Prioritization in working memory reduces interference via beta band-linked stimulus transformations

We studied the effects of prioritization in a two-step retrocuing task in which male and female humans hold two items in working memory, and the item not cued by the first cue cannot be dropped because it may be prioritized by the second cue. In Experiment 1, using a dense sampling procedure, recall performance oscillated at 15 Hz ("low-beta") in the prioritization task, in comparison to 20 Hz ("higher-beta") in a matched neutral-cue task. Furthermore, the prioritized item was shielded from bias exerted by the uncued item, as well as by items from the previous trial. In Experiment 2, we sought EEG correlates of these effects while participants performed variants of the two tasks. The prioritization cue uniquely triggered a phase reset at 15 Hz and an increase in oscillatory peaks at the "low-beta" frequency. Burst analysis ruled out bursting as a possible underlying factor. Self-correlation analysis of the EEG time series revealed that the prioritization cue triggered greater reorganization of the whole-topography EEG pattern than the neutral cue, and for the uncued item than for the cued item. These results provide evidence that the shielding effects of prioritization may arise from the transformation of the not-prioritized item into an "unprioritized" state that is implemented and maintained by a mechanism that cycles in the "low-beta" frequency range (centered on roughly 15 Hz).Significance statement When multiple items are held in working memory, the brain must prioritize the subset of information needed to guide impending action while also retaining the other information that remains potentially relevant for future actions. Through behavior and electroencephalography, we show that prioritizing one item in working memory shields it from interference from the not-prioritized item and that this shielding may be implemented by transforming the representational state of the unprioritized item. Behavioral signatures of prioritization and the underlying neural dynamics both cycle at a frequency in the low-beta band (∼15 Hz). These findings suggest that the brain uses an oscillatory mechanism-distinct from previously described beta-bursting inhibitory control-to organize and protect the contents of working memory from inter-item competition.