Academic journal article Psychonomic Bulletin & Review

Selective Storage and Maintenance of an Object's Features in Visual Working Memory

Academic journal article Psychonomic Bulletin & Review

Selective Storage and Maintenance of an Object's Features in Visual Working Memory

Article excerpt

It has been shown that we have a highly capacity-limited representational space with which to store objects in visual working memory. However, most objects are composed of multiple feature attributes, and it is unknown whether observers can voluntarily store a single attribute of an object without necessarily storing all of its remaining features. In this study, we used a masking paradigm to measure the efficiency of encoding, and neurophysiological recordings to directly measure visual working memory maintenance while subjects viewed multifeature objects and were required to remember only a single feature or all of the features of the objects. We found that measures of both encoding and maintenance varied systematically as a function of which object features were task relevant. These experiments show that individuals can control which features of an object are selectively stored in working memory.

Our ability to temporarily maintain information is limited by the small capacity of approximately three to four objects of visual working memory (VWM; Irwin & Andrews, 1996; Luck & Vogel, 1997; Vogel, Woodman, & Luck, 2001). This seemingly unworkable limitation can be overcome by powerful selection mechanisms that regulate access to VWM so that only the most relevant objects consume its capacity (Chun & Potter, 1995; Potter, 1976; Schmidt, Vogel, Woodman, & Luck, 2002; Vogel, Luck, & Shapiro, 1998). Although individuals differ in how effectively they implement these processes, it is clear that we can control which objects are held in VWM on the basis of current task goals (Vogel, McCollough, & Machizawa, 2005). However, most objects in the environment are composed of multiple features, and it is unclear whether we obligatorily encode all of an item's features into VWM when an object is selected or whether only the task-relevant features are stored in memory. That is, when asked to remember only the color of an object, must we also represent all of the other attributes of the object, such as its shape and texture?

Evidence from the object-based attention literature appears to support the notion of obligatory storage of all features of an attended object. These studies often report that attention to an object automatically activates an object representation containing all of its features (Duncan, 1984; O'Craven, Downing, & Kanwisher, 1999; Vecera & Farah, 1994). Indeed, previous work examining VWM capacity could be interpreted as supporting this general view. Specifically, we presented arrays of multifeatured objects (e.g., color, orientation) and asked subjects to remember either one feature or all of the features of objects (Luck & Vogel, 1997; Vogel et al., 2001). We found that subjects were just as accurate at remembering all object features as they were at remembering single features. We took this as evidence that the storage capacity of VWM is determined by the number of objects in memory rather than the amount of feature information represented. However, this conclusion rests on one critical, but untested assumption: that in the single-feature conditions, subjects were capable of remembering just the one feature from each object without necessarily storing the other visible, but irrelevant features. This seems plausible, given that previous studies of temporary memory storage (Stefurak & Boynton, 1986) and betweentrial priming during visual search (e.g., Kristjansson, 2006a; Maljkovic & Nakayama, 1994) suggest that such feature-selective processing can occur. Consequently, an alternative interpretation of these results is that subjects are incapable of selectively remembering only one feature of an object and thereby obligatorily store all features, which would explain why there was equivalent performance in the single-feature and multifeature conditions.

In contrast to the obligatory storage hypothesis, there is considerable neurophysiological evidence that cortical neurons preferentially represent only the task-relevant properties of objects during memory retention intervals (see, e. …

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