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© 2007 Kai Hamburger and Arthur Shapiro
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Drifting Background Illusion
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(© 2007 Masaharu Kato)
In the illusion , a small pink object can be seen moving back and forth in front of three types of background. When observers track the pink target moving back and forth in front of a background consisting of dynamic noise, they report the percept of a drifting background. The direction of this drift is opposite to that of the small pink object, even though the background in fact does not move into a particular direction. This illusory motion arises for a static gray Gaussian background, but is actually much stronger when the background is dynamic random noise. However, the illusion does not occur when the background consists of static random noise.
Swimmers, Eels and Other Gradient-Gradient Illusions
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(© 2007 Emily Knight and Arthur Shapiro)
The red button adds/removes half of the background grating. The swimmers bob up and down when they are in front of the grating but not when they are in front of a uniform background
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Kaleidoscopic Motion and Velocity Illusions
(© 2007 Peter van der Helm) Note: you need java installed in your computer to see this illusion.
You will see a rotating wheel that pulsates each time it aligns with two stationary shapes. You may also see that, at the same time, the inner stationary shape wiggles. The pulsations seem to be caused by color assimilation, and the other effects by ambiguous figure-ground segregation.
Read more about the illusion and possible explanations at Peter van der Helm’s website
For another interactive version of this Illusion, see Michael Bach’s “Optical Illusions & Visual Phenomena” website.
Kaleidoscopic motion and velocity illusions Peter A. van der Helm Vision Research, 2007. 47:460–465
It’s a Circle, Honest!
(© 2007 David Whitaker)
The illusion in the figure on the left consists of two sinusoidal gratings at 45° and 135° which combine to form a plaid. The contrast of this plaid is windowed by a perfect circle. Despite this, the percept is far from circular – rather, it appears octagonal with distinct sides. The percept is generated by attraction and repulsion of the circular envelope in the orientation domain by the sinusoidal carrier gratings. It relies upon the sharp transition between Fraser illusion (attraction) and Zöllner illusion (repulsion) at the knee-points of the octagon.
Whilst the illusion is scale-invariant in that it does not change with viewing distance, if the scale of the carrier grating is lowered (Figure on the right) relative to the circle, the percept changes from an octagon to a diamond. This is well-predicted by the variation in the strength of the Fraser and Zöllner illusions as the relative spatial scale of carrier and envelope is varied (Skillen et al. (2002) Vision Research 42, 2447-2455).
The Freezing Rotation Illusion
2006 First prize
(© 2006 Max Dürsteler)
An object (e.g. airplane) is turning on a surround (greenhouse), which is swaying back and forth. Observe the rotation of the object. Is it turning smoothly all the time? Or does it “freeze” from time to time? Convince yourself by covering the swaying surround that the object is really turning continuously. If the object is swaying back and forth and the surround is turning continuously we do not perceive a slow-down of the surround. Assuming a stable surround, our visual system probably uses the surround as a reference to measure motion of the included objects.
Read more about the illusion and possible explanations
See an interactive version of the The Freezing Rotation Illusion at Michael Bach’s “Optical Illusions & Visual Phenomena” website
The Freezing Rotation IllusionMax R. DürstelerNature Precedings 2007. 371.1
The Infinite Regress Illusion
2006 Second prize
Dartmouth College, USA
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(© 2006 Peter Tse)
Fixate the black fixation point on the far left side of the image. Note that the figure appears to move steadily away from the fixation point, even though it is in fact only moving up and down.
See another version of the illusion
The infinite regress illusion reveals faulty integration of local and global motion signals Peter U. Tse & Po-Jang Hsieh Vision Research. 2006. 46:3881-5
The Bar-Cross-Ellipse Illusion
2006 Third prize
(© 2006 Gideon Caplovitz & Peter Tse)
Here we present a new multistable stimulus generated by continuously rotating an ellipse behind four fixed occluders. Observers can perceive one of four percepts: (1) a continuously morphing cross, (2) two independent perpendicular bars oscillating in depth, (3) a rigidly rotating ellipse observed behind the occluders, or (4) a fixed cross observed through a continuously rotating, elliptical aperture.
The bar – cross – ellipse illusion: Alternating percepts of rigid and nonrigid motion based on contour ownership and trackable feature assignment Gideon P. Caplovitz & Peter U. Tse Perception. 2006. 35:993-7
Gradient-Offset Induced Motion
(© 2006 Po-Jang Hsieh)
When a gradient stimulus, whose luminance contrast ranges gradually from white on one side to black on the other, is made to disappear all at once so that only the uniform white background remains visible, illusory motion is perceived. This motion lasts ~700ms, as if the stimulus moves from the low to the high luminance contrast side. This gradient-offset induced motion does not occur for equiluminant color-defined gradient offsets, suggesting that it relies mainly on the magnocellular pathway. We hypothesize that this illusion is caused by the difference of decay rates within the gradient afterimage.
See different versions of the illusion
Illusory motion induced by the offset of stationary luminance-defined gradients Po-Jang Hsieh, Gideon P. Caplovitz & Peter U. Tse Vision Research. 2006. 46:970-8
