TechFlesh Blog

10 Best illusions of 2011

Visual researchers have come up with some mind-bending new illusions this year at the Best Illusion of the Year Contest in Naples, Florida. Here are the top ten.

1st Place: Colour-blinding wheel wins illusion contest

See an award-winning brain trick that shows how motion affects our perception of colour.

Motion can affect how we perceive changes in colour, as demonstrated in an illusion created by Jordan Suchow and George Alvarez at Harvard University that won first place last week at this year’s Best Illusion of the Year Contest in Naples, Florida.

While watching the animation above, fix your eyes on the white dot in the center. When the surrounding ring is stationary, you’ll notice the dots inside changing colour. But as the wheel rotates, the flashing circles should appear to switch colour less often or not at all. In reality, the colours are changing at the same rate throughout the animation.

Suchow and Alvarez think that the phenomenon, called change blindness, occurs because specific brain areas monitors different locations in our visual field. When an object is moving fast, local detectors don’t have much time to register a colour change so they can remain undetected.

2nd Place: Change in contrast fools your brain

Watch a flashing pattern change before your eyes when the background is altered.

When we scan the world around us, our brain tends to group objects based on common attributes. Now a new illusion that won second prize in this year’s Best Illusion of the Year Contest, created by Arthur Shapiro from the American University in Washington DC and his team, shows that these groupings can be made based on changes of contrast (see video above).

In the first scenario, the dots at the top flash in sync, followed by the bottom ones. But when the same arrangement is placed on a split background, the diagonally-aligned discs seem to change together. In a second example, a flashing pattern on a plain background appears dramatically different when the background is replaced with the image of a shaded circle. Substituting a black and white picture split diagonally for the background, the flashing pattern in the third animation looks altered.

According to Gestalt psychology, our brain makes sense of what we see by classifying visual information based on factors like proximity, common background and similarity. But this illusion shows that we are also tuned to changes in contrast, which can override the other types of groupings. This method of classification uses spatial information rather than more apparent cues in the figure and background.

3rd Place: Turning wheel seems to jump backwards

In a new brain trick, a turning circle appears to skip in the opposite direction.

Fix your eyes on the red dot in the animation above. As the circular pattern turns, it may appear to jump backwards but the skipping motion is all in your mind. What’s actually happening in this illusion, created by Mark Wexler from Paris Descartes University, is that the random lines that make up the circle are suddenly replaced by a different pattern.

In the video above, you can see a few variations of the illusion that demonstrate that the effect is perceived regardless of the rotation’s direction. “The jumps can also be seen if white lines are suddenly made black and vice versa,” says Wexler:

If the lines are randomized again for a slightly longer duration, the jumps seem to go further back

There is currently no known explanation for this brain trick. But Wexler thinks it’s a type of motion after-effect, with two main differences. Typically, the illusory motion is much slower than the main one but in this case it’s extremely fast. In addition, many observers reported a change in amplitude accompanying the switch whereas motion after-effects don’t usually involve a change in position.

By making the change of pattern occur more slowly, Wexler found that many people perceived a net motion in the opposite direction to the original rotation. He says:

The illusory motion is more pronounced than the (real) motion we put in: a perceptual, perpetual motion machine!

Finalist 4: Spot the morphing face

Watch how a facial transformation can appear more or less dramatic depending on your eye movement.

Thanks to animation tools, a face can be made to morph into another. But a new illusion created by Rob van Lier and Arno Koning from Donders Institute in the Netherlands shows that your eye movement can affect how dramatic the transformation appears to be.

In the video above, follow the moving red dot superimposed on the face. When it stops moving, fix your eyes on the stationary spot. Did the morphing seem to be more pronounced?

According to van Lier, when our eyes are tracking a moving object we are less aware of changes in the scene, in this case moving eyebrows and colour fluctuations. He says:

The processing of incoming retinal information is attenuated. For example, try tracking your eyes when standing in front of a mirror – it’s hardly possible

When focusing on a stationary spot, the morphing effect is much stronger and can even appear to be blown-up. “We chose to use faces because small variations in features can induce completely different facial characteristics,” says van Lier. The team came up with the illusion while trying to combine different visual stimuli.

The illusion was a finalist at the Best Illusion of the Year Contest which took place last week in Naples, Florida.

Finalist 5: Masked face conceals a kiss

See how an ambiguous image can confuse your brain in this new illusion.

At first, it looks like a pensive face in a Venetian mask (see photo above). But take a closer look at its features and you’ll see that it conceals a couple kissing. Aptly named Mask of Love, the illusion was created by Gianni Sarcone, Courtney Smith and Marie-Jo Waeber from the Archimedes’ Lab in Genoa, Italy after discovering the blurry photograph.

But why are we more likely to see one face rather than the kissing duo? According to Sarcone, our visual system tends to group objects by how we expect to see them. The contours of the mask’s ornate headdress together with the background make most observers overlook the kiss. Once you detect the two faces however, your brain will typically alternate between both versions of the mask. Ambiguous figures cause fluctuations in visual awareness because they offer alternative and contradictory interpretations.

This illusion was a finalist at the Best Illusion of the Year Contest which took place last week in Naples, Florida.

Finalist 6: Tricky triangle dupes brain twice

Watch a new visual trick that combines an impossible triangle with an illusory one.

You’re probably familiar with the Penrose triangle, an impossible object that can’t exist in ordinary 3D space, and the Kanizsa triangle, an illusion that makes a triangular shape appear thanks to carefully-placed fragments. Now Christopher Tyler from the Smith-Kettlewell Institute in San Francisco has creatively combined the two brain tricks in an animation to produce a dual effect.

