This baffling optical illusion makes me question if I'm seeing straight

We love a good optical illusion here at Creative Bloq, and this has to be one of the best. It's a classic illusion that was first written about way back in 1861, and it continues to baffle people today.

The Hering Illusion comprises a two parallel lines over a radial background. The parallel lines (red in the example below) appear to bow outwards... but do they really?

Whether you use a ruler or remove the radial lines in Photoshop, the conclusion is the same: the red lines are straight. So why don't we see them as straight?

The Hering Illusion is named after the German physiologist Ewald Hering, who was the first person to write about it. Hering himself believed that the illusion was caused by the brain overestimating the angle at the points of intersection between the lines, which some scientists have since put down to lateral inhibition in visual cortex.

However, some disagree with Hering's original hypothesis and think that the illusion is caused by a temporal delay that causes our visual system to extrapolate information in order to predict how the world will look in the next millisecond. The image isn't moving, but the radial lines trick our visual system into thinking that it is, which causes us to perceive the lines as curved.

There are several variations of this famous optical illusion, including the Orbison illusion and the Wundt illusion, which has an inverted effect. Hans Kuiper created the square-shaped variation Three in One above based on Square of Three by Reginald H. Neal. In this case, it appears as if the square shapes have diagonal lines, but all of the purple lines are actually straight.

For more optical illusions, see our collection of optical illusions in space and the AI optical illusions that have become popular online.