Multiple Working Memory Items Research Articles

Alternating capture of attention by multiple visual working memory representations

Can we look for multiple objects simultaneously? Previous studies have proposed that the representation of an item in visual working memory (VWM) can bias the deployment of attention to memory-matching items in visual search. However, it is still controversial whether multiple VWM item representations are able to capture attention. In the present study, we adopted an eye-tracking technique to reveal this issue. In Experiment 1, we replicated Chen and Du’s Experiment 2 and adopted an eye-tracking technique to determine whether multiple VWM item representations are able to bias attention. In Chen and Du’s paradigm, the memory test was always followed by the search test, and the participants might intentionally prepare for the search task, which can affect the results of the research. Thus, in Experiment 2, we prevented participants from predicting the temporal occurrence of the visual search task by randomly conducting a search test or a memory test after memoranda. The findings of the present study suggested that only one working memory item at a time influences attention and multiple working memory items may affect attention through alternation.Protocol registrationThe stage 1 protocol for this Registered Report was accepted in principle on September 5, 2022. The protocol, as accepted by the journal, can be found at: https://doi.org/10.17605/OSF.IO/BE529.

Dynamics of Attentional Guidance by Multiple Working Memory Items: A Mouse Trajectory Analysis

Dynamics of Attentional Guidance by Multiple Working Memory Items: A Mouse Trajectory Analysis

Natural variation in the representational fidelity between multiple working memory items can explain which item guides attention

When holding a single item in working memory, visual attention is automatically guided towards objects that match its features, but results are mixed as to whether multiple concurrently stored items can also guide attention. These results are relevant to models of attention and working memory use the single-item guidance account as evidence for the structure of working memory comprising distinct states where one item is prioritized over all others (i.e., a special focus of attention). However, previous studies give little consideration to how memory strength for individual items affects guidance. We therefore test how multiple items interact with attention and how memory fidelity influences this relationship. Participants remembered one or two colors, then performed a visual search task, and finally reported one of the memory items using continuous report. We found reliable guidance when participants remembered one or two items, but the multiple-item effect could be explained by guidance from only one of the items on a proportion of trials. In Experiment 2, by precisely measuring memory for individual items, we show that items naturally vary in their representational fidelity, and that in general only items with the strongest representation guides attention. In Experiment 3, we demonstrate that no distinct states in working memory — i.e., no special focus of attention — is necessary to explain these single-item guidance effects. Instead, natural variation in representational fidelity between items can explain why some items have better memories than others and why those items guide attention. In particular, only very strong memories guide attention, and it is rare for more than one item to have such strong fidelity. These findings challenge current models of working memory and attention by suggesting that natural variation in representational fidelity, instead of distinct and prioritized memory states, determine which item guides attention on any given trial.

Concurrent guidance of attention by multiple working memory items: Behavioral and computational evidence

During visual search, task-relevant representations in visual working memory (VWM), known as attentional templates, are assumed to guide attention. A current debate concerns whether only one (Single-Item-Template hypothesis; SIT) or multiple (Multiple-Item-Template hypothesis; MIT) items can serve as attentional templates simultaneously. The current study was designed to test these two hypotheses. Participants memorized two colors, prior to a visual-search task in which the target and the distractor could match or not match the colors held in VWM. Robust attentional guidance was observed when one of the memory colors was presented as the target (reduced response times (RTs) on target-match trials) or the distractor (increased RTs on distractor-match trials). We constructed two drift-diffusion models that implemented the MIT and SIT hypotheses, which are similar in their predictions about overall RTs, but differ in their predictions about RTs on individual trials. Critically, simulated RT distributions and error rates revealed a better match of the MIT hypothesis to the observed data than the SIT hypothesis. Taken together, our findings provide behavioral and computational evidence for the concurrent guidance of attention by multiple items in VWM.

Combined Phase-Rate Coding by Persistently Active Neurons as a Mechanism for Maintaining Multiple Items in Working Memory in Humans

Maintaining multiple items in working memory (WM) is central to human behavior. Persistently active neurons are thought to be a mechanism to maintain WMs, but it remains unclear how such activity is coordinated when multiple items are kept in memory. We show that memoranda-selective persistently active neurons in the human medial temporal lobe phase lock to ongoing slow-frequency (1-7Hz) oscillations during WM maintenance. The propertiesof phase locking are dependent on memory content and load. During high memory loads, the phase of the oscillatory activity to which neurons phase lock provides information about memory content not available in the firing rate of the neurons. We provide a computational model that reveals that inhibitory-feedback-mediated competition between multiple persistently active neurons reproduces this phenomenon. This work reveals a mechanism for the active maintenance of multiple items in WM that relies on persistently active neurons whose activation is orchestrated by oscillatory activity.

Cross-frequency coupling supports multi-item working memory in the human hippocampus

Recent findings indicate that the hippocampus supports not only long-term memory encoding but also plays a role in working memory (WM) maintenance of multiple items; however, the neural mechanism underlying multi-item maintenance is still unclear. Theoretical work suggests that multiple items are being maintained by neural assemblies synchronized in the gamma frequency range (25-100 Hz) that are locked to consecutive phase ranges of oscillatory activity in the theta frequency range (4-8 Hz). Indeed, cross-frequency coupling of the amplitude of high-frequency activity to the phase of slower oscillations has been described both in animals and in humans, but has never been linked to a theoretical model of a cognitive process. Here we used intracranial EEG recordings in human epilepsy patients to test pivotal predictions from theoretical work. First, we show that simultaneous maintenance of multiple items in WM is accompanied by cross-frequency coupling of oscillatory activity in the hippocampus, which is recruited during multi-item WM. Second, maintenance of an increasing number of items is associated with modulation of beta/gamma amplitude with theta band activity of lower frequency, consistent with the idea that longer cycles are required for an increased number of representations by gamma cycles. This effect cannot be explained by a difference in theta or beta/gamma power. Third, we describe how the precision of cross-frequency coupling predicts individual WM performance. These data support the idea that working memory in humans depends on a neural code using phase information.

Maintenance of multiple working memory items by temporal segmentation

Experimental work based on single cell recordings supports the hypothesis that working memory representations are retained by sustained neuronal firing. While this hypothesis can account for the maintenance of a single memory item, it remains unclear how multiple working memory items are represented. This account will discuss the possible physiological mechanism responsible for the maintenance of multiple working memory items including mechanisms based on sustained firing and synaptic encoding. The focus will be on temporal segmentation by phase encoding, namely the idea that several working memory items are activated sequentially at different points in time. It has been proposed that a mechanism of nested gamma (30–80Hz) and theta (4–8Hz) oscillations is responsible for controlling the reactivation of the memory list. This mechanism has been shown to be compatible with multiple behavioral findings on working memory such as the data from the Sternberg experiment. The theta/gamma mechanism has also received support from a large set of electrophysiological findings, however, more experimental work is required to further substantiate or falsify the model.