Although infants use their memories to learn new information, few adults can remember events in their lives that happened prior to the age of three.
Researchers from Emory University in US interviewed children about past events in their lives, starting at age three.
Different subsets of the group of children were then tested for recall of these events at ages five, six, seven, eight and nine.
"Our study is the first empirical demonstration of the onset of childhood amnesia," said Emory psychologist Patricia Bauer, who led the study.
"We actually recorded the memories of children, and then we followed them into the future to track when they forgot these memories," Bauer said.
Scientists have long known, based on interviews with adults that most people's earliest memories only go back to about age 3. Sigmund Freud coined the term "childhood amnesia" to describe this loss of memory from the infant years.
Using his psychoanalytic theory, Freud made the controversial proposal that people were repressing their earliest memories due to their inappropriate sexual nature.
In recent years, however, growing evidence indicates that, while infants use memory to learn language and make sense of the world around them, they do not yet have the sophisticated neural architecture needed to form and hold onto more complex forms of memory.
The Emory University experiment began by recording 83 children at the age of three, while their mothers or fathers asked them about six events that the children had experienced in recently, such as a trip to the zoo or a birthday party.
"For example: "The mother might ask, 'Remember when we went to Chuck E. Cheese's for your birthday party?' She might add, 'You had pizza, didn't you?'" Bauer said.
"The child might start recounting details of the Chuck E Cheese experience or divert the conversation by saying something like, "Zoo!"
"Some mothers might keep asking about the pizza, while another mother might say, "Okay, we went to the zoo, too. Tell me about that," Bauer said.
Parents who followed a child's lead in these conversations tended to elicit richer memories from their three-year-olds, Bauer said.
After recording the base memories, the researchers followed up with the children years later, asking them to recall the events that they recounted at age three.
While the children between the ages of five and seven could recall 63 to 72 per cent of the events, the children who were eight and nine years old remembered only about 35 per cent of the events.
The study was published in the journal Memory.


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