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Trafton Drew, Todd Horowitz, Jeremy Wolfe, Edward K. Vogel; Neural measures of maintaining and updating object information. Journal of Vision 2009;9(8):172. doi: 10.1167/9.8.172.
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© ARVO (1962-2015); The Authors (2016-present)
Recently, we have reported ERP activity that appears to index both the number of items being maintained in visual working memory (VWM) tasks (Vogel & Machizawa, 2004), and the number of items being tracked during a multiple object tracking (MOT) task (Drew & Vogel, 2008). However, while a similar sustained contralateral negativity is observed for both VWM and MOT tasks, the amplitude of the activity is considerably greater during MOT than during VWM. We hypothesized that this amplitude increase is due to the additional demands of the MOT task over the VWM task. Specifically, while VWM tasks requires mnemonic representations to be maintained for each item, tracking tasks requires these representations to be continuously updated to reflect their present position. We tested this hypothesis by briefly stopping object motion during MOT trials, thus temporarily eliminating the need for spatial updating. This led to a significant decrease in ERP amplitude, which quickly recovered once the objects started moving again. This amplitude change could have been a response to the absence of motion rather than the task demands. In subsequent experiments, we presented subjects with moving displays and required them to either remember the starting values of targets (maintenance only) or to track targets (maintenance + updating). Despite equivalent task difficulty, we found a large amplitude increase in the tracking condition relative to the memory condition. Together, these experiments suggest that VWM and MOT are similar in that both require mnemonic representations of targets, but that MOT requires an additional updating process which leads to an increase in sustained contralateral negativity.
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