2.2 Essentials of Gestalt Theory
The phi phenomenon was the perception of a pure process, a transition that could not be composed from more primitive percepts of a single object at two locations. In other words, perceived motion was not added subjectively after the sensory registration of two spatiotemporal events but had its own phenomenological characteristics and ontological status. From this phenomenon, Wertheimer concluded that structured wholes or Gestalten, rather than sensations, are the primary units of mental life. This was the key idea of the new and revolutionary Gestalt theory, developed by Wertheimer and his colleagues in Berlin. An overview of how the Berlin school of Gestalt psychology distinguished itself from the dominant view of structuralism and empiricism, as well as of related Gestalt schools is given in .
Key claims by the Berlin school of Gestalt psychology in opposition to other schools
The notion of “Gestalt” had already been introduced into psychology by Christian von Ehrenfels in his essay “On Gestalt qualities” (1890
). Based on the observation that humans can recognize two melodies as identical even when no two corresponding notes in them have the same frequency, von Ehrenfels argued that these forms must possess a “Gestalt quality”—a characteristic that is immediately given, along with the elementary sensations that serve as its foundation, a characteristic that is dependent on its constituent objects but rises above them. For von Ehrenfels, Gestalt qualities rest uni-directionally on sense data: Wholes are more than the sums of their parts, but the parts are the foundation (“Grundlage”) of the whole. In contrast, Wertheimer claimed that functional relations determine what will appear as the whole and what will appear as parts (i.e., reciprocal dependency). Often the whole is grasped even before the individual parts enter consciousness. The contents of our awareness are by and large not additive but possess a characteristic coherence. They are structures that are segregated from the background, often with an inner center, to which the other parts are related hierarchically. Such structures or “Gestalten” are different from the sum of the parts. They arise from continuous global processes in the brain, rather than combinations of elementary excitations.
With this step, Wertheimer separated himself from the Graz school of Gestalt psychology, represented by Alexius Meinong, Christian von Ehrenfels, and Vittorio Benussi. They maintained a distinction between sensation and perception, the latter produced on the basis of the former. The Berlin school, represented by Max Wertheimer, Kurt Koffka, and Wolfgang Köhler, considered a Gestalt as a whole in itself, not founded on any more elementary objects. In their view, perception was not the product of sensations but it arose through dynamic physical processes in the brain. As a result, the Berlin school also rejected stage theories of perception proposed by the Leipzig school, represented by Felix Krüger and Friedrich Sander, in which the gradual emergence of Gestalten (“Aktualgenese” or “microgenesis”) played a central role. Although the Berlin theorists adhered to a nonmechanistic theory of causation and did not analyze the processes into stages, they did believe that the functional relations in the emergence of Gestalts could be specified by laws of perceptual organization.
2.3 Further Development, Rise, and Fall of Gestalt Psychology
Two major developments are generally considered as highlights in the history of Gestalt psychology: Köhler’s discussion of “physical Gestalten” (1920) and Wertheimer’s proposal of “Gestalt laws of perceptual organization” (1923
). Köhler (1920)
extended the Gestalt concept from perception and behavior to the physical world, thus attempting to unify holism (i.e., the doctrine stressing the importance of the whole) and natural science. He 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 such continuous field 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 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 do not show this mutual interdependence.
In addition, Köhler tried to construct a specific testable theory of brain processes that could account for perceived Gestalten in vision. He thought of visual Gestalten as the result of an integrated process in what he referred to as “the entire optical sector,” including retina, optical tract, and cortical areas, as well as transverse functional connections among conducting nerve fibers (i.e., a recurrent neural network in modern terms). He proposed an electrical field theory, in which “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” (Köhler, 1920/1938
, p. 50). In modern terms, Köhler had described the visual system as a self-organizing physical system.
These ideas led Köhler to postulate a psychophysical isomorphism between the psychological reality and the brain events underlying it: “actual consciousness resembles in each case the real structural properties of the corresponding psycho-physiological process” (Köhler, 1920/1938
, p. 38). By this he meant functional instead of geometrical similarity indicating that brain processes do not take the form of the perceived objects themselves. In addition, he insisted that such a view does not prescribe complete homogeneity of the cortex but is perfectly compatible with functional articulation. Experiments to establish the postulated connections between experienced and physical Gestalten in the brain were at the time nearly impossible to conduct, but decades later, Köhler attempted to do so (see below).
