The more-or-less morphing face illusion

Rob van Lier & Arno Koning
Donders Institute, Netherlands

(© 2011 Rob van Lier & Arno Koning)

The illusion comprises a morphing sequence between two faces. The observer has to fixate a dot superimposed on the morph. When the dot is moving, morphing can hardly be seen. However, when the dot suddenly stops, the morphing appears surprisingly strong. Subtle differences in, e.g., the shape of the eyes, the color of the skin, and even gender characteristics are “blown-up” perceptually. Apparently, such differences between faces are easily overlooked when following a moving-dot, but are highly salient when our eyes rest at a single point on the morphing faces.

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Illusory gloss

Maarten Wijntjes & Sylvia Pont

Delft University of Technology, The Netherlands

(© 2010 Maarten Wijntjes & Sylvia Pont)

The movie shows a Brownian surface (which has a fractal structure, but this does not seem to be important for the illusion). The appearance seems to change between matte and glossy, as the ruler illustrates. However, the surface is continuously rendered with matte (Lambertian) reflectance. What is happening is that the height of the surface is stretched in the viewing direction. The illumination direction is transformed together with the stretching to keep the cast shadows constant. This combined transformation of the light and surface height results in an illusory gloss. We initially though that the effect could be attributed to a luminance histogram skew transformation, but this seems not the case. A simple version of the current explanation is that stretching a surface together with the light direction (the so-called Bas-Relief transformation), induces illusory highlights due to darkening at points where the surface normal points away from the optical axis.

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Filling in the Afterimage after the Image

2008 First prize
Rob van Lier & Mark Vergeer

Radboud University Nijmegen, The Netherlands

© 2008 van Lier & Vergeer

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.

See more demos.

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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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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Kaleidoscopic Motion and Velocity Illusions

Peter van der Helm

Radboud University Nijmegen, The Netherlands

Animation

(© 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

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Catching Patches

Rob Van Lier & Mark Vergeer

Radboud University Nijmegen, The Netherlands
Catching Patches

(© 2006 Rob Van Lier & Mark Vergeer)

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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Healing Grid

Ryota Kanai

Utrecht University, The Neatherlands

(© 2005 Ryota Kanai)

The image is regular at the center, but the grid pattern is less regular at the peripheral parts of the images (both on the left and right edges). As you stare at the center of the grid for say 20 seconds, the regularity of the grid pattern at the center spreads into the irregular parts in the periphery. This illusion seems to indicate the preference of the visual brain to see regular patterns.

Read more about the illusion and possible explanations

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