Clocking the Mind

Mental Chronometry and Individual Differences

Arthur R. Jensen

• Publisher: Elsevier Science
• Year: 2006
• eBook ISBN: 9780080463728
• Topic: Psychology
• Subtopic: Probability & Statistics
• Index: Psychology

Mental Chronometry (MC) comprises a variety of techniques for measuring the speed with which the brain processes information.First developed in mid-1800, MC was subsequently eclipsed by more complex and practically useful types of psychometric tests stemming from Alfred Binet. This class of mental tests, however, has no true metric relating the test scores to any specific properties of the brain per se. The scores merely represent an ordinal scale, only ranking individuals according to their overall performance on a variety of complex mental tasks. The resulting scores represent no more than ranks rather than being a true metrical scale of any specific dimension of brain function. Such an ordinal scale, which merely ranks individuals in some defined population, possesses no true scale properties, possessing neither a true zero or equal intervals throughout the scale. This deficiency obstructs the development of a true natural science of mental ability. The present burgeoning interest in understanding individual differences in mental abilities in terms of the natural sciences, biology and the brain sciences in particular, demands direct measures that functionally link brain and behavior. One such natural ratio scale is time itself - the time it takes the brain to perform some elementary cognitive task, measured in milliseconds. After more than 25 years researching MC, Jensen here presents results on an absolute scale showing times for intake of visual and auditory information, for accessing short-term and long-term memory, and other cognitive skills, as a function of age, at yearly intervals from 3 to 80 years. The possible uses of MC in neurological diagnosis and the monitoring of drug effects on cognition, the chronometric study of special time-sensitive talents such as musical performance, and presents a theory of general intelligence, or g, as a function of the rate of oscillation of neural action potentials as measured by chronometric methods. Finally, Jensen urges the world-wide standardization of chronometric methods as necessary for advancing MC as a crucial branch of biopsychological science. - Provides a different scale to report Mental Chronometry (MC) findings - Argues for the global adoption of an absolute scale as opposed to the traditional ordinal scale - An important contribution to MC researchers and psychologists and neuroscientists

Chapter 1

A Brief Chronology of Mental Chronometry

Publisher Summary

This chapter presents a brief chronology of mental chronometry. Psychology as a quantitative, experimental science began with mental chronometry, the empirical study of reaction time (RT). The chapter briefly reviews some earlier history in philosophy and physiology. It discusses the philosophic background and the introduction of RT measurement in physiology. The chapter also presents a discussion on the experimental psychology of RT. The history of this subject is virtually a microcosm of the development of what is referred to as the “two disciplines of scientific psychology” —differential and experimental. Differential psychology as a quantitative science began with a practical interest in the measurement of individual differences in RT. Experimental psychology began with the investigation of the effects of manipulating various external conditions on variation in the measurements of RT.RT research also had another origin—in astronomy. The experimental psychology of Wundt paid no attention to individual differences, except as a source of “nuisance” variance that had to be minimized or controlled by “averaging out” its effects over a number of individuals. More recent historical landmarks in RT research, both in experimental and differential psychology, are presented.

The Two Disciplines of Scientific Psychology

Psychology as a quantitative, experimental science began with mental chronometry, the empirical study of reaction time (RT). The history of this subject, beginning early in the nineteenth century, is virtually a microcosm of the development of what Lee J. Cronbach (1957) referred to in his famous presidential address to the American Psychological Association as the “two disciplines of scientific psychology” — differential and experimental. Differential psychology as a quantitative science began with a practical interest in the measurement of individual differences in RT. Experimental psychology, as a discipline distinct from physiology, began with the investigation of the effects of manipulating various external conditions on variation in the measurements of RT. Taken up earnestly in 1861 by Wilhelm Wundt (1832–1920) who founded the first psychological laboratory in Leipzig, RT research became so prominent that the most famous historian of experimental psychology, Edwin G. Boring (1950), wrote that “the late nineteenth century is properly known as the period of mental chronometry” (p. 147). To appreciate its significance for psychology’s aspiration to become a natural science, we must briefly review some earlier history in philosophy and physiology.

The Philosophic Background

The work of the German philosopher, Immanuel Kant (1724–1804), was undoubtedly known to virtually all eighteenth century scholars who had an interest in understanding the human mind. Few other philosophers since Plato and Aristotle had a greater influence than Kant in the emergence of psychology as a discipline distinct from philosophy. But Kant’s influence was antithetical to psychology’s development as a natural science. He was committed to dualism and viewed the mind as beyond the reach of empirical science. He believed that mind had no physically measurable attributes and therefore could not be a subject for research by objective methods. In one of his major works, Anthroponomy (1798), he held that even if the expression of mind is mediated by physical structures including the brain, its properties could never be measured because nerve conduction has infinite velocity.

