This week after a quick warm-up with a couple of new teasers, we're looking at optical illusions, which demonstrate how the mind deals with visual information.
7. Cranberry switch:
You have six glasses in a row. Three of them are full of cranberry juice and three are empty. By moving only one glass, arrange the glasses so the full and empty ones alternate. See answer
8. Red hat, purple hat:
The famous hat designer, Guido, wants to give presents to his three favourite supermodels, Anastasia, Babette and Kiki – but he’s not going to make it easy for them.
First, he shows them five gorgeous hats: three red and two purple. Then he asks them to stand in a row, one behind the other, all facing the same way. He puts a hat on each of their heads. Each woman can see the model(s) in front of her, but not her own hat or anything behind her.
“Darlings,” says Guido, “If you can name the colour of the hat you’re wearing, you get to keep it!”
Anastasia says she doesn't know the colour of her own hat. Babette, too, admits defeat. But clever Kiki immediately knows what colour hat she’s wearing. How does Kiki know? And what colour is her hat? See answer
Most of the time, the brain is really good at working out the colour, size, distance, motion and importance of objects in everyday life. But in unusual situations, the brain can be tricked into interpreting an image as something strange or even impossible: an optical illusion. “Illusion” sounds like a cheap trick, but these illusions are studied by serious neuroscientists because they show us how the brain is adapted to make sense of visual information.
Here’s one interesting illusion. (Don’t worry if you can’t see it! A small percentage of normal people are unable to see certain optical illusions.)
9. Lilac chaser:
Keep your eyes focused on the central point. While staring at the centre, you should start to notice something happening in the surrounding circle of dots.
Most people first see a gap moving around the circle of lilac discs. Then, the gap is replaced by a green moving disc. Finally, the lilac spots disappear and you see only a green spot moving in a circle on the grey background.
In actual fact, there is no green disc on your screen: only lilac dots flashing on and off.
How does it work? See explanation
10. Magic castle:
This illusion uses some of the same tricks as “lilac chaser”. Play the video, staring as fixedly as you can – try not to blink – at the dot in the centre. After a while, you should see something interesting …
Did you see the castle in colour for a few moments? But the video contains no true-colour image. Replay and check! The first, unnatural colour image changes straight to black and white. So where do the naturalistic colours come from? See explanation
- Compiled by Olivia Rose-Innes and Senora Sine Thirteen, Health24, July 2011
Lilac chaser: Image author: Jeremy Hinton. The author created this image and also devised the visual illusion which it exemplifies. Further information about the Lilac chaser from Michael Bach.
Lloyd Kaufman, Sight and Mind: An Introduction to Visual Perception (NY: Oxford University Press, 1974)