Yeshiva University Journal of Medicine and Dentistry

Introduction: Defining the Problem

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What do humans mean when speaking of intelligence? Is the individual with a low IQ but savant-like memory of historical events truly unintelligent? Is the individual who is a Nobel laureate more intelligent than the average London taxi driver? These questions have plagued intelligence researchers for well over 100 years. The way intelligence has been defined and studied has been debated since it emerged as a term and idea. The focus of this paper will be to trace the long, scientifically shaky lineage of intelligence testing methods and definitions offered, and to assess the validity of such tests in light of current findings. Of critical importance, is the history of intelligence testing and hypothesizing according to psychologists, and more recently neuroscientists as its focus has been shifted from the theoretical and psychoanalytical, to imaging-based and statistical. 

 

To assess the history and validity of these tests, one must realize the plurality of existent definitions lent to the term ‘intelligence’ alone. This can lay the foundation for scientific investigation and testing for intelligence by providing a proper, estimable definition of intelligence, and the barriers to its definition. For the purposes of this paper, here are four definitions of intelligence from four distinct sources: 

 

1. The Encyclopaedia Britannica (author, noted authority on intelligence, the psychologist Robert Sternberg): “human intelligence, mental quality that consists of the abilities to learn from experience, adapt to new situations, understand and handle abstract concepts, and use knowledge to manipulate one’s environment.” [1] 

 

2. The Cambridge English Dictionary: “the ability to learn, understand, and make judgments or have opinions that are based on reason.” [2] 

 

3. The American Psychological Association Task Force on Intelligence (1996): “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.” [3]  

 

4. Richard Haier [4], psychologist and editor-in-chief of Intelligence: “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.” [5] 

 

Synthesizing the ideas of the two scientific and two ‘popular’ definitions, intelligence can be generally defined as the ability to learn from, understand, and respond to situations. The fluidity of definition, however, could suggest the possibility of multiple intelligences, with anywhere from three to more than a thousand variants [6, 7, 8].

 

Discussion

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A Brief History and Assessment of Intelligence Testing and Theories 

This paper will review the history of intelligence testing, required to understand the new technologies and techniques employed in its analysis, and the quest for its neuroscientific/neurological basis. 

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Quantifications of intelligence through devised exams arose in 1905 when the French psychologist Alfred Binet and his colleague Theodore Simon were commissioned by the French government to devise the first-ever intelligence test, to project which students would likely experience learning difficulty at school. The Binet-Simon scale, [10]  and later the Stanford University psychologist Lewis Terman tweaked the test, creating the 1916 Stanford-Binet scale [11]. The test-takers score was represented by a single number, known as the intelligence quotient (IQ), and has remained a popular means of denoting and measuring individual intelligence in human populations. 

The American psychologist David Wechsler believed that different mental abilities could be considered manifestations of overall intelligence, producing the Wechsler-Bellevue Intelligence Scale in 1939 and in 1955, the Wechsler Adult Intelligence Scale (WAIS), which represents and reflects the percentage of US nonwhite individuals, improving the applicability to diverse populations. British-American psychologist Raymond Cattell promoted a “culture-free” variant [12], which has its origin in empirical studies of lesioned brains. The theory, driven by psychometrics, divides the g-factor (ie. general intelligence factor) into fluid intelligence (gf) - the ability to reason novelly - and crystallized intelligence (gc) - the ability to deduce abstractly based on previously learned relational abstractions.16 

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Robert Sternberg and Howard Gardner have further explored intelligence complexity, while Sternberg’s Triarchic proposes that intelligence can be categorized as: practical, or the ability to socially adapt to different contexts and settings; creative, or the ability to produce original thoughts; and analytical, or the ability to evaluate given information and solve complex problems or tasks resultant.6 Gardner wrote the Theory of Multiple Intelligences, introducing eight categories of intelligence: Linguistic, (ability to express what is thought); Logical/Mathematical (ability to quantify, hypothesize and test experimentally); Spatial (ability to visualize the world in three dimensions); Bodily-Kinesthetic, (ability to coordinate the mind/body movement); Musical (ability discern sounds, pitch, tone, etc.); Interpersonal, (ability to sense people’s feelings, motives, and empathize); Intrapersonal, (ability to

self-reflect and introspect); and Naturalist (ability to understand living things/nature).7 These theories are rejected principally by many intelligence researchers for their lack of empirical backing.4,15 One common critique of these theories, is the de-emphasis on the g-factor, while most current neuroscientific studies “use various measures with high g-loadings.”4 Gardner’s theory likewise proves impractical in school environments for assessment, planning, and intervention.16 Linda Gottfredson criticizes Sternberg’s triarchic theory of practical intelligence, finding no advantage over IQ tests nor any difference.17 

