ability to comprehend words (as required for the understanding of words and reading), Verbal fluency (as required in writing and when creating words), the numerical ability (as used in the process of solving basic numerical computations and reasoning challenges), spatial visualization (as required in visualizing and manipulating things, like fitting a set of suitcases in the trunk of an automobile), Inductive reasoning (as used in the completion of an array of numbers or forecasting the future on the foundation of previous experiences), memory (as used in recollecting the identities of the names and faces of individuals and speed of perception (as required in the quick correction of typographical mistakes in text).

While the dispute between Spearman and Thurstone is still unsolved, others psychologists, such as Canadian Philip E. Vernon and American Raymond B. Cattell--have claimed that both were correct in a few aspects. Vernon and Cattell considered the concept of intellectual abilities as hierarchical, including the g, which is a general capability that is in the uppermost part of the hierarchy. Below the g are levels of gradually decreasing abilities ending with particular abilities identified by Spearman.

Cattell stated in 'Abilities: Their Structure, Growth, and Action' (1971) the idea that general abilities can be divided into two distinct types "fluid" and "crystallized." These abilities involve thinking and problem-solving skills that are measured using tests that include the use of analogies, classifications as well as series completions. Crystallized capabilities, believed to stem from fluid skills, encompass the ability to comprehend vocabulary, general knowledge as well as knowledge of particular fields. American psychotherapist John L. Horn said that crystallized capabilities tend to increase over the course of a person's lifetime, and fluid abilities grow during the earlier years and diminish during later years.

The majority of psychologists believed Spearman's division of talents was not sufficient. However, many did not agree that the division should be a hierarchical one. The American psychologist Joy Paul Guilford proposed structure-of-intellect theory, which in its earlier versions postulated 120 abilities. In the book 'The Nature of Human Intelligence' (1967), Guilford stated that capabilities could be separated into five different types of operations, four varieties of content, and six different types of products. They can be put together to create 120 distinct capacities. A good example of such an aptitude would be cognition (operation) that is based on semantic (content) relationships (product). Guilford then increased the range of skills he envisioned in his theories to reach 150.

In the end, it was evident that there were some serious issues in the fundamental approach to psychometric theory. Furthermore, psychometricians (as the practitioners of the field of factor analysis were called) were unable to find a scientific method of reconciling their differences. Any approach that supported the various theories appeared to be suspicious. But, most importantly, the theories of psychometrics failed to reveal any fundamentals regarding the mechanisms that underlie intelligence. It's one thing to debate "general ability" or "fluid ability"; however, it is quite another to explain what exactly is taking place in our minds while exercising our intelligence ability. According to cognitive psychologists, the answer to these issues was to investigate specifically the brain processes that underlie intelligence and, in a way, connect them to the aspects of intelligence suggested by psychometricians.

The American psychology expert John B. Carroll, in Human Cognitive Abilities (1993), suggested the concept of a "three-stratum" psychometric model of intelligence, which grew on previous theories about intelligence. A lot of psychologists view Carroll's concept as definitive since it was based on the reanalysis of thousands of information sets. In the initial stratum, Carroll discovered limited capabilities (roughly 50), which included seven main abilities outlined by Thurstone. According to Carroll, his middle stratum comprised vast abilities (approximately 10), like learning, retrieving information, speediness, vision, perception, fluid intelligence, and the creation of concepts. The third stratum was comprised entirely of the overall g factor, which was defined by Spearman. This may seem obvious that the factor on top is the primary one, but it's not the case, as there is no assurance that there exists a general factor at all.

The modern and traditional psychometric theories are not without their problems. The first is that it hasn't been proven that a general capability that encompasses the entire spectrum of mental capabilities is actually present. The book 'General Factor of Intelligence: How General Is It?' (2002), edited by psychologists Robert Sternberg and Elena Grigorenko, offered contrasting opinions on the G factor, with a number of authors saying that special skills are more valuable in comparison to general capabilities in particular because they are better in explaining the individual differences in cognitive functioning. The second issue is that psychometric theories are unable to accurately describe all the things that go within the brain. The third issue is that it's not certain if the tests upon which the psychometric theories are built can be used in all kinds of cultures.

Actually, there's the notion that a successful score during a test to measure aptitude or intelligence depends on the individual's knowledge within the frameworks of culture. In 1997, in her paper "You Can't Take It with You: Why Ability Assessments Don't Cross Cultures," the American psychologist Patricia M. Greenfield found that one test could measure different capabilities within different cultural contexts. The findings of her research say that it is important to consider issues of generalization across cultures when designing tests to measure abilities.