Around the same time, Max Wertheimer further developed his Gestalt epistemology and 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. Wertheimer called for descriptions of conscious experience in terms of the units people naturally perceive, rather than the artificial ones imposed by standard scientific methods. By assuming that conscious experience is composed of units analogous to physical point-masses or chemical elements, psychologists constrain themselves to a piecemeal inquiry into the contents of consciousness, building up higher entities from constituent elements, using associative connections. In fact, such and-summations (“Und-Summe”), as Wertheimer called them, appear “only rarely, only under certain characteristic conditions, only within very narrow limits, and perhaps never more than approximately” (Wertheimer 1922/1938
, p. 13). Rather, what is given in experience “is itself in varying degrees ‘structured’ (‘gestaltet’), it consists of more or less definitely structured wholes and whole-processes with their whole-properties and laws, characteristic whole-tendencies and whole-determinations of parts” (Wertheimer 1922/1938
, p. 14). The perceptual field does not appear to us as a collection of disjointed sensations, but possesses a particular organization of spontaneously combined and segregated objects.
In 1923, Wertheimer published a follow-up paper, which was an attempt to elucidate the fundamental principles of that organization. The most general principle was the so-called law of Prägnanz, stating, in its most general sense, that the perceptual field and objects within it will take on the simplest and most encompassing (“ausgezeichnet”) structure permitted by the given conditions. For Köhler (1920)
, this tendency towards the Prägnanz of the Gestalt was just another example that phenomenal Gestalten were like physical Gestalten: As shown by Maxwell and Planck, all processes in physical systems, left to themselves, show a tendency to achieve the maximal level of stability (homogeneity, simplicity, symmetry) with the minimum expenditure of energy allowed by the prevailing conditions. More specific principles that determine perceptual organization according to Wertheimer were proximity, similarity, uniform density, common fate, direction, good continuation and “whole properties” (or “Ganzeigenschaften”) such as closure, equilibrium, and symmetry.
Empirical work on these principles existed before Wertheimer’s landmark paper (for a recent review, see Vezzani, Marino, & Giora, 2012
), but now the general claim that perceptual experience is organized was turned into a complex open-ended research program aimed at the discovery of the laws or principles governing perceptual organization in both its static and dynamic aspects. It is this research program that Wertheimer, Koffka and Köhler started to work on with their students, once they had acquired professorships at major universities in Germany in the 1920s and 1930s. We cannot cover this flourishing period of the Berlin school of Gestalt psychology extensively here, but a few highlights that deserve mentioning in passing are studies by Kurt Gottschaldt on embedded figures (1926
), Joseph Ternus on phenomenal identity (1926
), Karl Duncker
on induced motion (1929), Wolfgang Metzger on a homogeneous Ganzfeld (1930
) and motion in depth (1934
). 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), and on thought (e.g., Karl Duncker). Later, Gestalt theory was also applied to action and emotion (by Kurt Lewin), to neuropathology and the organism as a whole (by Adhemar Gelb and Kurt Goldstein), and to film theory and aesthetics (by Rudolf Arnheim). This period 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.
Around this time, Gestalt theory also started to have some impact on research in the U.S., mainly owing to Wolfgang Köhler and Kurt Koffka (see King & Wertheimer, 2005
, Chapter 10). For instance, Koffka’s (1935)
notion of vector fields inspired some interesting empirical work published in the American Journal of Psychology (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, Koffka had published a full account of the Gestalt view on perception in Psychological Bulletin.
