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23 January 2020, 11:16 | Updated: 27 January 2020, 11:47
We bet if you looked at these two blocks, you'd assume they weren't the same colour, right?
However, if you simply place your finger in between the two, you'll have your mind blown.
Smooth's Kate Garraway posted the image on Instagram last night (January 22), and now we're not totally sure what's reality or not anymore.
Have a go for yourself below:
The two blocks are actually the exact same colour, and only appear different due to the darker and lighter shading across the middle.
The optical illusion was first noted by experimental psychologist Tom Cornsweet in the 1960s, and it is named after him: the Cornsweet illusion.
Cornsweet explained that humans see colour and shade of 3D images in a certain way depending on how the item is lit, and the way shadows fall.
If the light falls from the upper left and the two blocks appear tilted away, we see the upper block as light and the lower block in shadow, as the light source comes from the upper left of the image.
Along with the contrasting shading in between the two blocks, our brain takes the top block as dark and the bottom one as light.