updated 9/1/2010 9:38:30 AM ET 2010-09-01T13:38:30

There may be a reason grandparents repeat the same stories over and over again. According to a new study, older people are more likely than younger people to forget with whom they've shared information.

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The study investigated two types of memory: source memory, or your recollection of who told you a piece of information; and destination memory, which is your recollection of which people you've informed. Not only were older people bad at remembering to whom they'd told information, they were very confident in their mistaken memories.

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"Older adults are additionally highly confident, compared to younger adults, that they have never told people particular things when they actually had," study co-author Nigel Gopie, a cognitive scientist at the Rotman Research Institute in Toronto, said in a statement. "This over-confidence presumably causes older adults to repeat information to people."

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To investigate the effects of aging on destination and source memory, researchers recruited 40 college students between the ages of 18 to 30, and 40 older adults between the ages of 60 to 83. In one experiment, participants read 50 facts aloud to the images of 50 celebrities on a computer screen. Next, they were asked to remember which fact they told to which person. For example, they might have told a picture of Oprah Winfrey that "A dime has 118 ridges around it." This experiment measured destination memory: Whom did you tell what?

In the second study, the "celebrities" read the facts to the participants, who then had to remember which celebrity told them each fact. This experiment measured source memory: Who told you what?

The results suggested that aging has little effect on source memory. Young people scored about 60 percent when recalling who told them what, while old people scored 50 percent.

However, in the destination-memory experiment, older adults scored 21 percentage points lower than younger adults.

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The researchers suspect that older adults are more prone to destination-memory failure because they lose the ability to focus and pay attention with age. In other words, older adults use so much of their attention sharing the information, they forget to take notice of whom they were talking to when they shared it.

But lack of focus can also boost memory: A study published in January in the journal Psychological Science showed older people have the unique ability to "hyper-bind" the irrelevant information gleaned when they get distracted, essentially tying it to other information that is appearing at the same time.

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