The internet loves optical illusions, ones that are particularly popular feature two cute animals that seem to have magically merged into one, or family photos with one family member showing one too many arms. These images are incredibly convincing, you might even think there’s something wrong with your glasses when you look at them! There are several types of optical illusion, we go through the different types and explain the link they have with our vision.
What is an optical illusion?
An optical illusion is defined as “something that deceives the eye by appearing to be other than it is.” - an optical illusion uses imagery to cause your brain/eyes to perceive things differently. It could be that you see more than one thing within an image, or it could be that you see a 3D image that is really 2D. These types of illusions demonstrate the relationship between the brain and the eyes and how they must work together to help you see. Optical illusions also show how there can be a difference between perception and reality.
Can optical illusions improve eyesight?
Psychologists at the Universities of York and Glasgow from the department of psychology found that staring at an optical illusion can improve visual acuity and allow you to see small print, thanks to something called expanding motion aftereffect, which causes you to see things as bigger than they are.
After looking at the illusion, people reading the Logmar eye chart (the chart that shows a set of letters ranging from large to small in size) could read the small print, whereas previously they couldn’t. This proves that certain types of optical illusion can improve the ability to read, although only temporarily. How we perceive things is just as important as the health and age of your eyes in helping you to read and understand visuals.
What type of optical illusions are there?
Here are some examples of optical illusions:
When you stare into the centre of this image, the black part appears to take over and start moving! When we focus on things within the centre of our vision, things around that point in our peripheral vision appear to vanish, of course they don’t really vanish, it’s just an illusion.
Can you see a vase in the picture, or can you see 2 people facing each other? This is a type of cognitive illusion, in which an image causes us to interpret it one or several ways, depending on the experience or assumptions we have about the world.
Is the hand giant, or is it just far away from the Eiffel tower? This is a very popular optical illusion trick tourists love to do with famous landmarks! This is a perspective illusion, if we were further to the left or right in this scene, we would see that the hand is much further away from the building.
These flowers look as if they are moving. This type of illusion is called illusory motion which is when a static image appears to be moving due to the position of contrasting colours/shapes.
Psychological illusions – afterimage
Psychological illusions are a result of overstimulation of the eyes that creates an afterimage, such as the grey spot you see in the centre of your vision after being exposed to bright light.
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