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weiwei zhang, Steve Luck; Can Observers Trade Resolution for Capacity in Visual Working Memory?. Journal of Vision 2010;10(7):723. doi: 10.1167/10.7.723.
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The storage capacity of visual working memory (VWM) is strongly correlated with broad measures of cognitive abilities, but the nature of capacity limits has been the subject of considerable controversy. Some researchers have proposed that VWM stores a limited set of discrete, fixed-resolution representations, whereas others have proposed that VWM consists of a pool of resources that can be allocated flexibly to provide either a small number of high-resolution representations or a large number of low-resolution representations. To distinguish between these possibilities, we asked whether the resolution and capacity of stored representations in VWM is under top-down strategic control. That is, can VWM store more coarse-grained representations or fewer fine-grained representations depending on task demands? To address this question, we used a short-term color recall task in which observers attempted to retain several colors in VWM over a 1- second retention interval and then reported one of them by clicking on a color wheel (Zhang & Luck, 2008, Nature). In one condition, the colors varied continuously across the color wheel, encouraging the retention of precise color information. In a second condition, the color wheel was divided into 9 or 15 homogeneous color wedges, reducing the degree of precision necessary to perform the task. The flexible resource hypothesis predicts that VWM should store fewer colors with higher resolution in the continuous color wheel condition but more colors with lower resolution in the discrete color wheel condition. In contrast, the fixed resolution hypothesis predicts that VWM resolution and capacity must remain constant across conditions. We found that VWM resolution and capacity remained constant across conditions, supporting the fixed resolution slot hypothesis. Follow-up experiments using other methods of manipulating the need to maintain precise representations also found no evidence that subjects could increase the number of items in VWM by storing them with less precision.
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