Optical, or visual, illusions come in many forms. They delight children and puzzle scientists and psychologists. In essence, all visual illusions trick the brain into false perceptions that defy reality. Illusions can take the shape of simple geometric patterns, stereographic images, hidden and impossible objects, and more. Some, like the famous works of M.C. Escher, are viewed as works of art and even mathematical enigmas. Venture into the strange world of illusion with these examples from educators, students, and enthusiasts.
Motion & Time
Motion and time illusions lead our brains to believe that static images are in motion; famous examples include the Pinna Illusion and Rotating Snakes. Viewers often see these images moving in different directions and may need to use peripheral vision to see the effect. Some motion illusions even cause the eye to erase portions of an image.
- Motion Induced Blindness
This illusion causes colored dots to appear and disappear. Dr. Baldwin explains the illusion and draws correlations to psychological dissociative experiences.
- Pinna Illusion
The Pinna illusion is an early example of a static image creating the illusion of motion. Two rings seem to rotate when vision is focused in the center of the image.
- Rotating Snakes Static Motion Illusion
Rotating Snakes is a more advanced version of the static rotation illusion. This article explains an in-depth experiment that was done using the illusion and offers images by A. Kitaoka.
- Illusory motion in Enigma
This article offers experiments and results of a psychophysical investigation using Leviant’s Enigma illusion. Several versions of the illusion are included.
- Kaleidoscopic Motion and Velocity Illusions
A rotating wheel illusion is explained here. Visitors can also create their own rotating wheel illusions using the interactive application on the page.
Luminance & Contrast
Some visual illusions play on the interaction between lightness and intensity. These illusions can cause the brain to perceive colors that are not there. The mind distorts shape and size, and brightness levels can be misinterpreted. A well-known example is Hermann’s Grid, which causes blobs of color to appear in the white space between grids of colored squares.
- Hermann Grid Illusion
The Hermann Grid is a simple illusion that causes viewers to see color where there is only white space. The site offers further resources that explain how the illusion works.
- Munker-White Illusion
This interactive illusion shows how colors can be distorted simply by changing the background they are on.
- The Lazy Shadow Phenomenon
This page allows users to explore the lazy shadow phenomenon with an interactive widget. It also provides an overview and history of the illusion.
- Simultaneous Brightness Contrast
Dr. Dale Purves explains the simultaneous brightness contrast effect. Several illustrations of the illusion are included.
- Lightness Perception and Lightness Illusions
This scholarly study of lightness illusions offers in-depth discussion of the phenomena and offers several examples.
Color illusions use the visual system to change image perception. After-image illusions will cause the brain to see an image on a blank canvas after having viewed it for some time. Some color illusions combine shape, color, and placement to create the effect of motion. Still, others lead us to see color where there is none.
- Lilac Chaser
The Lilac Chaser is a fun illusion that causes the eye to see a rotating dot that changes from lilac to green.
- Watercolor Illusion
The watercolor illusion causes faint washes of color to appear on a white background.
Assimilation is a color study that examines the effect of background color. Images look brighter or darker depending on the color behind them.
- Color Phenomena
This illusion is another example of how colors seem to change when placed on varying backgrounds.
- Contrast/Color Illusions
This page offers interactive examples of the checkerboard and Rubik’s cube illusions.
Geometric & Angle Illusions
Perhaps the most well-known category of optical illusions, geometric and angle illusions use simple lines and shapes to fool the mind. These illusions are often part of early childhood puzzles but do not dismiss them as merely juvenile games. Patterns, like those used in the Café Wall Illusion, have inspired advanced studies of the effect. Designers have even constructed entire buildings using the pattern.
- Visual Illusions
This page offers an overview of many illusions, including the Pembrose Illusion, impossible objects, and several illusions involving shape.
- Poggendorff Illusion
This illusion asks users to line up two diagonal lines behind a black box.
- Fraser Spiral
The Fraser Spiral makes the mind see a spiraling image despite it being made up of concentric circles.
- Café Wall Illusion
This educational paper offers a background on the Café Wall Illusion as well as demonstrating the laws behind it.
- Geometric Illusions
This site offers geometric illusions, including Café Wall, spirals, waving squares, and moving patterns.
- Geometry in Optical Illusions
This page explores geometrical illusions and how they can be used in classroom teaching.
Space, 3D, & Size Constancy
Objects are not always the size they appear, as is often illustrated in visual illusions. Take, for example, how large the moon looks at the horizon and how small it is when higher in the sky. Colors and shapes can hide objects or make them appear to float in space. As the Necker Cube points out, they can also seem to move back and forth.
- The Muller-Lyer Illusion
The Muller-Lyer illusion pushes the limits of depth perception. Several variations are given here.
- The Moon Illusion
This page explains why the moon appears to change size in the night sky.
- The Necker Cube
The Necker Cube is a 2D image that the brain perceives as 3D. The image appears to flip in and out, as it is viewed.
- Dr. Kitaoka’s Stereograms
Stereoscopic illusions of all sorts are offered here, with a focus on distorted angles.
- Adding Depth to Illusions
This page includes illusions that incorporate depth perception and isometric shapes.
Cognitive illusions use our brain’s ability to fill in the blanks to make us see things that are not there. This can result in familiar objects appearing in images that, at first glance, are nothing more than dots. Cognitive and Gestalt effects can also produce beautiful and mind-bending art, like the work of M.C. Escher. His tessellation images and impossible waterfall still boggle some of the world’s greatest minds.
- Kanizsa Figure
Kanizsa Figures cause the brain to fill in the blanks and make shapes appear when no clear boundary lines are present.
- Dalmatian Illusion
Color and texture can be used to camouflage familiar objects as illustrated here.
Hallucii is a short movie about a man trapped in an Escher-esque staircase. The movie offers a few illusions itself for the careful observer.
- UMD Physics Department Optical Illusions
This collection features images of the Ames room, along with sidewalk art and models of Escher’s impossible waterfall.
- Gestalt Laws
This page examines the Gestalt laws and how the brain tends to group objects by proximity.
- Relativism and the Constructive Aspects of Perception
This academic paper explores cognitive illusions. Famous examples are included, including the rabbit and duck.
- MC Escher Gallery
MC Escher was a master of mathematics and illusion. This page showcases his work with tessellation.
Specialties with Faces
Facial illusions are often ambiguous images. People see different results from one another, or perspective may change depending on viewing distance. A modern example, dubbed Thatcherization, inverts faces and expressions with interesting results. Other illusions using faces involve ghost images and overlays.
- Mona Lisa
This illusion uses a famous painting to explain the inverted face illusion.
- Gazing at Each Other
This article examines human eye gaze and includes a fairly modern optical illusion, the Ghostly Gaze.
- Optical Illusions
This page includes a wide array of optical illusions, including ambiguous and hidden faces.
Thatcherization, or inverted faces, is explored here. The page includes a brief background and several examples.
- Dr. Angry and Mr. Smile
This PDF from MIT is a reprint of the paper by Philippe G. Schyns and Aude Oliva. It examines hybrid faces and how spatial scale changes the image you see. The illusion is illustrated on page five.
- Rocky Faces
Hidden object fans will enjoy the Rocky Faces images. Viewers are asked to find all the faces hidden in a woodland scene.