Academic journal article Perception and Psychophysics

The Role of Closure in Defining the "Objects" of Object-Based Attention

Academic journal article Perception and Psychophysics

The Role of Closure in Defining the "Objects" of Object-Based Attention

Article excerpt

Many recent studies have concluded that the underlying units of visual attention are often discrete objects whose boundaries constrain the allocation of attention. However, relatively few studies have explored the particular stimulus cues that determine what counts as an "object" of attention. We explore this issue in the context of the two-rectangles stimuli previously used by many investigators. We first show, using both spatial-cuing and divided-attention paradigms, that same-object advantages occur even when the ends of the two rectangles are not drawn. This is consistent with previous reports that have emphasized the importance of individual contours in guiding attention, and our study shows that such effects can occur in displays that also contain grouping cues. In our divided-attention experiment, however, this contour-driven same-object advantage was significantly weaker than that obtained with the standard stimulus, with the added cue of closure-demonstrating that contour-based processes are not the whole story. These results confirm and extend the observation that same-object advantages can be observed even without full-fledged objects. At the same time, however, these studies show that boundary closure-one of the most important cues to objecthood per se-can directly influence attention. We conclude that object-based attention is not an all-or-nothing phenomenon; object-based effects can be independently strengthened or weakened by multiple cues to objecthood.

Visual attention is fundamentally a process of selection: It helps us deal with a potentially overwhelming amount of incoming information by selecting only some information for further processing. A considerable amount of research in the past few decades has been devoted to determining the nature of this selection process, and in particular to exploring the nature of the underlying units of selection. Most traditional theories of attention either assumed or explicitly argued that attentional selection was a spatial operation; attention was characterized as a spotlight or zoom lens that focused processing resources on whatever visual information fell within the attended spatial region (for a review, see Cave & Bichot, 1999). Such spatial models inherently ignored the actual structure of the attended information: The process of selection was based not on the information itself, but rather on an extrinsic filter (the "spotlight") through which the information was gated. More recent models of attention, in contrast, have stressed the complex interplay between attention and the actual structure of the attended information. For example, many studies of object-based attention have demonstrated that the underlying units of attention are often discrete visual objects: Rather than spreading uniformly through a spatially defined region, attention flows more readily through individual objects and/or is constrained by their boundaries (for a review, see Scholl, 2001).

Although many studies of object-based attention have contrasted objects and locations, relatively few studies have explored in detail what can count as an object of attention in the first place. Objects are sometimes contrasted with other high-level classes of entities, such as groups (e.g., Driver, Davis, Russell, Turatto, & Freeman, 2001), parts (e.g., Vecera, Behrmann, & Filapek, 2001; Vecera, Behrmann, & McGoldrick, 2000), and nonsolid substances (e.g., vanMarle & Scholl, 2003). For the most part, however, the stimuli used in studies of object-based attention are defined only intuitively, with little attention paid to the individual image cues from which objects are formed (for a few recent exceptions, see Avrahami, 1999; Barenholtz & Feldman, 2003; Marrara & Moore, 2003; Reppa & Leek, 2003; Scholl, Pylyshyn, & Feldman, 2001; Watson & Kramer, 1999). Here, we explore the importance of a particular cue, closure, using what is perhaps the best known and most often studied type of stimulus in research on object-based attention: the tworectangles display, originally studied by EgIy, Driver, and Rafal (1994) and since used in various forms by many other researchers (e. …

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