The Influence of Identical Objects on Visual Working Memory Capacity: Electrophysiological Evidence

Identical memory items have the potential to reduce cognitive demands on visual working memory (VWM) and enhance its precision. Previous studies have investigated this question preliminarily. However, there is still some controversy surrounding this question, as we cannot confirm whether the benefits from identical items can be generalized to complex stimuli. This study aimed to explore it further. We investigated whether individuals compress the identical items within their memory range to reduce VWM capacity consumption. Participants performed a change detection task, memorizing the orientations of the memory array, which included three conditions: 1) four-same orientations, 2) two pairs of same orientations, and 3) four-different orientations. Using the contralateral delay activity (CDA), an event-related potential component that is sensitive to the number of items stored in VWM, we found that the CDA amplitude in late-time window was significantly lower for the all-same condition compared to the partial same and all-different conditions, with no significant difference between the latter two conditions. Our findings suggest that participants compress identical information, reducing VWM capacity consumption and increasing the number of items that can be remembered. However, this compression is conditional and occurs only when the strategy is most efficient, as in the all-same condition.