From the hidden cigar in the brickwork to the infamous debate over 'The Dress', optical illusions have a long history of confounding the public. Now, a new and particularly bizarre example shared by a BBC biologist on TikTok is leaving viewers questioning their own perception, as it tricks the brain into seeing two identical eyes as completely different colours.
The Illusion That Deceives Your Senses
Dr Dean Jackson, a biologist and presenter for the BBC, recently posted a video that has rapidly gained traction. The clip features a cartoon face split directly down the middle. The left half of the face and background are tinted a vivid red, while the right half is a deep blue. At the centre of this split are the figure's two eyes, which to most observers appear to be different colours – one seeming to take on a bluish hue, the other a reddish one.
In a voiceover, Dr Jackson delivers the mind-bending truth: "This girl's eyes are the same colour as each other." He explains that viewers are indeed seeing the same colour, but their brains are processing the surrounding coloured areas as two separate filters. The brain then attempts to cleverly calculate what the eyes would look like under each of those filters, ultimately creating a false perception of differing colours. "But it's actually being too clever for its own good," he remarks.
Proof in the Grey Bars
To demonstrate the reality of the situation, Dr Jackson first displays a plain grey square on the screen, confirming that this is the true, uniform shade of both eyes. "Both of her eyes are that shade of grey, but your brain is telling you otherwise," he states.
The conclusive proof comes when he overlays grey bars, matching the exact colour of the eyes, across the coloured background. "I'm not changing the colour of the girl's eyes, I absolutely promise you of that," he reassures viewers. As the bars cover the red and blue sections, the illusion instantly shatters, revealing beyond doubt that the two eyes are perfectly identical. The visual trick relies entirely on the powerful influence of contextual colour on human perception.
Viewer Reaction and a History of Colour Tricks
The baffling clip has sparked hundreds of confused and amazed comments on TikTok. One user exclaimed, "I saw her left eye as blue and her right eye as yellow! I love your content but I'm now finding it difficult to trust my own brain!!!!" Another simply pleaded, "THE EYES ARE NOT GREY! HELLPPP." A third user joked about the betrayal, writing, "My brain is not my friend, pranking me like this."
This is not Dr Jackson's first foray into colour-based perceptual puzzles. Earlier this year, he posted another viral video featuring a picture of a red fire truck. After applying a cyan filter over the entire image, he asked followers what colour the truck appeared. While most instinctively answered 'red', he revealed that under the cyan filter, the truck was actually grey. "Red light cannot pass through a cyan filter, it just can't," he explained. "So now there is no red light in that picture, I can promise you. And yet your brain is still telling you that it's red."
These illusions serve as powerful reminders of how our brains actively construct our visual reality, often making assumptions based on context that can lead us astray. The work of experts like Dr Jackson and earlier researchers, such as Professor Richard Gregory who famously documented the Café Wall illusion in Bristol in 1979, continues to illuminate the fascinating and sometimes flawed mechanics of human sight.