Cognitive Theories

In the period of dominance by psychometric theories, research on intelligence was heavily influenced by the researchers studying the individual variations in scores on tests. In a speech addressed to the American Psychological Association in the year 1957, American psychologist Lee Cronbach, a leader in the field of testing and a prominent psychologist, criticized the absence of a common thread between psychologists that studied individual differences in individuals and those studying commonalities within human behavior. Cronbach's appeal to join "two disciplines of scientific psychology" resulted in the creation of cognitive theories of intelligence and of the underlying processes proposed in the theories.

Fair assessments of performance require an understanding of the processes that underlie intelligence. Otherwise, the risk is of coming to conclusions that could be misleading or even wrong in assessing overall scores and other tests of the performance. For instance, suppose the student is performing poorly in the area of verbal analogies in a psychometric test. It is possible to conclude that the student doesn't reason well. An equally plausible explanation is that the student isn't able to comprehend the words or fails to read them at all. The student who is unable to comprehend the concept "audacious is too pusillanimous as mitigate is to __" could be a brilliant rationalist yet has a limited vocabulary, or vice versa. With the aid of cognitive analysis, the interpreter for tests can be in a position to identify the extent of the score that results from a weak reasoning capability as well as the extent to which the reason for it lies in not comprehending the meaning of the terms.

What underlies the majority of cognitive models of intelligence is the idea that intelligence includes cognitive representations (such as images or propositions) of information as well as functions that operate upon these representations. More intelligent people are believed to have a better understanding of information and operate more efficiently on the representations. Researchers have tried to gauge the speed of different types of mental processes. Mathematical modeling divides the total duration required for completing an activity into parts of time required to complete every mental task. They generally assume that these procedures are performed in succession (one after the next) so that processing times are additive. Some researchers permit parallel processing where multiple processes are being executed simultaneously. No matter what algorithm is used, the primary element of analysis remains similar to the mental process that is based on mental representation.

A variety of theories of intelligence were developed. One of them is the one developed by American psychologists Earl B. Hunt, Nancy Frost, and Clifford E.

Lunneborg and colleagues, in 1973, presented a way that psychometrics and cognition modeling can be integrated. Instead of starting with standard tests of psychometrics, they began by examining the tasks experimental psychologists used in their research labs to investigate the fundamental phenomena of cognition. These included perception, learning as well as memories. The researchers found that the differences between individuals on these tests, which were never previously taken into consideration, were actually closely related (although only in a weak way) to the patterns of variations in psychological tests of intelligence scores. The findings suggested that essential cognitive processes constitute the foundational elements of intelligence.

The following illustration illustrates what kind of work Hunt and his co-workers did in their study: the person is presented with a set of letters such as "AA," "Aa," or "Ab." The person's job is to reply in the quickest way possible to one of the two following inquiries: "Are the two letters the same physically?" or "Are the two letters the same only in name?" In the first pair of letters, they are physically the same, but in the second pair, the letters are identical only in their names.

Psychologists believe that one of the key abilities behind intelligence is a rapid recall of lexical information like letter names out of memory. Thus, they were interested in how long it took to respond to the query concerning the names of letters. By subtracting the time needed to react to the question on physical matches from the time needed to react to the query about names, they were able to isolate and set aside the time required for the sheer speed of reading letters and pushing buttons on a computer. They discovered that the score variations were able to predict the scores on psychometric tests, particularly for tests that test verbal abilities, like comprehension. Hunt, Frost, and Lunneborg found that those who are verbally facile are able to absorb and then retrieve from memory large amounts of verbal information in short amounts of time. Time was the most significant aspect of the research.

Then, a few years later, Sternberg proposed the possibility of an alternative strategy that could solve the ambiguity between psychometric tasks and cognitive tests. He claimed that Hunt, along with his colleagues, tested on tasks only limited to the low-level processes of cognitive processing. Even though these cognitive processes are associated with the development of intelligence, Sternberg said they are peripheral instead of central. He suggested that psychologists research the kinds of tasks they find in intelligence tests and discover the mental techniques and methods people employ to complete those tasks.

