It is possible to consider the individual differences in memory from two different standpoints: they relate either to the content or to the dynamic form of the function. A. has an excellent memory for numbers, B. for names, C. for places, D. for tones: this is one dimension for differentiation. The other is depicted, for example, by the following characteristics: One person learns easily and forgets easily; another finds it more difficult to learn but retains the learned material better. One person is never let down by his memory, while another person frequently is, and a third suffers from regular illusions of memory, etc.

As is well known, the term reaction time refers to the time from the moment at which a sensory stimulus acts on an organ through to the time at which the subject reacts to the stimulus with a movement. This “simple reaction” is so important psychologically because it can be seen as a prototype of human behavior to the extent that it is determined by external influences.

When making judgments, how do people behave with regard to external influences? Here, we raise a question which appears to apply only to the intellectual side of a personality since it penetrates deep into the heart of mental individuality. I wish to avoid going into detail about the difficult theory of judgment here. Let me simply point out one thing: Judgment is more than an indifferent mental content, more than a representation or accumulation of representations; it is an active positioning of the personality as a whole vis-à-vis the content currently present and, as such, counts as one of the acts of the will. Consequently, the dynamics of judgment that can be observed in any specific individual are related to the characteristic way in which his acts of will emerge and proceed in general. Characteristics such as decisiveness, reliability, suggestibility can refer just as much to the execution of actions as they can to the making of judgments, and the so-called “temperament” of a person shines through not only in his practical but also in his theoretical behavior with regard to things.

This chapter discusses the intellectual context within which William Stern’s call for a ‘differential’ psychology arose and unfolded, beginning with the time of his doctoral studies in Berlin during the 1890s and extending through his academic years at the universities of Breslau (now Wroclaw, Poland) and Hamburg, to his eventual flight, with wife Clara, from Nazi Germany in 1934 to Durham, NC, USA, where, as a member of the faculty at Duke University, he died in 1938. The discussion highlights Stern’s understanding of ‘differential’ psychology both as an intermediary discipline between basic experimental psychology, on the one hand, and, on the other, an applied psychology addressed to real-world challenges arising outside of controlled laboratory settings. The chapter further highlights Stern’s ‘critically personalistic’ philosophical perspective on the crucially important role that a meticulously developed program for systematically studying individual and group differences in various domains of human mental functioning could play in complementing the general experimental psychology and, in the process, advance the discipline’s scientific agenda while enriching our understanding of human individuality.

We have, thus far, discussed two aspects presented for differential study by the realm of representations: the utilization of certain perceptual data and the ability to memorize and retain representations. These are joined by a third aspect and one that is accessible to experimentation: associations.

While we shall concern ourselves in another context with the temporal circumstances of attention, its duration and constancy, there is one qualitative fact, which I shall term its constitution, that requires special explanation. In using this term, I am thinking of the image of the national constitution. An object can rule consciousness monarchically in such a way that it makes it difficult or even impossible for the other contents of consciousness to assert themselves simultaneously or even to replace it. However, a more republican constitution can also reign, in which multiple objects can share the office of power or can easily replace one another. Naturally, there are also many gradations. The constitution of attention may change in one and the same person depending on the circumstances: when taking an important examination, the one center of interest reigns monarchically; hunger, loud noises and other otherwise disruptive external and internal stimuli are powerless to redirect the mental activity, even temporarily. During a leisurely stroll, by contrast, the content of the representation currently in the focus of consciousness is easily displaced by a new impression.

The problems of differential psychology are numerous and difficult. Which paths must we take in order to master them? We shall see that all the methods that have been developed in general psychology can also be pressed into service for our purposes. They will simply be organized differently. We shall subdivide these methods into six categories which, admittedly, owe their origins less to logical than to opportunistic reasons: self-observation, observation of others, consideration of history and poetry, cultural studies, mass investigations (surveys), and experiment. Of these, the first five will concern us only briefly; the last of them, however, we shall consider more extensively.

Mental life constitutes a very complex and still little known energy system which expends energy in work, thought, volition, attention, observation; energy which is then replenished during relaxation, rest and sleep. If metaphysical parallelists want to trace all mental energy without exception back to physical energy, so be it. Empirically speaking, mental force is activated and mental work is performed, and we hold fast to this empirical fact.

One of the few features seemingly common to all earlier efforts toward a scientific psychology was that the problem was seen as -- and only as -- a general one. The investigations were concentrated on the most basic elements out of which all psychological life is built up, on the general laws [die allgemeinen Gesetzen] according to which mental phenomena occur. In this work, the attempt was made to abstract as much as possible from the unending multi-faceted quality of psychological being as we encounter it in different individuals, peoples, social classes, genders, etc.; the objective was precisely to distill from this multifaceted reality that which is common [das Gemeinsame] and the research findings have been related, sometimes justifiably, sometimes not, to mental life, and not to this or that particular instantiation of a psychological event. Abstraction of this sort is justified so long as it emerges from a judicious insight into the limits of our abilities at any given time: but the danger is only too great (and is also not always avoided) that one forgets that one is dealing with an abstraction and believes that through a general treatment of this sort all problems entailed in psychological investigation can be solved. Fortunately, we are seeing more and more, in contrast to this view, the emergence of an awareness that the material that has to this point been neglected, specifically the differential peculiarities [Eigentümlichkeiten] of the psyche deserves attention. Here is repeated something that has occurred often in the history of sciences and especially our science: that which has been regarded up to a certain point as a source of error, as a nuisance to be offset by any available means, suddenly becomes seen as a problem in and of itself. Individual differences were a crucible for hypothesizing -- if I may put it this way -- a template of the human psyche: they become an object of inquiry in their own right. Differential psychology seeks to take its place alongside of, and to supplement, general psychology.

