Attentional constraints on target selection for smooth pursuit eye movements.

Saccadic eye movements are strongly influenced by shifts of attention to non-target objects. In contrast, we have shown previously that the initiation of smooth pursuit eye movements is relatively unaffected when attention is shifted to objects that are either stationary or move in the same direction as the pursuit target (Souto & Kerzel, 2008). Here, we asked how attention interacts with target selection when a choice has to be made between objects moving in opposite directions. In a dual-task paradigm, observers had to pursue a designated object while making a perceptual judgment on an object moving in the opposite direction. The perceptual target was briefly presented after motion onset and disappeared before the eye started to move. The priority assigned to the perceptual and pursuit task was varied. When priority of the perceptual task was equal or greater than priority of the pursuit task, observers frequently pursued the wrong target and pursuit was delayed. We conclude that when an oculomotor choice is to be made between two equally salient motion signals, the successful initiation of pursuit eye movements depends on the presence of an attentional bias towards the target location.