Study respondents who closed their eyes scored 23 percentage points higher on a memory test than those who did not

If you can’t remember your PIN number, try closing your eyes.

Experiments show that recall is boosted when we shut out the outside world.

It is thought that blocking out distractions frees up the necessary brainpower to remember things.

Psychologists from the University of Surrey put the theory to test by showing almost 200 men and women short films and asking them a series of questions about what they had seen.

The first film clip was silent and showed an electrician stealing as he carried out jobs in a house.

The volunteers then answered a series of questions about what they had seen – and half of them did this with their eyes closed.

Those whose eyes were open got just 48 per cent of the answers right on average – a score much lower than the 71 per cent achieved by those who had shut their eyes.

Having built up a rapport with the questioner boosted scores further.

The second film clip came from the BBC series Crimewatch and included sound as well as images.

Closing eyes boosted recall of facts heard and seen.

It had been argued that the technique improves memory by allowing people to build a detailed mental image of the thing they are trying to recall.

The finding that the trick also made it easier to remember auditory information shows this is not the only explanation.

Researcher Robert Nash said it is likely that those who shut their eyes also benefit from blocking out distractions.

Police have long encouraged witnesses to close their eyes when trying to remember the details of crimes

He said that police forces have long been aware of the benefits of asking eyewitnesses to shut their eyes during interviews.

His study, published in the journal Legal and Criminological Psychology, suggests that police will glean even more information if they build up a rapport with the interviewee.

Dr Nash believes that a simple closing of the eyes will also be of benefit in everyday situations, such as recalling pin numbers and remembering shopping lists.