Dynamic upper and lower visual field preferences within the human dorsal frontoparietal attention network.

Both in nonhuman primates and in humans, behavioral differences between the upper and lower visual field have been identified in distinct subprocesses of attention. Advantages of the lower field have been explained by its higher spatial resolution; those of the upper field by its higher efficiency in attentional shifting. The physiological basis of visual field asymmetries within in the frontoparietal attention network (FPN) remains unclear. This study investigates the physiological correlates of upper and lower field preferences within the FPN using event-related functional magnetic resonance imaging. The paradigm separated two attentional subprocesses during a visual search task. Whether in the upper or lower field, the attention of subjects was first directed at stationary locations (spatial orienting) and then shifted between locations to search for a target (visual search) in easy or difficult search displays. Depending on the task phase (spatial orienting vs. easy visual search), upper and lower visual field preferences in the FPN changed. The analysis revealed a lower field preference during stationary spatial orienting and an upper field preference during visual search. We conclude that also higher areas represent upper and lower visual field asymmetries depending on distinct subcomponents of visuospatial attentional processing.