The white dots on black background in the neighbouring image do not seem to form any recognizable Gestalt. However, as soon as you start the movie, a vivid figure emerges. Try pausing the movie – does the figure remain visible?
Johansson (1973) attached small points of light at the joints of human actors, and filmed them moving about in the dark. Observers viewing the film reported vivid impressions of human figures, even though the images contained only a few isolated bright points. This demonstration of the effect was created using a computer rather than real actors, but the result is similar. For more information, see George Mather’s page.
With kind permission from George Mather.
You may also want to look at Niko Troje’s beautiful demos, or these ones from Randolph Blake’s lab.
Johansson G (1973) Visual perception of biological motion and a model for its analysis. Perception and Psychophysics 14:201–211
“Forerunner” Muybridge, impressive Gallery
The picture on the left remains mysterious until you start the movie. It is based on a kind contribution from Joe the Juggler. Thanks, Joe!
The movie on the right belongs to the category of “ASCII art”. It has too much detail to count as “biological motion”, but it’s nice anyway. I found it “somewhere in the Internet”, and the source there was given as “somewhere in the Internet”… I would gladly acknowledge the original source, were I to know it ;-)
Update 2005-08: It may well be based on Chris Pirazzi’s “ttyvideo” from ≈1990 or its derivative, the “ASCIIMoviePlayerSample” for QuickTime.
Update 12-2006: As Sean Lavelle kindly pointed out: by blurring the image (e.g. by squinting), the illusion of a walking man is markedly enhanced. In all probability this is related to the Lincoln illusion.