The way in which older and younger adults encode and recall distracting, or irrelevant, information has been analyzed in a new study.
The results can help scientists better understand memory and aging.
"Our world contains so much information; we don't always know which is relevant and which is irrelevant," said Nigel Gopie, who co wrote the study with Fergus I.M. Craik and Lynn Hasher, all from the University of Toronto's Rotman Research Institute.
Most psychological scientists have focused on the relevant: on learning what we intend to learn. But the background noise also gets into our heads and influences our behavior-differently at different ages.
The study recruited about 125 subjects, in two groups, average ages 19 and 69.
It tested two kinds of memory - 'implicit' memory, which influences behaviour without awareness, such as purchasing the snacks we've seen 'product-placed' in a film; and 'explicit' memory, the kind we enlist to reconstruct a shopping list left at home.
At the start, participants pressed buttons in response to the colours of words and random letter strings on a screen. What mattered was the colour; the words themselves were irrelevant.
Then they were instructed to complete word fragments. In one test, the earlier task was not mentioned; this accessed implicit memory. In the other, the subjects were told to use words from the colour task to complete the fragments, employing explicit memory.
The older people showed better implicit than explicit memory and better implicit memory than the younger.
In the younger participants the pattern was reversed: better explicit than implicit memory and better explicit memory than their elders.
"We believe younger people remember in deep, elaborative ways: conceptually-spontaneously creating semantic or imaginary associations among words and ideas," said Gopie.
"Older people encode things 'perceptually,' in a more sensory way," he added.
They also don't filter out irrelevant stimuli. All of the information ends up 'all over the place', and is more accessible in the implicit mode. When trying to remember explicitly-say, a person's name-elders are often stumped.
This shallower processing may be related to a decline in mental 'resources' as we age.
To test this, the researchers 'made the younger people more like the older people' by taking away some of their resources.
While performing the colour task, the participants had to listen to numbers and say the second of any two consecutive odd numbers aloud. While their attention was divided, the younger people performed as their elders did - better on implicit than explicit memory.
The study suggests potential uses from age-specific marketing to assisting older learners.
The study is published in Psychological Science.