Scientists believe they have found a way to probe the mysterious phenomenon of feeling you have witnessed something before - deja vu.
Deja vu may be down to a mix-up in the brain
Leeds Memory Group researchers say they have gone some way to recreating the sensation in the lab using hypnosis.
New Scientist magazine reports the researchers hope their work will shed light on the fundamental workings of the human memory.
It is estimated that as many as 97% of people have experienced deja vu.
In some severe cases it can be distressing to the point of causing depression and some sufferers have been prescribed anti-psychotic medication.
However, experts suspect that many people who experience the sensation are unwilling to discuss it with their doctor.
Two stage process
Two key processes are thought to occur when someone recognises a familiar object or scene.
First, the brain searches through memory traces to see if the contents of that scene have been observed before.
If they have, a separate part of the brain then identifies the scene or object as being familiar.
In deja vu, this second process may occur by mistake, so that a feeling of familiarity is triggered by a novel object or scene.
The Leeds team set out to create a sense of deja vu among volunteers in a lab.
They used hypnosis to trigger only the second part of the recognition process - hoping to create a sense of familiarity about something a person had not seen before.
The researchers showed volunteers 24 common words, then hypnotised them and told them that when they were next presented with a word in a red frame, they would feel that the word was familiar, although they would not know when they last saw it.
Green frames would make them think that the word belonged to the original list of 24.
After being taken out of hypnosis, the volunteers were presented with a series of words in frames of various colours, including some that were not in the original 24 and which were framed in red or green.
Of the 18 people studied so far, 10 reported a peculiar sensation when they saw new words in red frames and five said it definitely felt like deja vu.
Researcher Akira O'Connor presented the findings to an International Conference on Memory in Sydney, Australia.
He told New Scientist: "This tells us that it is possible to experimentally dissociate these two processes, which is really important in establishing that they are indeed separate."
Some people with temporal lobe epilepsy report frequent deja vu.
And previous work in France has found that electrically stimulating parts of the temporal lobe can trigger a sensation of familiarity with everything a person encounters.
Professor Alan Brown, an expert in deja vu at South Methodist University in Dallas, said: "Using hypnotic suggestion to either stimulate, or simulate, a deja vu experience could potentially be a very fruitful way to explore this phenomenon.
"I don't have a lot of detail about the Leeds project but from what I know it certainly seems to be solid work with an intriguing outcome."