Huiqin Chen¹ (), Piotr Styrkowiec², Edward K. Vogel¹; ¹University of Chicago, ²Uniwersytet Wrocławski

Tracking objects that move between visual fields requires coordination between the two hemispheres. The CDA is a sustained negative EEG voltage over the hemisphere contralateral to the positions of the tracked targets. When targets cross the vertical midline, the CDA “flips” in polarity, revealing a handoff of information between the hemispheres (Drew et al., 2014). More recent work has shown that this CDA flip reflects the immediate demands of tracking the target position rather than reflecting prospective allocation of attention to the new region because it still occurs even when the target is expected to return to its original hemifield (Chen et al., VSS 2025). However, it is unclear which aspect of the immediate tracking demands triggered this hemispheric handoff because, during the crossing there was both movement of the target’s absolute position in space as well as relative movement between the positions of the target and its accompanying distractor. Here, we tested whether the change in absolute position on its own was sufficient to trigger the CDA flip even in the absence of relative changes in the positions of the target and distractor during the crossing. In a condition with both types of motion, we replicated the CDA flip as the target moved between fields and then “flipped back” as it returned to its original field. We compared this to a “no relative motion” condition in which the relative positions of the target and distractor were “frozen” as the items moved between visual fields. The CDA flip still occurred as the target crossed visual fields suggesting that this interhemispheric exchange did not depend on resolving the relative positions of the target and distractor. Thus, the need to track changes in the absolute position of the target appears to be the critical feature for triggering the handoff between hemispheres.