EXPERIMENTAL PSYCHOLOGY. - The use of the experimental method in psychology, that is, the carrying out of observations in a systematic way, under well-determined conditions in order to identify the causes of phenomena, followed upon the advances in the physiology of the nervous system in the first half of the nineteenth century. Johannes Mueller (1801-58), considered the founder of experimental physiology, asserted in 1826 that the diversity of the impressions we receive from the different senses depends on an effect specific to each of them, and that it is not produced by others (the optic nerve always gives a luminous sensation, the acoustic one always an auditory sensation, whatever the manner in which it is stimulated).
E. H. Weber (1795-1878) discovered that the perceptible difference between two different weights or between two lines of different length is always in relation to the magnitude of the objects under examination: a difference of a few grams is noticed between two not very heavy objects, but escapes us between two other objects that have a greater weight. G. T. Fechner (1801-87) in his Elemente der Psychophysik (Leipzig 1860), further studied the relationship between the intensity of the stimulus 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 exact but more comprehensible terms, this means that in order to have a sensation of double the intensity of another it is necessary to quadruple the intensity of the stimulus: this can also be understood reciprocally, that is, that from the intensity of the stimulus one can evaluate the intensity of the sensation. In this way Müller studies experimentally the problem of sensory qualities, Weber that of the comparison of sensations of different intensity, and Fechner suggests a possibility of exact measurement of sensation through the measurement of the corresponding stimuli. These are therefore psychological problems studied experimentally. This direction was accentuated by the studies of H. von Helmholtz (1821-94) on the speed of the nervous impulse, in his classic works Physiologische Optik (1856-66) and Lehre von den Tonempfindungen (1863) containing, besides fundamental physical and physiological data, a study also of optical and acoustic perceptions.
Wilhelm Wundt (1832-1920) published in 1873 the first systematic treatise of experimental psychology under the title Physiologische Psychologie and in 1879 founded the first laboratory of experimental psychology in Leipzig. Wundt is considered for these two reasons the initiator of experimental psychology. Accepting the concept of sensation and of association as it had been 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 that regulate their connection.
One year after the publication of Wundt's Physiological Psychology, there appeared a small volume by the philosopher Franz Brentano (1838-1917): Psychologie vom empirischen Standpunkt, which was to exercise a profound influence on experimental psychology. While Wundt fixed his research on the "contents" of consciousness (the sensations), Brentano pointed out the importance of the "acts" of consciousness that refer to "contents," the acts of ideation, of judgment, of feeling, of desire, of decision. To Brentano is also linked Oswald Külpe (1862-1915), first an assistant of Wundt, then a professor at Würzburg, who conceived and partially carried out through the research of his pupils a grand plan of experimental study of the "higher processes," of thought and of will. Through his pupils (K. Stumpf of Berlin, C. von Ehrenfels and A. Meinong, an Austrian) Brentano also prepared the ground for Gestalt psychology.
In the Anglo-Saxon countries experimental psychology took on a character of its own. Sir Francis Galton (1822-1911), profoundly influenced by the biological conceptions of his cousin Charles Darwin, can be considered the founder of the statistical method applied to biology and to psychology. Convinced that the study of human nature is the prerequisite for a progress of humanity founded on scientific bases, Galton personally studied many psychological problems with a note of realism and practicality in sharp contrast with the somewhat theoretical tendencies of the German psychologists. Galton also attempted a measurement of human capacities and of individual differences, and in this respect can also be considered the initiator of mental "tests." William James (1842-1910), although he appreciated experimental research and had started a small laboratory at Harvard in 1875 (therefore prior to Wundt), exercised an enormous influence through his Principles of Psychology (1890) pervaded by a lively interest not only in scientific problems, but in those of concrete life, and enlivened by an incomparable style. William James aims against the atomism of the German schools and at the importance of "action" in psychic life, as adaptation to reality and as effort toward success. In the wake of W. James, John Dewey and James Angell propose a "functional psychology," not in the sense of the study of psychic functions as they were understood by Brentano, but rather as an interpretation of psychic activity "in function" of the needs of organisms.