In 1994 Richard J. Herrnstein and Charles Murray published The Bell Curve: Intelligence and Class Structure in American Life. This monograph was an argument by the authors that intelligence is, to a high extent, influenced by a combination of genetic and environmental factors, allowing for better prediction of personal outcomes such as financial and occupational stability, and criminality, as opposed to the study of an individual's socioeconomic background. The book implicates many sensitive social and policy issues regarding financial and racial burdens within the United States. Some scientists have noted this book has a startling lack of peer review, diminishing the value of the book as a scholarly text.18,19 The evolutionary biologist Stephen Jay Gould publicly stated the book has misleading assumptions about intelligence.20 

Two responses to the book caused equal criticism and controversy. The first was an attempt by Gottfredson to publish a statement signed by many intelligence researchers, which turned out to have been signed by a small percentage of identified intelligence researchers,21 with some signatories being tied to a white supremacy group.22 The American Psychological Association in 1996 published a task force response, clarifying that Herrnstein and Murray’s conclusions regarding the correlation of race and IQ as a result of environmental or economic factors, could not be so easily quantified as they had suggested.3 

 

Valid or Bunk? 

The history of intelligence tests is fraught with a lack of legitimisation of its empirical methods of measurement. But the question remains as to whether intelligence tests actually contribute to the scientific understanding of what exactly characterizes intelligence, and what such results can produce and suggest for society at large. With no consensus of opinion, there still remains bias and outside influences amongst experts as to how useful and how quantifiable IQ tests are.23 Likewise, some questions arise from the exams regarding racial bias, socio-cultural bias, attention deficits, motivation and capability of the test-takers, and the projected value of the test on the test taker’s future.24,25,26 Haier rejects the notion of bias in intelligence testing: “For a test to be biased, there needs to be a consistent failure of prediction in the wrong direction. The lack of any prediction is not bias; it means the test is not valid.”4

 

In a small-scale study of Canadian school children, each of four intelligence tests was able to predict the average school grades of the children three years lantern, corroborated by a recent German study, suggesting the potential validity of its use in school-psychological practice.30 Intelligence tests have likewise been shown to predict academic success31 and job performance.32 The longitudinal studies correlate IQ with talent.33,34,35 This may, in fact, explain why IQ tests are generally found more commonly in educational settings, where assessments provide insight into student educational capabilities, identifying special needs.27 Furthermore, intelligence is not a rigid, endowed ability, but rather subject to improvement through enrichment with education. Some studies have indicated that intelligence test scores are positively correlated with the duration and level of education.28 However, environments have also been demonstrated to affect a child’s cognitive abilities to some extent.29 

Another key limitation is that intelligence testing can only estimate intelligence quantitatively, not qualitatively. The scientific community has yet to accurately measure intelligence according to a true definition and understanding of the word/concept. There is no ratio scale by which intelligence is truly measured in individuals; thus intelligence test scores are only meaningful relative to other people by which scores can be compared.4 

 

The New (Neuro-)Science of Intelligence 

The neuroscientific view focuses intelligence research on genetics and neuroimaging. Genome-wide research has overwhelmingly demonstrated a relationship and major role for certain genes in explaining the variance of intelligence, with less demonstrable association with some studies.4,35, 36 

The role of neuroimaging in intelligence measurement has advanced with the improvement of technology. In the 1980s, positron emission tomography (PET) of young men, while performing cognitive tests revealed no one area of the brain area is implicated, suggesting the possibility of a relationship between efficiency and density of neural circuits with metabolic rate in the brain.37 The study revealed and suggested that the brain’s intelligence was not simply measured by how the brain works, but by its metabolic and neural efficiency, as was suggested and backed by later studies conducted.4,38 The findings of these early studies have revealed the following key observations4: 1) Intelligence test scores are related to brain glucose metabolism. 2) Efficiency means there may be little brain activity in those with higher intelligence scores. 3) Given the role of brain efficiency, enhancement may be possible. and 4) Not all brains are the same - PET-scan differences exist between males and females, and between those of higher and lower intelligence. 