Later on, physiologists resisted Kant’s dualistic notion and put forth widely ranging conjectures of a finite nerve conduction velocity (NCV). The leading physiologist of his time, Johannes Müller (1801–1858), thought that NCV was 60 times faster than the speed of light. Estimates by other physiologists were much less fantastic. They derived their estimates by incredible arcane reckoning and came up with such amazingly ranging values as 150, 32,400, and 57,600,000,000 ft/s.

The Introduction of RT Measurement in Physiology

It was not until 1850 that it occurred to anyone to actually measure NCV directly. The physicist and physiologist Hermann von Helmholtz (1821–1894) first did it on bullfrogs, using the nerve-muscle preparation known to all students of physiology, whereby the hind leg’s gastrocnemius muscle and its attached nerve are isolated and the nerve is simulated by a fine electrode at various distances from its attachment to the muscle, while the resulting muscle twitch is recorded by a spring kymograph (invented by Helmholtz). The NCV as measured by Helmholtz was between 25.0 and 42.9 m/s. A similar but less invasive method had to be used for humans. Helmholtz measured RT to a cutaneous stimulus. When an electrode was applied to either the toe or the thigh or the jaw, the subject pressed a telegraph key. Thus the distance between these points of stimulation divided by the difference between their respective RTs gave the first realistic measure of peripheral NCV in humans. Values ranged between 50 and 100 m/s, which is comparable to modern measurements. We now know that NCV is not at all a specific value like the speed of light, but varies widely, from about 0.5 to 90 m/s, as a function of certain physical and chemical conditions of the axon. There is a positive relation of NCV to axonal diameter and degree of myelination, variables that vary markedly in different regions of the nervous system.

Boring (1950) assessed this bit of history as follows: “In Helmholtz’s experiment lay the preparation for all the later work of experimental psychology on the chronometry of mental acts and reaction times” (p. 42).

Astronomers’ Interest in RT

RT research also had another origin — in astronomy. The story is now legendary. In 1795, England’s Astronomer Royal, Nevil Maskelyne, at the Greenwich Observatory, discovered that his assistant, David Kinnebrook, was consistently in “error” in his readings of the time that a given star crossed the hairline in a telescope. He was usually about half a second behind Maskelyne’s measurements. This was intolerable for a calibration considered essential for standardizing the accuracy of time measurement for the whole world — the so-called “standard mean Greenwich time.” It was Maskelyne’s responsibility to ensure the exactitude of its measurement. After repeated warnings to Kinnebrook that he must bring his readings of various stellar transits into agreement with Maskelyne’s, Kinnebrook was still unable to correct his average constant “error.” So Maskelyne, on the assumption that his own readings were absolutely correct, fired poor Kennebrook, who returned to his former occupation as a schoolmaster (Rowe, 1983). The task that Kinnebrook had “failed” was rather similar to a standard paradigm used in present day RT research, known as “coincidence timing.” While observing a computer monitor, the subject depresses a telegraph key as a spot of light begins moving horizontally across the screen and the subject releases the key the instant the moving spot is seen to coincide with a vertical line in the middle of the screen. There are consistent individual differences in the degree of “accuracy” in estimating the time of coincidence of the spot and the line.

The Prussian astronomer F. W. Bessel (1784–1846) read of the Maskelyne-Kinnebrook incident in a report issued from the Greenwich Observatory, and in 1820 he began systematically studying individual differences in the kind of coincidence timing that had led to the firing of Kinnebrook. Bessel indeed found reliable differences between subjects, which he termed the personal equation. These measures of individual differences were used to achieve more accurate astronomical timings. The invention of efficient and more accurate electrical and photographic techniques for this purpose came about much later. But over the next 50 years astronomers devised more precise reaction timers, called chronographs. The first one was created in 1828 by the German astronomer Respold. A much improved model was produced in 1850 by the United States Coast Survey. Countless individuals’ RTs were measured as astronomy journals published data on the personal equation and its practical use in their research, for which metrical precision, then as now, is sine qua non. The standard unit of time until recently was the second, defined by astronomers as 1/86400 part of the mean solar day, the time averaged over the year, between successive transits of the center of the sun’s disc across the meridian. This definition of the second has proved to be too imprecise for certain researchers in modern physics. So today the most precise standard measurement of the second is rendered by an atomic clock, with an accuracy to within a few billionths of a second per day. The present international standard measure of a second is 9,192,631,770 vibrations of a cesium 133 atom in a vacuum.

The term reaction time was coined in 1873 by an Austrian physiologist, Sigmund Exner (1846–1926). He is also credited with discovering the importance of “preparatory set” in the measurement of RT. Lengthening the preparatory interval (i.e., the elapsed time between the “ready” signal and the onset of the reaction stimulus) increases the trial-totrial variability of the subject’s RTs, thereby increasing the measurement error of the mean RT measured in a given number of trials. Since Exner’s discovery, the use of a specified or optimal preparatory interval became standard procedure in RT measurement.

