In many natural scenes, portions of occluding surfaces and contours can be camouflaged by having an identical color as their background. It is now well known that the visual system will often generate illusory contours and surfaces in order to fill-in this missing information. It is widely believed that the visual system does this in order to provide the best overall “explanation” of the images that form in our eyes. In this illusion, four circular disks are simply translated back and fourth over a thin square outline. Although all of the image data is fully “explained” by the visible disks, the visual system generates a strong and clearly visible additional illusory contour inside the square outline. This illusion cannot be understood with any known mechanism or theory that has been proposed to explain the formation of illusory contours. This quicktime movie is best viewed by downloading it and playing it in “loop” mode.

Fix your gaze on the central black point on the bird, as well as while the sky flashes. When the bird starts to fly, follow it, and keep staring at the black fixation point. You’ll start to notice, that the “empty bird” is filled-in with a color similar to the previous background’s color. The colored image produces illusory colors, an afterimage on “empty” shape, which induces an effect opposite to the well known “afterimage” effect. The common “afterimage” effect yields perceived complementary color, whereas the current effect shows an appearance of a color similar to that of the background, where originally, no physical color was present in the empty shape.

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.

Read more about the illusion and possible explanations

Read more about the illusion and possible explanations

(© 2006 Peter Tse)

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.

(© 2006 Peter Tse)

Fixate the central fixation spot. Notice that the two balls on the left and right appear to be bouncing toward fixation, even though they are in fact remaining at a constant distance from the fixation point. Best viewed on a large screen.

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

(© 2005 George Mather)

The illusion contains two pattern frames depicting a moving image (hence two-stroke) which are displayed using a technique that creates an impression of continuous forward movement.

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Two-stroke: a new illusion of visual motion based on the time course of neural responses in the human visual system George Mather Vision Research. 2006. 46:2015-8