Whenever I teach about memory in my child development class at Rutgers University, I start by asking my students to recall their earliest memories. Some students talk about their first day of preschool; others talk about a time when they were hurt or upset; some cite the day their younger brother was born.
Despite the vast differences in detail, these memories have a few things in common: they are all autobiographical, or memories of significant experiences in a person’s life, and typically didn’t happen before the age of two or three. In fact, most people can’t remember events from the first few years of their lives — a phenomenon researchers dubbed childhood amnesia. But why can’t we remember the things that happened to us when we were children? Does memory start working only at a certain age?
Here’s what researchers know about babies and memory.
Babies can form memories
Despite the fact that people can’t remember much before the age of 2 or 3, research suggests that babies can form memories — but not the kinds of memories you tell about yourself. In the first few days of life, babies can remember their own mother’s face and distinguish it from a stranger’s face. A few months later, babies can demonstrate that they remember many familiar faces by smiling more at the ones they see more often.
In fact, there are many different types of memories besides those that are autobiographical. There are semantic memories, or memories of facts, like the names of different varieties of apples, or the capital of your home state. There are also procedural memories, or memories of how to perform an action, such as opening the front door or driving a car.
Research from the lab of psychologist Carolyn Rovee-Collier in the 1980s and 1990s showed that babies can form some of these other types of memories from an early age. Of course, babies can’t say exactly what they remember. So the key to Rovee-Collier’s research was to develop a task that was sensitive to the rapid changes in babies’ bodies and abilities, in order to assess their memories over a long period of time.
In the version for babies aged 2 to 6 months, the researchers place the baby in a crib with a mobile hanging over its head. They measure how much the baby kicks to get an idea of his natural propensity to move his legs. Then they tie a string from the baby’s leg to the end of the mobile so that whenever the baby kicks, the mobile moves. As you can imagine, babies quickly learn that they are in control – they enjoy watching the mobile move and therefore kick more than before the rope was attached to the leg, showing that they have learned that kicking makes the mobile move.
The version for babies aged 6 to 18 months is similar. But instead of lying in the crib – which this age group doesn’t do for long – the baby sits on the parent’s lap with their hands on a lever that will eventually make a train move on a track. At first, the lever doesn’t work, and researchers measure how much a baby naturally presses. Then they turn on the lever. Now, every time the baby presses it, the train moves around its tracks. Babies again learn the game quickly and press the lever significantly more when it makes the train move.
What does this have to do with memory? The smartest part of this research is that after training babies in one of these tasks for a few days, Rovee-Collier later tested whether they remembered. When the babies returned to the lab, the researchers simply showed them the mobile or train and measured whether they were still kicking and pressing the lever.
Using this method, Rovee-Collier and colleagues found that at six months, if babies are trained for one minute, they can remember an event a day later. The older the babies, the longer they remembered. She also found that you can make babies remember events longer by training them for longer periods of time and giving them reminders – for example, by showing them the cell phone moving quickly by itself.
Why not autobiographical memories?
If babies can form memories in the first few months, why don’t people remember things from that early stage of life? It’s still unclear whether people experience childhood amnesia because we can’t form autobiographical memories, or if we just can’t retrieve them. No one is quite sure what is going on, but scientists have a few hunches.
One is that autobiographical memories require you to have some sense of yourself. You need to be able to think about his behavior in relation to how he relates to others. Researchers have tested this ability in the past using a mirror recognition task called the rouge test. It involves marking a baby’s nose with a smear of red lipstick or blush — or “rouge,” as they said in the 1970s, when the task was created.
Then the researchers place the baby in front of a mirror. Babies under 18 months just smile at the cute baby in the reflection, showing no evidence that they recognize each other or the red mark on their face. Between 18 and 24 months, children touch their own nose, even though they look embarrassed, suggesting that they connect the red dot in the mirror with their own face – they have some sense of themselves.
Another possible explanation for infantile amnesia is that because babies do not have language until later in their second year of life, they cannot form narratives about their own lives that they can remember later.
Finally, the hippocampus, which is the region of the brain that is largely responsible for memory, is not fully developed in childhood.
Scientists will continue to investigate how each of these factors might contribute to why you can’t remember much or anything about your life before the age of two.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Image credit: Humphrey Muleba / Unsplash