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Historical and conceptual background: Gestalt theory

Johan Wagemans

Laboratory of Experimental Psychology University of Leuven

To appear in: Oxford Handbook of Perceptual Organization Oxford University Press Edited by Johan Wagemans

Acknowledgments I am supported by long-term structural funding from the Flemish Government (METH/08/02).

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1. Introduction In 2012, it was exactly 100 years ago since Wertheimer published his paper on phi-motion (1912)― perception of pure motion, that is, without object motion―which many consider to be the start of Gestalt psychology as an important school of thought. The present status of Gestalt psychology is quite ambiguous. On the one hand, most psychologists believe that the Gestalt school has died with its founding fathers in the 1940s, after some devastating empirical findings regarding electrical field theory in the 1950s, or as a natural decline because of fundamental obstacles against further progress and stronger theoretical and experimental frameworks arising and gaining dominance since the 1960s and 1970s (e.g., cognitive science, neuroscience). On the other hand, almost all psychology textbooks still contain a Gestalt-like chapter on perceptual organization (although often quite detached from the other chapters), and new empirical papers on Gestalt phenomena are published on a regular basis. I believe that Gestalt psychology is quite relevant to current psychology in several ways. Not only has contemporary scientific research continued to address classic questions regarding the emergence of structure in perceptual experience and the subjective nature of phenomenal awareness (e.g., visual illusions, perceptual switching, context effects), using advanced methods and tools that were not at the Gestaltists’ disposal. I also believe that the revolutionary ideas of the Gestalt movement can still function as a dissonant element to question some of the fundamental assumptions of mainstream vision science and cognitive neuroscience (e.g., elementary building blocks, channels, modules, information-processing stages). Indeed, much progress has been made in the field of non-linear dynamical systems, theoretically and empirically (e.g., techniques to measure and analyze cortical dynamics), which allows us to surpass some of the limitations in old-school Gestalt psychology as well as in mainstream vision research. To be able to situate all the reviews of a century of theoretical and empirical work on perceptual organization in this handbook against the background of this special position of Gestalt psychology, I will first introduce the key findings and ideas in old-school Gestalt psychology, its historical origin and development, rise and fall. I will sketch only the main lines of thought and major steps in the history. For a more extensive treatment of the topic, I refer to Ash (1995). 2. Early history of Gestalt psychology 2.1. Wertheimer’s discovery of phi motion (1912) What Max Wertheimer1 discovered was not the phenomenon of apparent motion―that is, the perception of motion between two stationary light sources flashing on and off at given intervals, but a special case. It concerned perceived motion without seeing an object moving, so rather than the standard case of seeing an object first at location a, and then, after an interval φ, at location b (i.e., apparent motion from a to b), here it concerned pure φ, without a percept of a or b. The general phenomenon of apparent motion had already been observed as early as 1850 by the Belgian physicist Joseph Platteau, Sigmund Exner (one of Wertheimer’s teachers) had obtained it with two electric sparks in 1875, and in 1895 the Lumière brothers had patented the “cinématographe”, an invention based on the phenomenon. (For an excellent discussion of its historical importance, see Sekuler, 1996; for a demonstration of the phenomenon and for a review of its misrepresentation in later sources, see Steinman, Pizlo, & Pizlo, 2000; for a recent review of apparent motion, see Herzog & Ogmen, this volume.)

1 The names in boldface are the historically most important Gestalt psychologists, whose photograph and short biographical

notes appear in figures.

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According to a famous anecdote, Wertheimer came to the idea for this experiment when he saw alternating lights on a railway signal, while on his way from Vienna to the Rhineland for vacation in the autumn of 1910. He got off the train in Frankfurt, bought a toy stroboscope and began constructing figures to test the idea in his hotel room. He then called Wolfgang Köhler, who had just begun to work as an assistant at the Psychological Institute there. Köhler provided him with lab space and a tachistoscope with a rotating wheel, especially constructed by Schumann (the Institute’s Director) to study successive expositions. According to the conventional view of apparent motion perception, we see an object on several positions successively and something is then added subjectively. If this were correct, then an object would have to be seen moving, and at least two positions, the starting and end points, would be required to produce seen motion. Neither of these conditions held in the case of phi motion. By systematically varying the form, color, and intensity of the objects as well as the exposure intervals and stimulus distances between them, and by examining the role of attitude and attention, Wertheimer was able to refute all of the current theories of motion perception. In the standard experiment, a white strip was placed on a dark background in each slit, while the rotation speed of the tachistoscope wheel was adjusted to vary the time required for the light to pass from one slit to the next. Above a specific threshold value (~ 200 ms), observers saw the two lines in succession. With much faster rotation (~ 30 ms), the two lines flashed simultaneously. At the so-called optimal stage (~ 60 ms), observers saw a definite motion that could not be distinguished from real motion. When the time interval was decreased slightly below 60 ms, after repeated exposures, observers saw motion without a moving object. Although he used only three observers (Wolfgang Köhler, Kurt Koffka, and Koffka’s wife Mira), he was quite confident in the validity of the results: The characteristic phenomena appeared in every case unequivocally, spontaneously, and compellingly. After confirming Exner’s observation that apparent motion produces negative after-images in the same way as real motion, Wertheimer proposed a physiological model based on some kind of physiological short circuit, and a flooding back of the current flow, creating a unitary continuous whole-process. He then extended this to the psychology of pure simultaneity (for the perception of form or shape) and of pure succession (for the perception of rhythm or melody). This extension was the decisive step for the emergence of the Gestalt theory. 2.2. Implications: Gestalt theory The phi phenomenon was simply a process, a transition (“an across in itself”) that cannot be composed from the usual optical contents of single object percepts at two locations. In other words, perceived motion was not just added subjectively after the sensory registration of two spatio-temporal events (or snapshots) but something special with its own phenomenological characteristics and ontological status. Indeed, based on the phi phenomenon, Wertheimer argued that not sensations but structured wholes or Gestalten are the primary units of mental life. This was the key idea of the new and revolutionary Gestalt theory. The notion of “Gestalt” was already introduced into psychology by Christian von Ehrenfels in his essay “On Gestalt qualities” (1890), one of the founding document of Gestalt theory. Because we can recognize two melodies as identical even when no two notes in them are the same, he argued that these forms must be something more than the sum of the elements. They must have, what he called “Gestalt quality,” a characteristic which is immediately given, along with the elementary presentations that serve as its fundament, dependent upon the objects but rising above them. In his discussion of the epistemological implications of his discovery of phi motion, Wertheimer went considerably beyond von Ehrenfels’s notion of one-sided dependence of Gestalt qualities on sense data, which made wholes more than the sums of their parts, while maintaining the parts as foundations (“Grundlage”). He claimed instead that specifiable functional relations exist which

