Motion trajectory illusion and eye movements

We describe a visual illusion where a moving target produces an illusionary trajectory. Previously it has been suggested that this illusion is related to eye movements, but the exact nature of the relation, as well as relevant stimulus conditions and eye movement type were unknown. In two experiments, we varied critical stimulus conditions, recorded eye movements and judgments of trajectories. In Experiment 1, a visual cue led to a reduction of the illusion, however, only if a saccadic eye movements preceded the target's change of direction within a critical interval. assessed by SacOA (Saccadic Onset Asynchrony). In Experiment 2, an analogous result was found under conditions of sudden velocity changes. The results are explained by;critical timing between smooth pursuit and different phases of saccadic eye movements.