Breathing Square

Occluder Size

In the figure above, a green square is being obscured (or occluded) as it rotates behind the gray squares. Although it appears to grow and shrink, its size actually remains constant. The "breathing" effect is a result of how our brain recognizes the boundaries of shapes over time, though its exact cause is still unknown. Use the button and the slider to control the strength of the illusion.


[1] M. Shiffrar and M. Pavel, "Perception of rotation through apertures," Journal of Experimental Psychology: Human Perception and Performance, vol. 17, pp. 749–761, 1991.
[2] N. Bruno N, "Breathing illusions and boundary formation in space-time," in From Fragments to Objects: Segmentation and Grouping in Vision (Advances in Psychology), Eds. T. F. Shipley and P. J. Kellman, pp. 531–556
[3] M. Bach, "Breathing Square," Jun. 8, 2009. [Online]. Available: http://www.michaelbach.de/ot/mot_breathingSquare/index.html. [Accessed: Mar 13, 2010].