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decide what will appear or function as a whole and as parts (i.e., two-sided dependency). Often the whole is grasped even before the individual parts enter consciousness. The contents of our awareness are mostly not summative but constitute a particular characteristic “togetherness”, a segregated structure, often comprehended from an inner center, to which the other parts of the structure are related in a hierarchical system. Such structures were called “Gestalten,” which are clearly different from the sum of the parts. They were assumed to arise on the basis of continuous whole-processes in the brain rather than associated combinations of elementary excitations. With this significant step, Wertheimer separated himself from the Graz school of Gestalt psychology, represented by Alexius Meinong, Christian von Ehrenfels, and Vittorio Benussi, who maintained a distinction between sensation and perception, the latter produced on the basis of the former (Boudewijnse, 1999; for further discussion, see Albertazzi, this volume). The Berlin school, represented by Max Wertheimer, Kurt Koffka, and Wolfgang Köhler, went further and considered a Gestalt as a whole in itself, not founded on any more elementary objects. Instead of perception being produced from sensations, a percept organizes itself by mutual interactions, a percept arises non-mechanically by an autonomous process in the brain. The Berlin school also did not accept a stage theory of perception, and hence distinguished itself from the Leipzig school, represented by Felix Krüger, Friedrich Sander and Erich Jaensch, in which the stepwise emergence of Gestalten (“Aktualgenese” or “microgenesis”) played a central role (see van Leeuwen, this volume). Although the Berlin theorists adhered to a non-mechanistic theory of causation and did not want to analyze the processes into stages, they did believe that the critical functional relations in the emergence of Gestalts could be specified by several so-called Gestalt laws of perceptual organization. They were inspired by Johann Wolfgang Goethe, who introduced the notion of “Gestalt” to refer to the self-actualizing wholeness of organic forms. For Goethe, the functional role of an organism’s parts is determined by a dynamic law inherent in the whole, filled with comings and goings, but not mechanical operations. The ideal end results of these dynamic interactions are classically proportioned forms, signs of balance, lawfulness, and order realizing itself in nature, not imposed upon it by an ordering mind. But at the same time, the Berlin theorists wanted to give this notion a naturalistic underpinning to avoid the anti-physicalist attitude of Felix Krüger’s holistic psychology (“Ganzheitspsychologie”), which was characteristic of the Leipzig school.

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Figure 1. Three key figures before the start of the Berlin school of Gestalt psychology.

They were all trained in experimental psychology by Carl Stumpf in Berlin, who strongly believed in the immediately given as the basis of all science (cf. Brentano) and in the lawfulness of the given, which included not only simple sensations of color or tone, but also spatially and temporally extended and distributed appearances, as well as relations among appearances, such as similarity, fusion, or gradation. The laws of these relations are neither causal nor functional but immanent structural laws according to Stumpf. It is these structural laws that the Berlin school was about to uncover. Already at a meeting of the Society for Experimental Psychology in 1914, Wertheimer announced that he had discovered a general kind of Gestalt law, a tendency towards simple formation (“Gestaltung”), called the law of the Prägnanz of the Gestalt. Unfortunately, the promised publication did not appear until 1923, although the experiments were essentially from the years 1911-1914. 3. Further developments of Gestalt psychology Although Max Wertheimer could be considered as the founding father of the Berlin school, his younger colleagues, Kurt Koffka and Wolfgang Köhler were just as important in its further development. The initial period was characterized by explaining how radically revolutionary the new Gestalt theory was. For instance, in his essay “On unnoticed sensations and errors of judgment,” Köhler (1913) criticized the tendency shared by Helmholtz and Stumpf to regard perceptions and sensations as unambiguously determined by peripheral stimulation as much as possible. In the same spirit, Koffka (1914) argued that a complete transformation of perceptual theory had occurred because sensation was now understood from the point of view of perception, instead of the other way around. Koffka clarified this position in a 1915 polemic against Vittorio Benussi, a vehement proponent of the Graz school, which became the first full statement of Gestalt theory as a

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psychological system. The fundamental break with the Graz school was a radical revision in the meaning of the world “stimulus.” In this new conception, this word no longer referred to a pattern of excitations on a sense organ, as it had throughout the 19th century, but to real objects outside of and in functional relation to a perceiving and acting organism. Benussi, being trained in ontology by Meinong (see Albertazzi, this volume), insisted on maintaining the distinction between stimulation and perception. In fact, he distinguished sensory responses from different kinds of presentations (“Vorstellungen”), for instance, elementary ones and perceived Gestalts, the latter being produced from the former in different phases (Albertazzi, 2001). Koffka instead cared only about psychological experience, not in the analysis of the building blocks or processing phases or stages. After this dispute, Koffka went further to expand the Gestalt notion from perception to motor action, which became considered as an organized whole process too, with a structure that cannot be reduced to a bundle of reflexes. As Koffka boldly asserted, “there are real Gestalten.” After this initial period, two major developments are generally considered as highlights in the history of Gestalt psychology: Köhler’s “physical Gestalten” (1920) and Wertheimer’s Gestalt laws” (1923).

