Abstract
Prior work on attentional tracking has suggested that it is supported by independent attentional resources in each cerebral hemisphere. For example, tracking performance is better when targets are evenly distributed between both visual hemifields (i.e., tracking uses resources of both hemispheres) rather than when targets are confined to a single hemifield (i.e., tracking loads resources of only one hemisphere). Moreover, tracking targets in a single hemifield produces sustained EEG responses over the contralateral hemisphere. Because of this lateralized organization of tracking resources, objects that move between hemifields necessitate a handoff of tracked target information between the hemispheres. Here, we present two experiments in which we explore in more detail attentional tracking within and between visual hemifields. In both experiments, participants held central fixation and were presented with rotating discs located in both visual hemifields, and the task was to track the target disc(s) in a single hemifield. In the EEG experiment, we replicated prior findings by observing a large sustained contralateral delay activity relative to the position of the tracked targets that was also modulated by the tracking load. In the second experiment, we tested the impact of the brief occlusion of objects on tracking performance as the items moved either between or within hemifields. Occlusion negatively impacted performance in both conditions, but showed a much larger impact in the between hemifield condition. Overall, these results are consistent with a hemispheric handoff model, which predicts that limited visibility of tracked objects would be most disastrous when it occurs during the exchange between hemispheres.