mmg1design | Getty Images
Whenever I teach memory in my children’s development class at Rutgers University, I start by asking my students to recall their very first memories. Some students talk about their first day of pre-K; others talk about a time when they got hurt or upset; some mention the day their younger sibling was born.
Despite great differences in detail, these memories have a number of things in common: they are all autobiographical, or memories of important experiences in a person’s life, and they usually did not take place before the age of 2 or 3. Most people cannot even remember remembering events from the first few years of their lives — a phenomenon researchers have termed infantile amnesia. But why can’t we remember the things that happened to us when we were babies? Does the memory only start working 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 age 2 or 3, research suggests that babies can form memories — just not the kind of memories you tell about yourself. Within 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 show that they remember many familiar faces by smiling most at the faces they see most often.
In fact, there are many different types of memories, in addition to those that are autobiographical. There are semantic memories, or memories of facts, such as the names for different varieties of apples, or the capital of your home state. There are also procedural reminders, or reminders for performing an action, such as opening your front door or driving a car.
Research by psychologist Carolyn Rovee-Collier’s lab in the 1980s and 1990s famously showed that babies can form some of these other types of memories at an early age. Of course, babies can’t tell you exactly what they remember. So the key to Rovee-Collier’s research was to devise a task that was sensitive to babies’ rapidly changing bodies and abilities to assess their memories over a long period of time.
In the version for babies 2 to 6 months old, researchers place a baby in a crib with a mobile overhead. They measure how much the baby kicks to get an idea of their natural tendency to move their legs. Then they tie a string from the baby’s leg to the end of the mobile so that when the baby kicks, the mobile moves. As you might imagine, babies quickly learn that they are in control – they like to see the mobile movement and so they kick more than before the string was attached to their leg, demonstrating that they have learned that kicking is the mobile moves.
The version for babies from 6 to 18 months old is similar. But instead of lying in a crib – which this age group just won’t do for long – the child sits on their parents’ laps with their hands on a lever that will eventually make a train move along a track. At first, the lever doesn’t work, and the researchers measure how much a baby naturally pushes down. Then they turn on the lever. Every time the child presses it, the train moves on its track. Babies quickly learn the game again and press the lever significantly more as the train moves.
What does this have to do with memory? The smartest thing about this study is that after Rovee-Collier trained babies on one of these tasks for a few days, they later tested whether they remembered it. When babies came back to the lab, researchers simply showed them the cellphone or train and measured whether they were still kicking and pressing the lever.
Using this method, Rovee-Collier and colleagues found that, if trained for one minute, infants as young as 6 months old can recall an event a day later. The older babies were, the longer they remembered. She also discovered that you can make babies remember events longer by training them for a longer period of time and by giving them memories, for example by showing them the mobile very briefly on their own.
