Long-Term Memories Form in Toddlerhood

Study finds babies can remember tasks in second year

WEDNESDAY, Oct. 30, 2002 (HealthDayNews) -- Babies develop remarkable long-term memories for certain tasks in their second year of life, new research shows.

Experts have known for some time that 6-month-old babies have good short-term memories. If you hide a ball under a box in front of them, chances are good they will pick up the box to find the ball.

Now researchers have found that if a 17-month-old is shown how to do something and given a short time to practice it, he or she will remember what to do a long (in the life of a child) four months later. This is something that a 9-month-old infant is as yet unable to do.

"The brain is still growing in the first few years of life," explains Jerome Kagan, a research professor of psychology at Harvard University and co-author of a study appearing in tomorrow's issue of Nature.

What is new is that "this was long exposure, then they imitated the act and remembered it four months later instead of 40 seconds [later]," as with other research, Kagan says.

The study started with 12 children in each different age group: 9 months old, 17 months old and 24 months of age. The researchers spent about 30 minutes with each child, showing them tasks, such as cleaning a table with a paper towel and then disposing of the towel in the trash. Verbal cues -- such as the announcement of "Clean-up time!" -- were also given. The child was then allowed to repeat the task. While the older groups of children had three tasks shown to them four times, and then two opportunities to repeat each task, the 9-month-olds were shown how to perform the tasks six times, in consideration of their young age.

The children were not exposed to those activities shown to them for the experiment for four months.

At follow-up, all but five of the original 36 children participated. When being re-tested, they were given props for each task they originally witnessed, such as a paper towel and table, and researchers repeated the verbal cue: "Clean-up time!"

While the now 21-month-old and 28 month-old babies knew what to do, the 13-month-olds did not.

Six children, matched for age, were given the same props and cues without ever having been shown how to perform the tasks, to prove that the older infants did not perform well by chance.

The researchers admit that the failure of the smallest youngsters to perform the tasks at follow-up could be due to their never having registered what happened in the first place. "We can't tell whether the 9-month-olds who did poorly didn't look carefully at the acts or couldn't retrieve it," Kagan says. But she adds, "I think it's the retrieval."

Conor Liston, the primary author of the paper who is now a medical student at Cornell University, adds that while this study shows how infants do with imitation activities, other types of memories, such as that of recalling a face, might work differently. "It is likely that face recognition taps neural structures and cognitive processes that are distinct from those required for deferred imitation. Our finding that 13-month-olds cannot recall events that occurred at nine months does not preclude the possibility that children at that age can recognize their grandparents."

Anthony DeCasper, interim head of the psychology department at the University of North Carolina, Greensboro, thinks the study is interesting. "It clearly shows that 21-month and 28-month-old babies remember over that [four-month] period. Thirteen-month-olds don't appear to have long-term memory of four months.

"But we don't know why they don't," he adds.

While the study authors hypothesize that certain parts of the frontal lobe of the brain are not yet fully developed at that age, DeCasper isn't so sure: "It may or may not be due to the hippocampus."

He says young babies may not understand what the researchers were saying or "maybe the 28-month-olds have much more experience in imitating adults and they find the task easier."

One thing we do know, he notes: "Memory gets better the older you get."

What To Do

Those interested in the memories of babies can visit the University of North Carolina at Chapel Hill. You could also read this piece from the American Psychological Association.

SOURCES: Jerome Kagan, Ph.D., research professor, psychology, Harvard Medical School, Boston; Conor Liston, M.D./Ph.D. student, Cornell Medical School and Rockefeller University, New York City; Anthony DeCasper, Ph.D., interim head, psychology, University of North Carolina, Greensboro; Oct. 31, 2002, Nature
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