Intelligence and Personality

Bridging the Gap in Theory and Measurement

Janet M. Collis, Samuel J. Messick, Ulrich Schiefele

• Publisher: Psychology Press
• Year: 2012
• Print ISBN:
  9780415648622
• eBook ISBN:
  9781135671730
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

This volume brings together leading researchers in a major new effort to bridge the historical gap between the domains of ability and personality. The result is a remarkable collection of chapters analyzing critical issues at the interface--style, structure, process, and context. Contributors address:
* intelligence and its relation to temperament and character-hierarchical models of cognition and personality; judgmental data in personality research; and structural issues in ability and personality;
* intelligence and conation-goal theories; the role of conation in the learning environment; motivation and arousal;
* intelligence and style-stylistic preferences; the role of disposition; cognitive style and its measurement; test taking style; and
* intelligence and personality in context-regularities of functioning; contextual effects in cultural variation; control and consistency; the concept of "successful intelligence."

Part I
Intelligence in
Relation to
Temperament and
Character

1

Spearman’s Hypothesis

Arthur R. Jensen

University of California

This occasion is a pleasure and a privilege for me, because Charles Edward Spearman (1863–1945) occupies a high position in my personal pantheon of pioneers in the history of psychology. Along with Sir Francis Galton and Edward Lee Thorndike, Spearman is one of my few heroes, at least in the behavioral sciences. Indeed, my book on the g-factor (Jensen, 1998) is dedicated to the memory of Spearman.

My pleasure is diminished, however, by my disappointment and deep regret that Professor Hans Eysenck, who was originally invited to give The Spearman Address, has had to curtail his activities for a time because of a serious illness, and I wish him well.¹ I have known Eysenck for 41 years, initially having done a 2-year Post-doc with him, way back in the mid-1950’s. Some years later, I spent my first sabbatical year from Berkeley at Eysenck’s lab. My time with Eysenck, I must say, was among the most valuable experiences in my life and there is no one else to whom I feel more indebted professionally. As the leading exponent of the London School of differential psychology founded by Galton and Spearman, Eysenck’s presence at this Spearman Seminar is greatly missed.

If Eysenck were with us, I imagine that an important part of his message would include a concern he expressed in a passage he wrote about Spearman’s thought in his book The Structure and Measurement of Intelligence (Eysenck, 1979):

The isolation of a psychometric and factor analytic work from the experimental and theoretical tradition of psychology has had many unfortunate consequences, which were foreseen by Spearman, who insisted on the dual psychological study of intelligence: the psychometric study of individual differences, and the experimental study of the general laws of intellectual functioning. It is unfortunate that his successors embraced wholeheartedly the psychometric method, and disregarded the experimental method. It is only recently that the process of unification has begun, and our success in gaining a proper understanding of intelligence depends very much on the continuation of this unification, (p. 29)

Now, 18 years later Eysenck’s statement deserves repetition because the conceptual confusion between these two domains mentioned by Eysenck still exists. It is especially evident in the two liveliest and most promising branches of behavioral science—experimental cognitive psychology and cognitive neuroscience. My reading in these fields and discussion with scientists working in them has revealed a conceptual confusion that simply should not be allowed to persist. It is the result of a failure to recognize the essential distinction implied by Spearman’s notion of the dual nature of the study of intelligence, or what he preferred to call mental abilities. This confusion, in fact, has led some of the scientifically most respectable cognitive psychologists and neuroscientists to ignore or dismiss Spearman’s major theoretical contribution, even his empirical work, and much of the research that has sprung from Spearman’s ideas in the half-century since he died in 1945.

Modern brain science, with its emphasis on many highly specialized functions of various neural processes and anatomically distinct modules that process different classes of information, would seem to contradict the existence of a general mental ability, or Spearman’s g. Some, indeed, argue that the findings of modern neuroscience contradict the existence of a small number of very broad group factors and are incompatible with any hierarchical theory of mental abilities. A few experimental psychologists and neuroscientists pooh-pooh factor analysis altogether, viewing it as merely a kind of hocus pocus numerology or pseudoscience. The essence of this rejection lies in the confusion between two conceptually distinct aspects of what we may call cognitive abilities.

