The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
I ask my students to recall their first memories whenever I teach memory in my child development class . Some students recall their first day of preschool, while others remember a time when it was difficult or stressful. Others mention a time when their younger sibling was born.
Despite vast differences in the details, these memories do have a couple of things in common: They’re all autobiographical, or memories of significant experiences in a person’s life, and they typically didn’t happen before the age of 2 or 3. In fact, most people can’t remember events from the first few years of their lives – a phenomenon researchers have dubbed infantile amnesia. Why can’t we recall the things that happened when we were infants, though? Is memory only developed at a certain age?
Here are the facts that researchers have discovered about memory and babies.
Infants can form memories
Despite the fact that humans can’t remember much prior to the age of 2, or 3, research shows that infants can make memories. But not the memories you tell about yourself. Within the first few days of life, infants can recall their own mother’s face and distinguish it from the face of a stranger. A few months later, infants can demonstrate that they remember lots of familiar faces by smiling most at the ones they see most often.
In fact, there are lots of different kinds of memories besides those that are autobiographical. There are semantic memories. These memories include memories of facts like the names of different apples or the capital of your state. There are procedural memories. These memories tell you how to do something, such as opening your front door or driving.
Research from psychologist Carolyn Rovee-Collier’s lab in the 1980s and 1990s famously showed that infants can form some of these other kinds of memories from an early age. However, infants don’t always remember what they are remembering. Rovee-Collier’s research focused on creating a task that was sensitive and flexible to babies’ changing bodies and abilities, in order to assess their memory over a long time.
In the version for infants aged 2-6 months, researchers place an infant in an infant’s crib with a mobile suspended above. To get an idea about their natural propensity for moving their legs, they measure how much the baby kicks. The string is tied to the mobile’s end by attaching it to the baby’s legs. This will allow the mobile to move whenever the baby kicks. As you can see, infants quickly learn to control their movements. They kick more than they did before the string was attached to the leg. This is a sign that they have learned that kicking makes the move mobile.
The version for 6- to 18-month-old infants is similar. Instead of being in a crib, which is not an option for this age group, the infant lies on their parent’s lap and holds a lever that will eventually cause a train to move around a track. The lever doesn’t work at first and the experimenters measure the amount a baby presses down. The lever is then turned on. The train will now move around its track every time the infant presses the lever. The game is again easy to learn for infants. They press harder on the lever when the train moves.
What does this have to say about memory? Rovee-Collier later tested if infants remembered the task after they had been trained on it for a few days. This is the best part of this research. Researchers simply showed the mobile or train to infants when they returned to the lab. Then, they measured how much kick they had and pressed the lever.
Rovee-Collier, along with colleagues, discovered that infants can recall an event as soon as they are trained for just one minute. The longer they remembered, the older the infants. She also found that you can get infants to remember events for longer by training them for longer periods of time, and by giving them reminders – for example, by showing them the mobile moving very briefly on its own.
Why not autobiographical memories
If infants are able to form memories within the first few months of their lives, then why can’t we remember things at our earliest stages of life? It isn’t known if infantile amnesia occurs because we don’t have the ability to form autobiographical memories or if we simply have no way of retrieving them. Scientists have a few theories, but no one knows for certain what’s happening.
One: Autobiographical memories require that you have a sense of self. You must be able to see the relationships between your behavior and 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 spot of red lipstick or blush – or “rouge” as they said in the 1970s when the task was created.
Then, researchers place the infant in front a mirror. Infants younger than 18 months just smile at the cute baby in the reflection, not showing any evidence that they recognize themselves or the red mark on their face. Between 18 and 24 months, toddlers touch their own nose, even looking embarrassed, suggesting that they connect the red dot in the mirror with their own face – they have some sense of self.
Another possible explanation for infantile amnesia is that because infants don’t have language until later in the second year of life, they can’t form narratives about their own lives that they can later recall.
Finally, the hippocampus, which is the region of the brain that’s largely responsible for memory, isn’t fully developed in the infancy period.
Scientists continue to explore how each of these factors may contribute to your inability to remember much about your life prior to the age of 2.