Gengshi Hu¹ (), Chong Zhao¹, Edward K. Vogel¹; ¹University of Chicago

In visual working memory (VWM) tasks the contralateral delay activity (CDA) scales with the number of items stored, while the N2pc component—reflecting attentional selection—does not vary with set size. This dissociation has been replicated many times and suggests that VWM load effects emerge mainly during maintenance, not initial selection. A notable exception is found in multiple object tracking (MOT) tasks, where the N2pc reliably increases with the number of tracked targets. Because the N2pc in MOT appears within ~250 ms of stimulus onset—well before objects begin to move—tracking cannot explain this early modulation. Instead, a key difference between MOT and standard VWM tasks is that in MOT, the target location at test differs from the object’s original position, whereas in VWM tasks, the probed item generally reappears at its initial location. To test whether expectations about future spatial transformations drive N2pc load sensitivity, subjects performed a VWM task with two block-wise conditions. In the baseline condition, the probed item appeared at the same location in which it was encoded. In the spatial-shift condition, the probe was always displaced inward within the same hemifield. Crucially, the encoding displays were physically identical between conditions, and the N2pc was measured prior to any spatial shift. Behaviorally, memory performance was equivalent across conditions. Replicating prior work, the N2pc was insensitive to set size in the baseline condition. Strikingly, in the spatial-shift condition, the N2pc showed a reliable set-size effect, with larger amplitudes for four versus two items. These findings demonstrate that the anticipatory structure of the task—specifically, whether object positions are expected to change—alters how items are individuated during selection. Expectations about future spatial uncertainty appear to recruit enhanced target individuation at encoding, revealing that attentional selection mechanisms are more flexible and forward-looking than previously assumed.

Acknowledgements: This research was supported by the funding from National Institute of Mental Health (grant ROIMH087214); Office of Naval Research (grant N00014-12-1-0972).