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Halely Balaban, Trafton Drew, Roy Luria; Neural evidence for a dissociation between the pointer system and the representations of visual working memory. Journal of Vision 2019;19(10):82c. doi: https://doi.org/10.1167/19.10.82c.
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Our goal was to show that visual working memory (VWM) representations are distinct from the pointer system that supports them. The pointer system is a stable mapping between an item in the environment and its VWM-representation, which allows VWM to track and access the appropriate representation. Accordingly, when this mapping is invalidated, VWM resets by discarding the original representations and creating new representations and pointers. This happens, for example, when a uniform object separates into halves, because a single pointer cannot support the two independent objects following the separation. Similar object-separation results in updating the original representation (without resetting) when there are two pointers to begin with, e.g., when each half can be individuated based on distinct colors. We used a shape change-detection paradigm, where each shape-half had a different task-irrelevant color. The items moved during the memory array, which was task-irrelevant but allowed us to manipulate grouping or ungrouping. In the critical condition, two shape-halves first moved separately, then met and moved together, but then re-separated. The neural marker of VWM (the contralateral delay activity) indicated that two pointers were allocated and maintained throughout the trial, because the separation was not followed by a resetting process. Conversely, the movement caused VWM-representations to transform from separate to grouped (following the joint movement) to ungrouped (following the re-separation). This dissociates the number of representations, which changed from two to one and back to two, from the number of active pointers, which remained two throughout the trial. We argue that one pointer is allocated to one object, but several distinct objects along with their pointers can be grouped into a single VWM-representation. The grouping can be undone, by accessing the still-valid independent pointers. This dissociates VWM-representations and their supporting pointers, thus revealing an important characteristic of our cognitive system.
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