This bewildering optical illusion will make you literally double-take

Another day, another optical illusion. We've seen rotating horses, we've seen three-headed deer, we've seen floating ships, we've seen any number of geometric shapes that aren't moving even though they somewhat appear to be moving. And the latest to appear on TikTok will quite literally make you double-take – as in, you'll need to look at it twice to get the full effect.

Optical illusion pedlar Dean Jackson has shared an image that appears entirely different the second time you look at it. While the photo of the bridge appears black and white at first, the second time around it's in glorious technicolour. If you've followed the instructions properly, that is. (Looking for more inspiration? Check out the best optical illusions we've seen.)

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♬ original sound - Dean Jackson

"If you're here for the first time you're seeing a black and white photo of a bridge. If you're back here for the second time you're hopefully seeing in colour," Jackson says. All you have to do is stare at the white dot in the centre of the screen throughout the video, including when it transforms into negative colours halfway through. 

Sure enough, once the video looped back to the beginning, I was seeing the bridge in colour. "I honestly thought it was a different pic when the vid started again," one user comments, while another adds, "This worked, threw me off at how vibrant the colours are."

And now for everyone's favourite part: the science. What Jackson doesn't share is that this is a well-known phenomenon called Afterimage. According to Vox, this occurs when "you look at an object without moving your eyes for about 20 seconds or more. During this time, the receptor cells in your eyes responsible for converting light into an electrical signal (which goes to your brain) gradually become desensitized, because they run out of the photopigments needed to conduct that signal. Your brain compensates by adapting to their decreasing signal level."

And this isn't the first illusion we've seen in which a black and white image appears in colour. Last September, the internet went wild for a catchily titled colour assimilation grid illusion, where a tiny coloured grid appears to transform the entire image. Looking for more wild examples? Check out the best optical illusions we've seen this year so far. 

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• This optical illusion reveals if you're young at heart (apparently)