Figure 2. The triumvirate of the Berlin school of Gestalt psychology.

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3.1. Köhler’s “physical Gestalten” (1920) and isomorphism In 1920, Wolfgang Köhler published “Die physischen Gestalten in Ruhe und im stationären Zustand,” in which he extended the Gestalt concept from perception and behavior to the physical world, and thus attempted to unify holism and natural science in a way that was very distinct from the holistic psychology of the Leipzig school. Inspired by work of his friends in physics (Albert Einstein, James Clerk Maxwell and Max Planck), Köhler proposed to treat the neurophysiological processes underlying Gestalt phenomena in terms of the physics of field continua rather than that of particles or point-masses. In a well-insulated ellipsoid conductor, for instance, the density of charge is greatest at the points of greatest curvature and smallest at the points of least curvature. The distribution of charge in such a conductor thus depends on the shape of the conductor (i.e., the system’s topography), but is independent of the materials used or the total quantity of charge involved. In such physical systems, which he called “strong Gestalten,” the mutual dependence among the parts is so great that no displacement or change of state can occur without influencing all the other parts of the system. Köhler then showed that stationary electric currents, heat currents, and all phenomena of flow are strong Gestalten in this sense. These he distinguished from what he called “weak Gestalten,” which are not immediately dependent on the system’s topography (e.g., a group of isolated conductors connected by fine wires). Weak Gestalten are satisfactorily treated with simultaneous linear algebraic functions whereas strong Gestalten must be described either with integrals or with series of partial differential equations. In addition, Köhler tried to construct a specific testable theory of brain processes that could account plausibly for perceived Gestalten in vision. In short, he presented visual Gestalten as the result of an integrated Gestalt process in which the whole optic sector from the retina onward is involved, including transverse functional connections among conducting nerve fibers. The strongest argument for proposing that the brain acted as a whole system was the fact that Gestalts were found at many different levels: seen movement, stationary Gestalten, the subjective geometry of the visual field, motor patterns, and insightful problem solving in animals. This theory had dramatic consequences. For Gestalt theory, the 3-D world that we see is not constructed by cognitive processes on the basis of insufficient sensory information. Rather, the lines of flow are free to follow different paths within the homogeneous conducting system, and the place where a given line of flow will end in the central field is determined in every case by the conditions in the system as a whole. In modern terms, Köhler has described the optic sector as a self-organizing physical system. Based on this general theory of physical Gestalten and this specific theory of the brain as a self-organizing physical system within which experienced Gestalten emerge, Köhler then came to the postulate of “psychophysical isomorphism” between the psychological facts and the brain events that underlie them. With this he meant, as Wertheimer before him, functional instead of geometrical similarity, so it is not the case that brain processes must somehow look like perceived objects. Köhler also insisted that such a view does not prescribe featureless continuity in the cortex but is perfectly compatible with rigorous articulation. He conceded that experiments to establish the postulated connections between experienced and physical Gestalten in the brain were nearly unthinkable at the time from a practical point of view but that this should not detract from its possibility in principle. In the meantime, Köhler tried to show that his postulate was practical by applying it to the figure-ground phenomena first reported by Edgar Rubin in 1915. Decades later, after Köhler emigrated to the U.S., he attempted to carry out such experiments (see Section 4.3.1 below). All of the examples Köhler had offered of physical Gestalten were equilibrium processes, such as the equalization of osmotic pressures in two solutions by the migration of ions across the boundary between them, or the spontaneous distribution of charged particles on conductors. As Maxwell’s field diagrams showed, we could predict from a purely structural point of view the movements of

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conductors and magnets, and the groupings of their corresponding fields, in the direction of increased evenness of distribution, simplicity, and symmetry. This was a qualitative version of the tendency (described by Planck) of all processes in physical systems left to themselves, to achieve the maximum level of stability―which is synonymous with the minimum expenditure of energy―allowed by the prevailing conditions. Köhler explained this tendency―based on the second law of thermodynamics or the entropy principle―with an example from hydrostatics. When dipping wire frames of different forms into a solution of water and soap, one can see that such physical systems tend toward end states characterized by the simplest and most regular form, a tendency which Köhler called the tendency to the simplest shape or toward “the Prägnanz of the Gestalt,” alluding to the principle already enunciated but rather vaguely by Wertheimer in 1914. 3.2. Wertheimer’s “Gestalt laws” (1923) Around the same time, Max Wertheimer developed his Gestalt epistemology further and he outlined the research practice of experimental phenomenology that was based on it. He first stated the principles publically in a manifesto published in Volume 1 of Psychologische Forschung in 1922: “Untersuchungen zur Lehre von der Gestalt, I: Prinzipielle Bemerkungen.” There he called for descriptions of conscious experience in terms of the units people naturally perceive, rather than the artificial ones assumed to be in agreement with proper scientific method. Implicit in conventional psychological descriptions is what he called a mosaic or bundle-hypothesis―the assumption that conscious experience is composed of units analogous to physical point-masses or chemical elements. By making this assumption, psychologists constrain themselves to link contents of consciousness in a piecemeal fashion, building up so-called higher entities from below with the help of associative connections, habits, hypothesized functions and acts or a presupposed unity of consciousness. In fact, however, such “and-sums,” as Wertheimer delightfully called them, appear only seldom (i.e., under certain characteristic, limited conditions) and perhaps even only in approximation. Rather, the given is in itself formed (“gestaltet”): Given are more or less completely structured, more or less determinative wholes and whole-processes, each with its own inner laws. The constitution of parts in such wholes is a very real process that changes the given in many ways. In research, therefore, proceeding “from below to above” (“von unten nach oben”) would not be adequate but rather the way “from above to below” (“von oben nach unten”) is often required. Note that this twin-set of concepts is not what we nowadays indicate by “bottom-up” and “top-down,” respectively. The latter notions refer more to “sense-driven” and “concept-driven,” respectively, and in this regard Gestalts are more sense-driven or bottom-up, by being based on autonomous tendencies, not depending on previous knowledge, expectations, voluntary sets, observer intentions, etc. Wertheimer offered evocative examples of what he meant by working “from above” instead of “from below” in 1923, when he presented a full account of the “Gestalt laws” or tendencies that he had announced in 1914. The perceptual field does not appear to us as a collection of sensations with no meaningful connection to one another, but is organized in a particular way, with a spontaneous, natural, normally expected combination and segregation of objects. Wertheimer’s (1923) paper was an attempt to elucidate the fundamental principles of that organization. Most general was the law of Prägnanz. This states, in its broadest form, that the perceptual field and objects within it take on the simplest and most impressive structure permitted by the given conditions2. More specific were the laws of proximity, similarity, closure, and good continuation. These laws are discussed in more detail

