Gestalt theory reconfigured: Max Wertheimer's anticipation of recent developments in visual neuroscience

In the 1920s Max Wertheimer enunciated a credo of Gestalt theory: the properties of any of the parts are governed by the structural laws of the whole. Intense efforts at the time to discover these laws had only very limited success. Psychology was in the grips of the Fechnerian tradition to seek exact relationships between the material and the mental and, because the Gestalt movement could not deliver these, it never attained a major standing among students of perception. However, as neurophysiological research into cortical processing of visual stimuli progresses the need for organizing principles is increasingly making itself felt. Concepts like contour salience and figure segregation, once the province of Gestalt psychology, are now taking on renewed significance as investigators combine neural modeling and psychophysical approaches with electrophysiological ones to characterize neural mechanisms of cognition. But it would be perilous not to take heed of some of the lessons that the history of the Gestalt movement teaches.     

Gestalt Issues in Modern Neuroscience

We present select examples of how visual phenomena can serve as tools to uncoverbrain mechanisms. Specifically, receptive field organization is proposed as a Gestalt-like neural mechanism of perceptual organization. Appropriate phenomena, such as brightness and orientation contrast, subjective contours, filling-in, and aperture-viewed motion, allow for a quantitative comparison between receptive fields and their psychophysical counterparts, perceptive fields. Phenomenology might thus be extended from the study of perceptual qualities to their transphenomenal substrates, including memory functions. In conclusion, classic issues of Gestalt psychology can now be related to modern “Gestalt psychophysics” and neuroscience.     

Beyond mind-reading: multi-voxel pattern analysis of fMRI data

A key challenge for cognitive neuroscience is determining how mental representations map onto patterns of neural activity. Recently, researchers have started to address this question by applying sophisticated pattern-classification algorithms to distributed (multi-voxel) patterns of functional MRI data, with the goal of decoding the information that is represented in the subject's brain at a particular point in time. This multi-voxel pattern analysis (MVPA) approach has led to several impressive feats of mind reading. More importantly, MVPA methods constitute a useful new tool for advancing our understanding of neural information processing. We review how researchers are using MVPA methods to characterize neural coding and information processing in domains ranging from visual perception to memory search.     

From elements to perception: local and global processing in visual neurons

Gestalt psychologists in the early part of the century challenged psychophysical notions that perceptual phenomena can be understood from a punctate (atomistic) analysis of the elements present in the stimulus. Their ideas slowed later attempts to explain vision in terms of single-cell recordings from individual neurons. A rapprochement between Gestalt phenomenology and neurophysiology seemed unlikely when the first ECVP was held in Marburg, Germany, in 1978. Since that time, response properties of neurons have been discovered that invite an interpretation of visual phenomena (including illusions) in terms of neuronal processing by long-range interactions, as first proposed by Mach and Hering in the last century. This article traces a personal journey into the early days of neurophysiological vision research to illustrate the progress that has taken place from the first attempts to correlate single-cell responses with visual perceptions. Whereas initially the receptive-field properties of individual classes of cells--e.g., contrast, wavelength, orientation, motion, disparity, and spatial-frequency detectors--were used to account for relatively simple visual phenomena, nowadays complex perceptions are interpreted in terms of long-range interactions, involving many neurons. This change in paradigm from local to global processing was made possible by recent findings, in the cortex, on horizontal interactions and backward propagation (feedback loops) in addition to classical feedforward processing. These mechanisms are exemplified by studies of the tilt effect and tilt aftereffect, direction-specific motion adaptation, illusory contours, filling-in and fading, figure--ground segregation by orientation and motion contrast, and pop-out in dynamic visual-noise patterns. Major questions for future research and a discussion of their epistemological implications conclude the article.     

