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Perspective |
1 Both authors: Department of Radiology, Indiana University School of Medicine, 702 Barnhill Dr., Rm. 1053, Indianapolis, IN 46202-5200.
Received October 8, 2007; accepted after revision November 18, 2007.
Address correspondence to R. B. Gunderman
(rbgunder{at}iupui.edu).
OBJECTIVE. The Gestalt theory of modern psychology is grounded in the ideas that holistic rather than atomistic approaches are necessary to understand the mind, and that the mental whole is greater than the sum of its component parts. Although the Gestalt school fell out of favor due to its descriptive rather than explanatory nature, it permanently changed our understanding of perception. For the radiologist, such fundamental Gestalt concepts as figure–ground relationships and a variety of "grouping principles" (the laws of closure, proximity, similarity, common region, continuity, and symmetry) are ubiquitous in daily work, not to mention in art and personal life.
CONCLUSION. By considering the applications of these principles and the stereotypical ways in which humans perceive visual stimuli, a radiology learner may incur fewer errors of diagnosis. This article serves to introduce several important principles of Gestalt theory, identify examples of these principles in widely recognizable fine art, and highlight their implications for radiology education.
Keywords: education • Gestalt • image interpretation • perception • psychology • radiologists • radiology
For many physicians, the term "Gestalt theory" evokes several associations, including the familiar aphorism "the whole is greater than the sum of its parts" and images of Necker cubes, Rubin vases, and indistinct-appearing Dalmatians. For those who enjoy a background in psychology, this term conjures up such names as Wertheimer, Koffka, and Köhler—men whose seminal work helped define the modern notion of perception. However, it often goes unnoticed that several principles of Gestalt psychology are ubiquitous in our daily life and work and have played a crucial role in defining our contemporary understanding of perception. From organizational development to Internet security, and from educational psychology to clinical medicine, our daily work is powerfully shaped by the principles of Gestalt theory. As one of modern medicine's paradigmatically visual fields, radiology can be illuminated by Gestalt theory and its implications for visual perception. For that reason, radiologists in training should enjoy the opportunity to develop a basic familiarity with Gestalt principles.
The Gestalt movement developed in Austria and Germany near the turn of the 20th century, largely through the work of Max Wertheimer, Kurt Koffka, and Wolfgang Köhler. Translated from German, Gestalt can be taken to mean "whole" or "form," an apt summary of this psychologic approach [1]. Expanding on the ideas of earlier theorists, these psychologic pioneers developed an encompassing definition of perception that differed quite strikingly from that of atomism, the predominant psychologic theory at the time. Atomists such as Wilhelm Wundt, regarded by many as the father of modern psychology, believed that perception could be broken down into discrete units, each playing a finite role in shaping the conscious experience. Gestalt theorists criticized this perspective and argued for a more holistic approach [2]. They believed that the perception of any given object or experience exhibits intrinsic qualities that cannot be completely reduced to visual, auditory, tactile, olfactory, or gustatory components. Gestalt psychologists held that perceptions are not constructed in a "bottom-up" fashion from such elements but are instead perceived globally, in a more "top-down" fashion. They proposed that we have an innate tendency to organize sensory inputs in a manner that creates the most coherent, seamless perception possible [2].
The term "Gestalt" is familiar to many physicians [3]. For example, medical students and residents learn to develop a global impression of a patient's health status within seconds of entering the room. To arrive at such an assessment, there is not sufficient time for "bottom-up" processing. Radiologists, too, have recognized the importance of Gestalt. For example, an experienced radiologist typically engages in two distinct processes when interpreting a chest radiograph: a rapid global search, which quickly identifies normal anatomic content and identifies suspicious deviations from it (i.e., pathologic abnormalities), and a secondary systematic scan, which involves a careful, algorithmic study of the radiograph [4]. The first phase of radiographic interpretation exemplifies a Gestalt perspective. This global approach plays in invaluable role in the detection of lung lesions—a role so important that its absence cannot be compensated for by a careful algorithmic analysis of the radiograph [5]. There is evidence that a Gestalt approach plays an important role in the interpretation of other types of radiologic examinations, such as nuclear medicine ventilation–perfusion lung scans [6].