2 The German word “Prägnanz” is derived from the verb “prägen,”―to mint a coin. Hence, by describing the principle of

Prägnanz as the tendency towards the formation of Gestalten which are as regular, simple, symmetric (“ausgezeichnet”, according to Wertheimer’s term) as possible given the conditions, a connection is made to the notion of “Gestalt” as the characteristic shape of a person or object, or the likeness of a depiction to the original (which was the colloquial German meaning before Goethe and von Ehrenfels assigned it its more technical meaning as we know it today). For this reason, “Prägnanz” has often been translated as “goodness.”

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in many of the chapters to follow (e.g., Brooks, this volume; Kubovy, this volume) but here I will attempt to remove some common misunderstandings about them. Wertheimer was not the first to outline these principles. Indeed, Schumann (1900) and Müller (1904) had mentioned the existence of such tendencies in perception much earlier, but they had said only that these tendencies make the perception of stimulus patterns easier (for a recent review of this history, see Vezzani, Marino, & Giora, 2012). Wertheimer, instead, maintained that they are determinative for the perception of figures and for form perception in general. Wertheimer also recognized the powerful effect of observers’ attitudes and mental set, but by this he understood primarily a tendency to continue seeing the pattern initially seen, even under changed conditions. Nor did he deny the influence of previous experience, such as habit or drill, but he insisted that these factors operate only in interaction with the autonomous figurative forces at work in the immediate situation. Moreover, Wertheimer did not exclude quantitative measurements from his program but he made it clear that such measurements should be undertaken only in conjunction with detailed phenomenological description to discover what ought to or meaningfully could be measured. In fact, Wertheimer had not elaborated a finished theory but had presented an open-ended research program. He converted the culturally resonant term “Gestalt” and the claim that the given is “gestaltet” into a complex research program to discover the principles of perceptual organization in both its static and dynamic aspects. 4. The rise and fall of Gestalt psychology 4.1. Significant expansion in 1920-1933 The development of Wertheimer’s open-ended research program was significantly facilitated by the establishment of a real Gestalt school. The founding fathers acquired professorships at major universities in Germany (Koffka in Giessen in 1919, Köhler in Berlin in 1922, and Wertheimer in Frankfurt in 1929), and they founded the journal Psychologische Forschung in 1921. Together they supervised a large number of PhD theses, which amounted to unpacking the empirical and theoretical implications of Wertheimer’s (1923) paper. The initial steps were usually disarmingly simple demonstrations. Friedrich Wulf (1922) had already attempted to demonstrate the applicability of the law of Prägnanz to memory before Wertheimer’s paper appeared. Wilhelm Benary (1924) employed an experiment devised by Wertheimer to test the law of Prägnanz on a phenomenon of brightness contrast, and introduced the principle of “belongingness”. Following up on Koffka’s (1923) experimental proof that achromatic (black-white) color contrast does not depend on the absolute amount of available light but on what he called “stimulus gradients,” Susanne Liebmann (1927) pursued this line of investigation further by relating chromatic color to principles of organization, specifically to the figure-ground phenomenon originally studied by Edgar Rubin (1915). In 1923, Adhemar Gelb and Ragnar Granit had already demonstrated that thresholds for seeing a given color were lower when it was regarded as figure than when it was seen as background. Perhaps the most spectacular demonstration of the fundamental role of organization in perception came from Wolfgang Metzger’s (1930) research with a homogeneous “Ganzfeld” (i.e. a way to stimulate an observer’s visual field uniformly and remove all structure from it). Kurt Gottschaldt (1926, 1929) tested Wertheimer’s claim that habit and drill are secondary to organization, and showed that so-called “embedded figures” were not found more easily in a group of subjects that had seen them in isolation 520 times compared to a group of subjects that had seen them only 3 times. Herta Kopfermann (1930) explored the role of the Gestalt tendencies in the appearance of plane figures as 3-D.

