An exercise in human pattern perception. The pattern slowly appears as apparently random discs. At some point your mind will suddenly recognise the pattern. The pattern then slowly disappears. At some point, your mind will lose its grip on the pattern and it will become just a random collection of discs. There seem to be three stages of perception: with few discs it appears a random collection of discs. with many discs it appears as a regular pattern with pieces missing, in between is a region where an initially random-looking set of discs can be discerned to have a pattern.
At right are shaded triangles, showing how many of our experimental subjects could see the pattern at each step during the appearing and disappearing stages. "Balancing the expected and the surprising in geometric Op art", N. A. Dodgson, Computers & Graphics 33(4):475-483, Aug 2009, ISSN 0097-8493 DOI link: http://dx.doi.org/10.1016/j.cag.2009.04.001 Poster: http://www.cl.cam.ac.uk/~nad10/pubs/CandG09-poster-A3.pdf