Voluntary saccades are thought to be preceded by shifts of covert attention (although saccades do not necessarily follow shifts of covert attention) and there is mounting evidence that the two processes rely on similar mechanisms (e.g., Bisley & Goldberg,
2003; Corbetta, Akbudak et al.,
1998; Deubel,
2008; Deubel & Schneider,
1996; Eimer, Van Velzen et al.,
2006; Moore & Armstrong,
2003; Peterson, Kramer et al.,
2004; Sato, Watanabe et al.,
2003; Van Ettinger-Veenstra, Huijbers et al.,
2009; Walker, Techawachirakul et al.,
2009). Similarly, stimuli that capture covert attention automatically also produce oculomotor capture, a phenomena where saccadic eye movements are automatically directed toward salient objects (e.g., Godijn & Theeuwes,
2002; Hunt, Olk et al.,
2004; Hunt, von Muhlenen et al.,
2007; Irwin et al.,
2000; Mulckhuyse, van Zoest et al.,
2008; Theeuwes, Kramer et al.,
1999). Patterns of saccadic eye movements therefore reflect shifts of covert attention and can be used as an indicator of attentional selection. As compared to studies of covert attention where only one measurement of RT or accuracy is acquired at the end of each trial, saccade data in a free viewing paradigm provides higher resolution measurements of behavior throughout a single trial. Such data were instrumental in our task for dissociating mechanisms of top-down selection that produce similar performance in final RT and accuracy.