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In research on motion and organization, there was a progression from relatively simple demonstration experiments to more complicated apparatus-driven designs. Josef Ternus (1926) asked what kinds of perceived motion are needed to experience “phenomenal identity”, i.e. unified moving objects. In a spectacular demonstration of both Prägnanz and depth effects in motion perception, Wolfgang Metzger (1934) used an ingenious setup of his own design, which he called a rotating light-shadow apparatus, yielding what is now known as the “kinetic depth effect” (Wallach & O’Connell, 1953; see also Bressan et al., this volume). In-between Ternus and Metzger, Karl Duncker (1929) altered both the research modus and the terms of discourse about these issues in his research on what he called “induced motion.” In this work, he combined some remarks from Wertheimer’s 1912 paper about the role of the observer’s position in motion terminology with terminology from relativity theory in physics (borrowing the term “egocentric frames of reference” from Georg Elias Müller). More parametric follow-up studies were carried out by J. F. Brown (1931a,b,c) and Hans Wallach (1935). For recent reviews of motion perception in the Gestalt tradition, see Herzog & Ogmen, this volume; Bruno & Bertamini, this volume).

Figure 3. The second generation of Gestalt psychologists who stayed in Germany.

In the meantime, Gestalt thinking also affected research on other sense modalities (e.g., binaural hearing by Erich von Hornbostel), on learning and memory (e.g., Otto von Lauenstein and Hedwig von Restorff, both working under Köhler in search for physiological trace fields), and on thought (e.g., Karl Duncker’s work on stages in productive thinking, moving away from Wertheimer’s work on re-centering and Köhler’s work on sudden insight). At first sight, Gestalt theory seemed to develop rather consistently, from studying the fundamental laws of psychology first under the simplest

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conditions, in rather elementary problems of perception, and then including more and more complex sets of conditions, turning to memory, thinking, and acting. At the same time, however, the findings did not always fit the original theories, which constituted serious challenges to the Gestalt framework. This was even more true for applications of Gestalt theory to action and emotion (by Kurt Lewin), to neuropathology and the organism as a whole (by Adhemar Gelb and Kurt Goldstein), to film theory and aesthetics (by Rudolf Arnheim). In sum, the period from 1920 to 1933 marked the high point but not the end of Gestalt psychology’s theoretical development, its research productivity, and its impact on German science and culture. At the same time, Gestalt theory had some impact on research in the U.S. as well, mainly owing to Kurt Koffka (e.g., the notion of vector field inspired some interesting empirical work published in the American Journal of Psychology; see Brown & Voth, 1937; Orbison, 1939). Reviews of Gestalt psychology appeared in Psychological Review on a regular basis (e.g., Helson, 1933; Hsiao, 1928), a comprehensive book on state-of-the-art Gestalt psychology was published as early as 1935 (Hartmann, 1935), and three years later Ellis’s (1938) influential collection of translated excerpts of core Gestalt readings made some of the original sources accessible to a non-German-speaking audience. Already in 1922, at Robert Ogden’s invitation, he had published a full account of the Gestalt view on perception in Psychological Bulletin. He emigrated to the U.S. mainly for professional reasons, after accepting a job at Smith College in 1927, long before such a step became politically necessary, as for many other Gestaltists. 4.2. From 1933 to World War II 4.2.1. General situation In this period, many of the psychology professors at German universities lost their posts because of their Jewish origin, and many emigrated to the U.S. taking on new positions there (e.g., Wertheimer at the New School for Social Research in New York in 1933, Kurt Lewin at Cornell University in 1934). Wolfgang Köhler, who was not a Jew, protested frequently and resisted for a long time but then accepted a position at Swarthmore College in 1935. Rudolf Arnheim first moved to Rome, then to England, and finally to the U.S. Others stayed, like Wolfgang Metzger, Kurt Gottschaldt, and Edwin Rausch. Much has been said and written about the relationships between the Gestalt psychologists at German universities during this period and the political attitudes and acts of the Nazi regime (e.g., Mandler, 2002; Prinz, 1985; Wyatt & Teuber, 1944), which clearly went beyond pragmatic survival behavior in some cases (e.g., Erich Jaensch’s empirical anthropology). I will focus only on the scientific contributions and impact on Gestalt psychology here. Compared with the flourishing previous period, the institutional conditions for Gestalt-theoretic research in the Nazi period were considerably reduced, but it was possible to continue at least some of the lines of work already begun.

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Figure 4. The second generation of Gestalt psychologists who emigrated to the U.S.

After the appearance of a pioneering monograph, “Thing and Shadow,” by Vienna psychologist Ludwig Kardos in 1934, Gestalt researchers pursued the issue further, for instance, examining spatial effects of brightness contrast or applying Duncker’s work on induced motion to brightness perception. Perhaps the most interesting research in this period was Erich Goldmeier’s study of judgment of similarity in perception, published in 1937. His starting point was the problem originally raised by Harald Höffding and Ernst Mach in the 1890s: How do we know an object or features is the same as one we have seen before; or, how do we recognize forms as the same even when they are presented in different positions? In Goldmeier’s view, his results showed that what is conserved in perceived similarity are the phenomenal function of the parts within the perceived whole or the agreement of those qualities which determine the phenomenal organization of the field in question. He found that similarity of form properties was best preserved by proportional enlargement, while it was best to keep their measure constant for the similarity of material properties. Around the same time, two major developments in Gestalt theory occurred that have generally been ignored outside Germany: Edwin Rausch’s monograph on “summative” and “nonsummative” concepts (1937) and Wolfgang Metzger’s theoretical masterpiece, “Psychology.” 4.2.2. Edwin Rausch Rausch’s aim was to develop a more systematic account of the concepts of part and whole, with the aid of innovations in symbolic logic pioneered by Bertrand Russell, Rudolf Carnap, Giuseppe Peano, and others. Despite some conceptual difficulties, Rausch’s work had an immediate impact (although not outside Germany). In an analysis of the Gestalt concept published in 1938, the emigrated logical empiricist philosophers Kurt Grelling and Paul Oppenheim attempted, in explicit agreement with