At first sight, Gestalt theory seemed to develop rather consistently, from studying the fundamental laws of psychology first under the simplest conditions, in elementary problems of perception, before including complex sets of conditions, and turning to other domains such as memory, thinking, emotion, aesthetics, and so forth. At the same time, however, the findings obtained did not always fit the original theories, which posed serious challenges to the Gestalt framework. Even more devastating to the development of Gestalt psychology was the emergence of the Nazi regime in Germany from 1933 to World War II. In this period, many of the psychology professors at German universities lost their posts because of the discrimination and prosecution of Jews, so they emigrated to the U.S. to take on new positions there. The works by German psychologists who stayed, for instance, Edwin Rausch’s monograph on “summative” and “nonsummative” concepts (1937
) and Wolfgang Metzger’s (1941)
psychology textbook, were largely ignored outside Germany. Metzger’s synoptic account of research on the Gestalt theory of perception entitled “Gesetze des Sehens” (“Laws of seeing”), first published in 1936
and later reissued and vastly expanded three times, was only translated into English in 2006.
After emigrating to the U.S., the founding fathers of Gestalt psychology did not perform many new experiments. Instead, they mainly wrote books in which they outlined their views (e.g., Koffka, 1935
; Köhler, 1940
; Wertheimer, 1945
). The major exception was Köhler who had taken up physiological psychology using EEG recording and other methods in an attempt to directly verify his isomorphism postulate. Initially, his work with Hans Wallach on figural aftereffects appeared to support his interpretation in terms of satiation of cortical currents (Köhler & Wallach, 1944
). Afterwards, he was able to directly measure cortical currents—as EEG responses picked up from electrodes at the scalp—whose flow direction corresponded to the direction of movement of objects in the visual field (Köhler & Held, 1949
Soon after that breakthrough, however, 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 indeed reflected 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 the perception of these visual figures. 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, demonstrating that global cortical currents were not a necessary condition for pattern perception. In subsequent experiments, Sperry and colleagues (Sperry, Miner, & Myers, 1955
) performed extensive 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 distorted variants). Together, these two studies effectively ruled out electrical field theory as an explanation of cortical integration and undermined the empirical basis of any isomorphism between cortical flows of current and organized patterns of perception. Köhler (1965)
naturally reacted to these developments but his counterarguments and suggestions for further experiments were largely ignored, and to most scientists at the time, the matter was closed. Electrical field theory, which had been one of the pillars of Gestalt psychology’s scientific basis, was considered dead and buried.
While Gestalt psychology declined in the English-speaking world after World-War II, Italy remained a stronghold of Gestalt psychology. For instance, Metzger dedicated the third edition of his “Gesetze des Sehens” to 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 of Gestalt psychology in Italy and training important students in this tradition—most notably Metelli and Kanizsa, whose contributions continue to be felt today. Fabio Metelli is best known for his work on the perception of transparency (e.g., Metelli, 1974
). Gaetano Kanizsa’s most famous studies were performed in the 1950s with papers on subjective contours (e.g., the so-called Kanizsa triangle), modes of color appearance, and phenomenal transparency (Kanizsa, 1954
), although their impact came much later, when he started to publish in English (Kanizsa, 1976
In addition to Italy, Gestalt psychology was also strong in Belgium and in Japan. Albert Michotte became famous for his work on the perception of causality (1946/1963
), arguing strongly against an inferential, associationist, empiricist account of it, like other Gestalt psychologists had done for other aspects of perception. For him, causality is perceived directly, not derived from more primitive sensations through some cognitive operation, and this percept could be shown to be tightly coupled to specific higher-order attributes in the spatiotemporal events presented to observers. He also introduced the notions of modal and amodal completion (Michotte, Thinès, & Crabbé, 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 in Japan after World-War II. For instance, Oyama did significant work on figural aftereffects (e.g., Sagara & Oyama, 1957
) and perceptual grouping (e.g., Oyama, 1961
2.4 The Current Status of Gestalt Psychology
