Posterior alpha and frontal delta oscillations interactively support priority switches within visual working memory.

Abstract

Visual search is assumed to be guided by an active visual working memory representation of what we are currently looking for. This attentional template can be dissociated from accessory memory representations that are only needed prospectively, for a future task, and that until then should be prevented from guiding attention. Little is known about how the brain sequentially prioritizes, and switches between memory representations for successive task goals. We measured EEG while human observers performed two consecutive working memory-guided visual search tasks. Prior to the first search task, a cue instructed observers which item to look for first (current template), and which second (prospective template). During the first delay, leading up to the first of the two searches, posterior alpha power (8-14 Hz) was more suppressed contralateral to the memory item. These lateralized alpha dynamics were stronger if the lateralized item was the imminent search target (current template), than when it was the subsequent search target (prospective template). To investigate the electrophysiological mechanisms underlying the switch in priority, on 40% of the trials an auditory cue replaced the first search, telling observers that at this point the first template could be dropped, in favor of now prioritizing the second, prospective template. Dropping the first template resulted in clear alpha enhancement, while turning the former prospective template into the current search target resulted in alpha suppression. Furthermore, this switch in posterior alpha lateralization was predicted by an increase in frontal delta/low theta (2–6 Hz) power. This increase in low-frequency power in frontal regions also predicted faster response times on the second search task. We thus obtained evidence for large-scale network interactions during the flexible "juggling" between priority states of multiple memory items in between search tasks. Meeting abstract presented at VSS 2018