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

The Contralateral delay activity (CDA) of the human EEG has been used to examine the handoff of attended targets as they move from one visual field to the other (Drew et al, 2014). Specifically, CDA is a sustained negative voltage over the hemisphere that is contralateral to the positions of the tracked targets. As tracked targets begin to cross the vertical midline, the CDA shows an apparent polarity "flip" (i.e., contralateral positivity), in which the originally ipsilateral hemisphere now has the tracked target in its contralateral field. This CDA flip has been proposed to reflect a handoff of the attended information between the hemispheres which was triggered by the immediate attentional demands of tracking the target as it moved through space. However, in those studies targets that crossed visual fields were always ultimately tested in the new field. Consequently, the hemispheric flip during tracking could instead be driven by the future demands of making a target discrimination and response in the new hemifield. Here we tested between these alternative accounts of the CDA flip. Specifically, we tested whether the CDA flip would still be observed if the subjects knew in advance that targets would ultimately return to their original hemifield before being tested. We found that the CDA flip occurred as items initially crossed visual fields and then also flipped back again as the tracked targets returned to the original hemifield. These results are consistent with the account of the CDA flip as reflecting an attentional handoff in support of the immediate needs of tracking the position of targets rather than the future needs of making a response.