Contralateral delay activity tracks storage load in visual working memory: Evidence from the multiple object tracking task

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 a multiple-object tracking (MOT) task. This study aimed to determine whether the CDA observed was due to the storage requirements of VWM hiding behind the MOT task, potentially stemming from the feature (cue) masking of target items. To test this, whether participants needed to remember the tracked items were manipulated as masked or unmasked condition during the tracking phase. Our experiment showed that CDA occurred in both the masked and unmasked conditions, but the amplitude of CDA was sensitive to the load of items being tracked only in the masked condition. These findings suggest that CDA may be linked to both sustained attentional activation and representational storage, with the effect of tracking load on CDA seen only when storage in VWM is necessary during tracking. These results support the conclusion that CDA primarily be sensitive to VWM storage rather than the current focus of spatial attention.