知觉整体优先性的研究及其进展

知觉的性质是整体的还是分析的 ?这是心理学家们长期争论不休的问题。本世纪 70年代以来 ,一些认知心理学家提出知觉加工的整体优先性假设 ,强调整体在知觉加工中的优先地位。这一假设激发了大量整体 /局部范例的研究。本文综述了这方面的研究 ,分析了它们的理论假设 ,指出了这方面研究的局限以及替代的探讨。     

Connectedness affects dot numerosity judgment: Implications for configural processing

Participants judged the number of dots in visual displays with brief presentations (200 msec), such that the numerosity judgment was based on an instantaneous impression without counting. In some displays, pairs of adjacent dots were connected by line segments, whereas, in others, line segments were freely hanging without touching the dots. In Experiments 1, 2A, and 2B, connecting pairs of dots by line segments led to underestimation of dot numbers in those patterns. In Experiment 3, we controlled for the number of freely hanging line segments, whereas Experiment 4 showed that line segments that were merely attached to dots without actually connecting them did not produce a considerable underestimation effect. Experiment 5 showed that a connectedness effect existed when stimulus duration was reduced (50 msec) or extended (1,000 msec). We conclude that connectivity affects dot numerosity judgments, consistent with earlier findings of a configural effect in numerosity processing. Implications of the role of connectedness in object representation are discussed.     

The rod-and-frame effect: the whole is less than the sum of its parts

Since the discovery of the influence of the tilted frame on the visual perception of the orientation perceived as vertical (VPV), the frame has been treated as a unitary object-a Gestalt. We evaluated the effect of 1-line, 2-line, 3-line, and 4-line (square frame) stimuli of two different sizes, and asked whether the influence of the square frame on VPV is any greater than the additive combination of separate influences produced by the individual lines constituting the frame. We found that, for each size, the square frame is considerably less influential than the additive combination of the influences of the individual lines. The results conform to a mass action rule, in which the lengths and orientations of the individual line components are what matters and the organization of the lines into a square does not-no higher-level Gestalt property is involved in the induction effect on VPV.     

Substituting objects from consciousness: A review of object substitution masking

Object substitution masking (OSM) occurs when a sparse (e.g., four-dot), temporally trailing mask obscures the visibility of a briefly presented target. Here, we review theories of OSM: those that propose that OSM reflects the interplay between feedforward and feedback/reentrant neural processes, those that predict that feedforward processing alone gives rise to the phenomenon, and theories that focus on cognitive explanations, such as object updating. We discuss how each of these theories accommodates key findings from the OSM literature. In addition, we examine the relationship between OSM and other visual-cognitive phenomena, including object correspondence through occlusion, change blindness, metacontrast masking, backward masking, and visual short-term memory. Finally, we examine the level of processing at which OSM impairs target perception. Collectively, OSM appears to reflect the conditions under which the brain confuses two visual events for one when they are encoded with low spatiotemporal resolution, due to processing resources being otherwise occupied.     

Impairment in holistic face processing following early visual deprivation

Unlike most objects, faces are processed holistically: They are processed as a whole rather than as a collection of independent features. We examined the role of early visual experience in the development of this type of processing of faces by using the composite-face task, a measure of holistic processing, to test patients deprived of visual experience during infancy. Visually normal control subjects showed the expected composite-face effect: They had difficulty perceiving that the top halves of two faces were the same when the top halves were aligned with different bottom halves. Performance improved when holistic processing was disrupted by misaligning the top and bottom halves. Deprived patients, in contrast, showed no evidence of holistic processing, and in fact performed significantly better than control subjects when top and bottom halves were aligned. These findings suggest that early visual experience is necessary to set up or maintain the neural substrate that leads to holistic processing of faces.     

Effects of irrelevant object structure on early attention deployment

Event-related potential (ERP) studies have suggested that Gestalt principles or grouping factors in a visual scene modulate attention deployment in early visual processing. The present study examined the effects of an extrinsic grouping factor, region commonality, on early ERP spatial attention. Effects of sex were also explored, since the processing of task-irrelvant objects may differ between the sexes. Twenty-four participants were required to discriminate one side of rapidly-presented bilateral letters, and attention effects were indexed by hemispheric lateralization accroding to attended visual fields. In results, an early P1 attention effect (70–110 ms) increased when the letters were surrounded by an object, compared to the control stimulus without a complete object, and this result was more prominent in women than in men. The present study demonstrates that visual object and sex differences play a novel role at very early cortical stages of processing in attention deployment to a task-irrelevant visual structure.     

