Figure 1
Gestalt perception is the name given to various perceptual phenomena and theoretical principles associated with the school of GESTALT PSYCHOLOGY (Koffka 1935). Its most important contributions concerned perceptual organization: the nature of relations among parts and wholes and how they are determined. Previously, perceptual theory was dominated by the structuralist proposal that complex perceptions were constructed from atoms of elementary color sensations and unified by associations due to spatial and temporal contiguity. Gestalt theorists rejected both assumptions, arguing that perception was holistic and organized due to interactions between stimulus structure and underlying brain processes.
Wertheimer (1923) posed the problem of perceptual organization in terms of how people manage to perceive organized scenes consisting of surfaces, parts, and whole objects coherently arranged in space rather than the chaotic, dynamic juxtaposition of millions of different colors registered by retinal receptors. He attempted to answer this question by identifying stimulus factors that caused simple arrays of elements to be perceived as organized in distinct groups. The factors he identified are usually called the laws (or principles) of grouping, several of which are illustrated in figures A - F: proximity (A), similarity of color (B), similarity of size (C), common fate (D), good continuation (E), and closure (F). More recently other principles have been identified (Palmer and Rock 1994), including common region (G) and element connectedness (H). In each case, elements that have a stronger relation in terms of the specified property (i.e., those that are closer, more similarly colored, etc.) tend to be grouped together. These "laws" are actually ceteris paribus rules: all else being equal, the elements most closely related by the specified factor will be grouped together. They cannot predict the result when two or more factors vary in opposition because the rules fail to specify how multiple factors are integrated. No general theory has yet been formulated that overcomes this problem.
Figure 1
A second important phenomenon of Gestalt perception is figure-ground organization (Rubin 1921). In figure I, for instance, one can perceive either a white object on a black background or a black object on a white background. The crucial feature of figure-ground organization is that the boundary is perceived as belonging to the figural region. As a result, it seems "thing-like," has definite shape, and appears closer, whereas the ground appears farther and to extend behind the figure. Gestalt psychologists identified several factors that govern figure-ground organization, including surroundedness (J), size (K), contrast (L), convexity (M), and symmetry (N). These principles are also ceteris paribus rules: all else being equal, the surrounded, smaller, higher contrast, more convex, or symmetrical region tends to be seen as the figure. They therefore suffer from the same problem as the laws of grouping: they cannot predict the result when two or more factors conflict.
A third important phenomenon of Gestalt perception is that certain properties of objects are perceived relative to a frame of reference. MOTION and orientation provide two compelling examples. In induced motion (O), a slowly moving larger object surrounds a smaller stationary object in an otherwise dark environment. Surprisingly, observers perceive the frame as still and the dot as moving in the opposite direction (Duncker 1929) -- for example, when the moon appears to move through a cloud that appears stationary. In the rod-and-frame effect (P), observers perceive an upright rod as tilted when it is presented inside a large tilted rectangle in an otherwise darkened environment (Asch and Witkin 1948), much as one perceives a vertical chandelier as hanging askew inside a tilted room in a fun house. Larger, surrounding objects or surfaces thus tend to be taken as the frame of reference for the smaller objects they enclose.
Several other organizational phenomena are strongly identified with the Gestalt approach to perception. Amodal completion refers to the perception of partly visible figures as completed behind an occluding object. Figure Q, for example, is invariably perceived as a complete circle behind a square even though only three-fourths of it is actually showing. Illusory contours refer to the perception of a figure defined by edges that are not physically present in the image. As figure R illustrates, an illusory figure is perceived when aligned contours in the inducing elements cause them to be seen as partly occluded by a figure that has the same color as the background (Kanisza 1979). Color scission (figure S) refers to the splitting of perceived color into one component due to an opaque figure and another component due to a translucent figure through which the farther figure is seen (Metelli 1974).
Although these examples do not exhaust the perceptual contributions of Gestalt psychologists and their followers, they are representative of the phenomena they studied in the visual domain. They also investigated the perceptual organization of sounds, a topic that has been extended significantly by modern researchers (Bregman 1990). Recent studies of PERCEPTUAL DEVELOPMENT demonstrate that, contrary to the nativistic beliefs of Gestalt theorists, most principles of organization are not present at birth, but develop at different times during the first year of life (Kellman and Spelke 1983).
