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Keisuke Fukuda, Edward K. Vogel; Oscillatory mechanism underlying the VSTM capacity limit: In mind, out of phase. Journal of Vision 2012;12(9):346. doi: 10.1167/12.9.346.
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Visual short term memory (VSTM) enables us to hold a limited amount of information online. ERP studies have discovered a neural correlate of VSTM capacity called the contralateral delay activity (CDA) that tracks how many objects are maintained in VSTM when presented in a single visual hemifield. However, the oscillatory activity that underlies this averaged signal is not well understood. To examine the neural mechanisms, we analyzed the time frequency signals from scalp EEG while participants were performing a whole field change detection task. Specifically, participants were presented with either 1,2,3,4,6, or 8 colored squares for 150ms across the whole visual field, and they were asked to remember as many of them as possible across a 1300ms long retention interval. Here we found that power in the alpha frequency band (8~14hz) during the VSTM retention interval showed a linear reduction from 1 to 3 items, reaching a plateau for larger array sizes. Furthermore, the amount of alpha power reduction in the supra-capacity set sizes (i.e. 4,6 and 8 items) relative to the sub-capacity set sizes (1 and 2 items) highly correlated with individuals’ VSTM capacity estimates such that high capacity individuals successfully reduced the alpha power even in the supra-capacity set sizes whereas low capacity individuals could not. This pattern of power reduction is in line with the phase-shifting account of VSTM capacity (e.g. Siegel, Warden, & Miller, 2009, Raffone & Wolters, 2001) in which object representations in VSTM are individually coded with a carrier frequency (e.g. alpha) separated in phase.
Meeting abstract presented at VSS 2012
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