What are these dual aspects conceived by Spearman? On the one hand, there are the neural mechanisms, what might be called the essential design features of the brain or its basic operating principles. These features make possible such mental functions as perception, discrimination, attention, learning, memory, and reasoning—all of the conceptually distinguishable aspects of information processing that we subsume under the term intelligence. In the light of what we now know about mammalian evolution and human evolution in particular, it is most unlikely that there are any differences among living Homo sapiens in the essential design features of the brain or in its basic operating principles. At this level of analysis involving neural mechanisms, modules, and the like, it is most unlikely that there are any intraspecies differences among biologically normal human beings, which includes all humans without major gene defects, chromosomal anomalies, or neurological damage due to trauma or disease.

On the other hand, there are conspicuous individual differences in the behavioral manifestations of these design features of the brain. It is only these individual differences that are dealt with in psychometrics and factor analysis. Without reliable individual differences, of course, correlational analysis or factor structure would be meaningless. Further, it is known from research in behavioral genetics and from the correlations between psychometric test scores and various measures of individual differences in physical brain variables—such as brain size, evoked potentials, glucose metabolic rate, and intracellular pH level—that psychometric variance is not exclusively the product of different learning experiences. Rather, it is known that it has a substantial biological basis that interacts with, and in large part determines, experiential differences.

The biological basis of individual differences most probably does not reside in the design features and operating principles of the brain. These are common to every biologically normal member of the species Homo sapiens. Although these design features are the principal subject matter of research in cognitive neuroscience, they reveal only half of the picture.

Here I wish to emphasize the hypothesis that the biological basis of individual differences is distinct from and, as it were, superimposed upon, the species-common brain mechanisms, modules, and the like, that make possible the various functions that are generally viewed as constituting intelligence. I would suggest also that the biological basis of individual differences has been on a different evolutionary time track from the species-common neural basis of cognitive functions. As a crude analogy, consider the many makes of gaspowered automobiles. Although they all operate according to the principles of the internal combustion engine, they show differences in variables such as horsepower, maximum speed, fuel efficiency, and the like because of quantitative differences in the number and cubic capacity of the cylinders, the tolerance and lubrication of the moving parts, the octane rating of the gas, and the like. Electric cars and steam engine cars, with their quite different operating principles, are analogous to different species or genera.

In this dual view of the neurophysiology of mental ability, consisting of the design features of the brain on the one hand and individual differences on the other, there is no conflict at all between the aims and findings of cognitive neuroscience and the structure of individual variation in abilities as represented by factor analysis. Both realms of phenomena are proper grist for research and are essential for a comprehensive science of human abilities. And both are biological as well as behavioral.

The biological basis of individual differences could reside in quantitative variation in neural structures, such as the number or density of neurons, the number of their synapses, and the amount of dendritic arborization. Among individuals, there is also quantitative variation in extraneural structures such as the degree of myelination of the axons, the richness of glial cells, nerve conduction velocity, glucose metabolic rate, the chemical neurotransmitters, and other elements of brain chemistry, such as intracellular pH level, all acting more or less generally throughout the central nervous system.

If the operating efficiency of the brain’s functional mechanisms were all more or less homogeneously affected by individual variation in any one or more of these superimposed quantitative features, individual differences in various mental abilities would, of course, be positively correlated with one another in the population. A hierarchical factor analysis would reveal the g factor, as was originally hypothesized by Galton (1869) and discovered empirically by Spearman (1904), (Jensen, 2000).

