Academic journal article Memory & Cognition

Visual Working Memory for Global, Object, and Part-Based Information

Academic journal article Memory & Cognition

Visual Working Memory for Global, Object, and Part-Based Information

Article excerpt

We investigated visual working memory for novel objects and parts of novel objects. After a delay period, participants showed strikingly more accurate performance recognizing a single whole object than the parts of that object. This bias to remember whole objects, rather than parts, persisted even when the division between parts was clearly defined and the parts were disconnected from each other so that, in order to remember the single whole object, the participants needed to mentally combine the parts. In addition, the bias was confirmed when the parts were divided by color. These experiments indicated that holistic perceptual-grouping biases are automatically used to organize storage in visual working memory. In addition, our results suggested that the bias was impervious to top-down consciously directed control, because when task demands were manipulated through instruction and catch trials, the participants still recognized whole objects more quickly and more accurately than their parts. This bias persisted even when the whole objects were novel and the parts were familiar. We propose that visual working memory representations depend primarily on the global configural properties of whole objects, rather than part-based representations, even when the parts themselves can be clearly perceived as individual objects. This global configural bias beneficially reduces memory load on a capacity-limited system operating in a complex visual environment, because fewer distinct items must be remembered.

As we move through the world in daily life, we must remember the identity of objects and their locations in the visual environment. Working memory (WM) research has demonstrated that visual WM is limited to around three to four items (Duff & Logic, 1999; Intraub, 1997; Kumar & Jiang, 2005; Logie, 1995; Luck & Vogel, 1997; Vogel, Woodman, & Luck, 200 1 ). In this article, we propose that visual memory for objects depends on the abstraction of incomplete, holistic representations constrained by the limited capacity of visual WM.

Researchers have posited two kinds of holistic representations in visual WM: global configurai and objectbased representations. Global configurai representations permit focus on overall structural properties, rather than on pieces of the visual environment. Focusing on such properties may allow compression of visual information in WM because exact details of scenes are not encoded. The use of object-based representations offers another possible method by which to reduce WM load. Focusing on objects, rather than on object parts, would limit memory load requirements, because not all parts of objects would need to be encoded distinctly. Object-based representations differ from global configura! representations in that the representation is focused on only a limited area, rather than on the complete visual scene,

Results from several visual WM studies indicate that global configurai information, such as the spatial location of visual features relative to one another, are well remembered. Santa (1977) found that participants encoded the spatial locations of three geometric shapes (e.g., a square, a triangle, and a circle) even when they were explicitly instructed to encode only the identity of the shapes, and not their locations. When the participants were tested on their recognition memory for shapes whose locations had been changed, accuracy decreased, as compared with when the locations remained the same. In another study, changing the spatial location of individual objects impeded short-term memory for colors and shapes, but changing the shape or color of the objects did not decrease shortterm memory for locations (Jiang, Olson, & Chun, 2000). When the orientation of elongated lines of dots changed between the target and the probe, memory for the location of the dots decreased, as compared with when the direction of the elongated lines remained the same even when the participants were instructed to ignore the lines (Jiang, Chun, & Olson, 2004). …

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