You’d be forgiven for thinking that all optical illusions simply exist to baffle us – there’s one that can actually help our eyesight.
Looking at one particular optical illusion can improve our ability to see fine details, including writing, according to researchers from the University of York and University of Glasgow.
This particular illusion is called the “expanding motion aftereffect”. Looking at it can make objects appear bigger than they really are.
The researchers asked 74 people to watch the spiral pattern, either rotating clockwise or anticlockwise for 30 seconds. One group would have seen an expanding motion, and the others, a contracting one.
This is the exact image they watched:
They were then asked to identify a set of letters on a logMAR eye chart – the one you're asked to recite at the optician’s, with the increasingly small rows of letters. They did this task beforehand, too.
The researchers found that the participants’ vision differed depending on which spiral they watched. Those who looked at the clockwork spirals experienced improved vision afterwards.
But those who saw the anticlockwise spirals actually performed worse than before - proving that staring at optical illusions can also temporarily worsen vision, too.
The fact that what they watched was either a contracting or expanding motion, the study states, meant that "the ensuing motion aftereffect created illusory expansion or contraction in the test images".
The only downside is that the improvement to vision wasn't permanent.