World’s Largest Lightness Illusion

Barton Anderson & Jonathan Winawer

University of South Wales, Australia & MIT, USA

(© 2005 Barton L. Anderson & Jonathan Winawer)

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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Attention-Induced Brightness Changes

Peter Tse

Dartmouth College, USA

(© 2005 Peter U. Tse)

Attention-induced brightness changes occur over bistable transparent surfaces. Fixate any of the points above and shift your attention to one disk or other without moving your eyes. The attended disk appears to change brightness. We believe that this happens because attention biases figure formation such that filling-in happens differently within the attended region than in the unattended region. In particular, the features from the overlap region spread within the boundaries of the attended figure, and not within the boundaries of the unattended region. This happens only for bistable transparent surfaces because only then is it ambiguous over which surface or layer the visual system should carry out the filling-in operation.

Read more about the illusion and possible explanations

Voluntary attention modulates the brightness of overlapping transparent surfaces Peter U. Tse Vision Research. 2005. 45:1095-8

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