Theoretically, Gestalt psychologists maintained that these phenomena of perceptual organization support holism, the doctrine that the whole is different from the sum of its parts. They attempted to explain such holistic effects in terms of their principle of Prägnanz (or minimum principle), the claim that the percept will be as "good" as the stimulus conditions allow. This means that the preferred organization should be the simplest, most regular possibility compatible with the constraints imposed by the retinal image. Unfortunately, they did not provide an adequate definition of goodness, simplicity, or regularity, so their central claim was untestable in any rigorous way. Later theorists have attempted to ground these concepts in objective analyses, suggesting that simple perceptions correspond to low information content, economy of symbolic representation, and/or minimal transformational distance. Non-Gestalt theorists typically appeal instead to HELMHOLTZ's likelihoodprinciple that the perceptual system is biased toward the most likely (rather than the simplest) interpretation. The difficulty in discriminating between these two alternatives arises in part from the fact that the most likely interpretation is usually the simplest in some plausible sense. (See Pomerantz and Kubovy 1986 for a review of this issue.)
Most phenomena of Gestalt perception have resisted explanation at computational, algorithmic, and physiological levels. Köhler (1940) suggested that the best organization was achieved by electromagnetic fields in the CEREBRAL CORTEX that settled into states of minimum energy, much as soap bubbles stabilize into perfect spheres, which are minimal in both energy and complexity. Although subsequent physiological findings have discredited the brain-field conjecture, the more abstract idea of a physical Gestalt is compatible with modern investigations of RECURRENT NETWORKS (e.g., Grossberg and Mingolla 1985) that converge on a solution by reaching a minimum in an energy-like function. This suggests new theoretical approaches to the many important organizational phenomena Gestalt psychologists discovered more than a half century ago.
Asch, S. E., and H. A. Witkin. (1948). Studies in space orientation: I and II. Journal of Experimental Psychology 38:325-337, 455 - 477.
Bregman, A. S. (1990). Auditory Scene Analysis: The Perceptual Organization of Sound. Cambridge, MA: MIT Press.
Duncker, K. (1929). Über induzierte Bewegung. Psychologishe Forschung 12:180-259. Condensed translation published as Induced motion, in W. D. Ellis (1938), A Sourcebook of Gestalt Psychology. New York: Harcourt, Brace, pp. 161 - 172.
Grossberg, S., and E. Mingolla. (1985). Neural dynamics of form perception: boundary completion, illusory contours, and neon color spreading. Psychological Review 92:173-211.
Kanisza, G. (1979). Organization in Vision. New York: Praeger.
Kellman, P. J., and E. S. Spelke. (1983). Perception of partly occluded objects in infancy. Cognitive Psychology 15:483-524.
Koffka, K. (1935). Principles of Gestalt Psychology. New York: Harcourt Brace.
Köhler, W. (1940). Dynamics in Psychology. New York: Liveright Publishing Corp.
Metelli, F. (1974). The perception of transparency. Scientific American 230(4):90-98.
Pomerantz, J. R., and M. Kubovy. (1986). Theoretical approaches to perceptual organization. In K. R. Boff, L. Kaufman, and J. P. Thomas, Eds., Handbook of Perception and Human Performance. Vol. 2, Cognitive Processes and Performance. New York: Wiley, pp. 36-1 to 36 - 46.
Palmer, S. E., and I. Rock. (1994). Rethinking perceptual organization: the role of uniform connectedness. Psychonomic Bulletin and Review 1:29-55.
Rubin, E. (1921). Visuell Wahrgenommene Figuren. Copenhagen: Glydendalske.
Wertheimer, M. (1923). Untersuchungen zur Lehre von der Gestalt, II. Psychologische Forschung 4:301-350. Condensed translation published as Laws of organization in perceptual forms, in W. D. Ellis (1938), A Sourcebook of Gestalt Psychology. New York: Harcourt, Brace, pp. 71 - 88.
Copyright © 1999 Massachusetts Institute of Technology