Academic journal article Perception and Psychophysics

Closure of Salient Regions Determines Search for a Collinear Target Configuration

Academic journal article Perception and Psychophysics

Closure of Salient Regions Determines Search for a Collinear Target Configuration

Article excerpt

Grouping operations offer an effective mechanism by which to structure complex visual scenes. Among the various principles that support element integration, closure may be regarded as a main factor in shape extraction. In five experiments, we investigated the impact of grouping by closure on search for target configurations made up of collinearly arranged corner junctions. Systematic variations in the configuration of distractor elements were explored to investigate how the figural information of distractors interferes with target detection. The results showed no search interference for distractor configurations that were open forms. By contrast, distractors making up closed forms reduced the efficiency of search performance, indicating closure as a major contributor to form detection in multielement configurations. In conclusion, the effects reported may be considered to arise from mechanisms of unit formation that support the rapid extraction of salient regions to guide search.

Unit formation can be regarded to be a major function in the organization of perceptual information. Gestalt psychology (Koffka, 1935; Wertheimer, 1923) originally demonstrated that the association of distinct elements into groups is subject to a set of basic principles (e.g., similarity, closure, and proximity), which are regarded as primary operations forming perceptual units prior to detailed analysis. In contrast, constructivist approaches assume that visual perception proceeds from the analysis of elementary features and progresses by the integration of features into coherent objects, which involves visual attention (Treisman & Gelade, 1980). Psychophysical investigations in support of a constructivist position have identified a number of visual primitives, organized in terms of separable dimensions of such basic features (e.g., luminance, color, or orientation; see Treisman & Gormican, 1988; Wolfe, 1998; Wolfe & Horowitz, 2004).

Besides basic primitives, visual processing of more complex units has been documented, with unit formation operating in an effortless manner. Support for this idea is provided by evidence that perceptual configurations may be detected more efficiently than their isolated features (Pomerantz, Sager, & Stoever, 1977; see also Treisman & Paterson, 1984). In addition, visual search studies have shown that component parts may be grouped prior to the engagement of attention (e.g., Moore & Egeth, 1997; Rensink & Enns, 1995), and that search may be more effectively guided by integrated shapes than by corresponding local features (Found & Müller, 1997). Moreover, there is evidence that early visual, or preattentive, processes operate on the basis of a variety of grouping principles-notably, similarity (Duncan, 1984; Duncan & Humphreys, 1989; Humphreys, Quinlan, & Riddoch, 1989), closure (Elder & Zucker, 1993; Han, Humphreys, & Chen, 1999a; Kovács & Julesz, 1993), and proximity (Han, Humphreys, & Chen, 1999b). These studies complement those in which the primitive features have been described by showing that complex visual units are, at least to some extent, available at early stages of processing.

In general, models of perceptual grouping assume that element integration is achieved on the basis of similarity and proximity, segregating distinct regions within the visual field (e.g., Geisler & Super, 2000). Moreover, collinearity and closure supply critical information for shape extraction, supporting the separation of figure from ground (e.g., Elder & Zucker, 1993; Field, Hayes, & Hess, 1993; Kovács & Julesz, 1993). Visual search studies have demonstrated that the integration of separate collinear vertices into closed forms permits efficient processing, whereas groupings that do not exhibit closure are processed relatively inefficiently (Donnelly, Humphreys, & Riddoch, 1991; Donnelly, Weekes, Humphreys, & Albon, 1998). For instance, search for a misoriented vertex element was performed efficiently and independently of the number of distractor vertices when the distractor elements could be grouped on the basis of collinearity and closure to form a coherent shape description. …

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