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Rausch, to clarify the notions of sum, aggregate, and complex, in a way that would elucidate the actual content of von Ehrenfels’s and Köhler’s Gestalt concepts and differentiate them from one another. Such analyses could have saved the Gestalt concept from the recurring charge of vagueness, if they had not been ignored at the time. However, because they presupposed an empiricist standpoint, Grelling and Oppenheim failed to engage the epistemological core of Gestalt theory―Wertheimer’s claim that Gestalten are immanent in experience, not categories imposed upon experience. For a thorough discussion, see Smith (1988). 4.2.3. Wolfgang Metzger After Wertheimer’s dismissal, Wolfgang Metzger became de facto head of the Frankfurt Institute, and he was able to maintain his major lines of research by taking a collaborative stance regarding the Nazi regime. In 1936, Metzger published a synoptic account of research on the Gestalt theory of perception entitled “Gesetze des Sehens” (“Laws of seeing”), since reissued and vastly expanded three times, and translated in 2006. Even more important from a theoretical perspective was Metzger’s (1941) book, “Psychology: The development of its fundamental assumptions since the introduction of the experiment.” The original title was “Gestalt theory,” but he changed it to make clear that his aim was to make Gestalt theory the conceptual foundation of general psychology. To achieve this, he employed a strategy rather different from that of Kurt Koffka’s major text of the same period, “Principles of Gestalt psychology” (1935), which he wrote in the U.S. Koffka wrote mainly against positivism (materialism, vitalism, E. B. Titchener, and behaviorism), while Metzger wrote mainly against non-positivists who opposed natural-scientific psychology, or those who criticized Gestalt theory for its alleged lack of biological orientation. Koffka structured his textbook in a standard way, enunciating general Gestalt principles and then applying them to standard topics, beginning with a detailed account of visual perception, proceeding to a critical reworking of Lewin’s work on action and emotion, incorporating research by Wertheimer, Duncker, and Köhler on thinking, learning, and memory, and finally applying Gestalt principles to personality and society. Metzger, however, presented not a conventional textbook but an attempt to revise the theoretical presuppositions of modern psychology. His hope was that this approach would put an end to the misunderstanding that Gestalt theory was merely a psychophysical theory that seeks to explain the entire psychical realm at any price by means of known physical laws. The assumption that he questioned was that real causes of events must be sought only behind, not within phenomena. The strategy he employed was to convert Gestalt principles into metatheoretical concepts and depict them as names for intrinsic natural orderings. His chapter headings were therefore not standard textbook topics but rather terms from Gestalt-type phenomenology of perception, such as qualities, contexts, relational systems, centering, order, and effects. Of particular interest and originality was Metzger’s discussion of psychological frames of reference or relational systems. The presupposition under attack was that of psychological space as a collection of empty, indifferent locations. Instead, he argued that all location in space and time, as well as all phenomenal judgment, is based on relations in more extended psychological regions. To explain why relatedness is ordinarily hidden from immediate experience and that in ordinary life the absolute quality of things appears their most outstanding characteristic, he recognized that Wertheimer’s application of the word Gestalt to both seen objects and the structure of the perceptual field as a whole required modification. Specifically, Metzger acknowledged that the characteristic membership of regions in a relational system is correlative to but different from the relation of parts to their whole. A true part is in a two-sided relation with its whole; a part of a relational system is in a one-sided, open-ended relation with the system as a whole. A thing in space, for example, leaves no gap on removal but a piece of a puzzle does. With this modification, Metzger could get a conceptual grip

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on the myriad tendencies he and his students had to suppose to account for the results that could not be explained by simple analogies to Wertheimer’s Gestalt laws. To cover these, he posited a principle of branched effects, which stated that wherever the experienced field had more dimensions than the stimulus field, an infinite variety of experiences can emerge from the same stimulus constellation, depending on the structure of the environmental situation and the state of the perceiving organism. With this principle, it became possible to portray processes considered psychological, such as attention and attitudes, as relational systems, and thus bring them into purview of Gestalt theory. It also implied the possibility of extending Gestalt theory from perception and cognition to personality and the social realm.

Metzger’s book was an eloquent statement of Gestalt principles and their conceptual foundations but it was problematic both as a summary of what Gestalt theory had achieved and as a response to its critics. Unexperienced entities as Gestalt centers of gravity are not causes of what we perceive but part of a larger, self-organizing Gestalt context which included the given. In addition, the organism-environment nexus is a relational system, not a Gestalt. In this way, Metzger had reached Gestalt theory’s conceptual limits for which he tried to compensate in part with terminological concessions to Leipzig’s holistic psychology. Like that of Koffka from the same period, Metzger’s book considerably expanded the conceptual range of Gestalt theory. Precisely that elaboration gave Gestalt theory a new, more finished look―the look of a system―during the 1930s, which it had not had before. However, because it now lacked the necessary institutional base in Germany (e.g., very few PhD students), the book did not have a major impact on the field as a whole in this period. Hence, this was at the same time the culmination of Gestalt theory and the start of its decline. 4.3. After World-War II 4.3.1. In the U.S. After their emigration to the U.S., the founding fathers of Gestalt psychology did not perform much new experimental work. Instead, they mainly wrote books in which they outlined their views (e.g., Koffka, 1935; Köhler, 1940; Wertheimer, 1945). The big exception was Köhler who had taken up physiological psychology, using EEGs and other methods in an attempt to verify his isomorphism postulate directly. Initially, his results with Hans Wallach on so-called figural aftereffects appeared to support his interpretation in terms of satiation effects of direct cortical currents (Köhler & Wallach, 1944). Afterwards, he was able to directly measure cortical currents―as EEG responses picked up from electrodes at the scalp―which flow in directions corresponding to some bright objects moving in the visual field (Köhler & Held, 1949). However, soon after that breakthrough, Lashley and colleagues (Lashley, Chow, & Semmes, 1951) performed a more critical test of Köhler’s electric field theory (and its underlying postulate of isomorphism). If the flows of current picked up from the scalp in Köhler and Held’s experiments were supposed to reflect the organized pattern of perception and not merely the applied stimulation, and if that pattern of perception would result from a global figure-field across the whole cortex, a marked alteration of the currents should distort visual figures and make them unrecognizable. By inserting metallic strips and metal pins in large regions of the visual cortex of rhesus monkeys, Lashley et al. could short-circuit the cortical currents. Surprisingly, the monkeys could still perform the learned shape discriminations, which demonstrated that global cortical currents were not necessary for pattern perception. In subsequent experiments, Sperry and colleagues (Sperry, Miner, & Myers, 1955) performed extensive subpial slicing and dense impregnation with metallic wires across the entire visual cortex of cats, and showed that these animals too could still perform rather difficult shape discriminations (e.g., between a prototypical triangle and several different ones with small distortions). Together, these two studies effectively ruled out electrical field theory as an explanation of cortical integration, and therefore removed the empirical basis of isomorphism between cortical flows of current and organized patterns of perception.