Sternberg began his studies using the analogies that he had previously cited: " lawyer is to the client as a doctor is to __ ." He concluded that the answer to these analogies calls for a number of cognitive components that were identified by him as- Encoding of analogy terms (e.g., retrieving from memory aspects associated with the words client, lawyer, and the like), inferring the relationship between the initial two phrases that make up the analogy (e.g., understanding the fact that a lawyer can provide professional services to clients); mapping that relation to the second part of the metaphor (e.g., finding out that both lawyers and a doctor offer professional services); applying the relation in order to create a completion (e.g., realizing that the individual to whom a doctor provides professional services is called a patient); and finally responding to the question.

By applying mathematical modeling techniques to reaction-time data, Sternberg determined the elements of information processing. He determined if each experimental subject actually utilized these processes, the way the processes were combined, and the degree to which each process could be erroneous. Sternberg discovered later that these same cognitive functions are at work in a range of intellectual activities. Then he concluded that similar factors are the basis for scores on tests of intelligence. The theory, formulated by psychologist Robert J. Sternberg, claims that there exist three kinds of intelligence which include practical (the ability to work with others in a variety of situations), creative (the capacity to think up fresh concepts), and analytical (the capability to analyze data and work out solutions).

Another approach was employed by British psychologist Ian Deary, among others. He argued that time for inspection is an especially effective method for assessing intelligence. There is a belief that individual variations in intelligence could result partly from variations in the amount of information absorbed and processing of simple stimuli information. When performing inspection-time tasks, the participant is shown two vertical lines with different lengths and then is required to decide which one has the greater length. Inspection time is the amount of time that every person needs to discern the line that is longer. Research suggests that intelligent people can distinguish between the lines in a shorter amount of time.

Other cognitive psychologists have also studied the human mind by creating computer models of human cognition. Two pioneers in this area were American computer scientists Allen Newell and Herbert A. Simon. In the late 1950s and the early 1960s, they collaborated together with computer scientist Cliff Shaw to develop a computer model for human solution-oriented thinking. It was called "The General Problem Solver, which could provide solutions to many types of structured issues, including logical proofs as well as math word problems. The research, which was founded on an algorithmic technique known as "means-ends analysis," resulted in Newell and Simon developing a general theory of problem-solving in the year 1972.

The majority of the issues investigated in the work of Newell and Simon were well-structured, and they could identify the actions that lead from the beginning to the final solution of a particular issue. Others have dealt with other types of questions, like the way in which texts are interpreted or the way people get reminded of what they already know from reading a text. Psychologists Marcel Just and Patricia Carpenter have, for instance, demonstrated complicated intelligence-test items, such as figural matrix problems involving reasoning with geometric shapes, could be solved using the use of sophisticated computer software in a manner that has performance comparable to humans who take tests. In this manner, it is evident that computers exhibit an aspect of "intelligence" like the human brain. The main difference is that programmers design the computer's problems and also create a program that allows computers to tackle the issues. Humans "encode" information themselves and do not have programmers managing their processing. If there exists a "programmer," it is actually the individual's brain.

The cognitive theories that have been discussed thus far depend on what psychologists refer to as the "serial processing of information." This means that, within these instances, cognitive functions are performed sequentially, one following one. However, the notion that we process information in chunks, one step at a time, may be incorrect. A number of psychologists have suggested that the process of cognitive processing takes place parallelly.

It's been difficult, nevertheless, to discern between the parallel and serial models of processing information (just the way it was difficult in the past to distinguish among different theories of intelligence in humans). The most advanced techniques for computational and mathematical modeling have been applied later to this issue. Solutions, including "parallel distributed processing" models of the brain, were proposed by psychologists David E. Rumelhart and Jay L. McClelland. They proposed that multiple kinds of information processing happen in the brain simultaneously instead of simply one or two at a given time.

Computer-based modeling is yet to address some significant issues regarding what makes up intelligence. As an example, American psychologist Michael E. Cole and other psychologists have claimed that cognitive processing does not allow for the possibility that representations of intelligence can vary from culture to culture and also among different cultural subgroups. Additionally, common experience has demonstrated that tests of conventional nature can provide a prediction of academic performance but are unable to accurately determine the ways in which the intelligence of a person will be applied (i.e., in terms of work performances or any other situations outside). Because of the distinction between academic and real-world performances, psychologists are studying cognition in the context of the environment in which it operates instead of studying it in isolation.

Cognitive-contextual Theories

Cognitive-contextual theories address the ways in which cognitive processes operate in various environments. Two main theories that fall into this category include those given by Howard Gardner and Sternberg. In 1983, Gardner was adamant about the idea of one single intelligence by suggesting a theory that posits " multiple intelligences." Theorists of the past were able to claim that intelligence includes many capabilities. But Gardner went one step further, arguing that intelligence can be multiple and include eight independent abilities. These are linguistic, logical-mathematical, spatial, musical, bodily-kinesthetic, interpersonal, intrapersonal intelligence, and naturalistic intelligence.

