Optical illusion created around 1915 by Danish psychologist Edgar Rubin.

Have you seen the duck which is also a rabbit? How about the Spinning Dancer who seems to be moving in a clockwise as well as a counter clockwise direction? These are some of the more popular optical illusions. What do you think an optical illusion is? If you think that the word “optical” has something to do with eyes, you are already half correct. The word “illusion” is derived from a Latin verb which means “to mock”. When you think about it, illusions trick people into seeing things which are not. The best way to learn about optical illusions is to experience them first hand. After you have checked the following links, you will have a much clearer idea about optical illusions. Have fun!

Motion & Time

• Stepping Feet: The yellow and blue feet seem to be “stepping” when the grid is visible but in reality, their movement is parallel.
• Motion Induced Blindness: Focus on the dots. Do the dots really disappear?
• Motion Silencing: When the ring rotates, the dots seem to have stopped changing colors. Is it true?
• Rotating Snake: The “snakes” seem to be rotating but are they?
• Pinna-Brelstaff Illusion: Fix your eyes on the blue cross, then move your face towards the screen, and away.
• Waterfall Illusion: Use the Start and Stop buttons to experience this phenomenon.
• Stereokinetic Phenomenon: The motion “changes” a 2D image into a 3D image.
• Reverse Spokes: Try and see if you can make the spokes stay put.
• Enigma: Start by fixing your eyes on the center. Do you see how things are starting to move and rotate?
• Biological Motion: In motion, you can see a figure which is not there when there’s no motion.

Luminance & Contrast

• Hermann Grid: Can you see the dark patches at the intersections other than the one you are looking at?
• Scintillating Grid: See the differences in this modification of the Hermann Grid.
• Craik-O'Brien-Cornsweet Illusion: Do you believe that the upper and lower blocks are actually the same shade of gray?
• Koffka Ring: Learn about how backgrounds affect the gray rings.
• The Pyramid Illusion: Try to pick the dot which is closest to the pyramid’s center.
• Munker-White Illusion: Do you think the two blue bars have the same luminance? Remove the black bars to find out.
• Adelson’s Checker-Shadow Illusion: Are squares A and B the same shade?
• Corrugate Plaid Illusion: How can two squares of the same shade appear so different?

Color

• Lilac Chaser: Focus on the black cross. Do you see the moving dot turning green and then all the dots disappear?
• Benham’s Disk: Learn how to make these cool optical illusion spinners.
• Neon Color Spreading: Good demonstration of this amazing phenomenon.
• Rotating Sphere: Play with the controls to learn about structure from motion.
• Color Mixing: Here’s a great place to experiment with color mixture.

Geometric & Angle Illusions

• Tilting Table: The table is not tilting, it’s really horizontal!
• Hering Illusion: The two straight vertical lines are actually parallel but they appear different.
• Poggendorff Illusion: A good place to learn about this interesting illusion.
• Fraser’s Spiral: Are the overlapping black arc segments really a spiral?
• Triangle Puzzle: Why is there an empty square in the bottom triangle?

Space, 3D & Size Constancy

• Muller-Lyer Illusion: Do you know why the lower line appears longer?
• Solstice Moon Illusion: Find out why the solstice moon appears so big.
• Shepard’s Tables: Animation shows how the identical tables can be made to look different.
• Terror Subterra: Are the two monsters the same size and identical?
• Necker Cube: This experiment will explain much about the Necker Cube.
• Depth Perception: Describes about the eye’s ability to perceive depth.
• Reverse Perspective: Some examples of reverse perspective illusions.
• Anamorphosis: Learn about this type of optical illusion in art.

Cognitive/Gestalt Effects

• Darwin Illusion: Try to find the second face on the white background.
• Kanizsa Triangle: A good place to learn about this strange triangle.
• Hidden People: Take some time to find the 9 hidden people in this picture.
• Impossible Shapes & Peculiar Landscapes: Examples of illusions that don’t make much sense.
• Hallucci: Take a look at this “impossible” movie.
• Impossible Waterfall: An interesting movie about M.C. Escher’s idea.

Specialties with Faces

• Coffee Beans: Try to find the man in the coffee beans.
• Face on Mars: Do you know they found the face of a man on Mars?
• Thatcher Effect: Learn about the Margaret Thatcher illusion here.
• Ghostly Gaze: One of the famous illusions of 2008.
• Multiple Spatial Frequency Scales: Includes hybrid images of Dr. Angry and Mr. Smile.
• Mona Lisa & Abraham Lincoln: What’s common between them?

Websites Dedicated to Optical Illusions

• New Optical Illusions: Collection of visual, scary and funny illusions. Visitors can submit additional visual illusions to be published on the site.