Although Gestalt theory did not completely explain how perception works, it elucidated several perceptual principles that remain vital to contemporary perceptual psychologists and radiologists alike. These include the principle of figure–ground relationship, and the grouping principles of closure, proximity, similarity, common region, continuity, and symmetry [2, 7, 8]. By exploring these principles and the benefits and risks associated with them, we can help radiology learners gain a better understanding of visual perception, potentially improving their diagnostic performance.
Figure–Ground
According to Gestalt theory, one of the most important principles organizing our perception is the figure–ground relationship. It is an automatic feature of the visual system in which the focus of attention becomes the figure and all other visual input becomes the ground [8]. For any given image, the same visual stimulus can trigger multiple perspectives, depending on what is taken to be figure and what is taken to be ground [1]. Consider the classic illusion of the Necker cube, an object that withholds the depth and spatial cues that we rely on for static perception (Fig. 1). Depending on where we train our eyes, the spatial characteristics of the Necker cube appear to change markedly, a phenomenon commonly referred to as figure–ground reversal [9].
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The figure–ground principle is manifest in our tendency to focus on objects that are smaller, brighter, and more centrally located in an image [2]. This phenomenon is exemplified brilliantly in Las Meninas (1656) (see www.museodelprado.es/en/bienvenido/15-masterpieces/ficha-obra/the-family-of-felipe-iv-or-las-meninas) by Diego Velázquez (1599–1660), famous portrait of the Spanish court of King Philip IV. At first glance, the viewer's eyes are drawn to the infanta Margarita, because of her central location and radiant gown [9]. On further inspection, however, we realize that the young princess is not the focal point of the portrait, but an observer of another portrait that is in the process of being painted. Even closer inspection reveals that the artist positioned off to the left side of the canvas is none other than Diego Velázquez, who is painting a portrait of someone who shares the same vantage point as the observer. If princess Margarita is not the subject of this portrait, then who is? A thorough search reveals the answer—King Philip IV and Queen Mariana, whose figures are recognizable in the mirror that is hanging behind princess Margarita.
Faulty figure–ground processing in interpreting radiologic images can lead novices astray, as when our eyes are drawn to the bright heart at the center of a chest radiograph, causing us to neglect a thorough scan of the darker and more peripheral lung fields and surrounding soft tissues. Likewise, a neophyte interpreting an abdominal CT examination may focus excessively on bright areas of contrast enhancement, while ignoring darker features such as pneumoperitoneum. Poor appreciation of our stereotypical ways of handling figure–ground relationships can lead to misdiagnosis and detrimental outcomes for patients. Developing an appreciation for the implications of this Gestalt principle may represent a vital step in the transformation of a novice into a competent radiologist.
Closure
Another key Gestalt principle is closure, which suggests that our minds have a tendency to fill in empty spaces in an apparently incomplete image to create a complete and unified figure [8] (Fig. 2). To visualize this principle, consider the Cubist movement in Modern art. The works of Pablo Picasso (1881–1973) and Georges Braque (1882–1963) rely heavily on this grouping principle, which is observed readily in Braque's Violin and Candlestick (1910) (see collections.sfmoma.org/OBJ89.htm). A prototypic example of analytic cubism, this painting is constructed of multiple open geometric figures that serve as 2D reductions of the objects' true 3D forms. Through the principle of closure, an observer can effortlessly identify both the violin and the candlestick in this painting.
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For the radiologist, the principle of closure is at play when we review and interpret sequential axial images from a CT or MRI examination. Such planar images of internal anatomy differ markedly from the 3D appearance of each organ, yet the experienced radiologist instantly perceives the whole organ's morphology, which novices may find difficult or even impossible. The principle of closure is also at work in numerous imaging artifacts. Often radiologists are called on to interpret imaging studies that contain artifacts, such as beam-hardening artifact on CT, which distort the appearance of adjacent tissues. Consider, for example, the impact of the dense skull base on visualization of the posterior fossa and brainstem [11]. Similar pitfalls can be iatrogenic, such as the orthopedic hardware that can compromise interpretations of MR angiograms [12]. In such cases the novice not only must search for lesions but also must be mindful of the principle of closure and its quality control implications.
