Disentangling gaze shifts from preparatory ERP effects during spatial attention.

After a cue directing attention to one side, anterior event-related potentials (ERPs) show contralateral negativity (anterior directing attention negativity, ADAN). It is unclear whether ADAN effects are contaminated by contralateral negativity arising from residual gaze shifts. Conversely, it is possible that ADAN-related potentials contaminate the horizontal electrooculogram (HEOG), via volume conduction. To evaluate these possibilities, we used high-resolution infrared eye tracking while recording EEG and HEOG in a cued spatial-attention task. We found that, after conventional ERP and HEOG preprocessing exclusions, small but systematic residual gaze shifts in the cued direction can remain, as revealed by the infrared measure. Nevertheless, by using this measure for more stringent exclusion of small gaze shifts, we confirmed that reliable ADAN components remain for preparatory spatial attention in the absence of any systematic gaze shifts toward the cued side.