Yesterday I got into an argument over this visual illusion (via MindHacks). Although it's a pretty simple effect, it's one of the best visual illusions I've seen. First the woman goes around one way, then suddenly, for no apparent reason, she switches. Impressive - once you see it.
The argument started out over whether the graphic itself is reversing its direction (it's not) and ended up at the very doors of perception:
"But," she said. "It means I can't trust anything if my brain is lying to me like this. I'm walking down the street, I go to cross the road, and BOOM, hit by a car which seemed to me to be travelling the other way!"
"No," I replied. "You're making too much of this. It's just an illusion."
"I'm not," she insisted. "This makes me question everything - if I can't trust my own eyes, what can I trust?"
So I tried to explain that this illusion is designed to fool you and is unlikely to occur in the natural environment, but it was to no avail. The eyes are lying and that is that.
This is the power of visual illusions: they remind us that what we see is not 'reality' but our perceptual interpretation of the objects around us. Our brains are working hard to fit all these moving objects, lines and colours into some kind of coherent picture that is useful to us. In many ways, everything we see is an illusion.
All of which inspired me to go on a Google-hunt for the best visual illusions on the web. Here are a few to get you going, but if your favourite isn't listed, comment away below and let everyone know about it.
A word of warning, though, before you dive in - some of these can really mess with your head. That's why I've given each a 'sick rating' from one star (* suitable for small children and animals) to five stars (***** have a sick-bag at the ready).
1. Start off with all the ones that you'll come across in intro psych text books at AllPsych Online. Sober. (Sick rating: *)
2. Once you can cope with that, it's time to move to the next rung. These visual illusions were created by Akiyoshi Kitaoka, a professor in the department of psychology at Ritsumeikan University. The page opens with a warning that the illusions can make you feel sick. Some of them actually look like sick. (Sick rating: *****)
3. Although Professor Kitaoka has a lot of illusions on his site, he's rivalled by Prof. Michael Bach who works in the ophthalmology department at the University of Freiburg in Germany. His site dates back to 1997 and is nicely organised with the visual illusions in categories. There's also plenty more academic referencing for those who like that sort of thing. (Sick rating: **** - and that's just for the eyes that follow your cursor around the page)
5. Talking of games, here's a site that's devoted to teaching kids about visual illusions. (Child-friendly sick rating: *)
6. There are quite a few explanations on the web - including in the sites above - of how many of these illusions work. But the best (because of simplicity) is here. Most of the illusions you'll see are variations on these themes. (Sick rating: N/A)
7. If you're more interested in the technical side of visual illusions then Professor Richard Gregory's work will be of interest.
This is just a taster from the huge range of websites available although many of them do repeat the same illusions.
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