Optical illusions that will have you seeing double
Wait, what am I looking at?
Another day, another optical illusion - but this time it's how your eyes and brain work together that is being tested.
A series of four patterns, relying heavily on colours, use how quickly you get the answer to measure how your brain perceives information.
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So give your eyes a work out now and try all four:
1. How many colours can you see?
Answer: There are three colours - red, blue and yellow. But what colour were the central squares? They are all in fact red, but a process called chromatic assimilation (or contrast) could have you seeing orange, depending on the background colour.
2. How many colours can you see?
Answer: Yes there are only two - black and white. If you're also seeing grey spots, that's down to the way different parts of your retina are reading the white lines horizontal and vertical. It's an effect called lateral inhibition.
This was discovered by physiologist Ludimar Hermann, from Germany, 200 years ago and is now eventually named after him.
3. Which orange circle is bigger?
Answer: They're the same! Yes, really. That is because the surrounding grey circles are distracting your eyes and giving you a false idea of perspective.
4. How many colours are named?
Answer: Seven - green, black, blue, orange, purple, red and yellow. This one is a little bit of a test of comprehension. Your brain is tricked into counting the colours you can see, as opposed to those you can read, which is what the question really asks.
How well did you do? And are your brain and/or eyes hurting now?