However, it is not yet known which properties of the brain cause the positive correlations among virtually all cognitive abilities where there are individual differences and that give rise to the phenomenon that Spearman labeled g. But this, too, is a question that goes beyond psychometrics and factor analysis and will be fruitful territory for neuroscientists, provided they come to realize that it is both conceptually and physically distinguishable from the brain’s species-characteristic operating principles. It may well be possible to discover the biological basis of g sooner (and more easily) than to discover the neurological mechanisms that mediate all of the diverse information processing functions that make up what is referred to as “intelligence” (Jensen, 1997).

Spearman realized clearly that research on these two aspects of mental ability is two distinct tasks. Intelligence consists of all of the cognitive functions attributed to it. The existence of the g-factor, on the other hand, depends on the empirically established phenomenon of positive correlations among all of the measurable behavioral attributes and manifestations of intelligence. Failure to recognize this critical distinction between intelligence and g is a roadblock to discovering the biological basis of g.

Discovering the biological bias of g, which was virtually impossible with the technology of Spearman’s time, was nevertheless Spearman’s greatest wish, the ultimate outcome of the line of research he initiated. He stated that the final understanding of g “…must come from the most profound and detailed direct study of the human brain in its purely physical and chemical aspects” (p. 403).

Although Spearman was generally regarded as Britain’s leading psychologist during the latter part of his career and was accorded such distinguished recognition as Fellowship in the Royal Society and honorary membership in the United States National Academy of Sciences, I believe his stature has steadily grown in the 5 decades since his death. In noting the many citations of Spearman’s work in my extensive reading of the literature on mental ability over the years, I have gained the impression that behavioral scientists have shown a steadily increasing interest in an appreciation of Spearman.

To determine if my subjective impression has any objective validity, I recently asked the Institute for Scientific Information (ISI), which produces the Science Citation Index (SCI) and the Social Science Citation Index (SSCI), to provide me a citation count on Spearman’s work in every 5-year interval during the half-century since his death, that is, from 1945 to 1995. Figure 1.1 shows a plot of these citations.

FIG. 1.1. Number of citations of Spearman’s works per each 5-year interval over a 50-year period after his death.

There is a correlation of +0.97 between the number of Spearman citations and the number of years since his death. This confirms my initial impression. Skinnerians might better appreciate Figure 1.2, which shows the same data presented as a cumulative record. It forms a perfect, positively accelerated growth curve. The ISI informed me that the frequency of citations of Spearman’s cited works, just since his death, places them at the 99.98th percentile of all works ever cited at least once in the Citation Index. While serving on faculty search committees, I have heard it claimed that a good prognosis for a better-than-average career in research is the candidate’s having independently published a journal article even before doing the PhD dissertation. Well, Spearman published two articles 2 years before getting his PhD (in Wundt’s lab), and both articles are still frequently cited in recent years. One is a true landmark in the history of our field and is frequently cited right up to the present day—93 years since the appearance of his famous 1904 article in the American Journal of Psychology.

FIG. 1.2. A cumulative frequency distribution of Spearman citations during the 50 years following his death.

This is indeed exceptional. As a rule, the number of citations of the vast majority of psychologists who are ever cited at all, even the very famous ones, rapidly dwindles to near zero after their death.

What is responsible for this increasing interest in Spearman’s work? It is known, of course, that he made a number of important contributions—several statistical methods (which now are frequently used but seldom cited), as well as empirical and theoretical discoveries and formulations. He is usually regarded as the inventor of factor analysis (although that is a historically complicated claim) and he is certainly the acknowledged father of what we now call “classical test theory.” But with the overshadowing ascendance of item response theory (IRT) in the last 20 years, it is unlikely that the increasing interest in Spearman reflects his historic role in the development of classical test theory. That appears now to be past history. Judging from his works that are the most frequently cited in the modern literature, particularly his most fam...

Table of contents

• Cover Page
• Half Title page
• Title Page
• Copyright Page
• List of Contributors
• Contents
• Preface
• Part I Intelligence in Relation to Temperament and Character
• Part II Intelligence and Conation
• Part III Intelligence and Style
• Part IV Intelegence and Personality in Context
• Author Index
• Subject Index