Grouping by Contrast

2011 Second prize
Erica Dixon, Arthur Shapiro & Kai Hamburger
American University, USA, Universität Giessen, Germany
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Luminance levels of four disks modulate in time. The top two disks become white when the bottom two disks become black, and viceversa. When placed against a split background, the disks group together along the diagonals. This grouping pattern follows the contrasts of the disks relative to their backgrounds.

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’Weaves’ and the Hermann Grid

Kai Hamburger & Arthur Shapiro

University of Giessen, Germany, and Bucknell University, USA
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Swimmers, Eels and Other Gradient-Gradient Illusions

Emily Knight & Arthur Shapiro

Bucknell University, USA
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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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Catching Patches

Rob Van Lier & Mark Vergeer

Radboud University Nijmegen, The Netherlands
Catching Patches

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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World’s Largest Lightness Illusion

Barton Anderson & Jonathan Winawer

University of South Wales, Australia & MIT, USA

In this illusion, it appears that there is one set of black figures and one set of white figures. In fact, the two sets of figures are exactly identical. They appear different because the surrounding regions they are on cause the visual system to segment the images into layers. Thus one set appears to be white figures behind dark clouds, and the other set appears to be dark figures behind light clouds. If you cut out the figures you will see that they are identical!

See the illusion: movie

Read more about the illusion and possible explanations

Image segmentation and lightness perception Barton L. Anderson & Jonathan Winawer Nature. 2005. 434:79-83

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