Proximity
The principle of proximity states that image components that are physically near each other tend to be perceived as belonging to a group [2] (Fig. 3). This principle is ubiquitous in personal life as well as in art, and it describes perhaps the most basic definition of a group—namely, multiple objects in close spatial proximity. Consider, for example, the allegorical painting Fight with Cudgels (1820–1823) (see eeweems.com/goya/cudgels.html), by the Spanish painter Francisco Goya (1746–1828). Widely regarded as both the last of the Old Masters and the father of modern art, Goya painted this work as a reaction to the civil war and class disputes that had embroiled Spain. Painted late in his life and after a series of illnesses that left him deaf, this work stands out among "the Black Paintings" because of its expansive background and small, simplistic figures. In this work, the principle of proximity is intentionally used twice. At first glance, we notice two men engaged in brutal combat; however, when visualized against the expansive backdrop of the meadow landscape, the principle of proximity causes the observer to perceive the combatants as belonging together, suggesting some degree of alliance. In this case, Goya used the principle of proximity to create a perception that the two fighters are fellow countrymen. The men's legs also disappear deep into the quagmire below them. This fusion with the earth creates the perception that these men share a strong association with the very land (i.e., the Iberian Peninsula) they are fighting over.
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The principle of proximity has metaphoric applications as well. It is common for physicians to perceive radiologists as isolated from the rest of the hospital. The radiology department is often located on a different floor or in a different wing and generally exhibits a highly distinctive ambience, including very low levels of ambient lighting and noise. Such factors can lead to the impression that radiologists are medical outsiders. Means of counteracting such an impression would include locating radiologists' work areas nearer to or even inside patient care areas and getting radiologists out of the radiology department and into patient care areas on a regular basis (e.g., holding ICU–radiology rounds in the ICU) [13]. In the increasingly crowded environment of medical imaging, it is vital that we remind radiology residents of the importance of their own visibility.
Similarity
The principle of similarity holds that like-appearing objects tend to be perceived as a group [1] (Fig. 4). This Gestalt principle can be appreciated artistically in The Burial of the Count of Orgaz (1586–1588) (see www.wga.hu/frames-e.html?/html/g/greco_el/09/index.html) by Doménicos Theotokópoulos (1541–1614), better known as El Greco. This painting depicts the burial of the pious Don Gonzalo Ruíz de Toledo, who, according to legend, was laid to rest by Saints Augustine and Stephen [14]. One of the striking features of this work is the delineation of subjects into groups based on their similar appearances. For example, centered at the bottom of the painting are two men (St. Augustine and St. Stephen) whose brilliant gold and red vestments allow them to be instantly perceived as belonging to a group entirely different from the men in black civilian dress (the gentlemen of Toledo) or those wearing cassocks and chasubles (the priests).
The principle of similarity plays an important role in radiology education because the ability to formulate an extensive and appropriate differential diagnosis is an important factor that separates a novice from a competent radiologist. A major component of formulating a differential diagnosis is perceiving similarities and differences between imaging findings. Consider the finding of an abnormally increased cardiothoracic ratio on a frontal chest radiograph. Presented with such a finding, the neophyte may immediately launch into a differential diagnosis of cardiomegaly, including congestive heart failure, dilated cardiomyopathy, valvular heart disease, metabolic disorders, and so on. Only with experience does the learner appreciate that there are a number of important cardiomegaly mimics, including antero-posterior technique, underinflation, pectus excavatum, and pericardial effusion. Moreover, only with experience does the radiology student become adept at correlating the perception of similar appearing abnormalities with accurate differential diagnoses.