Psychophysical magic: rendering the visible 'invisible'

What are the neural correlates of conscious visual awareness? Tackling this question requires contrasting neural correlates of stimulus processing culminating in visual awareness with neural correlates of stimulus processing unaccompanied by awareness. To produce these two neural states, one must be able to erase an otherwise visible stimulus from awareness. This article describes and assesses visual phenomena involving dissociation of physical stimulation and conscious awareness: degraded stimulation, visual masking, visual crowding, bistable figures, binocular rivalry, motion-induced blindness, inattentional blindness, change blindness and attentional blink. No single approach stands above the others, but those producing changing visual awareness despite invariant physical stimulation are clearly preferable. Such phenomena can help lead us ultimately to a comprehensive account of the neural correlates of conscious awareness.     

Visual object agnosia as a problem in integrating parts and part relations

Current models of vision generally assume that the recognition of visual objects is achieved by encoding their component parts, as well as the spatial relations among parts. The current study examined how the processing of parts and their configurations may be affected in visual agnosia due to brain damage. Both a visual agnosic patient (AR) and healthy control subjects performed a visual search task in which they had to discriminate between targets and distractors that varied according to whether they shared their parts and/or their configuration. The results show that AR's visual search rates are disproportionally slow when targets and distractors share the same configuration than when they have different configurations. AR is also found to be disproportionately slow in discriminating targets and distractors that share identical parts when the targets and distractors share the same configuration. With differently configured targets and distractors, AR shows no part sharing effect. For controls, in contrast, the part and configuration sharing effects occur independently of one another. It is concluded that AR's object recognition deficit arises from difficulties in discriminating objects that share their configuration, and from an abnormal dependency of part information processing upon object configuration.     

Perceptual wholes can reduce the conscious accessibility of their parts

Humans can rapidly extract object and category information from an image despite surprising limitations in detecting changes to the individual parts of that image. In this article we provide evidence that the construction of a perceptual whole, or Gestalt, reduces awareness of changes to the parts of this object. This result suggests that the rapid extraction of a perceptual Gestalt, and the inaccessibility of the parts that make up that Gestalt, may in fact reflect two sides of the same coin whereby human vision provides only the most useful level of abstraction to conscious awareness.     

Dynamics of perceptual grouping: Similarities in the organization of visual and auditory groups

In vision, the Gestalt principles of perceptual organization are generally well understood and remain a subject of detailed analysis. However, the possibility for a unified theory of grouping across visual and auditory modalities remains largely unexplored. Here we present examples of auditory and visual Gestalt grouping, which share important organizational properties. In particular, similarities are revealed between grouping processes in apparent motion, auditory streaming, and static 2-D displays. Given the substantial difference in the context, within which the phenomena in question occur (auditory vs. visual, static vs. dynamic), these similarities suggest that the dynamics of perceptual organization could be associated with a common (possibly central) mechanism. If the relevance of supramodal invariants of grouping is granted, the question arises as to whether they can be studied empirically. We propose that a “force-field” theory, based on a differential-geometric interpretation of perceptual space, could provide a suitable starting point for a systematic exploration of the subjective properties of certain classes of auditory and visual grouping phenomena.     

Visual apparent motion can be modulated by task-irrelevant lexical information

Previous studies have repeatedly demonstrated the impact of Gestalt structural grouping principles upon the parsing of motion correspondence in ambiguous apparent motion. Here, by embedding Chinese characters in a visual Ternus display that comprised two stimulus frames, we showed that the perception of visual apparent motion can be modulated by activation of task-irrelevant lexical representations. Each frame had two disks, with the second disk of the first frame and the first disk of the second frame being presented at the same location. Observers could perceive either "element motion," in which the endmost disk is seen as moving back and forth while the middle disk at the central position remains stationary, or "group motion," in which both disks appear to move laterally as a whole. More reports of group motion, as opposed to element motion, were obtained when the embedded characters formed two-character compound words than when they formed nonwords, although this lexicality effect appeared to be attenuated by the use of the same characters at the overlapping position across the two frames. Thus, grouping of visual elements in a changing world can be guided by both structural principles and prior world knowledge, including lexical information.     