In the video above, the inner markings of an impossible triangle appear first. With the twirl of an animated magic wand, you start to see the full shape as the spinning stick induces illusory contours. Then three red spheres appear, reminiscent of the circles in Kanizsa’s famous trick, moving across the screen in different ways to infer contours once again. Finally, the balls settle into the corners of the triangle, superimposing the two classic illusions and creating the most pronounced combination of the two effects.

According to Tyler, depth processing, which occurs in the occipital lobe of the brain, helps us perceive the impossible triangle. Since the shape displays conflicting orientations, our brain picks one of these possible realities and switches between them. The triangle at the end of the video appears thanks to illusory contours, which are created as our brain choosees the most likely configuration given the visual information provided.

The illusion was short-listed at the Best Illusion of the Year Contest which took place last week in Naples, Florida.

Finalist 7: Fixed objects move before your eyes

Watch how your focus of attention can affect where an object seems to be.

You may think it’s easy to perceive an object’s location. But a new illusion created by Peter Tse from Dartmouth College, New Hampshire and his team shows that surrounding motion can trick our brain.

While looking at the animation above, pay attention to the moving layer of black dots while keeping your eyes fixed on the blue dot in the middle. When a pair of red dots is flashed on screen, how are they aligned? Now switch your focus to the spinning white layer. Do the red dots appear in the same place? Finally, look at the blue dot without focussing on either spinning layer and note the position of the red dots.

When paying attention to the black layer, the red dots should appear slanted to the left and when looking at the white layer they appear to be skewed to the right. But when the layers are ignored, the dots seem to be aligned vertically – which is in fact their true position in every case.

According to the researchers, the illusion is the strongest example to date for how attention can affect our perception of an object’s location. By using an identical stimulus with different layers to pay heed to, it clearly demonstrates how an object in a fixed place can appear to move around. For the effect to occur, the objects must be presented very briefly, there must be motion around them and they should appear at the moment when the surrounding motion is reversed.

The researchers haven’t yet figured out why we perceive this illusion but Tse has a theory. When we look at a scene where there is movement, he thinks that our brain accounts for the motion to compute the location of objects. So if an object quickly appears before our eyes, it’s unclear whether it’s part of the moving scene or not. Tse says:

In a sense the motion information sweeps the computed position along with it. If the object appears for a longer period of time, our brain is able to determine its correct position since there is no ambiguity about whether it’s part of the moving surface or not

This illusion was one of the finalists in this year’s Illusion of the Year contest, held in Naples, Florida.

Finalist 8: Harry Potter and the confusing crash

Watch how a collision between two characters changes depending on your viewpoint.

In this video, Harry Potter can appear to pass through Dobby the elf but it’s not magic. The illusion, created by Arthur Shapiro and Gideon Caplovitz from the American University in Washington, DC, is an example of the different ways our brain can link separate objects in a scene.

When watching the video above, focus on the spot where Harry and Dobby meet during the collision. What do you see? The two figures should appear to bounce off each other and return their separate ways. Now take a look at the scene again, this time while looking at something just above the video but keeping the characters in your peripheral vision. This time, Harry and Dobby should appear to pass through each other, even though they are actually bouncing.

We experience this phenomenon because our brain processes different features of a scene in parallel. Colour and motion, for example, are analysed separately, even though a moving coloured object would be perceived as a whole. In this case, it shows that features can bind to moving objects in different ways. Shapiro writes:

The apparent transfer of features contradicts what would be expected from theories that propose that perception is guided by intelligent inferences about how objects behave in the world.

This illusion was one of the finalists at this year’s Best Illusion of the Year Contest, held last week in Naples, Florida.

Finalist 9: Feel a shape that isn’t there

The world’s first printable tactile illusion lets you feel an invisible ridge.

Masashi Nakatani, a virtual reality researcher at Keio University in Japan, has a business card that’s sure to attract attention. It’s embossed with the first printable tactile illusion, a design that fools your brain into perceiving a ridge that isn’t there.

The illusion looks like a tiny fishbone and is made up of textured ribs branching out from a smooth spine (see photo above). As you run your finger along the backbone, you inevitably touch the rugged edges of the ribs as well, but what you sense is an indented surface when it’s actually flat.

The brain trick is likely to be caused by mixed signals since the same tactile nerves assess form and coarse texture. Because of the size of the print, the two textures are experienced at the same time and cause confusion.

Nakatani discovered the illusion while preparing the texture for an experiment. A conference paper (see Figure 5 and the appendix) includes details on how to craft your own tactile trick with a knife and paper.

The brain trick was a finalist at the Best Illusion of the Year Contest which took place last week in Naples, Florida.

Finalist 10: Morphing cluster of rings

Watch how visual cues can alter our perception of an ambiguous moving figure.

Do you see a twirling figure eight? Or perhaps three rotating rings? A new illusion created by Stuart Anstis from the University of California, San Diego, and Patrick Cavanagh from Paris Descartes University in France shows that adding visual cues to a moving ambiguous shape can change what we perceive (see video above).

Take a look at the animation above while keeping your eyes fixed on the dot at the center. In the beginning of the video, the intersection of the rings are highlighted but then the markings gradually fade away. You should initially perceive a figure eight revolving around a ring but once the spots disappear, three separate rings will seem to turn around each other.

According to Anstis, we experience this illusion because of cross-talk between brain circuits that detect motion and those that look out for position. “Somehow there is interaction between motion and position,” he says.

Anstis discovered the brain trick by chance while looking at another motion illusion. It was one of the finalists at this year’s Best Illusion of the Year Contest held last week in Naples, Florida.