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     There is no way to properly categorize illusions, as in many cases there are several underlying mechanisms contributing to an effect. In addition, not all illusions are completely understood. Therefore, the following illusion demonstrations will be presented in old-fashioned categories (even though these categories are completely misleading). Many of the interactive demonstrations require java and shockwave plugins.

Impossible Figures and Objects.  These charming impossible figures are spatially inconsistent and paradoxical, yet they can reveal important insights into how we interpret three-dimensional objects from two-dimensional images.

The Impossible Triangle    The Impossible Trident

The Impossible Staircase    Comprehensive Bibliography

Ambiguous Illusions.  In some cases the constraints for interpreting a scene or motion are ambiguous. Your visual system can interpret the scene in more than one way. Even though the image on your retina remains constant, you never see an odd mixture of the two perceptions -- it is always one or the other, although they may perceptually flip back and forth.

Ambiguous Images

Figure/Ground Ambiguity      Perceptual Ambiguity

Depth Ambiguity          Talking Vase   

Motion Ambiguity

Cast Shadow and Ball        Barber Pole Illusion

Breathing Square        Ouchi Illusion

Spinner              Wagon Wheel Illusion

Line Motion Effect

Distortion Illusions. Illusions that distort an image's size, shape, and length.

Size Constancy Illusions  Poggendorf Illusion

Twisted Cord Illusion  Cafe Wall Illusion

Fraser Spiral  Muller-Lyer Illusion

Zollner Illusion

Camouflage Illusions.  We hope you can find these interactive demonstrations!  What determines a figure from its ground?

Figure/Ground  Hidden Bird

Funny Places.  Tourist traps and extraordinary rooms!  Balls and water flow mysteriously uphill and people grow and shrink right before your eyes.

Ames Room  Anti-Gravity Houses and Hills

Plank illusion    Floating Boxes

Stereo Illusions.  The amazing world of 3-D.

Stereograms  Stereopictures

Anaglyphs  Tesseract

Afterimages, Motion Aftereffects, Lateral inhibition.  Mostly low level effects cause these effects. Images and colors that arenít really there.  Spots before your eyes, and motion where there is no motion.

Black and white afterimage  Color afterimage

Motion Aftereffect  Hermann Grid

Scintillating Grid  Filling-in Illusion

Color and Shadow Illusions.  Amazing illusions of color and shadow.

Shadow illusion  Adelson brightness illusions  Shape from Shading

Facial Illusions. Illusions of expression.

Margret Thatcher Illusion  Presidential Illusion.

Auditory Illusion. The famous illusion of circular pitch. The ascending scale seems to rise forever, but somehow keeping cycling like an M. C. Escher staircase. Shockwave required.

Auditory illusion  Cross-Modal Interaction

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