This illusion demonstrates the brain’s remarkable ability to see different things in the same scene, depending on your focus. For example, when you look at a pond, you may see clouds reflected on the surface, but with a subtle shift of attention you can instead find yourself observing the stones at the bottom. In the same way, as you shift your attention to a specific disk in Tse’s drawing, your brain suppresses the other disks and enhances the one you are focusing on. One reason our attentional systems may have evolved to work the way they do is to concentrate our limited neural resources—so we can make the best of them—on specific tasks. We simply don’t have the neural machinery to grasp all the sensory information around us in any depth, so our brains must pick and choose what to prioritize from one moment to the next. In that sense, our attentional focus is not a neural shortcoming but an enhancement. Human accomplishments such as science, technology, and even art would not exist but for people who were—and are—able to concentrate on minute areas of interest for extended periods of time, while taking no notice of most of the world around them.
ATTENTION TO AFTERIMAGES
BY PETER TSE
DARTMOUTH COLLEGE, U.S.A.
2010 FINALIST
In 2010, Tse showed that attention can also affect the perception of afterimages, the illusory visuals that linger after you look at a bright light or stare at a picture for a while. Focus your gaze on the center of the checkered pattern for one full minute, then shift your eyes to the empty rectangles at the right. You will see a colorful afterimage filling in the formerly empty frames. Now try paying attention to the vertical rectangle, and you will see an afterimage that matches it. Pay attention to the horizontal rectangle and you will see a different afterimage. You can go back and forth between the two afterimages simply by shifting your attention from one rectangle to the other.
Afterimages help scientists understand how neurons in our eyes and brains temporarily cease responding to an unchanging stimulus. The ghostly visions appear during the brief period before the neurons reset to their normal, responsive state. Neuroscientists know that retinal neurons play a role in the perception of afterimages, but it has been difficult to demonstrate the importance of neural processing at higher levels in the visual pathway from the eye to the brain. Tse’s illusion proves that afterimages can be strongly modulated by cognitive processes such as attention.
APPENDIX: DYNAMIC ILLUSIONS
Twenty-first-century illusion creators continue to produce printable illusions using still photographs or even just a few lines on paper, but computer and video technologies have made it possible to create increasingly complex moving-picture illusions. This appendix is dedicated to illusions that are best seen on the screen. To view them, visit the Best Illusion of the Year Contest website, http://illusionoftheyear.com.
GROUPING BY CONTRAST
By Erica Dixon, Arthur G. Shapiro, and Kai Hamburger • American University, U.S.A., and University of Giessen, Germany • 2011 Second Prize
This illusion expands on what researchers call the “Gestalt laws,” formulated by German psychologists in the 1920s to describe human perception. It shows that your brain tends to group objects together based on their absolute contrast—here your brain groups blinking dots in different ways, depending on their background.
ILLUSORY GLOSS
By Maarten Wijntjes and Sylvia Pont • Delft University of Technology, The Netherlands • 2010 Finalist
This illusion shows that an object’s surface can look either matte or glossy, depending on the direction of illumination.
SILENCING COLOR
By Jordan Suchow and George Alvarez • Harvard University, U.S.A. • 2011 First Prize
Suchow discovered this illusion when he dropped his laptop and noticed that a scintillating doughnut on the screen appeared to stop moving while the laptop was in midair—a phenomenon called “silencing,” by which our brain suppresses one kind of perception when confronted with another. Here the dots rapidly switch color but appear to stop when the doughnut begins rotating, even though they continue to change the entire time!
CONTRAST COLOR INDUCED BY UNCONSCIOUS SURROUND
By Haruaki Fukuda and Kazuhiro Ueda • University of Tokyo, Japan • 2009 Finalist
A simple children’s top can be a powerful visual neuroscience tool. Here the colored wedges blur into gray when the disk spins—but the black lines take on the opposite color of the wedges in which they are embedded. This color induction happens before your perception fuses the surrounding colors.