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Of course, Köhler (1965) reacted to these experiments. Lashley’s experiments he rejected because he thought that the inserted gold foils had probably depolarized at once, which would have made them incapable of conducting, deflecting the cortical currents, and thus disturbing pattern vision. Sperry’s results he found too good to be acceptable as reliable evidence. Based on the many deep cuts in large parts of the visual cortex, the cats should have been partially blind when they were tested, and yet they made very few mistakes on these difficult discrimination tasks. Because the learning was initially already so difficult (forcing reliance on local details), the animals probably learned to react not only to visual cues associated with the prototypical test figure (which was repeated over and over again) but to other, non-visual cues (e.g., smell) as well. The necessary methodological precautions to rule out these alternative cues (e.g., changing all objects from trial to trial) had not been taken. However, Köhler’s rather convincing counterarguments and suggestions for further experiments were largely ignored, and for most scientists at the time (especially, for physiological psychologists), the matter was closed and electrical field theory, which was one of the pillars of Gestalt psychology’s scientific basis, was considered dead and buried. 4.3.2. In Germany In Germany, Gestalt psychology did not make much progress anymore after World-War II. Under Metzger’s guidance, the Psychological Institute in Münster became the largest in Western Germany in 1965. This had much to do with Metzger’s public defense of experimental psychology, presenting Gestalt theory as a humanistic worldview based on experimental science. Metzger also worked steadily to develop links with American psychologists but that involvement did not actually rehabilitate the Gestalt position because in doing so he conceded much to conventional views of machine modeling as causal explanation. In contrast to Metzger’s broad range and willingness to address nonacademic audiences, Rausch devoted nearly all of his publications to extremely exact phenomenological illumination and conceptual clarification of issues from Gestalt theory. For instance, in a major essay on the problem of qualities or properties in perception (Rausch, 1966), he provided an exhaustive taxonomy of Gestalt qualities (in von Ehrenfels’s sense) and whole qualities (in Wertheimer’s sense) and he argued that whether a given complex is a Gestalt or not is not a yes-or-no decision but a matter of gradations on a continuum. Gottschaldt focused mainly on clinical psychology. 4.3.3. Elsewhere While Gestalt psychology declined in the English-speaking world after World-War II, Italy was a stronghold of Gestalt psychology. For instance, Wolfgang Metzger, the most important and orthodox Gestalt psychologist in Germany at the time, dedicated his “Gesetze des Sehens” (3rd ed., 1975) to the memory of his ‘Italian and Japanese friends’. Among his friends were Musatti, Metelli, and Kanizsa―three major figures in Italian psychology. In spite of being Benussi’s student and successor (from the Graz school), Cesare Musatti was responsible for introducing the Berlin school’s Gestalt theory in Italy and training important students in this tradition―most notably Metelli and Kanizsa, whose contribution continues to be felt today (see Bertamini & Casati, this volume; Bressan et al., this volume; Bruno & Bertamini, this volume; Gerbino, this volume; Kogo & van Ee, this volume; van Lier & Gerbino, this volume). Fabio Metelli is best known for his work on the perception of transparency (e.g., Metelli, 1974). Gaetano Kanizsa’s most famous work was performed in the 1950s with papers on subjective contours, modes of color appearance, and phenomenal transparency (Kanizsa, 1954, 1955a, 1955b; all translated in English in 1979).

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Figure 5. The second generation of Gestalt psychologists who stayed elsewhere in Europe.

