It's been a few days since we saw a good optical illusion, so we were due another dose of bewilderment. And sure enough, here's one that leaves us unable to believe our eyes – or the eyes in the illusion itself.
The optical illusion shows a series coloured eyeballs arranged in five columns. Each of the three eyeballs in each column appears to be a different colour. But alas, we're told that's not the case. Confused? So are we. It seems like this is another mind-bender for our list of the top optical illusions of all time.
The optical illusion shows a series of eyes organised into five columns, each with three rows that have foregrounds comprising coloured stripes. And despite appearances, we're told that the three eyes in each column are identical copies: all the same colour. It's only the colour of the lines that makes them look different. In the image below, we can see the original eye used in each column without the intervention of the stripes, and there are clearly five different colours.
So what's going on? Well this optical illusion, designed by contact lens supplier Lenstore (opens in new tab), is a version of what's known as the Munker-White optical illusion, which is based on a phenomenon called the Bezold effect. The German professor of meteorology Wilhelm von Bezold (1837-1907) noticed that our perception of colour can be skewed by adjacent colours.
If you look closely at the illusion, you'll see that the each of the three rows has different colour lines running across it. These have the effect of tinting the colour of the circles. Blue, green and red stripes tint the eyes in different ways, resulting in the apparent colour changes.
Scientists aren't quite sure what exactly happens in the brain – or where it happens – to cause this effect. Some think the illusion occurs in the initial stage of visual processing, when light first hits the retina, but others think the Bezold effect occurs later on when the brain processes the data it receives. Either way, it's another mind-bending illusion that opens questions about how we perceive colour (see more in our pick of the best optical illusions of this year).