People have always been fascinated by optical illusions. These are images that appear to be one picture for one moment, and then look something entirely different the next.
But scientists, until now, had never quite been able to put a finger on how our brain flips between the two images.
Now researchers from University College London are one step closer to answering why, with the discovery of what may be the relevant brain region.
The precise neural mechanism is unknown but it plays a major role in perception by acting as a sort of reality check, says Ryota Kanai.
"We need a trigger to prompt possible different interpretations so that we don't get stuck with a potentially incorrect interpretation of the world," New Scientist quoted Kanai as saying.
The team asked 52 volunteers to watch a video of a revolving sphere and press a button when the rotation of the sphere appeared to change direction.
However, the sphere was not changing direction; it could simply be perceived to be rotating in either direction.
Using MRI, they found that two areas (superior parietal lobes (SPL) towards the back of the head known to control attention and process three-dimensional images were highly active. People whose cortex was thicker and better connected in this region had faster switch rates.
And if either lobe was inactivated, the switch rate slowed down.
So either the SPL is sending a signal to 'reset' the illusion or it could be that people with a large SPL are better at noticing other possible interpretations for the ambiguous sphere, said Kanai.
Andrew Parker at the University of Oxford reckons there is more to be done to confirm that the region is directly involved in provoking these perceptual changes.