James R. Pomerantz

Imagery, propositions and the form of internal representations

This paper has four major sections: First, we review the basic arguments offered by Pylyshyn (Psychological Bulletin, 1973, 80, 1–24) and others against using imagery as an explanatory construct in psychology. Second, we consider each of these points and find none that speak against any but the most primitive notions of imagery. Third, we review the results of various experiments on imagery. In each case, we compare two explanations of the findings: one which assumes the existence of a surface image manifesting emergent properties, and one which assumes that all internal representations are coded in terms of “abstract propositions.” We find imagery hypotheses to be at least as adequate as those based on propositional representation. Finally, we conclude that debate about the ultimate foundations of internal representation is fruitless; the empirical question is whether images have properties that cannot be derived directly from more abstract propositional structures.

Global and local precedence: selective attention in form and motion perception.

: This study explores the perception of stimuli at two levels: local parts and the wholes that comprise these parts. Previous research has produced contradictory results. Some studies (e.g., Pomerantz & Sager, 1975) show local precedence, in which the local parts are more difficult to ignore in selective attention tasks. Other studies (e.g., Navon, 1977) have shown the opposite effect, global precedence. The present five experiments trace the causes of this discrepancy by exploring the effects of the relative discriminabilities of the local and global levels of the stimuli and the differences between two different measures of selective attention, namely, Stroop-type interference (attributable to incongruity on the irrelevant dimension) and Garner-type interference (attributable to variability on the irrelevant dimension). The experiments also examine whether the precedence effects previously examined in form perception generalize to motion perception. The results show that (a) some cases of global precedence are due solely to the greater perceptual discriminability of the global level and thus demonstrate only that more discriminable stimuli are harder to ignore; (b) instances of both local and global precedence can be demonstrated for certain types of stimuli, even when the discriminabilities of their local and global levels have been equated; and (c) the Stroop and Garner measures of selective attention are not equivalent but instead measure different types of interference. In addition, a distinction is made between two fundamentally different types of part-whole relationships that exist in visual configurations, one based only on the positions of the parts (Type P) and one based also on the nature of the parts (Type N). Previous research has focused on Type P, which appears to be irrelevant to the broader questions of Gestalt and top-down effects in perception. It is concluded that bona fide cases of both local and global precedence have been amply documented but that no general theory can account for why or when these effects will appear until we better understand both the nature of part-whole relationships and the perceptual processes that are tapped by different measures of selective attention.

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.

Grouping by proximity: Selective attention measures

The role of element proximity in perceptual grouping was examined in tasks requiring speeded discrimination of two-element visual patterns. Grouping of two elements was defined as the failure of attention to be focused on one element selectively in filtering tasks where only that one element was relevant to the discrimination. Failure of selective attention was measured by the degree of interference caused by variation of the irrelevant element. Grouping was shown to diminish monotonically as the spacing between two elements was increased. At a given spacing, grouping could be reduced or eliminated by the introduction of a third element into the stimulus field, presumably because the addition of this element triggered a reorganization of the perceptual field into a new grouping structure. Grouping appeared to facilitate performance on condensation tasks requiring distributed attention, to the degree that the condensation tasks were actually easier than the filtering tasks at close proximities. Paradoxically, for some tasks, moving an irrelevant element away from a relevant one actually impaired performance, suggesting that paying attention to irrelevant information could be beneficial. This result, if generalizable, suggests that grouping be conceptualized not as an automatic process under preattentive control but as an optional process under strategic control.

Asymmetric integrality with dimensions of visual pattern

Subjects performed speeded classification tasks with visual patterns that varied in two dimensions: the elements used to construct the patterns (the letters X, Y, V, and 0) and the configurations formed by the spatial arrangement of the elements. Neither dimension could be attended to selectively without interference from the other, indicating that the dimensions are integral. But the amount of interference between the two dimensions was asymmetrical; irrelevant variation of elements (while classifying by configuration) was harder to ignore than irrelevant variation of configuration (while classifying by elements). This held true whether the element or the configuration discrimination was easier in tasks with no irrelevant variation. It is concluded that the asymmetry is due to attentional strategies in the processing of these patterns and not to the discriminabilities of the dimensions used.

Grouping and emergent features in vision: toward a theory of basic Gestalts.

Gestalt phenomena are often so powerful that mere demonstrations can confirm their existence, but Gestalts have proven hard to define and measure. Here we outline a theory of basic Gestalts (TBG) that defines Gestalts as emergent features (EFs). The logic relies on discovering wholes that are more discriminable than are the parts from which they are built. These wholes contain EFs that can act as basic features in human vision. As context is added to a visual stimulus, a hierarchy of EFs appears. Starting with a single dot and adding a second yields the first two potential EFs: the proximity (distance) and orientation (angle) between the two dots. A third dot introduces two more potential EFs: symmetry and linearity; a fourth dot produces surroundedness. This hierarchy may extend to collinearity, parallelism, closure, and more. We use the magnitude of Configural Superiority Effects to measure the salience of EFs on a common scale, potentially letting us compare the strengths of various grouping principles. TBG appears promising, with our initial experiments establishing and quantifying at least three basic EFs in human vision.

Wholes, holes, and basic features in vision

A key issue for theories of perception is specifying the primitives used by the visual system to isolate and identify the objects in an image. Although local features are typically suggested, there is good reason to look for global, configural features as primitives too. Chen et al.s specific proposal of topological features is both explicit and capable of capturing important global information. It may seem surprising that topology can be detected by honeybees, but Chens results are in keeping with other findings from humans that global properties are sometimes perceived better than local ones and thus might be basic.

Perceptual organization and schizotypy

The preattentive visual information processing of hypothetically psychosis-prone college subjects was evaluated using three different paradigms, target detection (n = 57), visual suffix effect (n = 57), and configural superiority effect (n = 68). It was hypothesized that anhedonic subjects would show the same perceptual organization deficits reported in process schizophrenics and that perceptual aberration-magical ideation subjects and depressed subjects would perform similarly to control subjects. In each study, anhedonics performed similarly to each comparison group, even though there was adequate power to detect performance differences if they existed. A framework for understanding the visual information-processing deficits of schizophrenics and high-risk subjects is proposed.

Subjective contours can facilitate performance in a reaction-time task

Subjective contours were compared with objective contours in their ability to facilitate performance in speeded tasks that required judging the position of a dot or the slope of a line segment relative to the contour. Subjective contours were found to reduce both reaction times and error rates for dot localization but not for the more difficult slope discrimination task. These results add to the growing body of evidence suggesting that subjective contours have functional properties similar to those of objective contours.

The rubber pencil illusion

When a straight, rigid line segment is put into certain types of motion, it appears to an observer to lose its rigidity and become rubbery, as in the well-known “rubber pencil illusion.“ The factors controlling this illusion were examined, including the nature of the motion employed (harmonic or linear oscillation), the amplitudes of the translational and rotational components of the motion, and the phase relationship between these two components. The effect is shown to be due to visual persistence. The status of the illusion as a potential counterexample to the rigidity principle (that moving, two-dimensional arrays will be perceived as rigid) is discussed.