From "functionalism" descends "behaviorism," advocated, starting from 1913, by John Watson (b. 1878). Watson began his activity with studies of animal psychology and, reacting against a certain mentality that indiscriminately attributed to animals psychological characteristics proper to man, affirmed 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 man, and instead found psychology exclusively on the objective data of behavior, understood as a response to well-determined stimuli. This extreme position gradually softened, when Watson found himself having to reckon also with verbal report (verbal behavior), which forced him to readmit, under a different name, much introspectionism, which he had initially banished. Behaviorism stimulated experimental research and oriented psychology toward the study of conduct and of performance.
It should be remembered that, before behaviorism, the Objective Psychology of Bechterew (published in 1907) had proposed a psychology founded on external observation and on the concept of "reflex." Ivan Pavlov (1849-1940) confirmed this point of view with the doctrine of "conditioned reflexes." Besides congenital reflexes, which are known as an obligatory response to a stimulus (the contraction of the pupil in response to an intense light), Pavlov showed the existence of "conditioned reflexes," which is to say that they take place not because a stimulus is adequate to produce them, but because this stimulus has become effective, on "condition" of having been presented with an always efficient stimulus. (e.g., the cat runs at the noise produced by sharpening knives, not because it constitutes an obligatory attraction for it, but because this noise has become associated with the meat, which it may find). Conditioned reflexes, according to Pavlov, are formed in the cerebral cortex and allow the functional connection between even very distant zones of it. Although the work carried out by Pavlov's school is most valuable from the strictly physiological point of view, the question remains whether a fact passive in its very nature, as the reflex is, can be the linchpin of all psychic activity.
Behaviorism, as well as certain canons of Wundtian psychology, were vigorously attacked by the school of form (Gestaltpsychologie) founded in Germany by Max Wertheimer (1880-1943), Wolfgang Köhler and Kurt Koffka, and then transplanted to America, also as a consequence of the racial persecution that forced these scholars to leave Germany.
It is first of all a vigorous reaction against psychological atomism, and it affirms 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 into a unity, without falling into the fictitious analyses of introspectionism, nor renouncing, as behaviorism has done, the value of introspection. When we see a square, it is the square that we see: and not the sum of its elements, that is, of the sensations corresponding to the elements into which we think we can break it down. We see the "form" of the square, even when the elementary "sensations" of which it should be constituted change: that is, we see a square whether it is outlined by four perpendicular black lines, or colored, or dotted, or even is suggested by four isolated points in a characteristic mutual relationship. Gestalt psychology has contributed validly to the progress of certain problems of psychology, especially those of perception.
A mention should not be omitted of the hormic psychology of W. Mac Dougall (1871-1937), which emphasizes as the distinctive character of the psychic fact the active pursuit of an end or conclusion, and gives great importance to the study of the instincts. From hormic psychology and from the psychoanalytic schools (v. PSICANALISI) a strong impulse has been given to the study of affectivity and motivation.
"Mental tests," or "mental reactives" (as De Sanctis proposed to call them), are tests (whether in the form of a question or of a problem or of a task to be performed) devised in a simple and rapid way, to bring to light particular psychic functions or characters and to evaluate their efficiency, from the comparison among the performances of different individuals.
Mental reactives require a long work of preparation and trial on a large number of subjects to allow a measure, even if only relative, of different psychic activities. In this sense they are to be considered as "products" and "instruments" of experimental psychology.
It would seem that the great number of schools and the great variety of tendencies within psychology indicate its inadequacy for the task. This is in part true; but it is also true that, if many are the paths by which psychological problems are studied, and if not all of them reach the goal, all have brought their contribution to a science in rapid development, whose importance imposes itself more each day. Note, however, how experimental psychology, in the strict and broad sense of the expression, has established itself as the naturalistic study of the human factor. With this limitation it would wish deliberately to avoid problems of a philosophical order, but it cannot always do so, and often smuggles in philosophical conceptions, which must be evaluated and discussed. This is why it is to be hoped that psychology be flanked by a philosophy that understands its problems, accepts its results and frames them in a total conception of man.