Warning: these effects can be rather subtle.
The phenomena on this page rely on your eye movements. You will be moving them anyway (you can never keep your eyes really still), but the demonstrations are aided by moving your display (if possible), or by scrolling the page in small steps.
The first sample on the right is the “Ouchi Illusion” (Ouchi 1977, Spillmann et al 1986). When you shake your head rapidly, or better shake the display, a central disk will segregate as a distinct object, which in addition seems to be floating atop the background.
Akiyoshi Kitaoka’s image on the left is called “Out of Focus”. It also leads to a seeming shift of the central disk with respect to the surround. It is very effectively provoked by the eye movements occurring during reading. So, while you are reading this cast your “inner eye” to the left and watch for a seeming decoupling of disk and background. You may also observe that the disk floats above the background. (Image reproduced with kind permission.)
This sample called “Floating Motion” from Pinna & Spillmann (2002) also often appears very strong to me. I do not need to shake the screen, or the saccades from reading, just by exploratory eye movements over the image the centre square “decouples”. Here the background seems to move, while the central square remains in place, and seems to float on top. (Image redrawn with kind permission.)
Should the above still images not have worked for you, this should do it. Ikuya Murakami further developed his demo of retinal image slip from 1998 to a effective version, depicted here on the left. (Linked with kind permission.) Even if you try to fixate steadily on the yellow target, you make residual eye movements, which are apparent in relative shifts of the central blurred shape relative to the surround. A deeper explanation is provided by Ikuya Murakami in the papers referenced below.
[2012-01-17 In the paragraph above I had to remove the references to Ikuya Murakami’s web pages since they see no longer accessible.]
Hine T, Cook M, Rogers GT (1997) The Ouchi illusion: an anomaly in the perception of rigid motion for limited spatial frequencies and angles. Percept Psychophys 59:448–455
Kitaoka A • “Out of focus”
Murakami I & Cavanagh P (1998) A jitter after-effect reveals motion-based stabilization of vision. Nature 395:798–801
Olveczky B, Baccus S, Meister M (2003) Segregation of Object and Background Motion in the Retina. Nature 423:401–408
Ouchi H (1977) Japanese optical and geometrical art. Meneola, New York:Dover
Pinna B & Spillmann L (2002) A new illusion of floating motion in depth. Perception 31:1501–1502 (Fig. 1, “Floating Motion”)
Murakami I (2003) Illusory jitter in a static stimulus surrounded by a synchronously flickering pattern. Vision Research, 43, 957–969
Spillmann L, Heitger F & Schuller S (1986) Apparent displacement and phase unlocking in checkerboard patterns. 9th European Conference on Visual Perception, Bad Nauheim