Illustrations of the valid, neutral, and invalid trials (upper panel), and the cue and target stimuli (lower panel) used in the present study. For the unilateral (valid and invalid) cues, the cue stimulus appeared only in the left or right visual field. For the bilateral (neutral) cues, the cue stimulus appeared simultaneously in both the left and right visual fields. The perceptual load of the target stimuli was low or high with equal probability. The cue-elicited ERPs for the left, right, and bilateral cues were analyzed under active and passive viewing conditions, respectively. The ERPs elicited by the target stimuli were not analyzed in the present study.