Observe the animation on the right. Does it appear to ‘breathe’ in for 3 seconds, out for 3 seconds? Does it alternatingly move towards you (“loom”) and recede? This illusion of motion in depth can be enhanced by observing with one eye only. Also it seems stronger with a little blur (which can be adjusted).
All disks change their individual luminance in a sawtooth manner: slowly increasing black to white, then jumping to black again; this gives a looming illusion. During the other phase luminance jumps to white and then decreases slowly, give an illusion of receding into distance.
This illusion was developed by Frank Schäffel to stimulate accommodation without changes in focus and without actual motion. During our collaborative projects I saw it and was quite impressed, so I programmed this on-line version.
Kremers J, Lee BB, Pokorny J & Smith V (1993) Responses of macaque ganglion cells and human observers to compound periodic waveforms. Vision Research 33:1997–2011
Crewther DP Crewther SG (2002) Refractive compensation to optical defocus depends on the temporal profile of luminance modulation of the environment. Neuroreport 13:1029–1032
Weiss M, Seidemann A & Frank Schaeffel (2004) Stimulating human accommodation without changes in focus. Ophthal Physiol Opt 24:207–217