By quizzing small children about the first events they remember — a cousin misbehaving, a trip to a grocery store, a mother's bribe of red and green licorice — researchers have discovered that the earliest memories of children shift as they get older, and don't solidify into the first memories carried throughout life until about age 10.
The research, published Wednesday in the journal Child Development, could help psychologists better understand how people construct the life stories that help us understand ourselves, experts said.
"These are the memories we use to develop a sense of identity — who we are and where we come from," said study lead author Carole Peterson, a professor of psychology at Memorial University of Newfoundland in Canada.
Ask most adults to conjure up their earliest memories and they usually can't recall any that occurred before they were school age. This phenomenon, known as infantile amnesia, has been recognized for decades and studied closely in adults.
But the forgetting, it appears, happens slowly throughout childhood.
Peterson already had found in earlier work that children could remember traumatic experiences vividly, even when those events occurred at a very young age: Those as young as 7 or 8 remembered extraordinary events that had happened to them five years earlier. She then tested whether more mundane memories stuck with children too — or if they had infantile amnesia, like adults, for the less-intense events.
Her first study on the subject, published in 2005, found that younger children did report earlier first memories of this kind than older children. Kids ages 6 to 9, for example, had memories stretching back, on average, to when they were about 3 years old; 14- to 16-year-olds' first memories focused on incidents that had occurred when they were older than 4 on average.
In the new study, Peterson and her team re-interviewed 140 children two years after their initial interviews. As before, the children were asked to think of their three earliest memories. (The researchers confirmed with parents that the events had actually happened — or at least seemed plausible.)
They found that only five out of the 50 youngest children, whose ages ranged from 4 to 7 when first interviewed, could now recall their earlier first memories, even when reminded of their previous answers by the interviewers.
"The memories were just gone," Peterson said.
In contrast, 22 out of 61 children in the two oldest age groups — 10-11 and 12-13 — could still provide the same first memories.
Overall, 39% of the memories provided by 4- to 5-year-olds had vanished, as had 24% of the memories of 6- to 7- year-olds. But children older than 10 remembered nearly everything, Peterson said.
"By 10, their early memories are crystallized," she said. "Those are the memories they keep."
"This is the first study where we see that shift in time [of first memories] in the same children," said psychology professor Elaine Reese of the University of Otago in Dunedin, New Zealand, who was not involved in the research. She also noted an irony: "You think about the emphasis on 0 to 3 in early education, but as adults we can't remember that period," she said. "It's one of those enigmas of science we'd like to understand."
The subject is interesting to neuroscientists studying the workings of the brain, said Columbia University professor Eric Kandel, a Nobel Prize-winning neurobiologist who studies how memories are stored.
Kandel said one possible interpretation of infantile amnesia is that memories cannot be retained until key parts of the brain — the hippocampus and medial temporal lobe — reach maturity about 5 to 6 years of age.