Ruth Kimchi

A Century of Gestalt Psychology in Visual Perception: II. Conceptual and Theoretical Foundations.

Our first review article (Wagemans et al., 2012) on the occasion of the centennial anniversary of Gestalt psychology focused on perceptual grouping and figure-ground organization. It concluded that further progress requires a reconsideration of the conceptual and theoretical foundations of the Gestalt approach, which is provided here. In particular, we review contemporary formulations of holism within an information-processing framework, allowing for operational definitions (e.g., integral dimensions, emergent features, configural superiority, global precedence, primacy of holistic/configural properties) and a refined understanding of its psychological implications (e.g., at the level of attention, perception, and decision). We also review 4 lines of theoretical progress regarding the law of Prägnanz-the brains tendency of being attracted towards states corresponding to the simplest possible organization, given the available stimulation. The first considers the brain as a complex adaptive system and explains how self-organization solves the conundrum of trading between robustness and flexibility of perceptual states. The second specifies the economy principle in terms of optimization of neural resources, showing that elementary sensors working independently to minimize uncertainty can respond optimally at the system level. The third considers how Gestalt percepts (e.g., groups, objects) are optimal given the available stimulation, with optimality specified in Bayesian terms. Fourth, structural information theory explains how a Gestaltist visual system that focuses on internal coding efficiency yields external veridicality as a side effect. To answer the fundamental question of why things look as they do, a further synthesis of these complementary perspectives is required.

What Does Visual Agnosia Tell Us About Perceptual Organization and Its Relationship to Object Perception

The authors studied 2 patients, S.M. and R.N., to examine perceptual organization and its relationship to object recognition. Both patients had normal, low-level vision and performed simple grouping operations normally but were unable to apprehend a multielement stimulus as a whole. R.N. failed to derive global structure even under optimal stimulus conditions, was less sensitive to grouping by closure, and was more impaired in object recognition than S.M. These findings suggest that perceptual organization involves a multiplicity of processes, some of which are simpler and are instantiated in lower order areas of visual cortex (e.g., collinearity). Other processes are more complex and rely on higher order visual areas (e.g., closure and shape formation). The failure to exploit these latter configural processes adversely affects object recognition.

Microgenesis and Ontogenesis of Perceptual Organization Evidence From Global and Local Processing of Hierarchical Patterns

In two experiments, visual search and speeded classification were used to study perception of hierarchical patterns among participants aged 5 to 23 years. Perception of global configurations of few-element patterns and local elements of many-element patterns showed large age-related improvements. Only minor age-related changes were observed in perception of global configurations of many-element patterns and local elements of few-element patterns. These results are consistent with prior microgenetic analyses using hierarchical patterns. On the one hand, the rapid and effortless grouping of many small elements and the individuation of few large elements both mature by age 5. In contrast, the time-consuming and effortful grouping of few large elements and the individuation of many small elements improve substantially with age, primarily between ages 5 and 10. These findings support the view that perceptual organization involves multiple processes that vary in time course, attentional demands, and developmental trajectories.

Emergence of Global Shape Processing Continues Through Adolescence

The developmental trajectory of perceptual organization in humans is unclear. This study investigated perceptual grouping abilities across a wide age range (8-30 years) using a classic compound letter global/local (GL) task and a more fine-grained microgenetic prime paradigm (MPP) with both few- and many-element hierarchical displays. In the GL task, contrary to adults, both children and adolescents exhibited a classic local bias. In the MPP, all 3 age groups evinced a bias to individuate the few-element displays; however, the ability to encode the global shape of the many-element displays at the short prime durations increased with age. These results indicate that the full process of garnering shape information from perceptual grouping, which is essential for the ability to do fast and efficient object recognition and identification, develops late into adolescence.

Selective attention to global and local levels in the comparison of hierarchical patterns

Selective attention to the global and the local levels of hierarchical patterns was studied, using a simultaneous comparison task. Subjects were asked to determine whether two simultaneously presented patterns were the same or different at the designated level. On half of the trials the comparison outputs on the two levels were compatible, and on the other half they were incompatible. With patterns composed of many relatively small elements, global and local sameness and difference were detected equally fast in the compatible trials. When incompatible output was present, irrelevant global sameness and difference interfered with “same”/‘different” judgments on the local elements and on texture, but not vice versa. With patterns composed of a few relatively large elements, global dominance was observed in the compatible trials. In the incompatible trials the interference from conflicting irrelevant output was mutual and affected mostly “same” judgments. These results are discussed in terms of the interaction between the separability and integrality of the dimensions involved and task demands. It is proposed that dimensional analysis is necessary but not sufficient for successful selective attention to a stimulus dimension.

