This simple number optical illusion is breaking my brain

Optical illusions come in all forms, from mind-bending physiological phenomena to confusing cognitive images, but one variety that doesn't get nearly enough love is the humble ambigram. While these visual spectacles are often related to calligraphic design, this rotational ambigram example uses numbers to boggle our brains.

When we think of the best optical illusions, often our minds revert to vivid, undulating geometrical designs, but my personal favourites are always the simpler ones (and not just because it saves me a headache). The 23 illusion is a prime example of how visual suggestion can create a crafty illusion, even when we flip our perspective.

Hopefully, when you look at the illusion above, you'll see the number 23 – it's a great demonstration of the Gestalt Principle of closure, where our brains automatically fill in blank spaces to make sense of an ambiguous image. When flipped upside down, the illusion functions in the same way, making it a simple yet effective rotational ambigram.

There are plenty of examples of ambigrams in design, perhaps most famously in the Abba logo, which serves as a bilateral ambigram, reading the same when flipped from left to right thanks to its palindromic form (that's one for you language nerds out there). It's not just in design – optical illusions can appear anywhere, even in space. As if the universe wasn't brain-bending enough, check out these reality-defying optical illusions in space that blew our minds.