EXPERIMENTAL PSYCHOLOGY. – The use of the experimental method in psychology, that is, conducting observations in a systematic manner under well-defined conditions to identify the causes of phenomena, followed the advances in the physiology of the nervous system in the first half of the 19th century. Johannes Müller (1801–58), regarded as the founder of experimental physiology, stated in 1826 that the diversity of impressions we receive from different senses depends on a specific effect peculiar to each of them, and that this effect is not produced by others (the optic nerve always gives a luminous sensation, the auditory nerve always an auditory sensation, regardless of the manner in which it is stimulated).
E. H. Weber (1795–1878) discovered that the perceptible difference between two weights or two lines of different lengths is always in proportion to the magnitude of the objects under examination: a difference of a few grams is noticeable between two light objects, but escapes us between two heavier ones. G. T. Fechner (1801–87), in his *Elemente der Psychophysik* (Leipzig 1860), further studied the relationship between stimulus intensity and sensation, discovering that while stimuli increase in geometric progression, the corresponding sensation increases in arithmetic proportion; and that the relationship between stimuli and sensations is therefore represented by a logarithmic curve. In less precise but more comprehensible terms, this means that to have a sensation of one intensity after another, it is necessary to quadruple the intensity of the stimulus; this can also be understood reciprocally, namely that the intensity of the sensation can be evaluated from the intensity of the stimulus. In this way, Müller experimentally studied the problem of sensory qualities, Weber that of comparing sensations of different intensities, and Fechner suggested the possibility of exact measurement of sensation through the measurement of corresponding stimuli. These are thus psychological problems studied experimentally. This approach was further developed by the studies of H. von Helmholtz (1821–94) on the speed of nervous impulses, in his classic works *Physiologische Optik* (1856–66) and *Lehre von Tonempfindungen* (1863), which, besides fundamental physical and physiological data, also contain a study of optical and auditory perceptions.
Wilhelm Wundt (1832–1920) published in 1873 the first systematic treatise on experimental psychology under the title *Physiologische Psychologie*, and in 1879 founded the first laboratory of experimental psychology in Leipzig. For these two reasons, Wundt is considered the initiator of experimental psychology. Accepting the concept of sensation and association as formulated by the English empiricists, from John Locke to James Mill and John Stuart Mill, Wundt aimed to discover the psychological elements and the laws governing their connections.
A year after the publication of Wundt’s *Physiological Psychology*, a small volume by the philosopher Franz Brentano (1838–1917) appeared: *Psychologie vom empirischen Standpunkt*, which was to exert a profound influence on experimental psychology. While Wundt focused his research on the “contents” of consciousness (sensations), Brentano emphasized the importance of the “acts” of consciousness that refer to the “contents,” such as acts of ideation, judgment, feeling, desire, and decision. Brentano was also connected with Oswald Külpe (1862–1915), who was first Wundt’s assistant and later a professor in Würzburg. Külpe conceived and partially implemented, through his students’ research, a grand plan for the experimental study of “higher processes,” of thought and will. Through his students (K. Stumpf of Berlin, C. von Ehrenfels and A. Meinong of Austria), Brentano also prepared the ground for Gestalt psychology.
In the Anglo-Saxon countries, experimental psychology took on its own character. Sir Francis Galton (1822–1911), deeply influenced by the biological conceptions of his cousin Charles Darwin, may be considered the founder of the statistical method applied to biology and psychology. Convinced that the study of human nature is the prerequisite for the progress of humanity based on scientific foundations, Galton personally studied many psychological problems with a note of realism and practicality in sharp contrast to the somewhat theoretical tendencies of German psychologists. Galton also attempted to measure human abilities and individual differences, and in this respect may be considered the initiator of mental tests. William James (1842–1910), although he appreciated experimental research and had established a small laboratory at Harvard in 1875 (thus before Wundt), exerted an enormous influence through his *Principles of Psychology* (1890), imbued with a lively interest not only in scientific problems but also in those of concrete life, and enlivened by an incomparable style. William James opposed the atomism of the German schools and emphasized the importance of “action” in psychic life as adaptation to reality and as an effort toward success. Following W. James, John Dewey and James Angell proposed a “functional psychology,” not in the sense of studying psychic functions as understood by Brentano, but as an interpretation of psychological activity “in function” of the needs of organisms.