Unconscious and conscious priming by forms and their parts

Using metacontrast masking techniques, in two experiments we compare unconscious and conscious response priming by targets consisting of either whole forms or else their parts. In Experiment 1 we investigate the contribution of whole forms and their figural primitives, viz., edges and corners, to the unconscious priming effect. As expected, choice RTs were fast when the invisible target and visible mask shape pairings were congruent and slower when they were incongruent. This trend, while strongest for whole-targets, also held for the target primes composed only of corners but did not hold for target primes composed only of sides. Experiment 2 showed, replicating the results of Experiment 1, that while invisible corner targets produced weaker priming effects than invisible whole targets, paradoxically visible corner target produced stronger priming effects than visible whole targets. Taken together the results of the two experiments indicate (a) that unconscious target representations and, thus, unconscious priming effects are strongest when the target is a complete rather than a partial configuration, (b) that conjunctions of line or edge orientations forming corners produce stronger unconscious target representations and priming effects than do unconscious target representations formed from nonconjoined edge or line primitives, (c) that metacontrast masking of form occurs at or beyond levels of visual processing at which feature integration of visual form primitives occurs, and (d) that, when consciously perceived, partial forms can act as stronger primes than whole forms.     

Boundary completion, contrast polarity, and the perception of illusory tilt

What we perceive as a unitary object can be the result of integrative processes that generate a whole from parts. Although this issue of visual perception has been widely explored, recent experimental findings demonstrate that our knowledge is still incomplete. In particular, the question whether contour binding is affected by the sign of contrast (contrast polarity) across edges requires more in-depth examination. Here we show the effects of edge bindings that originate from the merging of laterally displaced edges with the same contrast polarity. We have studied a particular context in which such effects may emerge: a checkerboard with a series of alternated dark and light shapes superimposed on the corners of the squares. The phenomenal observations and experimental findings support the theories according to which boundary completions are originated by phenomena of edge propagation within a 'field of completion' (eg Shipley and Kellman, 2003 Perception 32 985-999) adjacent to an edge ending. Our findings conform to the Shipley and Kellman theory that boundary completion results from the interaction of edges as well as from edges and shapes lacking in oriented contours, the latter serving as 'receiving units', anchoring the paths of activations generated by oriented edges. We propose to integrate this theory with the hypothesis that interactions sensitive to the contrast sign generate conjunction paths of edges that alter their perceived orientation. Based on this perspective we propose an alternative account for the Café Wall illusion that can be extended to other phenomena of orientation misperception and to a Café Wall inversion effect that has not been observed previously.     

Formation of visual "objects" in the early computation of spatial relations

Perceptual grouping is the process by which elements in the visual image are aggregated into larger and more complex structures, i.e., "objects." This paper reports a study of the spatial factors and time-course of the development of objects over the course of the first few hundred milliseconds of visual processing. The methodology uses the now well-established idea of an "object benefit" for certain kinds of tasks (here, faster within-object than between-objects probe comparisons) to test what the visual system in fact treats as an object at each point during processing. The study tested line segment pairs in a wide variety of spatial configurations at a range of exposure times, in each case measuring the strength of perceptual grouping as reflected in the magnitude of the object benefit. Factors tested included nonaccidental properties such as collinearity, cotermination, and parallelism; contour relatability; Gestalt factors such as symmetry and skew symmetry, and several others, all tested at fine (25 msec) time-slices over the course of processing. The data provide detailed information about the comparative strength of these factors in inducing grouping at each point in processing. The result is a vivid picture of the chronology of object formation, as objects progressively coalesce, with fully bound visual objects completed by about 200 msec of processing.