Filling in the Afterimage after the Image

2008 First prize
Rob van Lier & Mark Vergeer

Radboud University Nijmegen, The Netherlands

To do:
Fixate your gaze on the center of one of the figures and stare at it for some time (20-30 seconds) while it cycles (without moving your eyes). After several iterations you’ll start noticing that the empty outlines fill in with ghostly redish or bluish colors! These illusory colors are called “afterimages”. Interestingly, the colors of the afterimages vary, which is puzzling because they come from the same original figure. Moreover, the shape of the outlines determines the filled-in color, which is complementary to the color of the same shape in the original figure.
What’s happening?
It is well known that viewing a colored surface can induce a vivid afterimage of the complementary color (for example, the color red induces a greenish/bluish afterimage). Our illusion shows that a colored image can produce different colored afterimages at the same retinal location. The perceived afterimage colors depend on the contours that are presented after the colored image. More specifically, the illusion shows that the afterimage colors spread and mix between those contours. In addition, alternating different contours after the original colored image causes rapidly switching afterimage colors.

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Read more about the illusion and possible explanations.

Van Lier, Vergeer, Anstis, 2009, Filling-in afterimage colors between the lines, Current Biology, 19 (8), R323-R324.

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Jenkins: Ghostly Gaze

2008 Second prize
Rob Jenkins

University of Glasgow, UK
This movie requires Flash Player 9

How do we tell where other people are looking? Conventional wisdom says the dark parts of their eyes give it away. But the Ghostly Gaze illusion reveals a more subtle process.
From a distance, the sisters seem to stare at each other, but as you bring them closer to you with the slider, they turn their eyes to you! This is not a computer trick – to convince yourself set the slider to ‘close’ and walk away from your computer screen while looking at the image: notice that when you are sitting in front of the monitor the sisters are looking at you, but when you are about 3-4 meters away they look at each other!
The illusion is based on the hybrid image technique, developed by Schyns and Oliva. Gaze direction is an extremely important social cue. The Ghostly Gaze illusion shows that details such as the outline of the iris can override larger patches of darkness.

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Rolling Eyes on a Hollow Mask

2008 Third prize

Thomas Papathomas

Rutgers University, USA

The well-known hollow-mask illusion: hollow masks appear as normal faces that “follow” viewers who move in front of them. Also, when a hollow mask rotates on a turntable, it appears to turn opposite to the actual direction of the turntable.
An interesting variant: If we add 3-D objects to the mask (e.g., a cigarette) or attach 3-D eyeballs on the whites of the eyes, what will the percept be when we turn the mask? Answer: The result is a compelling illusion in its own right; these objects appear to rotate in the opposite direction to that of the mask.

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Skyscrapers and Clouds

Sandro Bettella, Clara Casco and Sergio Roncato

Università di Padova, Italy
This movie requires Flash Player 9

Here is a novel illusion that everyone can experience when the jagged contours of skyscrapers appear against the cloudy sky: with the clouds still behind, the skyscrapers contours appear to bulge out and the effect magnifies when the clouds move.
Most illusory distortions of parallel lines disappear if contours are jagged, but not our new illusion: we experience the “Skyscrapers and clouds” illusion because the visual system relies on local luminance contrast to code local tilts and positions along the contour bordered by a thin outline.

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Stereo Rotation Standstill

Max Dürsteler

University Hospital Zurich, Switzerland
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A rotating spokes wheel defined only by disparity cues appears stationnary when fixating the center of rotation. With peripheral fixation, one can infer the wheel’s rotation by tracking single spokes. – While there exist cleary stereo motion detectors, stereo rotation detectors are either missing or inhibited by the presence of a stationary texture.

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Dramatically Different Percepts between Foveal and Peripheral Vision

Emily Knight, Arthur Shapiro & Zhong-Lin Lu

Bucknell University and University of Southern California, USA
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An object viewed directly (foveal vision) appears noticeably different from the same object viewed indirectly (peripheral vision). To investigate this aspect of how we see, our illusions accentuate the differences between foveal and peripheral perception. In one of these illusions, the “peripheral escalator,” zebra-like columns swing back and forth across the screen. Viewed foveally, the columns appear to move along a horizontal path; viewed peripherally (focus your gaze several inches above the screen), the columns appear to shift back and forth along a diagonal path. The results illustrate that peripheral vision is not just a blurry version of foveal vision.

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Pinball Wizard

Michael Pickard

Sunderland University, UK

The interesting thing about the Pinball Wizard illusion is that it breaks the ‘rules’. Whilst the classic Rubin Vase illusion demonstrates how we automatically segregate foreground and background in an image, in this illusion a single image is seen acting simultaneously as both, giving rise to an illusory sense of rotation.
Using visual cues to create an impression of depth and carefully chosen colour values, a static screen is combined with an animation of horizontally traversing spheres. The screen appears simultaneously as background and as foreground surface on the spheres – inducing a sense of rotation as the spheres move.

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Perpetual Collisions

Arthur Shapiro & Emily Knight

Bucknell University, USA
This movie requires Flash Player 9

In the perpetual collisions illusion, the pink and the yellow columns seem always to be headed towards (or away from) each other, but they never meet (and they never grow further apart). Actually, the colored fields are completely stationary; an appearance of motion is generated by the spinning black and white diamonds located alongside the columns. Click on the button to add diagonal bars and remove the edges from opposing diamonds. Notice that the information at the edges makes the colored fields move diagonally, yet when the bars are not there and all the edges are visible, the fields move horizontally.

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The Mutually Interfering Shapes Illusion (The MISillusion)

Maarten Wijntjes, Robert Volcic & Tomas Knapen

Utrecht University, The Netherlands

A circle’s a circle and a square’s a square, right? Wrong! Just look at the center of our MISillusion display and you’ll see why – Two dots are moving around bouncing off one another. Do you see a square and a circle? They really are! The illusion becomes even stronger when tracing the inner square closely: you’ll see the outer dot moving along four arcs instead of one circle. If you now follow the outer dot, the square suddenly seems curved inward!
So watch out next time you track a baseball pitch, your brain might just throw you a curveball!

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Yang’s Iris Illusion

Jisien Yang and Adrian Schwaninger

U. of Zurich, Switzerland; National Chung-Cheng U., Taiwan and Max Planck I., Germany
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Circumfluous contours can elicit a length-contrast illusion. Mirror-imaged faces are arranged with the four irises absolutely equidistant. The distance between the middle two irises is perceived as shorter than the distances between the left two or right two irises in an Asian face, whereas it is perceived as longer in a Caucasian face. This illusion remains when the irises are presented together with line drawings of the eye shape, but it disappears when only the isolated irises are presented. The illusion is independent of orientation (no inversion effect) and viewer”s race (no race effect).

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