From “functionalism” derives “behaviorism,” advocated from 1913 onward by John Watson (b. 1878). Watson began his work with studies in animal psychology and, reacting against a certain mentality that indiscriminately attributed to animals psychological characteristics proper to humans, asserted that just as one can study the “behavior” of animals without recourse to facts of consciousness, so one can also dispense with them in the study of humans, and instead found psychology exclusively on the objective data of behavior, understood as a response to well-defined stimuli. This extreme position was later mitigated when Watson found himself having to account for verbal reports (verbal behavior), which forced him to readmit them, albeit under a different name, as a form of introspection that he had initially banned. Behaviorism stimulated experimental research and oriented psychology toward the study of conduct and performance.
It should be noted that, before behaviorism, Bechterew’s Objective Psychology (published in 1907) had proposed a psychology based on external observation and the concept of “reflex.” Ivan Pavlov (1840–1940) confirmed this viewpoint with his doctrine of “conditioned reflexes.” In addition to innate reflexes, which are known as obligatory responses to a stimulus (e.g., the contraction of the pupil in response to intense light), Pavlov demonstrated the existence of “conditioned reflexes,” which occur not because a stimulus is adequate to produce them, but because this stimulus has become effective on the condition that it has been presented together with a stimulus that is always effective. (For example, a cat runs at the sound of knives being sharpened, not because this sound constitutes an obligatory call for it, but because this noise has become associated with the meat it may find.) According to Pavlov, conditioned reflexes are formed in the cerebral cortex and allow for functional connections between even very distant areas of II. Although the work carried out by the Pavlov school is highly commendable from a strictly physiological point of view, the question remains whether a phenomenon that is essentially passive, such as a reflex, can be the cornerstone of all psychic activity.
Behaviorism, as well as some tenets of Wundtian psychology, was strongly attacked by the school of Gestalt psychology (Gestaltpsychologie), founded in Germany by Max Wertheimer (1880–1943), Wolfgang Köhler, and Kurt Koffka, and later transplanted to America, partly as a result of the racial persecution that forced these scholars to leave Germany.
It is first and foremost a vigorous reaction to psychological atomism, and it asserts that psychology must turn to the study of total structures, which present themselves to our spontaneous observation, and to the system of internal forces that constitutes them as a unity, without falling into the artificial analyses of introspectionism, nor renouncing—as behaviorism does—the value of introspection. When we see a square, it is the square that we see: not the sum of its elements, that is, the sensations corresponding to the parts into which we think to decompose II. We see the “form” of the square even when the elementary “sensations” of which it is supposedly constituted change: that is, we see a square whether it is outlined by four black perpendicular lines, colored or dotted, or even suggested by four isolated points in a characteristic reciprocal relation. Gestalt psychology has made a valid contribution to the progress of certain problems in psychology, especially those of perception.
A mention must also be made of hormic psychology by W. MacDougall (1871–1937), which emphasizes as a distinctive feature of the psychic fact the active pursuit of an end or conclusion, and attaches great importance to the study of instincts. From hormic psychology and the psychoanalytic schools (v. PSYCHOANALYSIS) strong impetus has been given to the study of affectivity and motivation.
The “mental tests,” or “mental reagents” (as De Sanctis proposes to call them), are tasks (whether in the form of a question, a problem, or an assignment to be carried out) devised simply and quickly to reveal particular psychic functions or traits and to evaluate efficiency by comparing the performances of different individuals.
Mental tests require extensive preparatory work and testing on a large number of subjects to allow, even if only relatively, for the measurement of different psychic activities. In this sense, they should be regarded as “products” and tools of scientific psychology.
It might seem that the large number of schools and the great variety of trends within psychology indicate its inadequacy for the task. This is partly true; but it is also true that, while many are the paths by which psychological problems are studied, and while not all reach the goal, all have contributed to a rapidly developing science whose importance grows daily. It should be noted, however, that scientific psychology, in both its strict and broad sense, has established itself as the naturalistic study of the human factor. With this limitation, it deliberately seeks to avoid philosophical questions, but it cannot always do so, and often surreptitiously introduces philosophical conceptions that must be evaluated and discussed. This is why it is to be hoped that psychology will be accompanied by a philosophy that comprehends its problems, incorporates its findings, and frames them within a total conception of man.