Double-mirror illusion: a new class of 3D illusion that creates anomalous U-turn and anomalous translation simultaneously

This paper presents a new class of 3D optical illusion in which two types of mirror illusions occur simultaneously. The author previously reported the left–right reversal illusion, in which an object exchanges its left and right sides in a mirror, and the translation illusion, in which an object facing toward a mirror translates into the mirror instead of turning around. We will show that these two illusions can be created by a single object. If we place the object in front of two vertical mirrors meeting at the right angle, the object exchanges its left and right sides in one mirror and translates into the other mirror. As one variation of this double-mirror illusion, we create objects whose mirror reflections together with the original objects form a circular sequence oriented clockwise or counterclockwise uniformly. The mathematics behind these illusions and the origin of their robustness are also discussed.