Curved saccade trajectories: Voluntary and reflexive saccades curve away from irrelevant distractors

In this study we examined the impact of irrelevant distractors upon traject ories of reflexive and voluntary saccades. Observers made saccades to visua l targets above and below fixation as directed by target appearance (reflex ive) or by a central directional cue (voluntary) in the presence of an irre levant distractor stimulus (a cross) whose appearance was simultaneous with target onset. We recorded saccade latency, amplitude and the magnitude of saccade curvature relative to the direct route from the start-to-end of the saccade. Previous studies of saccades curvature have used distractors to p rovide information about the saccade task and, as a result, have only exami ned trajectories of voluntary saccades. However, we have shown that both re flexive and voluntary saccades curved away from irrelevant distractors. The effect of irrelevant distractors indicates that observers do not need to a ttend to distractors in a voluntary fashion for distractors to modify sacca de trajectories. Furthermore, it highlights an important parallel in curvat ure of saccades and reach trajectories, namely that both curve away from ir relevant distractors. The second important observation was that reflexive, as well as voluntary, saccades curved away from distractors. This suggests that curvature is not solely a consequence of voluntary control. These resu lts have been considered within the context of inhibition-based theories of curvature derived from studies of saccade and manual reach trajectories.