Despite signs of well-deserved respect in the U.S. and in Germany (e.g., Köhler’s APA presidency in 1957; Wertheimer’s posthumous Wilhelm Wundt Medal in 1983), the ideas of the Gestaltists were received with ambivalence. On the one hand, they were recognized for raising central issues and provoking important debates in psychology, theoretical biology, and other fields, but on the other hand, their mode of thinking and research style did not sit comfortably in the intellectual and social climate of the postwar world, and they were confronted with vehement criticism. Two sets of explanations have been given for this outcome (Ash, 1995
). The first emphasizes institutional, political, and biographical contingencies. Koffka, Köhler and Wertheimer all left for the U.S. and obtained positions where they could do excellent research but could not train PhDs. The Gestalt school’s further expansion was also handicapped by the early deaths of Max Wertheimer in 1943 and Kurt Koffka in 1941, as well as many other Gestalt psychologists of the first and second generation (e.g., Duncker, Gelb, Lauenstein, Lewin, von Restorff). In Germany, Metzger, Rausch, and Gottschaldt did have a large number of PhD students, but few of them carried on in the Gestalt tradition. A notable exception is Lothar Spillmann, who obtained his D. Phil. with Metzger in Münster in 1964 and who pioneered the impact of Gestalt ideas in modern neurophysiology ever since (e.g., Spillmann, 1999
The second set of explanations concerns scientific issues of a methodological and conceptual nature (summarized in the left column of ). Compared to the rigor of psychophysics and behaviorism, Gestalt psychology was severely criticized for offering mere demonstrations, using either very simple or confounded stimuli, formulating laws with little precision, and adding new “laws” for every factor shown to have an influence on perceptual organization. In the 1950s and 1960s, its critics increasingly insisted on causal explanations, by which they meant cognitive operations in the mind that could be modeled as computer algorithms or neural mechanisms that could be attributed to the properties of single cells that were discovered by Hubel and Wiesel in that period. In addition, serious conceptual limitations appeared when Gestalt thinking was extended to other areas such as personality and social psychology (e.g., Richard Crutchfield, Solomon Asch, Fritz Heider, David Krech). The further the metaphors were stretched, the harder it became to connect them to Köhler’s concept of a self-organizing brain and his speculations about electromagnetic brain fields.
Problems in old-school Gestalt psychology and how they are solved in contemporary research
Despite these criticisms, Gestalt thinking did not disappear from the stage completely. In the slipstream of Shannon’s information theory, a few researchers tried to provide a quantitative underpinning to the central Gestalt notion of simplicity (e.g., Attneave, 1954
; Attneave & Arnoult, 1956
; Hochberg & McAlister, 1953
; Leeuwenberg, 1969
; for a review, see Hatfield & Epstein, 1985
). A number of independent, original scientists working on perception and information processing kept some Gestalt issues on the research agenda (e.g., Fred Attneave, Wendell Garner, Julian Hochberg, Irvin Rock). These became more prominent again with the discovery of true Gestalt phenomena such as global precedence in hierarchical letters (e.g., Navon, 1977
), configural superiority effects based on emergent features (e.g., Pomerantz, Sager, & Stoever, 1977
), and the importance of hierarchical structure in perceptual representations (e.g., Palmer, 1977
). The experimental paradigms were derived from standard methods in cognitive psychology, and the results were incorporated into mainstream information-processing accounts (e.g., Beck, 1982
; Kubovy & Pomerantz, 1981
). In the major alternative approaches to visual perception—the ecological (e.g., Gibson, 1971
) and computational (e.g., Marr, 1982
) approaches—the influence of Gestalt thinking has also been acknowledged explicitly. In the last two or three decades, perceptual grouping and figure-ground organization—the most central topics of Berlin school research—have returned to center stage (e.g., Kimchi, Behrmann, & Olson, 2003
), although the relationship to the original Gestalt theory (e.g., two-sided dependency between wholes and parts, minimum principle) is not always clear.
In the remainder of this paper, as well as in a second more theoretically oriented paper (Wagemans et al., 2012
), we review the later developments in more detail (summarized in the right column of ). We start with research on perceptual grouping in simple displays (Section 3) and extend this to contour grouping, integration, and completion in more complex shapes and real-world images (Section 4). In the next section, we cover research on figure-ground perception, where many of the factors affecting grouping, in addition to unique factors, exert an influence (Section 5). Although links to neural mechanisms are mentioned throughout, we also provide a more integrated account of the literature on the neural mechanisms of contour grouping and figure-ground organization in a separate section (Section 6). This review demonstrates that research from the last two or three decades has addressed (and partially solved) some of the major methodological and conceptual shortcomings in old-school Gestalt psychology.