WHEN PRETTY FACES TURN UGLY
By Jason Tangen, Sean Murphy, and Matthew Thompson • University of Queensland, Australia • 2012 Finalist
Tangen and his colleagues caused perfectly normal-looking faces to appear grotesque by aligning them with other faces and displaying each image briefly. The illusion works because your visual system processes each face not as an isolated entity but in comparison with the faces that precede it.
ROTATING BY SCALING
By Attila Farkas and Alen Hajnal • University of Southern Mississippi, U.S.A. • 2013 Finalist
Rigid objects—or those that we expect to be rigid—appear to rotate when they are stretched (scaled) asymmetrically. In a dramatic example, created by the psychologists Attila Farkas and Alen Hajnal, a stationary computer-generated head appears to turn around a vertical axis when one half of the head is stretched and the other compressed.
COUNTERINTUITIVE ILLUSORY CONTOURS
By Barton Anderson • University of Sydney, Australia • 2010 Second Prize
A diamond shape alternately expands and shrinks as disks and dots move back and forth—but the diamond is entirely constructed by your visual system. Anderson’s illusion illustrates the brain’s ability to fill in much of the missing information in a scene, often creating complicated percepts from very simple constituents.
MUTUALLY INTERFERING SHAPES
By Maarten Wijntjes, Robert Volcic, and Tomas Knapen • Utrecht University, The Netherlands • 2008 Finalist
This illusion shows that the perceived trajectory of a dot depends on its position relative to other objects in the world. While an outer dot travels around a circle, an inner dot moves along the straight sides of a square—and yet it appears to follow a trajectory made up of concave curves.
TILT ILLUSION
By Siddharth Jain • U.S.A. • 2009 Finalist
A horizontally moving dot appears to follow a tilted trajectory, when it only shifts down a row. The effect may result from the phenomenon called “persistence of vision,” presented by Peter Mark Roget (who also wrote the famous thesaurus) to the Royal Society of London in 1824 as the ability of the retina to retain an image of an object for a twentieth to a fifth of a second after its disappearance—an illusion that is crucial to animation.
THREE-FOLD CUBES: AN OBJECT WITH THREE DIFFERENT FORM INTERPRETATIONS
By Guy Wallis and David Lloyd • University of Queensland, Australia • 2013 Finalist
The same object can look like two cubes, a single cube with a cube-shaped bite taken out of it, or a concave surface illuminated from below. The brain cannot decide, because each interpretation is equally correct. As a result, our perception cycles endlessly through the possibilities.
THE BAR-CROSS-ELLIPSE ILLUSION
By Gideon Caplovitz and Peter Tse • Dartmouth College, U.S.A. • 2006 Third Prize
Gideon Caplovitz and Peter Tse’s four-way illusion pushes the ambiguity envelope even further. Here the same unique moving object can be seen as a cross-shaped figure morphing nonrigidly in size and shape, an ellipse rigidly rotating behind four square occluders, two independent perpendicular bars rigidly oscillating in depth, or a stationary cross viewed through an elliptical aperture that is rotating rigidly.
TWO SINUSOIDS: SIX PERCEPTIONS IN ONE
By Jan Kremlá∘cek • Charles University in Prague, Czech Republic • 2010 Third Prize
Caplovitz and Tse’s 2006 record of a tetra-ambiguous illusion
stood until Kremlá∘cek created his six-in-one sinusoids in 2010. Kremlá∘cek’s illusion combines stationary and moving sinusoids in an animation that can be perceived in any of six different ways, including a rotating double helix, a waving ribbon, or a set of dots bouncing up and down.
ROLLING EYES ON A HOLLOW MASK
By Thomas Papathomas • Rutgers University, U.S.A. • 2008 Third Prize
This hollow mask is concave, but because your brain assumes that all faces are convex, that’s how it appears. Whereas a convex face would look in only one direction, a hollow face seems to look forward when the viewer is directly ahead, but at an angle when the viewer moves sideways. The vision researcher Thomas Papathomas attached three-dimensional eyeballs and a nose ring to a hollow mask; when the mask rotates, the eyeballs and nose ring appear to rotate in the opposite direction.
