Are the long lines tilted or parallel?

A cream and pink exhibit table and display board with the title 'Are the long lines really titled?'. Two squares with diagonal lines appear on the table top.

Lines can appear to change their tilt, possibly due to how the brain processes size and distance.

How it works

Slide a panel of short angled lines across a panel of long lines and notice whether the long lines change in appearance.

Things to try or ask around the exhibit

  • Do the long lines physically change, or is it simply the way your brain is processing information?
  • Why do the lines look different behind the striped panel?


Scientists are unsure why the Zöllner illusion works, but the short angled lines on top may fool your perception of depth and size constancy.

If a friend runs towards you, the image being projected onto your retina becomes larger, but your brain interprets this as your friend getting closer to you, instead of them becoming a giant (or getting smaller if your friend runs away). This is size constancy.

Your brain also judges the size of things against the angles of a horizon or room corners, which is possibly what your brain is trying to do with the lines of this illusion.

Finding the science in your world

Movie special effects sometimes use a similar effect to the Zöllner illusion. When setwork is built in certain angles and sizes, it enables movie makers to create the illusion that a character or their surroundings are disproportionately large or small.