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Tom Bullock, Mary MacLean, Barry Giesbrecht; Working memory reconstructions using alpha-band activity are disrupted by sensory input.. Journal of Vision 2017;17(10):334. doi: https://doi.org/10.1167/17.10.334.
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Recent work suggests that the spatial distribution of alpha-band activity across the scalp measured by electroencephalography (EEG) can be used to track specific spatial representations of stimuli held in working memory (WM; Foster et al. 2016). Here, we tested the extent to which these representations can be disrupted by sensory input. Participants (n=18) performed a simple recall task involving the presentation of a circular stimulus (250ms) at one of eight equally spaced locations circumventing fixation and the subsequent recall of the stimulus location following a brief retention period (1750ms). Critically, we manipulated the representation of the stimulus during the retention period by 1) requiring participants to close their eyes immediately after stimulus offset and 2) presenting a mask immediately after stimulus offset. Requiring participants to close their eyes eliminated the potential for continued spatial selection during the retention period, and masking reduced possible after-image effects. Participants engaged in four conditions while we recorded EEG at the scalp: eyes-open, eyes-closed, eyes-open/masked, eyes-closed/masked. We used an inverted encoding modeling technique to estimate location-selective tuning functions (TFs) from spatially distributed alpha activity measured across the scalp during the target and retention period (Foster et al. 2016). We then folded these TFs at center and calculated slope at each time-point. We observed a robust stimulus representation (greater positive slope) during the stimulus presentation, followed by a decline in the quality of the representation during the 500ms post-stimulus offset. Between 200-500ms post-stimulus the mask caused significant disruption to the spatial representation of the stimulus, relative to the unmasked conditions (p< .05). Furthermore, the stimulus representation was not reliable in the eyes-closed/masked condition during the final 1000 ms of the retention period (p< .05), and WM precision was reduced (p< .05). Together, these effects suggest alpha-band WM representations are not immune to disruption by sensory input.
Meeting abstract presented at VSS 2017
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