EXORCIST ILLUSION
By Thomas Papathomas, Tom Grace Sr., Marcel de Heer, and Robert Bunkin • Rutgers University, U.S.A. • 2012 Finalist
Papathomas and his colleagues also created a “hollow body” illusion, with a critical twist: they paired a hollow mask with a nonhollow torso, and vice versa. The sculptures have no moving parts, but when the head-torso composites are rotated, “the effect is a flexible, twisting neck out of a 3-D rigid [body], like in The Exorcist,” Papathomas says. This illusion reveals some of the biases the brain uses to interpret the orientation of faces and bodies. For example, your brain assumes that people’s faces and bodies are lit from above, by the sun. So when you view a hollow mask or body and the lighting orientation appears reversed, so does the rotational direction.
STEREO ROTATION STANDSTILL
By Max Dürsteler • University Hospital Zurich, Switzerland • 2008 Finalist
The wagon wheel shape in this illusion exists solely within stereoscopic space. When it rotates at an angular velocity greater than thirty degrees per second, the turning stutters and skips, and sometimes completely stops, even though it actually rotates smoothly.
TRANSLATION WITH A TWIST
By Jun Ono, Akiyasu Tomoeda, and Kokichi Sugihara • Meiji University, JST, CREST, Japan • 2013 First Prize
Ono, Tomoeda, and Sugihara showed that two identical stationary pinwheels appear to spin in opposite directions when a grid moves across them.
TUSI OR NOT TUSI
By Arthur G. Shapiro and Alex Rose-Henig • American University, U.S.A. • 2013 Second Prize
This illusion takes advantage of the fact that we group individual moving objects into global structures depending on the statistical relation among those objects. Depending on where you focus your attention, you’ll see different kinds of motion.
DANCING DIAMONDS
By Michael Pickard and Alessandro Soranzo • University of Sunderland and Sheffield Hallam University, U.K. • 2013 Finalist
Nothing actually moves in this illusion, though your brain begs to differ. The edges of the diamonds do not move, or even change—it’s the diamonds’ insides that cycle between dark and light—but there is a distinct sense of movement nevertheless. Further, the entire collection of diamonds appears to move as a whole—like objects drawn on an elastic surface that is blowing in the wind—rather than as individual parts.
PIGEON-NECK ILLUSION
By Jun Ono, Akiyasu Tomoeda, and Kokichi Sugihara • Meiji University, JST, CREST, Japan • 2014 Finalist
An object progressing at constant speed in front of a vertical grid of stripes appears to shift backward and forward. The motion is similar to the action of a walking pigeon’s neck.
HYBRID MOTION
By Arthur G. Shapiro and Oliver Flynn • American University, U.S.A. • 2014 Finalist
Shapiro and Flynn’s illusion consists of an array of rectangles that change from yellow to blue to yellow over time. The physical positions of the rectangles never change, but they appear to move in opposite directions, depending on whether the observer is close to the monitor or far from it.
THE WILE E. COYOTE ILLUSION
By Alan Ho and Stuart Anstis • Ambrose University College, Canada; and University of California, San Diego, U.S.A. • 2013 Finalist
Alan Ho noticed that a computer representation of a turning fan blade appeared to spin twice as fast after he doubled its number of blades. Likewise, cartoon animators often draw multiple legs and feet on fast-moving characters, such as Wile E. Coyote, to convey the illusory feeling of speed. Ho and Stuart Anstis showed that increasing the number of orbiting circles around a larger one makes the smaller circles seem to be moving faster, even though their speed remains constant. This illusion has commercial and practical applications for computer games, advertising, and even road safety.
THE LOCH NESS AFTEREFFECT
By Mark Wexler • Université Paris V, France • 2011 Third Prize
This illusion is named for a classic phenomenon known to the ancient Greeks and rediscovered in 1834 by Robert Addams at the Falls of Foyers, the waterfalls that feed Loch Ness in Scotland. Addams noticed that after he stared at the waterfalls for a while, stationary surfaces, such as the rocks and vegetation beside the falling water, appeared to drift upward. In Wexler’s illusion, the viewer stares at a red dot surrounded by a rotating ring of dashes. Suddenly the ring jumps in the opposite direction with a rapid rotation, before continuing to turn slowly in the original direction. Wait—the ring is not really jerking backward, but its elements are simply reassorted at random. The resulting illusory motion is more than a hundred times faster than the motion described by Addams.