Some of the abilities proposed by Gardner are similar to those that were proposed by psychometric theorists. In particular, the concept of a musical intelligence was not widely known, nor did the notion of bodily-kinesthetic intelligence cover the unique abilities of dancers and athletes. Gardner developed his list of cognitive abilities primarily from research on abnormal individuals, brain damage, and the ability to think across different cultures.

Gardner also suggested the possibility of having an existence-based intelligence (a focus on "ultimate" issues, such as life's meaning) but couldn't pinpoint an area in the brain devoted to the study of these issues. Gardner's study of multiple intelligences allowed him to assert that the majority of concepts about intelligence were ethnocentric and culturally biased. However, his definition of intelligence could be generalized as it was based on cultural and biological evidence and also on information derived from the cognitive performance of a wide variety of people.

An alternative method that takes the same view of cognition and contextual, cultural factors is Sternberg's "triarchic" theory. It was proposed by Sternberg in Beyond IQ: A Triarchic Theory of Human Intelligence (1985). Both Gardner and Sternberg were of the opinion that traditional notions of intelligence were too narrow. Sternberg was, however, skeptical of the extent to which psychologists could extend beyond the conventional notions in arguing that physical and musical abilities are simply talents, not intelligence since they are specific and are not prerequisites for adaptation in the majority of cultures.

Sternberg suggested the existence of three ("triarchic") integrated and interconnected aspects of intelligence. These focus on the person's inner world, external environment as well as perception. The first comprises the mental processes and representations that constitute the basis of all thought. The other aspect is the transfer of these processes and their representations to the outside world.

The triarchic model suggests that intelligent individuals are not simply those who are able to execute various cognitive tasks easily or efficiently; rather, their higher intelligence is evident in their ability to recognize their weaknesses and strengths and take advantage of their strengths while making up for weak points. The more intelligent people, therefore, identify an area that allows them to perform their best. The third element of intelligence is the ability to integrate the inner as well as external worlds through experience. It also includes the capacity to apply the knowledge that was previously acquired to completely unrelated circumstances.

The theory, formulated by psychologist Robert J. Sternberg, claims that there exist three kinds of intelligence. These include practical intelligence (the ability to work with others in a variety of situations), creative intelligence (the capacity to think up fresh concepts), and analytical intelligence (the capability to analyze data and work out solutions).

Many psychologists believe that intelligence is reflected in the ability to deal with a variety of new situations. That is the reason experience is very crucial. In this case, for instance, intelligence can be evaluated by putting individuals in an unfamiliar situation. According to Sternberg, one aspect of the experience that's crucial to evaluate intelligence is the automation of cognitive processing that happens when a new task is made to become familiar. When a person is able to automatize everyday tasks, they are able to use more mental abilities in dealing with new challenges.

Other theories of intelligence were proposed at the end of the 20th century. In 1990, psychologists John Mayer and Peter Salovey identified the term emotional intelligence as "the ability to perceive emotions, to access and generate emotions so as to assist thought, to understand emotions and emotional knowledge, and to reflectively regulate emotions so as to promote emotional and intellectual growth."

The four components discovered in the work of Mayer and Salovey are (a) being aware of one's own emotions and those of others, (b) applying emotions effectively to aid in thinking, (c) understanding the complexity of emotions and how they impact on subsequent states of emotionality and (d) possessing the capacity to regulate one's emotional state in addition to the emotions of other people. The idea of emotional intelligence became widely promoted by psychologist and journalist Daniel Goleman in books published during the 1990s. A variety of tests designed to assess emotional intelligence have revealed a moderate relationship between emotional intelligence and standard intelligence.

Biological Theories

The concepts discussed earlier attempt to comprehend intelligence in the context of possible mental concepts, regardless of whether they're aspects, cognitive processes, or processes of cognitive thought in connection with the context. The biological theories are a completely different approach to understanding mental structures. The advocates of these theories, often referred to as reductionists, believe that understanding of intelligence can be gained only through understanding its biological roots. The issue is not an easy one to answer, especially in the case where intelligence is considered to be something that goes beyond the simple processing of data. For instance, Howard Gardner pointedly said in the piece "What We Do & Don't Know About Learning" (2004):

"Can human learning and thinking be adequately reduced to the operations of neurons, on the one hand, or to chips of silicon, on the other? Or is something crucial missing, something that calls for an explanation at the level of the human organism?"

