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David Sutterer, Joshua Foster, Kirsten Adam, Edward Vogel, Edward Awh; Spatial selectivity of alpha band activity declines with increasing visual working memory load. Journal of Vision 2017;17(10):332. doi: https://doi.org/10.1167/17.10.332.
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Recent work has demonstrated that it is possible to reconstruct spatially-specific channel tuning functions (CTFs) during the encoding and delay period of a working memory (WM) task, using an inverted encoding model (IEM) and electroencephalography (Foster et al., 2016). These CTFs can be derived from the distribution of alpha-band (8-12hz) activity across the scalp, providing a temporally resolved measure of the location of a single position stored in WM. Recent, functional magnetic imaging (fMRI) work has demonstrated that feature specific patterns of bold activity degrade as memory load increases (e.g. Sprague, Ester, and Serences, 2014). Here, we show that the loss of feature specificity with increasing memory load extends to spatially specific patterns of alpha band activity. On each trial, participants encoded and maintained the location of either one or two colored dots while EEG was recorded. After a 1s delay period, participants were cued to report the location of one of the dots. We trained an IEM to assess CTF selectivity for each set-size and found that CTF selectivity decreased when participants maintained two items relative to a single item, consistent with behavioral performance decrements observed with memory load increases. A key debate is whether items are maintained simultaneously (each with lower precision), or if instead only a single item is actively represented at any given time-point (i.e. shifting 1-item focus of attention), but previous fMRI work lacked the temporal resolution to address this question. Simulations revealed that CTF selectivity was significantly higher for the observed two-item activity than would be expected if subjects only actively maintained one of the two items, suggesting that participants simultaneously represented two positions. Together this pattern of results supports the idea that oscillatory activity in the alpha band is integral to online spatial representations during memory maintenance.
Meeting abstract presented at VSS 2017
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