Most of us have ducked away from a 'madman' in the street, only to realise they are in fact using a Bluetooth headset.

Now a new University of Pennsylvania study shows that wandering along muttering, 'keys, keys, keys' can actually help (normal, sane) people find lost objects.

Saying a word helps focus the mind on something people are looking for - and it works more effectively than seeing a written description.

Repeating the word over and over again helps even more.

Previous work has suggested children speaking to themselves while performing step-by-step tasks, like tying shoelaces, can help guide their behaviour and let them focus on the job in hand.

However, scientists were not sure if speaking aloud when completing tasks could help adults in the same way, especially when looking for particular objects.

Prof Gary Lupan and Prof Daniel Swingley, writing for the Quarterly Journal of Experimental Psychology, believe the next time you lose your keys, muttering 'keys, keys, keys' while looking could in fact help people find them.

Inspired by viewing people audibly muttering to themselves as they try to find things like peanut butter in a supermarket, researchers conducted two experiments to see if this actually worked.

In the first, participants were shown 20 pictures of various objects and were asked to find a certain one, with some seeing a text label telling them what they were looking for.

These participants were then asked to search for the item again while saying the word to themselves, with results showing saying it aloud helped people find the object more quickly.

The second experiment saw participants performing a virtual shopping task, where they were shown photographs of items commonly found on supermarket shelves.

They were asked to find all instances of a particular item, so if they were asked for apples they had to find all the bags of apples, as quickly as possible.

The University of Wisconsin-Madison and University of Pennsylvania, both US, researchers found there was an advantage in saying the name of the product aloud when they were searching for something familiar.