Academic journal article Perception and Psychophysics

Object and Spatial Representations in the Corner Enhancement Effect

Academic journal article Perception and Psychophysics

Object and Spatial Representations in the Corner Enhancement Effect

Article excerpt

Cole, Gellatly, and Blurton (2001) have shown that targets presented adjacent to geometric corners are detected more efficiently than targets presented adjacent to straight edges. In six experiments, we examined how this corner enhancement effect is modulated by corner-of-object representations (i.e., corners that define an object's shape) and local base-level corners that occur as a result of, for instance, overlapping the straight edges of two objects. The results show that the corner phenomenon is greater for corners of object representations than for corners that do not define an object's shape. We also examined whether the corner effect persists within the contour boundaries of an object, as well as on the outside. The results showed that a spatial gradient of attention accompanies the corner effect outside the contour boundaries of an object but that processing within an object is uniform, with no corner effect occurring. We discuss these findings in relation to space-based and object-based theories of attention.

One issue that has dominated visual attention work for the past 2 decades concerns the perceptual units that the visual system uses to deploy resources across a visual scene. Originally, it was suggested that attention is allocated to unsegmented regions of space, with the common metaphor being an attentional spotlight (e.g., Broadbent, 1982). According to this space-based view of attention, a spotlight is said to traverse the visual field, selecting any stimuli that fall within its "illuminated" boundary for further processing. Although variations on the spotlight theme exist, such as gradient theory (Downing & Pinker, 1985; Hughes & Zimba, 1985; LaBerge & Brown, 1989) and the zoom lens model (Eriksen & St. James, 1986; Eriksen & Yeh, 1985), all these models implicate spatial location as the basis of selection. Other theories (Driver & Baylis, 1989; Duncan, 1984; Neisser, 1967), however, propose that attention is directed to objects and perceptual groups that have been parsed preattentively on the basis of Gestalt principles of perceptual organization. In some sense, these object-based theories view the selection of a spatial location as epiphenomenal, since objects necessarily occupy a region of space; however, the "real" basis of attention is seen as the object representation.

Although the debate has become polarized, whereby attentional allocation is seen as being either object-based or space-based, attention is likely to operate on both object and spatial representations. Indeed, a growing number of studies have demonstrated that selection can occur for both objects and space (e.g., Vecera, 1994). This point was emphasized by Duncan ( 1984) in an article commonly viewed as containing the original argument for object-based attention. Furthermore, Scholl (2001) has commented that the distinction between the processing of objects and spatial locations is somewhat blurred and that the two need not be mutually exclusive. For example, Scholl states that the shape of LaBerge and Brown's (1989) spatial spotlight may deform around an object (see also Vecera & Farah, 1994). The principal aim of the present research was to assess how a relatively new visual phenomenon, reported by Cole, Gellatly, and Blurton (2001), relates to space-based and object-based theories of attention. Specifically, we examined whether the distribution of attention following the onset of a new object can concur with both object-based and space-based views of attention.

Cole et al. (2001) showed that a stimulus presented in a region of space adjacent to a corner of a new object receives a processing advantage, as compared with a stimulus presented adjacent to one of the object's straight edges. For example, reaction time (RT) to detect a target presented next to a corner was relatively reduced, as compared with RT to detect a target presented next to a straight edge. We dubbed this phenomenon the corner enhancement effect (or simply, the comer effect). …

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