Academic journal article Memory & Cognition

Indirect Assessment of Visual Working Memory for Simple and Complex Objects

Academic journal article Memory & Cognition

Indirect Assessment of Visual Working Memory for Simple and Complex Objects

Article excerpt

Previous research has shown that visual search performance is modulated by the current contents in visual working memory (VWM), even when the contents of VWM are irrelevant to the search task. For example, visual search is faster when the target-rather than a distractor-is surrounded by a shape currently held in VWM. This study uses the modulation of visual search by VWM to investigate properties of VWM. Participants were asked to remember the color or the shape of novel polygons whose "goodness" of figure varied according to Garner's (1962) rotation and reflection transformation principle. During the memory retention interval, participants searched for a tilted line among vertical lines embedded inside colored polygons. Search was faster when the target-rather than a distractor-was enclosed by the remembered polygons. The congruity effect diminished with increasing memory load and decreasing figure goodness. We conclude that congruity effects in visual search can indirectly assess VWM representation strength.

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Many everyday tasks require us to buffer visual information for a few seconds after its disappearance. For example, when crossing a busy street, we must look left and right and remember momentary traffic conditions before deciding to cross. In team sports, players often need to remember the positioning of teammates and opponents in order to determine their next movement. The brief buffering and manipulation of visual information relies on visual working memory (VWM): an online memory that is important for maintaining temporal continuity. In the laboratory, VWM is often operationally defined by performance in a short-term, change-detection task in which observers judge whether two visual displays separated by a few seconds of retention interval are the same or different (Luck & Vogel, 1997; Pashler, 1988; Phillips, 1974; Rensink, 2002). Using this procedure, researchers have found that the capacity of VWM is no more than three or four objects (Alvarez & Cavanagh, 2004; Luck & Vogel, 1997; Olsson & Poom, 2005) and that the measured capacity varies for different visual attributes, such as colors, gabor patches, random polygons, and faces (Alvarez & Cavanagh, 2004; Eng, Chen, & Jiang, 2005; Olsson & Poom, 2005).

Although the change detection task has become the standard procedure for the assessment of VWM, several criticisms have been raised in regard to this task (Hollingworth, 2003; Landman, Spekreijse, & Lamme, 2003; Makovski, Sussman, & Jiang, 2008). Moreover, by inducing participants to remember information for the sake of producing a memory, the task takes a "static approach" toward working memory. This approach can be contrasted with everyday vision tasks, where working memory is often used dynamically. For example, Hayhoe and colleagues (Ballard, Hayhoe, & Pelz, 1995; Droll, Hayhoe, Triesch, & Sullivan, 2005; Hayhoe & Ballard, 2005) found that during visually guided motor tasks-such as picking up a blue block and placing it at a designated location-participants usually do not fill up their VWM capacity. Instead, they prefer to keep a single piece of information in VWM at once and look back at a display again when more information is needed. Thus, it is important that we assess the characteristics of VWM during online perception, which may differ from those of VWM in an idealized change-detection task.

Recent research by Soto, Downing, Woodman, and colleagues has revealed important interactions between VWM and online perception (Downing, 2000; Downing & Dodds, 2004; Soto, Heinke, Humphreys, & Blanco, 2005; Soto, Humphreys, & Heinke, 2006; Woodman & Luck, 2004, 2007; Woodman, Vogel, & Luck, 2001). For example, VWM can influence visual search when the contents of VWM are both relevant and irrelevant to the search task. Holding the exact target template in VWM and searching for that object results in faster search speed, in comparison with holding a general description of the target in working memory (Vickery, King, & Jiang, 2005; Wolfe, Butcher, Lee, & Hyle, 2003). …

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