Analogies that compare humans' brains with computers suggest that brain-based approaches to intelligence ought to be seen as supplementary instead of substituting other methods. For example, when someone is learning unfamiliar German words, they are aware of the relationship that could be between, for example, the German phrase Die Farbe and the English word color. However, a trail remains within the brain, which can be found when the data needs to be used. Though there isn't much knowledge about the biological basis of intelligence, advancements have been achieved in three distinct areas, each involving research on brain activity. They are mentioned below.

Hemispheric Studies

A different biological method has been centered around the types of performance in academic areas in relation to the brain regions that they come from. When she studied the roles of the brain's two hemispheres of the brain, psychologist Jerre Levy, along with others, discovered that the left side of the brain is more effective in analytical activities, like those that are involved in the usage of the language, while the right hemisphere performs better in spatial and visual tasks. In general, the right hemisphere appears to be more synthesized and more holistic in its operation as compared to the left. However, the patterns of hemispheric specialization are more complex than this and difficult to be generalized.

The distinctness between the hemispheres in the brain is illustrated through an early study conducted by Levy and American neurobiologist Roger Wolcott Sperry, who worked with split-brain patients -- that is, individuals whose corpus callosum had been severed. The corpus callosum is the link between both hemispheres. In individuals with damage to the corpus callosum, the two hemispheres operate independently.

Levy and Sperry asked patients suffering from split brains to hold wooden pieces that they couldn't visualize, either in their right or left hand, and then match the blocks with two-dimensional images. They discovered that people who used the left hand performed better in comparison to those with the right hand; however, they observed that the two types of patients used different approaches to solve the challenge. The study revealed that right-handers (dominated by the left side of our brain) performed better when it came to patterns that are easily written down yet are difficult to discern visually. Contrarily the left-handers (dominated by the right hemisphere) had a better understanding of visual patterns that required distinction.

Brain-wave Studies

German psychologist Hans Eysenck has studied the brain's patterns as well as the speed of responses of individuals taking intelligence tests. Previous research on brain waves has examined the connection between these brain waves and how people perform on tests of ability or other activities that require cognitive thinking. Researchers in some of these studies found a relationship between certain aspects of electroencephalogram (EEG) waves, event-related potential (ERP) waves, and scores on a standard psychometric test of intelligence.

Blood-flow Studies

The third and most current area of study is based on measuring blood flow within the brain. It can provide a direct measure of the brain's functional tissues. The amount and the location of blood flow within the brain are measured while people are performing cognitive tasks. Psychologist John Horn, an eminent researcher in this area, has found that people who are older exhibit a decrease in blood flow in the brain while performing cognitive tasks. These decreases are higher in specific parts of the brain compared to other areas, and these reductions are most noticeable in the areas that are responsible for the ability to maintain relative concentration as well as spontaneous alertness and the ability to encode newly acquired information.

By using the technique of positron emission tomography (PET), psychologist Richard Haier discovered that those who do better on standard tests of intelligence often have less stimulation within the relevant regions in the brain compared to people who do poorly. Additionally, neurologists Antonio Damasio and Hannah Damasio, along with their co-workers, employed PET scans as well as Magnetic resonance imaging (MRI) in order to examine the brain's function when subjects are performing task-based problem-solving. These results underscored the importance of studying intelligence as an innate ability that has evolved over the years.

Development Of Intelligence

There are a variety of methods for studying the process of the growth of intelligence. Psychometric theorists, for example, are trying to discover how the development of intelligence is a result of the changes in factors that affect intelligence. In particular, the notion of mental age was popular in the early part of the 20th century. It was pioneered by Alfred Binet and William Stern.

An individual's mental age was thought of as a measure of their capacity to function at a particular chronological age. So, a 12-year-old is likely to have a mental age of 12, but a 10-year-old child or a 14-year-old child could also have a mental age of 12. The idea of mental age was a subject that fell into dispute for two obvious reasons. The first is that the idea doesn't seem to be working after 16 years of age. The performance on mental tests for a 25-year-old person, for instance, is no better than the intelligence scores of a 24 or 23-year-old person, and as we move into the later years of adulthood, some tests appear to be falling. A second reason is that many psychologists think that intelligence growth does not show seamless continuous development as the notion of mental age seems to suggest. It is more likely that the process of development will be a series of irregular flashes of development, whose timeframe can vary from one child to the next.