The Experimental Psychology of RT

Research based on RT measurement can be said to have become truly mental chronometry in the work of the Dutch physiologist Frans C. Donders (1818–1889), whose research monograph,“On the speed of mental processes,” was published in 1868 (for English translation, see Donders, 1969). Donders complicated the RT procedure beyond the measurement of simple reaction time (SRT), or a single response to a single stimulus. He also measured RTs involving choice (CRT) and discrimination (DRT) between two or more reaction stimuli. By thus increasing the number of different reaction stimuli or the number of response alternatives, or both, he was able to subtract the simpler forms of RT from the more complex to obtain a measure of the time required for the more complex mental operations. For example, sensory and motor components in SRT could be subtracted from CRT, yielding the time taken for the “purely mental” processes involved in making the choice. Donders thought that these experimentally derived time intervals reflected hypothetical mental processes such as discrimination, association, and judgment. Though his RT measurements were accurate, the validity of his theoretical argument based on the subtraction method was strongly disputed. It was argued that the total RT is likely not a simple sum of the times taken for each of the hypothesized component processes. Therefore, subtracting the RT of a simple task (hence a relatively short RT) from the RT of a more complex task (hence a longer RT) leaves a remainder that is not clearly inter-pretable as the time taken by the hypothesized process that caused the more complex task to have the longer RT. Subsequent research showed that Donders’ subtraction method, though clever, was empirically unsupportable. But his contribution remained so influential to subsequent work in mental chronometry that a more detailed discussion must be postponed to Chapter 2, which reviews the various RT paradigms most commonly used in RT research.

Following Donders, experimental research on RT was among the first lines of study pursued assiduously in the world’s first psychological laboratory, founded in Leipzig by Wilhelm Wundt in 1879. Throughout the 1880s, RT was the chief activity in Wundt’s lab.

One of the notable products of this effort was the doctoral thesis of an American student, James McKeen Cattell (1860–1944), who, with his Ph.D. in experimental psychology, returned to the United States and, after 3 years on the faculty of the University of Pennsylvania, was called to found the psychology department at Columbia University, which he headed from 1891 to 1917. He became one of the most famous psychologists of his time.

Cattell’s Ph.D. research, carried out under Wundt’s guidance, was later published in the journal Mind in 1886, titled “The time taken up by cerebral operations.”¹ It began with the ambitious statement: “Mental states correspond to physical changes in the brain. The object of this paper is to inquire into the time needed to bring about changes in the brain, and thus to determine the speed of thought.” Much of Cattell’s experimental work on RT was strictly parametric, that is, it assessed how RT was affected by the procedural conditions in a given experiment. He discovered that RT was affected by the sensory mode and intensity of the reaction stimulus and by the mode of the subject’s motor or vocal response. For example, he invented a lip key and a voice key and discovered that reactions made by the speech organs averaged about 30 ms slower than those made by a movement of the hand. He also found that a subject’s RT was affected by varying degrees of attention, fatigue, and practice. All these variables were studied experimentally, so they could be controlled or taken into account in later experiments on the variables of primary interest to Cattell at that time; for instance, the time to distinguish one color from another, which varies for different colors and for color versus its total absence. Similarly, different letters of the alphabet printed even in the same size and style of type differ in discriminability as measured by a subject’s RT. The same was found for familiar words. The recognition times for familiar objects are generally longer than recognition times of the printed names of those same objects. But the real significance of Cattell’s work on RT lies less in the particulars of his findings than in his guiding philosophy of science, with its emphasis on a strictly naturalistic, objective, and quantitative methodology for experimental and differential psychology. He was contemptuous of the “mentalistic” and “introspectionistic” psychology that prevailed in the early history of psychology, and he seemed to take ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Preface
• Acknowledgments
• Chapter 1: A Brief Chronology of Mental Chronometry
• Chapter 2: Chronometric Terminology and Paradigms
• Chapter 3: Reaction Time as a Function of Experimental Conditions
• Chapter 4: The Measurement of Chronometric Variables
• Chapter 5: Chronometry of Mental Development
• Chapter 6: Chronometry of Cognitive Aging
• Chapter 7: The Heritability of Chronometric Variables
• Chapter 8: The Factor Structure of Reaction Time in Elementary Cognitive Tasks
• Chapter 9: Correlated Chronometric and Psychometric Variables
• Chapter 10: Sensory Intake Speed and Inspection Time
• Chapter 11: Theory of the Correlation Between Response Time and Intelligence
• Chapter 12: The Relation of RT to Other Psychological Variables
• Chapter 13: Clinical and Medical Uses of Chronometry
• Chapter 14: Standardizing Chronometry
• References
• Jensen References on Chronometry Not Cited in the Text
• Author Index
• Subject Index