COLOR WAGON WHEEL
By Arthur G. Shapiro, William Kistler, and Alex Rose-Henig • American University, U.S.A. • 2012 Third Prize
This illusion was inspired by a classic phenomenon known as the Wagon Wheel Illusion, in which nested circular rows of black disks rotate clockwise but appear to do so counterclockwise. Here some of the disks are colored yellow. The result is a novel and striking illusion: a wheel that spins simultaneously in both directions.
THE STEERABLE SPIRAL
By Peter Meilstrup and Michael Shadlen • University of Washington, U.S.A. • 2010 Finalist
Multiple moving spots—special visual objects called Gabor patches—travel in a spiral toward the center of a circle. Each of them contains a small grating that moves opposite to the spot’s direction of travel. When presented alone, each spot moves in a single, clear direction. But when multiple spots are in close proximity to each other, their internal motion confounds the brain’s movement-detection circuits, and produces the perception of a false direction. The effect is dramatic when you shift your gaze from the center of the spiral to the edge of the screen: the rotation direction reverses, but only in your mind!
MOTION-ILLUSION BUILDING BLOCKS
By Arthur G. Shapiro and Justin Charles • Bucknell University, U.S.A. • 2005 First Prize
A flashing square surrounded by a two-tone alternating frame results in illusory motion. Shapiro and Charles showed that you can combine illusory building blocks of motion to create countless new movement illusions. It’s like illusion Legos of the mind!
TWO-STROKE APPARENT MOTION
By George Mather • Sussex University, U.K. • 2005 Second Prize
This effect alternates two spatially shifted images—with a gray frame between the alternations—to create the illusion of a speeding motorcycle down a country lane. The “jump” between the pictures makes the images appear to move forward, as in a movie.
BACKSCROLL ILLUSION
By Kiyoshi Fujimoto • Kwansei Gakuin University, Japan • 2005 Finalist
An object in the foreground appears to move in one direction, while a flickering grating (or static noise) occupies the background—leading to the perception that the background is moving in the opposite direction to the foreground illusory motion! For example, when an animated cartoon character appears to walk toward the left in the foreground, the flickering background appears to go to the right.
THE WINDMILL ILLUSION
; By Baingio Pinna and Massimiliano Dasara • University of Sassari, Italy • 2005 Finalist
The windmill appears to turn, but it is actually stationary. Only the transparency of the middle ring causes your brain to believe that the windmill is moving. As the ring fades in and out of your vision, you are fooled into seeing the windmill turn in both directions.
THE FREEZING ROTATION ILLUSION
By Max Dürsteler • University Hospital Zurich, Switzerland • 2006 First Prize
A foreground object’s motion appears to vary with the rotation of an image in the background.
GRADIENT-OFFSET INDUCED MOTION
By Po-Jang Hsieh • Dartmouth College, U.S.A. • 2006 Finalist
When square-shaped grayscale luminance gradients disappear—all at once—you see ghostly movement that flows from left to right.
THE OCCLUSION VELOCITY ILLUSION
By Evan Palmer and Philip Kellman • Harvard Medical School and University of California, Los Angeles, U.S.A. • 2006 Finalist
When a moving object suddenly splits in half, masking the motion of one of the halves makes the two parts appear misaligned.
WHERE HAS ALL THE MOTION GONE?
By Arthur G. Shapiro and Emily Knight • Bucknell University, U.S.A. • 2007 Third Prize
If you cycle the background luminance behind a stationary gradient from black to white to black (and repeat), you can see illusory motion within the gradient. This motion illusion is strikingly enhanced when the gradient is blurred.
BOUNCING BRAINS
By Thorsten Hansen, Kai Hamburger, and Karl R. Gegenfurtner • University of Giessen, Germany • 2007 Finalist
Some of the brains in this illusion are lighter than the background, and others are darker. As the background luminance is modulated, the brains rotate and bounce. In certain areas of the image, the adjacent brains move in unison, creating an even greater illusory effect.
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