2006 Finalists | Best Illusion of the Year Contest

The Freezing Rotation Illusion

2006 First prize

Universitätsspital Zürich, Switzerland

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.

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

Peter Tse

Dartmouth College, USA

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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

Gideon Caplovitz & Peter Tse

Dartmouth College, USA

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

Po-Jang Hsieh

Dartmouth College, USA

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

Coffer Illusion

Anthony Norcia

Smith-Kettlewell Eye Research Institute, USA

First time viewers of this display invariably do not see the 16 circles segmented from the background. Rather, they see a series of rectangles that they frequently describe as “door panels”. The illusion pits segmentation cues against what appears to be a very strong prior to interpret the image as a series of 3-D structures “coffers” with closed boundaries. (A coffer is a decorative sunken panel.) It appears that the prior involves both closure and shape-from shading assumptions. The Coffer Illusion is a variation on Gianni Sarcone’s “Op Art illusion”.

The Occlusion Velocity Illusion

Evan Palmer & Phillip Kellman

Harvard Medical School & UCLA, USA

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The Occlusion Velocity Illusion shown in the video demonstrates that when one part of a moving object goes out of view before another part, the two pieces appear misaligned, even though they are not (top row). This illusion can be counteracted by misaligning one portion of the rod in the direction opposite to the perceived misalignment (middle row). If observers are instructed to attend to the rod’s shape only within the blue box, they are still subject to the illusion (bottom row). This final observation indicates that the illusion is obligatory and not under volitional control.

Clones and Donors Have Opposite Inclinations (in Vision)

Oronzo Parlangeli & Sergio Roncato

Università di Padova, Italy

Clones and Donors Have Opposite Inclinations (in vision)

Fig. 1 and Fig. 2 show the same inducing pattern.
However, if the blue lines in fig 1 are seen as donors, we can easily appreciate that when they give birth to two clones as in fig 2, these clones grow apart and they show a diametrically opposed inclination: convex lines become concave and concave lines becomes convex.
A clone for each donor is sufficient to produce the effect.

Sinha: Hidden Strength of the Classical Simultaneous Contrast Illusion

Pawan Sinha

MIT, USA

Dynamic Luminance-Gradient Effect

Alan Stubbs

University of Maine, USA

For the primary effect, one should sit at a comfortable distance and then move forward toward the center of the figure. An interesting change in apparent brightness and to some degree form will result—what may be called a “here comes the sun” effect. By moving back and forth, this apparent change will repeat.

See different versions of the illusion

A new set of illusionsthe Dynamic Luminance-Gradient Illusion and the Breathing Light Illusion Simone Gori & D. Alan Stubbs Perception. 2006. 35:1573-7

Catching Patches

Rob Van Lier & Mark Vergeer

Radboud University Nijmegen, The Netherlands

We present an illusion based on Hermann-grid like gratings in which the contours are quite randomly distorted. These distortions guarantee a severe reduction or complete disappearance of the visibility of the patches. Starting with these gratings we show that the patches at the crossings return when luminance edges are introduced and extended at the intersections. The ‘returned’ patches have the same relative lightness properties as they would have in a regular Herman grid (dark patches when the crossing bands are relatively light, and light patches when the crossing bands are relatively dark). In addition, the polarity of the perceived lightness difference does not depend on the lightness of the edges (i.e., whether they are dark or light). A remarkable effect here is that at the crossings the whole area between the edges is perceived to have a different lightness, irrespective of the shape of that area (i.e., whether the edges bend inward or outward etc.).

See Power Point presentation with different versions of the illusion

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