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Sun, 08/01/2010
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Anti-images
Pick a distinct point in the middle of this image and stare at it for 30 seconds. Do not let your gaze waver. Now close your eyes for several seconds until an image forms. Who do you see? What color is his shirt? What color is the sky? Did the colors and face appear at the same time and did they persist for the same duration? Find out more...
Backwards Speech
Speech is dependent upon the perception of complex auditory stimuli. Surprisingly enough, the sound itself can be altered quite dramatically without diminishing the ability to understand the speech. In this week's illusion, we present a sentence that has been altered. At first it makes no sense. However, listen to it again. You may be able to catch certain syllables and words. Find out more...
 The Café Wall Illusion
The "café wall" illusion is a study in how the visual system detects overall features of an image. When looking at the wall, one tends to see alternating layers that change in perspective with the lines of bricks appearing narrow on one side and wider on the other. The illusion is especially effective when the "mortar" between the layers of bricks is grey—purely white or black actually dispels the illusion. Find out more...
This experiment requires Macromedia's Shockwave.
The Hermann Grid
The Hermann Grid is a well-known illusion that demonstrates an important aspect of the visual process: gain control. All of the intersections appear grey, but any individual intersection appears white. This phenomenon is due to the way that our eyes adjust the brightness of an image, a process that is central to our ability to see detail. Find out more...
Motion Ambiguity
Many popular illusions take advantage of motion ambiguity. This week's illusion is a good example. When the yellow occluding squares are largest, the rotating blue square appears to pulsate. As the yellow occluders shrink, the effect of the illusion is reduced, and we see that the blue square isn't changing size at all. Find out more...
Shape From Motion
As noted last week, motion is processed separately from object properties such as color. However, motion can give information about an object's shape. The images above consist of the same set of random dots distributed over a cylindrical surface. In the image on the left, the dots are moved back and forth at a constant velocity. It appears as two sheets of dots moving in opposite directions. In the image on the right, the velocities mimic those that would be seen if the dots were indeed on a cylindrical surface that was spinning, and that is the percept that is generated. Find out more ...
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