Have you ever ended up arguing with someone because you remember an event differently?

Many of us will have had times when we’re certain our recollection is the correct one.

But ‘false memories’ are surprisingly common – from misremembered childhood moments or mistakenly ‘recalling’ that you locked the door.

Now, experts have come up with a way to settle any argument about memories once and for all.

And it’s all to do with your eyes.

In a new study, researchers from the Budapest University of Technology and Economics set out to test a theory that first arose more than 50 years ago.

A discovery in the 1970s revealed that people’s pupils dilate when they recognise something they have seen before.

This phenomenon, called the ‘pupil old/new effect’, has been confirmed in multiple experiments.

But now, experts wanted to find out whether pupil dilation might also reflect how clearly and precisely something is remembered.

The team recruited 28 participants in Hungary and asked them to study 80 two or three-syllable uncommon words that appeared around a circle on a screen.

Later, they were shown a mix of old and new words. For each word they recognised, they were asked to try and recall when it had originally appeared.

Throughout the experiment, their pupil size was tracked.

Analysis revealed that when people recognised a word they had seen earlier, their pupils dilated.

Most importantly, the effect was more pronounced when they could accurately remember the word’s original location

The findings suggest that our eyes reflect two layers of memory – a general sense of familiarity and the precision of specific details, researcher Ádám Albi told Popular Science.

‘To date, there is no consensus on the precise cognitive and neurobiological mechanisms that drive pupil responses during different forms of memory retrieval, such as recognition,’ he said.

The team suggest that a vivid memory demands our attention, triggering activity in a region of the brain called the locus coeruleus–noradrenergic system.

This system also causes pupils to dilate, recent research has found.

The findings could have practical implications for clinical assessment or even legal testimony, experts say.

Writing in the Journal of Experimental Psychology: Learning, Memory and Cognition they said: ‘This pattern of results suggests that the pupil old/new effect might originate from two distinct components: The first is related to the mere recognition of a word, whereas the second reflects the quality of recollected source information.’