Prioritization in working memory reduces interference via a beta band-linked transformation of the not-selected item

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 in the prioritization task, in comparison to 20 Hz 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 this frequency. Burst analysis ruled out bursting as a possible underlying factor. Time-resolved representational similarity analysis (RSA) revealed that the prioritization cue triggered representational transformations that were larger for the uncued 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 at 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 is implemented by transforming the representational state of the unprioritized item. Behavioral signatures of this transformation 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.