Wriggling motion trajectory illusion.

In this paper, we report on a novel visual motion illusion. When hundreds of dots move in straight trajectories and random directions without colliding, the trajectories are perceived as wriggling rather than straight (Experiment 1). We examined the nature of this "wriggling motion trajectory illusion" via six separate experiments. The illusion was most pronounced when there were a large number of dots (Experiment 2). The illusion was independent of both the distance covered (Experiment 3) and the observer's eye movements (Experiment 4) as well as the dot types (Experiment 5). We also showed that the proximity among the moving dots plays a role in the illusion (Experiment 6).