The science behind optical illusions: Video reveals how easy it is to fool our brains using simple tricks
- Light is converted into electrical signals that brains turn into an image in around one tenth of a second
- Our brains take in so much information this way, that they have to take shortcuts in processing information
- Video takes a look at how these shortcuts cause us to see things that aren't there, such as rotating snakes
Our eyes tend to skim over information and our brains often jump to conclusions.
This is because we take in so much visual information, that our brains need shortcuts to process it all.
The trait evolved to help early humans survive encounters with fast predators, but it also means that we can be easily fooled by simple illusions.
A new video, which is a collaboration between the American Chemical Society and Inside Science TV, explains the science behind this visual trickery.
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Take a look at the centre of this figure. It looks like an intricate pattern, nothing more. But when you look outside of it, it starts to move. 'Our brains are able to perceive lighter values much more quickly than dark values,' the video says. 'This explains why the discs seems to rotate in the direction of the lighter shades'
'When you look at something what you're really look at is light,' the video narrator explains. 'The light is then converted into electrical signals that your brain can turn into an image.
This process takes place in about one tenth of a second. So at any given moment, your eyes are taking in an incredible amount of information.
'It's really difficult for your brain to focus on everything at once, so our brain takes shortcuts, simplifying what we see to help concentrate on what's important,' it adds.
The video first looks at the Hering illusion with features two parallel straight lines that seem to change shape, size and angle.
Our eyes have a type of cell that has a way of 'leaking' this light information to neighboring cells. The video describes how this creates a visible halo when you're looking at certain high contrast images. The effect can be seen in this famous illusion, the Hermann grid
When you drop the lines in front of a radial pattern, they look warped even though they are actually straight.
'When your brain see that radial pattern, it focuses on the point in the middle,' the video explains.
'It looks like you're travelling towards it. Your brain then thinks these parallel lines are getting closer.
'That's why they seem to get larger as you approach the centre of the radial pattern, and that makes the lines look warped.'
Not all illusions can trick our brains into seeing motion. Some trick you into seeing colours or shades that aren't actually there.
For instance, the Mach Bands illusion exaggerates the contrast between edges of the slightly differing shades of grey, as soon as they contact one another. If you separated the bands, they would appear to be far more similar.
These are two identical, straight lines. But what happens when you change what's going on around them? All of a sudden, the lines look like they've changed size in relation to each other; they could shrink and grow (left) and they could change angle (right). 'Even though it would seem like the lines themselves are changing,' the video says, 'the only thing that's actually bending or buckling is your mind
Although the coils in the image appear to be rotating, in reality they're completely stationary. The effect works best in peripheral vision, so when you stare at one of the coils it will appear stationary while those around it will appear to rotate. Vision experts aren't exactly certain why it works; however, their research has revealed that the shading of the segments that make up the rings is crucial
'This is due to an automatic process in our brains called lateral inhibition that helps us define the edges of objects.'
The effect can also be seen in the Hermann Grid, where you can see a grey circle at the intersection of each square.
But perhaps the most famous, and dramatic, example is that of the rotating snakes.
Although the coils in the image appear to be rotating, in reality they're completely stationary.
The effect works best in peripheral vision, so when you stare at one of the coils it will appear stationary while those around it will appear to rotate.
The illusion was created by Japanese psychologist Akiyoshi Kitaoka from Ritsumeikan University in Kyoto.
The Mach Bands illusion, seen in these two images, exaggerates the contrast between edges of the slightly differing shades of grey, as soon as they contact one another. If you separated the bands, they would appear to be far more similar. On the right the Mach bands illusion makes the darker areas falsely appear even darker in the illusionary 'bands' stretching along boundaries
Vision experts aren't exactly certain why it works; however, their research has revealed that the shading of the segments that make up the rings is crucial.
These segments are arranged in a repetitive pattern consisting of a relatively dark area (yellow) followed by a brighter one (white), then a less bright one (blue), and finally the darkest area (black).
Information from high-contrast parts of the image (yellow-white, white-blue and blue-black) travels to the brain faster than that from low-contrast parts (blue-black).
It's believed that this 'staggered' information mimics the type of input that the eyes and brain receive when they see genuine motion, and so you end up believing that you're looking at actual movement.
'When you fixate on any point, the motion seems to stop,' the video states. 'This is in part, due to how we see light and dark and in part to our eye movements.'
'There are also key points where your perception of motion is reset: blinking, shifting your eyes, and looking away and back fuels the illusion of motion.
'So don't believe the cliché. What you see isn't always what you get.'
If you put a bike-spokes pattern behind two, straight horizontal lines, the lines will look warped, even though they are straight. When your brain sees the pattern, it focuses on the point in the middle, as if you're moving towards it. Your brain then thinks the two parallel lines are approaching you
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