False pop out.

A single, unique target often pops out quickly and efficiently from a field of homogenous distractors in visual search. Pop out has helped shape theories of visual attention and feature integration as well as to identify basic features in human vision. Here we report a new phenomenon, false pop out, wherein one of the homogenous distractors competes with the singleton target to pop out, perhaps by breaking an overall grouping or pattern emerging from the display. We show the effect occurs with more than 1 type of stimulus, and we discuss the implications of such a counterintuitive finding for theories of visual search.

The experience error and the perils of psychopsychology.

UNLABELLED: 'The stimuli were four similar yellow objects flashing on a white background'. These words might not raise eyebrows when read in a research paper, but they should, because they probably commit the experience error (EE), in which the structure of our percepts is attributed to the stimulus rather than to our perceptual system. These words are less a description of the physical stimulus than of how that stimulus appears to human observers. That is problematic because perception is often incomplete or illusory. When we commit the EE, we confuse the external, physical stimulus with a response, namely our perception of it. Thus, we may end up relating psychological responses to stimuli solely to our psychological descriptions of those stimuli. This in turn may transform psychophysics into 'psychopsychology' and thus inadvertently leave the physical world out of our explanation of perception; and it may potentially demote proper experiments to correlational studies that lack the capacity to support inferences about cause and effect. Identified long ago, the EE is nearly forgotten today. We aim to reintroduce, clarify, and illustrate the idea more clearly, as well as to suggest possible preventions or cures. WIREs Cogn Sci 2014, 5:509-517. doi: 10.1002/wcs.1302 For further resources related to this article, please visit the WIREs website. CONFLICT OF INTEREST: The author has declared no conflicts of interest for this article.

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 brain's 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 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.

Where similarity beats redundancy: the importance of context, higher order similarity, and response assignment.

People are especially efficient in processing certain visual stimuli such as human faces or good configurations. It has been suggested that topology and geometry play important roles in configural perception. Visual search is one area in which configurality seems to matter. When either of 2 target features leads to a correct response and the sequence includes trials in which either or both targets are present, the result is a redundant-target paradigm. It is common for such experiments to find faster performance with the double target than with either alone, something that is difficult to explain with ordinary serial models. This redundant-targets study uses figures that can be dissimilar in their topology and geometry and manipulates the stimulus set and the stimulus?response assignments. The authors found that the combination of higher order similarity (e.g., topological) among the features in the stimulus set and response assignment can effectively overpower or facilitate the redundant-target effect, depending on the exact nature of the former characteristics. Several reasonable models of redundant-targets performance are falsified. Parallel models with the potential for channel interactions are supported by the data.

Contour grouping inside and outside of facial contexts.

We examine how contours group in isolation compared with when they are embedded in face-like contexts. As previously shown, contours that seem to group by phenomenological observation also show powerful effects on task performance: with contours that group, selective attention to one while ignoring another is poor (as indexed by Garner Interference (GI), but not Stroop Interference), whereas divided attention across contours is good. With contours that do not group, however, the reverse happens. Here we test pairs of curved lines (parentheses) displayed either in isolation or within contexts including cartoon faces, where these curves may serve as mouths or eyebrows. The results with isolated contours replicate previous findings of poor selective attention, but within face-like contexts the same contours showed nearly perfect selective attention (i.e., zero GI). Thus, contour grouping was weaker inside than outside of faces, a finding that contrasts with the widely-held belief that faces are processed configurally, not by local features.

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 Chen's results are in keeping with other findings from humans that global properties are sometimes perceived better than local ones and thus might be basic.