As many people age they complain about not being able to remember things - and rather than thinking the cause could be anything as sinister as the first signs of dementia, say they have simply accumulated too much in their minds over the decades.

Now scientists say there is evidence that their explanation is more than an excuse.

New research indicates older people are less able to process information - including remembering things - because their memories tend to be cluttered with masses of information.

Mervin Blair, a PhD student at Concordia University in Montreal, Canada, led a study comparing how well people in their 20s and 60s recalled information.

He said: "Basically, older adults are less able to keep irrelevant information out of their consciousness, which then impacts on other mental abilities."

He and colleagues asked the two groups, each of about 30 people, to perform what he called a "working memory task".

This involved reading sentences and recalling parts of them accurately, including the last word in each.

"Overall, we showed that our older participants had reduced working memory compared to our younger participants," said Blair.

The two groups were also asked to memorise the order of a series of images and then tell researchers what that order was, while simultaneously being shown the images in a random order.

This "sequential memory task" was to examine how well participants could jettison irrelevant information and concentrate on the task at hand - technically called "inhibition deletion".

Blair said: "Older adults had poor inhibition, repeatedly responding to previously relevant images."

He suggested older people worried about mild memory lapses could improve their performance by "reducing clutter" through the use of "relaxation exercises".

He warned: "Reduce clutter, if you don't, you may not get anything done."

Karen Li, professor of psychology at Concordia, and the senior author of the study, commented: "Our study was novel because we looked at how the ability to recall and process information at the same time changes as people get older."

Gordon Wilcock, professor of geratology at Oxford University, and an expert on memory and ageing, welcomed the study for "suggesting mechanisms for phenomenae that trouble people".

He described it as "an interesting hypothesis", but added: "It doesn't fit will with other hypotheses that we have."

He also questioned whether the differences in results were truly explained by age.

Younger people might be better at this sort of memory retrieval because their brains had been primed to do so by early exposure to computer technology, he said, while members of the older group could have been on drugs for health conditions. The two groups should also be matched for IQ, he said.