Optical illusions may seem like nothing more than visual trickery. But they are actually a result of our brains trying to predict the future.
When light hits our retina, it takes about one-tenth of a second for our brain to translate that signal into perception. Evolutionary neurobiologist Mark Changizi says this neural delay makes our brains generate images of what it thinks the world will look like in one-tenth of a second. It's not always right.
“Your brain is slow, so you need to basically create perceptions that correct for that delay,” said Changizi, director of human cognition at 2AI Labs.
Creating an image of the very near future probably kept early humans alive because it kept them from bumping into dangerous objects or being attacked by a fast-moving predator.
Click through the following images and see how our ability to predict the future one-tenth of second in advance also messes with your mind.
When images of objects flow across the retina, it activates all these different neurons in our brains. This is the mechanism by which the brain figures out how to extrapolate the next moment.
“When you move through the world, your eyes take snapshots,” said Chingazi. “During that snapshot, as something moves across your visual field, you don’t just end up with a dot on your retina, you end up with a blurred line on your retina.”
Our perception doesn’t see them, but the blurred lines make our brains realize that something is in motion. From there we can determine the direction of an object moving in our world. Since the blurred lines are all emanating from a single point in your visual field, they can inform you on the direction you’re going.
“Once you know the direction you’re going, you can determine how all these things would change in the next moment,” said Chingazi.
Take the above photo of “warp speed.” You don’t even have to question in what direction those blurred lines are taking you. Little did you know, "Blurred Lines" is more than just the most over-hyped song of the summer.
Perhaps the best representation of blurred lines and how they apply to optical illusions is the Hering illusion. Its radial spokes are blurred lines, all emanating from a single point. Those lines tell us where we are heading: forwards, towards the center.
The reason the two vertical lines appear to bow in the middle is because the radial lines suck our field of vision towards the center, as if we were in motion. In fact, those vertical lines are parallel, despite what our brain tells us. Our perception is actually showing us what those parallel lines look like in the next tenth of a second, the moment our gaze “passes through” the vertical lines, towards the vanishing point of the radial lines.
To simplify things, Chingazi suggests we imagine walking through a very tall doorway of a cathedral. When we’re really far away, the doorway sides seem parallel to one another. The angular distance between the top, middle and bottom of the door are all roughly the same.
“Once you’re really close or going through the cathedral doorway, the parts at eye-level are going to be wider apart,” he said. “When you look up, they actually converge like railroad tracks in the sky.”
Essentially, this is the same phenomenon that happens in the Hering illusion.
GRAND UNIFIED THEORY
Shapes aren’t the only objects that change as we move forward. Other factors like angular size -- how much of our visual field is taken up by an object – speed, distance and the color contrast between an object and its background also contribute to optical illusions.
Changizi determined that many illusions can be defined within his future-seeing process, so he created a chart with 28 categories that help organize what he calls his “grand unified theory.”
“This seven-by-four table really has one hypothesis that explains them all,” he said. “It makes a prediction across these 28 categories about what kind of illusions you should expect and how the illusions will reveal themselves across these 28 kinds of stimuli.”
The above illusion was created by a former student of Chingizi’s, and it demonstrates elements of speed, size and contrast. Move your head towards the center and the bright-white center appears to quickly fill the circle. Move your head backward and the dark perimeter appears to close in on the white center.
The orange circle on the left appears much smaller than the one on the right, when in fact they are the same size. This is the classic Ebbinghaus illusion, named after Hermann Ebbinghaus, the German psychologist who discovered it. British psychologist Edward Titchener popularized the illusion in the early 20th Century, as the illusion is also known as “Titchener circles.”
The juxtaposition of the circles’ sizes and distance from each other make them appear incongruent.
It’s time to play magician and make the pink splotches disappear. Stare at the cross in the center of the image and before you know it, you have a completely gray rectangle.
If we fixate on one single point, we tend to keep our eyes still. Those blurry pink orbs are now on the periphery of our visual field and tend to disappear because we’re zeroing in on the cross. Despite being physically present, the pink smudges do not stimulate our neurons enough to maintain visual perception. The phenomenon is known as “Troxler’s fading,” discovered by Swiss physician Ignaz Paul Vital Troxler in 1804.
Although the pink dots are static, they’re actually a part of an animated illusion called the “Lilac Chaser,” created by Jeremy Hinton around 2005. In that illusion, a green dot seemingly “eats” the other dots in a clock-wise fashion, thus it’s sometimes known as the “Pac-Man” illusion.
CAFE WALL ILLUSION
This illusion is attributed to British psychologist Richard Gregory. Legend has it that his lab assistant saw this illusion in the wall tiles at a cafe in Bristol. The black and white pattern was offset by a half a tile, causing the illusion to appear.
Though they appear to be at an angular pitch, the horizontal lines are parallel. Distance and contrast are two operating variables in this illusion.
Interested in seeing the tiles at the original Bristol location? The cafe is still there, but it’s reportedly closed. However, curious trekkers can find it at the bottom of St. Michael's Hill.
So-called peripheral drift illusions, such as Japanese psychology professor Akiyoshi Kitaoka's “Rotating Snakes,” are motion illusions that occur in our visual periphery. These illusions work best when you look off to the side of the image.
Earlier studies of the “Rotating Snakes” suggested that perceived motion was triggered by eyes moving slowly across the images. But a 2012 study, led by neuroscientist Susana Martinez-Conde, showed that fast eye movement, some of which is microscopic, drive the perceived motion.
The scintillating grid is an illusion created by superimposing white dots at the intersection of gray lines on a black background. Dark dots seem to appear and disappear at the intersections, and jump around the grid, thus the term “scintillating.”
Trying to pin down one of the black dots with your gaze is like playing a hands-free version of Wack-a-Mole, as the dark spots only appear in your periphery.
One of the clearest examples of how sharp, black-and-white contrast effects the gray scale can be seen in the image above.
The gray bars between the black stripes appear darker than the gray bars between the white strips. However, the gray bars are the same shade. Chingizi’s “grand unified theory” states the higher the contrasts nearby an object, the lower in contrast that object will appear.
3-D CHALK DRAWINGS
Lady, look out for that giant snail, it’s about to attack! Oh wait, shwoo, it’s only one of Julian Beever’s pavement drawings.
The English artist and renowned darling of gotta-see Internet pics has been taking to streets and sidewalks all across the world since the mid 1990’s. He employs a projection technique called anamorphosis to give the illusion that his drawings are three dimensional when viewed from a certain angle.
3-D CHALK DRAWINGS, AGAIN
Shoppers in Camberley, England, got a glimpse of Santa in his snowy underground grotto courtesy of Julian Beever's amazing 3-D street art.
While this image looks like a model of the future’s coolest water slide, it’s artist Anh Pham’s version of a peripheral drift illusion.
Concentrate on one of the pink spots and you may be able to stop that ring from moving, but it’s a different story in your visual periphery. Good luck tearing yourself away from this one.
Go to any tourist destination in the world that has an iconic structure, such as the Eiffle Tour, the Taj Mahal or the Washington Monument, and you’ll find tons of fanny-packed shutter bugs creating their own optical illusions. Because objects in the distance appear smaller, altering your perception angle can make it seem like the Eiffle Tour is small enough to fit in the palm of your hand. Or that you can push against the Leaning Tower of Pisa to keep it from falling over.
As the above couple demonstrates with the incredible-shrinking-man illusion, altering your perspective can drastically change your perception.