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The Gestalt principle of common region states that objects or stimuli that are enclosed in a common region are likely to be perceived as a group, regardless of similarity or nearness of the constituent objects or stimuli [7] (Fig. 5). This principle is evident in the challenging artwork of the Belgian surrealist painter René Magritte (1898–1967), who is best known for taking ordinary objects and injecting them into unrealistic and impossible settings. Magritte frequently placed unrelated objects in common environs, causing the observer to perceive them as related to one another [15]. One such example is his painting Les Valeurs personnelles (Personal Values) (1952) (see www.sfmoma.org/msoma/artworks/5139.html), a surrealist investigation into the relationship between humans and ordinary personal items of daily life. When the artist places larger-than-life, incongruous objects such as a comb, a bar of soap, a wine glass, a matchstick, and a shaving brush within the confines of a bedroom, the observer perceives these seemingly unrelated objects as intrinsically connected, albeit a connection that the observer cannot readily identify. Magritte draws the observer into the work by inviting us to draw on our own experiences in seeking a unifying theme among the objects.
The principle of common region is a key grouping principle for the radiology learner because of its implications for the formation of appropriate differential diagnoses. For example, the mediastinum can be divided spatially into three compartments: anterior, middle, and posterior. When a mediastinal mass is identified on chest radiography or a chest CT scan, we attempt to locate it according to this anatomic scheme. Likewise, in interpreting images of the CNS, classifying a mass as intraaxial or extraaxial is a crucial step in formulating a differential diagnosis. The same can be said for intra- and extra-peritoneal processes, arterial versus venous processes, and abdominal versus pelvic processes. By developing an appreciation of our natural tendency to perceive objects compartmentally, a learner may become more adept at correlating imaging findings with pathologic processes.
Continuity
The principle of continuity states that smooth, continuous lines can be perceived more effortlessly than interrupted lines [2] (Fig. 6). This Gestalt principle was used by the enigmatic Marcel Duchamp (1887–1968) in his controversial work Nude Descending a Staircase (No. 2) (1912) (see www.philamuseum.org/collections/permanent/51449.html). Composed solely of interrupted lines painted in successive planes, we cannot perceive a static image of the nude figure due to perceptual limitations imposed by this principle. Instead, we perceive these broken lines in a staccato fashion, imparting the perception that the figure is in motion. One of the earliest artists to attempt to represent motion in paint, Duchamp used the hallmark techniques of analytic cubism (i.e., limited palette and form deconstruction) both to transcend the static confines of cubist art and to rebuke its pretensions [16].
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Symmetry
The Gestalt principle of symmetry holds that symmetric objects or stimuli tend to be perceived as a group regardless of proximity (Fig. 7). This is perhaps one of the most ubiquitous of the Gestalt grouping principles encountered in fine art and in daily life. Consider the iconographic painting The Marriage of Giovanni Arnolfini and Giovanna Cenami (1434) (see www.nationalgallery.org.uk/cgi-bin/WebObjects.dll/CollectionPublisher.woa/wa/work?workNumber=NG186) by Jan van Eyck (c. 1385–1441). At first glance, the symmetric positioning of the subjects, including the centrally located dog, leads us to suppose that the subjects belong together as a group. With further study, however, we can appreciate a hidden symbolism, which strongly suggests that the painting reflects either an engagement or marriage [9]. Consider also The Last Supper (c. 1495–1498) (see www.cenacolovinciano.it/html/eng/home.htm) by Leonardo da Vinci (1452–1519). The symmetry of the composition contributes to a one-point linear perspective, and it allows the apostles to be instantly perceived as belonging to a group, with all attention focused on Christ's head, the painting's focal point [9].
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Radiologists use the principle of symmetry regularly in evaluating the lungs, bones, and cerebral hemispheres, which are normally relatively symmetric. With experience, a competent radiologist will judiciously use this principle to detect various abnormalities that disrupt the anatomic symmetry. However, the same principle can mislead a novice when the pathology is bilateral and symmetric. Consider, for example, isodense bilateral subdural hematomas, or cleidocranial dysplasia, with the absence of the clavicles. To the veteran radiologist, these might represent rather straightforward diagnoses, but we must be mindful that learners can be fooled by pathology that is symmetric.
Conclusion
Gestalt principles of visual perception play an integral but often underappreciated role in both radiology practice and the training of future radiologists. By familiarizing ourselves with these ubiquitous principles at an early stage of training, we can help radiology students better understand the unconscious work involved in interpreting radiologic images and prepare them to avoid common perceptual pitfalls.
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