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Carson Pun, Stephen M. Emrich, Susanne Ferber; In and out of consciousness - the role of visual short-term memory. Journal of Vision 2010;10(7):722. doi: 10.1167/10.7.722.
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What is involved in holding a visual object in conscious awareness? We approached this question by using a typical shape-from-motion (SFM) display, in which fragmented line-drawings of an object move relative to a background of randomly oriented lines. When static, the fragmented line-drawings are indistinguishable from the line background, but when motion is added observers can readily distinguish the figure from the ground. The resulting percept of the object persists briefly even after the motion has stopped. During this persistence period, the object fades out of consciousness as it disintegrates and blends into the background. We wanted to examine whether visual short-term memory (VSTM) is involved in sustaining the percept during the persistence period. Participants observed SFM displays that were presented bilaterally and were asked to indicate with a button press for how long the object persisted after the motion stopped. While participants performed this task, we measured their brain activity using electroencephalography (EEG). Specifically, we examined the contralateral delay activity (CDA) which is a negative ERP waveform computed as the difference between contralateral and ipsilateral activity and whose amplitude correlates with VSTM capacity. In other words, we used a neural index of VSTM to test for its involvement. We observed a greater negativity (larger CDA amplitude) for conditions that induced perceptual persistence compared to a control condition. This suggests that VSTM is involved in holding a visual object in conscious awareness.
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