![]() ![]() Others show that combining similarity and proximity benefits performance additively ( Kubovy & van den Berg, 2008). In contrast, similarity benefits emerge when uniform connectedness is included ( Han et al., 1999a). ![]() One robust finding is that discrimination is facilitated by proximity more than by similarity ( Ben-Av & Sagi, 1995 Han, Humphreys, & Chen, 1999a Quinlan & Wilton, 1998) see Table 1. Secondly, although visual arrays incorporating Gestalt grouping principles facilitate perceptual task performance, the degree of improvement varies. As such, grouping appears to automatically facilitate visual perception. For example, perceptual discriminations remain accurate when stimulus arrays can be grouped by similarity, even during conditions of inattention ( Moore & Egeth, 1997). Support for this perspective stems from perceptual judgments of grouped elements being made in the absence of attention ( Driver, Davis, Russell, Turatto, & Freeman, 2001 Lamy, Segal, & Ruderman, 2006 Moore & Egeth, 1997 Russell & Driver, 2005). During this preattentive stage the visual field is divided into discrete objects based on Gestalt principles ( Duncan, 1984, Neisser, 1967). First, processing Gestalt grouping cues is thought to occur preattentively ( Duncan, 1984 Duncan & Humphreys, 1989 Kahneman & Treisman, 1984 Moore & Egeth, 1997 Neisser, 1976, but see also Ben-Av, Sagi, & Braun, 1992 Mack & Rock, 1998 Mack, Tang, Tuma, Kahn, & Rock, 1992). Several key findings are worth reviewing before returning to VWM. A large literature documents the effects of Gestalt grouping on visual perception. Similarity refers to grouping based on repetition of features such as color ( Wertheimer, 1924/1950). ![]() Uniform connectedness groups physically linked features into a single object ( Palmer & Rock, 1994). Proximity refers to grouping of objects in physical space ( Wertheimer, 1924/1950). Among the various types of Gestalt grouping three are particularly relevant here: proximity, uniform connectedness, and similarity. Gestalt principles make grouped objects appear to “belong together” ( Rock, 1986). ![]() These apparently biological constraints on VWM capacity prompt the following question: Can the storage of visual information within VWM be optimized by grouping cues that enhance perception? One relevant observation is that Gestalt principles of grouping facilitate visual perception ( Wertheimer, 1924/1950) and some evidence shows they may also benefit VWM. In both cases, the neural signature amplitude increases with set size and asymptotes at an individual’s VWM capacity limit (fMRI: Todd & Marois, 2005 CDA: Vogel & Machizawa, 2004). There is convergence between behavioral and neural estimates measured by an event-related potential component termed the contralateral delay related activity (CDA) ( Vogel & Machizawa, 2004) and functional magnetic resonance imaging (fMRI) data ( Todd & Marois, 2004 Xu & Chun, 2006). Behavioral estimates of VWM capacity, defined here as the number of item representations stored simultaneously, converge on a ~4 item limit ( Alvarez & Cavanagh, 2004 Awh, Barton, & Vogel, 2007 Cowan, 2001 Luck & Vogel, 1997). As such, it supports most cognitive tasks but it is limited in capacity. Visual working memory (VWM) allows us to temporarily store and process relevant information from the visual world across temporary interruptions such as saccades. Thus, the Gestalt principle of similarity benefits visual perception, but it can provide benefits to VWM as well. In short, the VWM performance benefit derived from similarity was constrained by spatial proximity such that similar items need to be near each other. Experiment 2 replicated and extended this finding by showing that similarity was only effective when the similar stimuli were proximal. Experiment 1 established the basic finding that VWM performance could benefit from grouping. Here, we investigated whether grouping by similarity benefits VWM. One prevalent Gestalt principle, similarity, has not been examined with regard to facilitating VWM. This introduces the question: do these perceptual benefits extend to VWM? If so, can this be an approach to enhance VWM function by optimizing the processing of information? Previous findings demonstrate that several Gestalt principles (connectedness, common region, and spatial proximity) do facilitate VWM performance in change detection tasks ( Woodman, Vecera, & Luck, 2003 Xu, 2002a, 2006 Xu & Chun, 2007 Jiang, Olson & Chun, 2000). Visual perception processing is facilitated by Gestalt principles of grouping, such as connectedness, similarity, and proximity. Visual working memory (VWM) is essential for many cognitive processes yet it is notably limited in capacity. ![]()
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