We make rapid eye movements to examine the world around us. Before an eye movement is made, attention is covertly shifted to the location of the object of interest. The eye typically will land at the position at which attention is directed. Previous research has shown that when searching for a colour singleton, top-down control cannot prevent attentional capture by an abrupt visual onset (see e.g., Theeuwes, 1994, Journal of Experimental Psychology: Human Perception & Performance, 20: 799-806).

In the present study we used a visual search task in which observers were required to make a voluntary, goal-directed saccade to a colour singleton target. In half of the trials, simultaneously with the presentation of the colour singleton target, a new object presented with an abrupt onset appeared somewhere in the display. The visual onset was never relevant for the task. The question addressed was whether the appearance of the new, yet irrelevant onset would disrupt the planning and execution of the goal-directed saccade towards the singleton target.

The results show that the goal-directed eye movement towards the colour singleton was disrupted by the appearance of the visual onset. In many instances, before the eye reached the singleton target, it started moving in the direction of the onset. The eye often landed for a very short period of time (25 - 150 ms) near the onset. The results provide evidence that top-down control can neither entirely prevent attentional capture by visual onsets, nor can it prevent the eye to start moving in the direction of the onset. The results suggests parallel programming of two saccades: one voluntary goal-directed eye movement toward the colour singleton target and one stimulus-driven eye movement reflexively elicited by the appearance of the visual onset. In line with the claims regarding the parallel programming of two saccades, there is neurophysiological evidence that there are two parallel pathways involved in the generation of saccades: a subcortical pathway depending on the superior colliculus, and a cortical pathway depending on the frontal eye field (e.g. Schall, 1995, Review in the Neurosciences, 6: 63-85) Presumably, the superior colliculus is involved in producing the reflexive movements while the frontal eye field may be involved in the goal-directed eye movements.