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In the edited volume, “Documents of Gestalt psychology” (Henle, 1961)―the most important collection of Gestalt work from the 1940s and 1950s, no Italian work was included. Although it was not recognized by the emigrated German psychologists in the U.S., the work put forward by the Italian Gestalt psychologists was in many respects very orthodox Gestalt psychology. For instance, Kanizsa (1955b/1979) took the phenomenon of “subjective contours,” already pointed out by Friedrich Schumann (1900), and gave a Gestalt explanation of the effect in terms of the tendency toward Prägnanz. He showed how the contour could affect the brightness of an area, just as Berlin Gestaltists had shown that contour could affect the figural character of an area. Kanizsa (1952) even published a polemic against stage theories of perception, in which he argued that, since according to Gestalt principles perception was caused by simultaneous autonomous processes, it was meaningless to hypothesize perceiving as a stage-like process. This work symbolized his complete separation from Graz thinking. In fact, one could talk about this tradition as the Padua-Trieste school of Gestalt psychology (see Verstegen, 2000). Except for Italy, Gestalt psychology was also strong in Belgium and in Japan. Albert Michotte became famous with his work on the perception of causality (1946/1963), in which he could demonstrate that even a seemingly cognitive inference like causality could be linked directly to specific higher-order attributes in the spatio-temporal events presented to observers. This work was very much in the same spirit as work by Fritz Heider on perceived animacy and attribution of intentions (Heider, 1944; Heider & Simmel, 1944), which was the empirical basis for his later attribution theory (Heider, 1958). Together with his coworkers, Michotte also introduced the notions of modal and amodal completion (Michotte et al., 1964), and studied several configural influences on these processes (for a further discussion of Michotte’s heritage, see Wagemans, van Lier, & Scholl, 2006). Building on earlier collaborations of Japanese students with major German Gestalt psychologists (e.g., Sakuma with Lewin, Morinaga with Metzger), Gestalt psychology continued to develop further in Japan after World-War II. For instance, Tadasu Oyama did significant work on figural aftereffects (e.g., Sagara & Oyama, 1957) and perceptual grouping (e.g., Oyama, 1961). The Gestalt tradition is still continued in Japanese perceptual psychology today (e.g., Noguchi et al., 2008), especially in their work on visual illusions (e.g., Akiyoshi Kitaoka). 5. Historical evaluation of Gestalt psychology Despite signs of well-deserved respect in the U.S. and in Germany (e.g., Köhler’s honorary degrees in 1967 and his APA presidency in 1957; Wertheimer’s posthumous Wilhelm Wundt Medal of the German Society for Psychology in 1983), the Gestalt theorists’ ideas were ambivalently received. They raised central issues and provoked important debates in psychology, theoretical biology, and other fields, but their mode of thinking and research style accommodated uncomfortably to the intellectual and social climate of the postwar world. Two explanations have been given for this outcome (Ash, 1995). One emphasizes institutional, political, and biographical contingencies. For example, Kurt Koffka received insufficient funding for his Giessen institute in the 1920s and the remaining leaders were cut off from their bases in Berlin and Frankfurt while they were still in their prime. The Gestalt school suffered severe personal blows with the early deaths of Wertheimer in 1943, Koffka in 1941, Gelb in 1935, and Lewin in 1947. In addition, three of Köhler’s most outstanding students―Karl Duncker, Otto Lauenstein, and Hedwig von Restorff―all died young. After they left Germany, the founders of Gestalt theory all obtained positions where they could do excellent research but could not train PhDs. The situation in Germany was different: Metzger, Rausch, and Gottschaldt produced more students between them than Köhler, Koffka, and Wertheimer did but relatively few carried on in the

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Gestalt tradition. They all broadened the scope of their research portfolio much beyond traditional Gestalt topics, in the direction of developmental psychology, educational psychology, sport psychology, personality, clinical psychology, psychotherapy, and so forth. The second explanation concerns conceptual issues. The strengths and limitations of Gestalt theory determined both how well it could live up to its creators’ own hopes for a new scientific worldview, and how well their students could adapt to social and cultural change. For instance, one of the issues that did not fit the Gestalt approach well was language. The reason for this is clear. In psychologies and epistemologies based on rationalist categories, language constitutes meaning. For Gestalt theory, in contrast, language expresses meaning that is already there in the appearance or in the world (e.g., Pinna, 2010). Orthodox Gestalt theorists also refrained from applying Gestalt thinking to personality and social psychology, fearing a lack of rigor. The preferred route to such extensions was analogy or metaphor, and the further the metaphors were stretched, the harder it became to connect them with Köhler’s concept of brain action. As the work of Rudolf Arnheim on expression and art, and of Kurt Lewin on action and emotion showed, extensions of the Gestalt approach were possible so long as one separated them from Köhler’s psychophysics. Further extensions in that direction were largely an American phenomenon (e.g., Solomon Asch). Ultimately decisive in the further decline of Gestalt theory was a meta-theoretical impasse between its theoretical and research styles and those of the rest of psychology. Gestalt theory was and remains interesting because it was a revolt against mechanistic explanations in science as well as against the non-scientific flavor of holism. Especially after 1950, its critics increasingly insisted on causal explanations, by which they meant positing cognitive operations in the mind or neural mechanisms in the brain. As sophisticated as the Gestalt theorists were in their appreciation of the way order emerges from the flow of experience, one must ask how such a process philosophy can be reconciled with strict causal determination, as Köhler at least wished to do. Koffka tried to accomplish this feat by insisting that the very principles of simplicity and order that the Gestalt theorists claimed to find in experience should also be criteria for evaluating both descriptions and explanations. For him, the best argument for isomorphism was his desire for one universe of discourse. But Koffka and his co-workers never succeeded in convincing their colleagues that it was logically necessary or scientifically fruitful to think that the external world, it’s phenomenal counterpart, and the brain events mediating interactions between them, all have the same structure or function, according to the same dynamical principles. James J. Gibson (1971) has written that the question Koffka asked in his “Principles of Gestalt psychology”―“Why do things look as they do?”―has fundamentally reshaped research on perception. In the last two decades, central issues of Berlin school research, such as perceptual grouping and figure-ground organization, have returned to center stage (e.g., Kimchi, Behrmann, & Olson, 2003; see also Wagemans et al., 2012a for a recent review), although concepts of top-down processing offered to deal with the question have at best a questionable relationship to Gestalt theory. The status of Wertheimer’s Gestalt laws and particularly of the so-called minimum principle of Prägnanz he enunciated remains contested, which is another way of saying that the issues involved are still important (e.g., Hatfield & Epstein, 1985; see also Wagemans et al., 2012b and van der Helm, this volume). Although it may be true that the Gestalt theorists failed to develop a complete and acceptable theory to account for the important phenomena they adduced, it is also true that no one else has either. The challenges for contemporary vision scientists are still significant.

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