Contralateral delay activity (CDA) is a measure used to assess the amount of information being stored in visual working memory (VWM). However, it has also been suggested that CDA reflects the current focus of spatial attention, as seen in the multiple object tracking task. This study aimed to determine whether the CDA observed in the multiple object tracking task is driven by VWM storage demands, potentially stemming from the feature (cue) masking of target features. To test this, we manipulated whether participants needed to remember the tracked items under masked or unmasked conditions during the tracking phase. Our experiment revealed that CDA occurred in both conditions; the amplitude of CDA was sensitive to the tracking load only in the masked condition. These findings suggest that CDA reflects both sustained attentional activation and representational storage, with the tracking load influencing CDA only when storage in VWM is required. These results support the conclusion that CDA is primarily sensitive to VWM storage rather than the current focus of spatial attention.

Recent studies of visual working memory (VWM) underscore a structured hierarchy of storage states. Memories that are not immediately relevant to the task at hand but are essential for later use are transferred to a passive state, which operates independently of actively maintaining and manipulating current memories. Note that stimulating passive memory forcefully can reactivate it into an active state, resulting in a competition with active memory. Thus, to remain stable representations for both states within VWM, passive memory might involve sustained suppression during activity-silent maintenance to prevent reactivation from disrupting the current active storage. To investigate this, we analyzed lateralized EEG signals while human participants (both women and men) were engaged in a sequential presentation memory task across two experiments. The results revealed positive contralateral delayed activity components and lateralized alpha enhancement for passive memory, neural indicative of suppression on passive storage. In addition, the suppression effect was independent of the memory load in both the active and the passive states. These findings support the notion of sustained suppression during activity-silent maintenance of passive memory, facilitating the stable maintenance of distinct storage states and advancing our understanding of the dynamic coding framework in VWM.