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Ingmar de Vries, Joram van Driel, Christian Olivers; Posterior alpha EEG dynamics dissociate visual search template from accessory memory items.. Journal of Vision 2016;16(12):761. doi: 10.1167/16.12.761.
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© 2017 Association for Research in Vision and Ophthalmology.
Current models of visual search assume that the brain maintains an active visual working memory (VWM) representation of what we are currently looking for: the "attentional template". Recent evidence suggests that template memory items can be dissociated from "accessory" memory items in VWM, which do not guide attention because they are needed for later use. However, it remains unclear which electrophysiological mechanisms dissociate between template and accessory memories. Here, we measured EEG of 20 human subjects while they performed a VWM task in which they remembered a lateralized item, followed by an 1800 millisecond delay, and then two consecutive search tasks. The order of the search tasks determined the status of the memory item during anticipation of the first search: the lateralized item was either needed in the first search task (template) or in the second search task (accessory). After the first search a second 1800 millisecond delay followed in which the item that was accessory during the first delay became the visual search template for the second search. Time-frequency analysis showed clear posterior alpha-band (8–14 Hz) lateralization effects during the first delay period, consisting of both local power suppression and reduced parieto-occipital interregional phase synchronization in regions contralateral compared to ipsilateral to the memory item. Importantly, these lateralization effects were stronger when the memory item was a template compared to when it was accessory. In contrast, event-related potential analysis revealed that the contralateral delay activity (CDA) was similar across all conditions. Together, these findings are consistent with the idea that alpha oscillations support a state of increased processing or excitability in task-relevant cortical regions. Our results may thus reflect enhanced cortical prioritization of the memory item when this item has the cognitive status of a visual search template.
Meeting abstract presented at VSS 2016
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