Why you lose your keys

Every driver has fallen victim to the curse.

Barely seconds after coming in with the shopping, you haven't a clue where you left your car keys.

Now scientists believe they know why so many of us have such poor short-term memories.

They say we can recall only four objects at a time - so if we put down the keys in a cluttered area, we are more likely to forget where they are.

Professor Rene Marois explained: "Though we have the impression we are taking in a great deal of information from a visual scene, we are actually very poor at remembering its contents in detail once it is gone from our sight.

'We found that the upper limit for visual short-term memory is just four objects. So if you come in and put your keys down with a load of shopping bags on a crowded table or worktop then you could find yourself almost immediately having problems remembering where you put them.

'Once you have turned away to do something else, the visual image of the keys in a certain location will be quickly replaced because they are in an area with more than four items.'

Professor Marois, a psychologist at Vanderbilt University in Nashville, Tennessee, tested the brain power of adults by showing volunteers scenes containing between one and eight coloured objects.

The images were removed and the subjects were then asked to recall as many as they could after a delay of just one second, reports the journal Nature.

They were almost always able to remember all the objects when they were presented with four or fewer.

But their ability to recall what they had seen rapidly diminished when they were shown more items.

Asked to recall eight objects, they scored an average of only 68 per cent.

The tests used magnetic resonance imaging scans, which detect increased blood flow, to focus on a region of the brain responsible for storing visual short- term memories.

Professor Marois said the tests showed that this area, known as the posterior parietal cortex, was responsible for determining how much short-term information we can retain at any one time.

'The results suggest that this is a key brain area which we rely on to store short-term memories,' he added.

'But due to its limitations, it is often the case that what is out of sight is out of mind.'

On the cars keys, he advised: 'We should put them somewhere less crowded if we want to find them again.'

r.yapp@dailymail.co.uk