MRI has been able to demonstrate the correlation between whole brain size/volume and intelligence; bigger brains are modestly higher in intelligence.38fMRI can demonstrate functional activity;

however, as of 2006, only 17 of the hundreds of studies conducted using MRI included any measure of intelligence. Within these early studies, the g-factor was not used for intelligence estimate, instead using working memory, chess aptitude, and deductive reasoning.39,40,41 

From a neuroscientific perspective, there stands perhaps one of the most complex and baffling scientific mysteries (and controversies) in the history of intelligence research, and particularly that from a neuroscientific basis: the case of Einstein’s brain. Though the findings were concluded in light of technical issues which may influence the interpretation of the results, Albert Einstein’s brain showed more tissue and glial cells in a posterior area of the brain.42,43 Interestingly this finding seems to correspond with a separate study demonstrating the same parietal area of the brain where men showed correlations with IQ yet women did not.44 Most interesting in Einstein’s case, however, is that his brain was shown to be no different in anatomy than any other brain, especially one of an individual baring low IQ. This stresses the importance of neuroimaging and quantitative image as the future of analysis in the neuroscience of intelligence, as it emerges as its own, more empirically grounded field. 

Moving Forward: Is ‘Intelligence’ Defined or Demonstrated? Goodbye IQ Tests? 

Intelligence is, for all of its complex history of devised tests, and various definitions produced, still not singularly defined, and not demonstrated as a singly definable trait or ability. Yet, intelligence testing has been performed and relied on for over 100 years. Intelligence tests, by limiting themselves to the analysis and scoring of abilities based purely on cognitive processing and abstract thinking, reflect a key fact about intelligence and the way humanity defines the subject, using the common individual and poorly analysing outliers like a savant musician, or an autistic mathematical genius. G-factor has such a narrow application that the only setting they can properly contribute to is the school setting. Rather than further promote the idea that intelligence is simply an ability for abstract thought processing, the psychology and neuroscientific community must embrace the possibility that intelligence is not simply abstraction of thought. In fact, the fMRI studies aforementioned highlight this very trend toward an open assessment of intelligence, and reflect the need to look past the g-factor, which has little direct empirical evidence, to explain intelligence. 

History has shown that IQ tests have been used for both good and bad, often for racist and pseudoscientific purposes. The Bell Curve, while trying to be scholarly in its own right, divided the intelligence research community by showing the true level of division between researchers. While there is certainly nothing wrong with the idea of creating and maintaining a dedicated research journal to the study of intelligence, the journal Intelligence itself has had several highly controversial board members, editorial staff, and contributors, like Robert Plomin, Arthur Jensen, Linda Gottfredson, and even explicit

promoters of eugenics and scientific racism such as the psychologist Richard Lynn and the biochemist Gerhard Meisenberg.45,46,47 

In 2017, an editorial in Nature cited that many psychology students’ curricula skip the discussion of intelligence, possibly due to lack of scientific strength.48 Studies show many experts disagree on the validity of such testing.22,25 Bias limits utility, as demonstrated by the evolution of IQ test versions. It is still unclear if the exams available are ethnically and racially inclusive, as the population has ever-more diversity since 1955.49 

Where can intelligence tests still be employed, and if so, how? One area of possibility is in the criminal justice system, whereby an intelligence test can determine the acceptability of a defendant’s contribution to their own court case.50 One may identify learning disabilities in children, helping start earlier interventions and special services.51 The tests may still play a role in determining the efficacy of certain therapies in pediatric brain tumours.52 Finally, and perhaps the most effective solution, is the reconfiguration and renaming of intelligence tests to a test of ‘cognitive abilities’ to reflect the inclusiveness of processes such as attention, perception, memory, and emotion (Urbina 2016). Increasing use of the term in replacement of intelligence is helpful because it allows for an easier and more lax definition of intelligence, without invoking a heavily emotional response to the stigma surrounding intelligence and its historical uses. Concludes Urbina: “What the tests do not measure, namely, characteristics such as motivation, flexibility, leadership ability, persistence, conscientiousness, and creativity, are as important as – or even more so than – the cognitive abilities the tests do measure in allowing individuals to behave intelligently and to cope with the challenges that life presents.”53 

In light of the history, evidence, and empirical findings of intelligence research in the fields of both psychology and neuroscience, it can be concluded easily that intelligence tests are quite flawed in their narrow definition and point of psychometric evaluation of test answers. Whereas theories of intelligence are not consistently in line with the established view of g-factor supremacy and IQ primacy in assessing intelligence, this could be remedied in numerous ways as previously discussed, starting with a more open path forward in the research. Overall, intelligence tests as they stand provide too much difficulty in quantifying and discovering true intelligence, and alternate research routes must be found relying on hard scientific evidence such as fMRI.