What is intellectual proficiency? Ebbinghaus gives the following answer:

Of far more importance than sensory acuity for the individual character is the qualitative significance that one or other sensory sphere may have for one’s perceptual life—and therefore also for higher mental functions such as speaking, learning, etc. I refer to the characteristic of a person defined in this way as his or her perceptual type, which appears to me to designate the essence of this type better than any of the terms which express only its sub-functions such as “memory type” or “language type”.

The word “tempo” is, first and foremost, a musical expression; it refers to the appropriate temporal measure of a sequence of sounds. Every melody has its own tempo, that is to say there is a speed for its progression which is suitable, in a way that no other speed is, for bringing out its content for esthetic appreciation. From this, we can already deduce that tempo is not only an objective melodic tempo but also a tempo of subjective apprehension. If we generalize this last observation then we arrive at a psychological phenomenon which has so far received curiously little attention in the scientific field. For every mental process that occurs over time there is a certain speed of progression which, on the one hand, subjects feel to be appropriate, natural, pleasing when compared to all other speeds and, on the other, which they themselves use entirely automatically, almost instinctively, if they are able to perform the mental process in the way they think fit. In the case of perception (listening to a melody or a speech), every listener is immediately able to judge whether they find the tempo of the acoustic impression pleasing. In the case of voluntary acts that are expressed using motor means, such as speaking, walking, playing a piece of music, etc., we choose a natural pace of our own volition; and thought, too, has its tempo.

As is almost always the case in modern psychology, our considerations start with sensory acuity, although we shall admittedly only touch on this question. This is not because there is little to say due to a lack of material, for there is no field in which the methods of experimental investigation are more numerous than they are here. However, there is also no field in which these methods are as easy to adapt for differential-psychological purposes as they are in the case of sensory perception. There is nothing essential to be changed in the known procedures with which we determine the threshold of stimulation and differentiation for colors and brightness, pitches and volumes, pressure, temperature, the movement of the limbs, visual and haptic acuity, visual evaluation etc. if, instead of using them to prove Weber’s or some other general law, we use them to identify individual deviations between one person and another. Anyone who wants to acquaint oneself with the whole breadth of such investigative possibilities should read the list of tests that Cattell presents at the end of his above-cited work, and which, out of a total number of 50 mental tests, contains 30 relating to the sensory perceptions.

The act by which the content of perception is internally appropriated, processed to form an image and linked to the mind’s existing store of representations is known as apprehension. In this case, differentiation between individuals is possible along several dimensions.

For the sake of completeness, and not because I have anything positive to add, I shall also mention the domain of feelings. Because in this field, even general psychology has little scope for experimental investigation, and differential psychology even less so.

AbstractAlthough The BellCurve represented Murray’s first published discussion of genes and intelligence—as tactical support for his preferred policies ending assistance to the poor—his co-author had been writing on the topic for more than two decades. Herrnstein’s initial interest in intelligence marked a radical departure from his previous work. As a Harvard graduate student in the early 1950s, he had studied with the famous behaviorist B.F. Skinner, specializing in operant conditioning with pigeons. Appointed to a junior faculty position at Harvard in 1958, he received promotion and tenure only three years later, after formulating the “matching law,” an important theoretical result predicting that, when an organism is offered two response alternatives, the ratio between them will match the ratio of reinforcements associated with each alternative. His reputation well established as one of the world’s experts on pigeon behavior, Herrnstein went on to occupy an endowed chair at Harvard.

AbstractIn the fall of 1994, the national obsession with the murder trial of a legendary football player was temporarily interrupted by a controversy over a book—not some sensationalized biography of a celebrity but a chart-filled 845-page tome, co-authored by a Harvard research psychologist and a policy wonk at the conservative think tank, the American Enterprise Institute. Despite its more than 100 pages of appendices on logistic regression and other technical, statistical issues, The Bell Curve: Intelligence and Class Structure in American Life became an instantaneous cause célèbre, providing its junior author, Charles Murray—Professor Richard J. Herrnstein having passed away only days before publication—with considerably more than his Warholian 15 minutes of fame and leading a reporter for the New York Times Magazine to designate him “the most dangerous” conservative in the country. Among the many “serious” periodicals to discuss the book at length, The New Republic devoted almost an entire issue to an essay by its authors along with a host of responses, and for some weeks Murray was a ubiquitous presence on television talk shows.

AbstractAlthough it was Herrnstein’s writing in the early 1970s that began widespread discussion of the concept, and The Bell Curve, which he co-authored with Murray that continued it, the truth is that the notion of a “meritocracy” has become an abiding conviction across much of the political spectrum in the United States. The belief that society’s “winners” deserve their hugely disproportionate share of resources because they are better—i.e., smarter—than others is not unique to conservatives and libertarians like Murray; it is also an article of faith for much of the so-called “New Democratic” establishment that has controlled the party from the Clintonthrough the Obama administrations. For both conservatives and many liberals, the meritocratic faith is not so much a way to explain inequality as to rationalize it; high-ranking officials involved in economic policy in both Republicanand Democratic administrations have considered inequality not only inevitable but the appropriate reflection of people’s economic value.