Figure-Ground Segmentation Can Occur Without Attention

The question of whether or not figure-ground segmentation can occur without attention is unresolved. Early theorists assumed it can, but the evidence is scant and open to alternative interpretations. Recent research indicating that attention can influence figure-ground segmentation raises the question anew. We examined this issue by asking participants to perform a demanding change-detection task on a small matrix presented on a task-irrelevant scene of alternating regions organized into figures and grounds by convexity. Independently of any change in the matrix, the figure-ground organization of the scene changed or remained the same. Changes in scene organization produced congruency effects on target-change judgments, even though, when probed with surprise questions, participants could report neither the figure-ground status of the region on which the matrix appeared nor any change in that status. When attending to the scene, participants reported figure-ground status and changes to it highly accurately. These results clearly demonstrate that figure-ground segmentation can occur without focal attention.

Hemispheric processing of global form, local form, and texture

Hemispheric processing of global form, local form, and texture of hierarchical patterns composed of many, relatively small elements and patterns composed of few, relatively large elements was examined in two experiments, employing a Stroop-type paradigm. In experiment 1 subjects were instructed to attend either to the global or the local level of the pattern and to identify the form at the designated level. In experiment 2 subjects were to identify the global form or the texture. A right visual field (left hemisphere) advantage was obtained for detection of local form, and a left visual field (right hemisphere) advantage was obtained for detection of global form. When many-element patterns were processed in terms of global form and texture, the results failed to show reliable hemispheric differences. The results suggest that the hemispheres differ in their sensitivity to the relatively more global versus the relatively more local aspects of visual patterns which require focused attention (as in global/local form detection). When the task involved distributed attention (as in texture detection) no lateralized effects were observed.

Perceptual grouping and attention: Not all groupings are equal

We examined grouping under inattention using Driver, Davis, Russell, Turatto, & Freeman’s (2001) method. On each trial, two successive displays were briefly presented, each comprising a central target square surrounded by elements. The task was to judge whether the two targets were the same or different. The organization of the background elements stayed the same or changed, independently of the targets. In different conditions, background elements grouped into columns/rows by color similarity, a shape (a triangle/arrow, a square/cross, or a vertical/horizontal line) by color similarity, and a shape with no other elements in the background. We measured the influence of the background on the target same-different judgments. The results imply that background elements grouped into columns/rows by color similarity and into a shape when no segregation from other elements was involved and the shape was relatively “good.” In contrast, no background grouping was observed when resolving figure-ground relations for segregated units was required, as in grouping into a shape by color similarity. These results suggest that grouping is a multiplicity of processes that vary in their attentional demands. Regardless of attentional demands, the products of grouping are not available to awareness without attention.

Automatic, stimulus-driven attentional capture by objecthood

In three experiments, we investigated whether the mere organization of some elements in the visual field by Gestalt factors into a coherent unit (an object), with no abrupt onset or any other unique transient, could attract attention automatically. Participants viewed a display of nine red and green elements, one of which was the target, and had to identify the target’s color. On some trials, a subset of the elements was grouped by Gestalt factors (collinearity, closure, and symmetry) into an object. The object was task-irrelevant and unpredictive of the target. Performance on trials with an object present in the display was faster than performance on trials with no object for targets in the object area (a benefit) but slower for targets in a nonobject area (a cost). These findings demonstrate that an object by itself can capture attention automatically in a stimulus-driven manner, much as exogenous cues can.

The perceptual organization of visual objects: a microgenetic analysis.

Primed matching was used to examine the microgenesis of perceptual organization for line configurations that vary in the connectedness between their four line components, and for hierarchical patterns composed of four outline closed figures. The results for the line configurations showed that the configural organization of the disconnected line segments was available for priming very early, and its effect outweighed possible effects of the line components. An early relative dominance of the components was observed for the stimuli whose components were closed figures. These results suggest that uniform connectedness is not necessary for the designation of entry-level units. Disconnected line segments are rapidly organized into configurations, provided the presence of collinearity and/or closure. Closed figural elements are individuated early and are grouped into higher-level units with time.