Scientists have discovered a new optical illusion that will screw up your brain big time. Focus on the red cross while the dots move. They are wriggling around, right? Wrong. All of them are moving "in straight trajectories and random directions without colliding."
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 (bottom). 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 (top). 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).
If you focus on one dot you will see it going on a straight line. But look at the cross and you will see the illusion of them wriggling around, trying avoid each other.