Attention regulates visual working memory (VWM) performance by determining how its resources are distributed among encoded information. During encoding, this process is both flexible and strategic: Resources are unequally allocated to items based on the probability that each will be probed for memory recall. Here we assessed whether VWM resources can be strategically re-distributed among encoded items during maintenance. Across three experiments, participants encoded the colours of various shapes and were given information about the probability that each remembered item would be probed for recall via a retro-cue prompting the prioritization of two (E1 and E2) or one (E3) representation(s). We observe a reliable benefit of the retro-cues in all three experiments such that cued items were recalled with greater precision than non-cued items; however, we observed no evidence that the magnitude of this benefit was affected by the probability assigned to the cues when two items were prioritized, and only marginal evidence for an effect when a single item was prioritized. We argue that, although resources can be re-distributed post-encoding, the mechanism underlying this capability lacks the flexibility of that which underlies resource distribution during encoding, highlighting an important limitation in how attention regulates VWM performance.
Although recent evidence suggests that visual short-term memory is a continuous resource, little is known about how flexibly this resource can be allocated. The current study used a continuous report procedure and attentional prioritization via probabilistic spatial cues to address three unknown properties of a flexible continuous resource. The first experiment measured multiple responses from each trial to assess whether multiple items could simultaneously be prioritized. Second, since past work has shown that participants could prioritize VSTM representations according to two states of attentional priority, we examined whether participants could maintain three levels of priority. Lastly, we examined whether flexible allocation is possible when the prioritization cues are provided after initial encoding (i.e. a retro-cue). The results demonstrated that when participants had to recall multiple items on each trial, there were clear differences in response precision between cued and uncued items; however, two items of the same category were not always stored with equal precision. When three attentional priority levels were provided, participants’ precision was no different between high- and medium-priority, but significantly improved over low priority items, suggesting participants did not assign different memory weights to the two higher-priority conditions. When prioritization was performed via retro-cues, participants could re-allocate memory resources, but not when more than one item was to be prioritized, suggesting limitations in the flexible allocation of resources after initial encoding. Together, the results provide evidence of a VSTM resource that is flexibly, but variably, allocated using up to two attentionally guided priority goals, primarily during encoding.
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