Shachar Lando^1,3 (), Roy Luria^1,2, Halely Balaban³; ¹Tel Aviv University, ²Sagol school of neuroscience, ³The Open University of Israel

Perceptual grouping plays a key role in enabling us to interact with a dynamic, details-rich visual world. Notably, while grouping cues such as Kanizsa figures demonstrate robust effects on various stages of visual processing, the cognitive processes responsible for grouping several objects into one unit are poorly understood. Here, we examined the interplay between perceptual grouping and the pointer-system, which is the mechanism implementing a steady correspondence between each object in the environment and its visual working memory (VWM) representation. Each unique pointer allows VWM to access the appropriate representation and modify it according to changes in the object’s state in the world. Our main hypothesis was that perceptual grouping does not reflect pointer-system dynamics: each object in the group should still retain its independent pointer, while VWM maintains a compressed representation of the entire group. In our experiment, participants performed a change-detection task where three Pac-Man stimuli could move independently or in form of a Kanizsa triangle. On some trials, one Pac-Man abruptly changed its trajectory during the movement, breaking the Kanizsa in the grouped condition. We recorded EEG and monitored the contralateral delay activity (CDA), a neural marker of VWM. Our results indicated a lower CDA amplitude for the Kanizsa condition relative to independent movement, demonstrating a compressed grouped representation in VWM. Importantly, previous research revealed that breaking an object invalidates its VWM pointer, with a CDA drop indicating the temporary loss of the correspondence. In contrast, we found that breaking the Kanitza did not result in a CDA drop but a gradual increase, demonstrating an uninterrupted un-grouping process. This suggests that strong perceptual grouping is not the product of allocating a single pointer to the group, but rather of compressing several independent objects into one VWM representation, while still maintaining the original pointers for each group member.