The following essay is covered in The Conversation, an online publication.

In my child development class at Rutgers University, I ask my students to recall their first memories whenever I teach about memory. Some students talk about their first day of pre-K, while others talk about a time when they were hurt or upset.

There are differences in the details of these memories, but they are all autobiographical and memories of significant experiences in a person's life, and they usually don't happen before the age of 2 or 3. Most people can't remember events from the first few years of their life. We can't remember what happened to us when we were babies. Is memory only able to work at certain ages?

Researchers know a lot about babies and memory.

Infants can form memories

Even though people can't remember much before the age of 2 or 3, research shows that infants can form memories, just not the kind of memories you tell about yourself. Babies can distinguish the faces of strangers and their mothers within the first few days of life. Babies can show that they remember a lot of faces by smiling at them.

There are more than one kind of memories besides those that areautobiographical. There are memories of facts like the names of apples or the capital of your home state. There are memories for how to open a door or drive a car.

According to research done in the 1980s and 1990s, infants can form some of these other types of memories. Babies can't say what they remember. A task that was sensitive to babies' rapidly changing bodies and abilities was the key to the research.

An infant is placed in a crib with a mobile hanging overhead in the version for 2 to 6 months old infants. They measure how much the baby kicks to see if they like to move their legs. They tie a string from the baby's leg to the end of the mobile to keep it from moving. Babies kick more when they see the mobile move because they learn that kicking makes the mobile move.

It's the same for 6- to 18-month-olds. The infant sits on their parent's lap with their hands on a lever that will eventually make a train move around a track. The experimenters measure how much a baby presses down when the lever isn't working. The lever will be turned on next. The train will move whenever the baby presses on it. When the train moves, infants press on the lever a lot more.

This has to do with memory. The most clever part of this research is that after training infants on one of these tasks for a couple of days, they were tested to see if they remember it. When infants came back into the lab, researchers showed them the train and asked if they still kicked the lever.

Babies can remember an event a day later if they are trained for a single minute. They remembered the older infants a long time. She found that you can teach infants to remember events for longer by training them for longer periods of time, and that you can remind them by showing them the mobile moving very briefly.

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Why not autobiographical memories?

Babies form memories in the first few months, so why don't people remember things from that point on? We don't know if people experience infantile amnesia because we can't form autobiographical memories or because we don't have a way to recover them. Scientists have a few guesses about what's happening.

A sense of self is one of the requirements for autobiographical memories. You need to be aware of how your behavior relates to others. The rouge test is a mirror recognition task that has been used by researchers to test this ability. They said in the 70s that the task was created to mark a baby's nose with red lipstick or blush.

Researchers put the baby in front of a mirror. Babies younger than 18 months don't show any evidence that they recognize themselves or the red mark on their face by smiling at the cute baby in the reflection. Between 18 and 24 months, toddlers touch their own noses, even looking embarrassed, suggesting that they connect the red dot in the mirror with their own face.

It is possible that because infants don't have language until later in the second year of life, they can't remember their own lives.

The hippocampus isn't fully developed in the infancy period, and that's a big deal.

Scientists will continue to investigate how each of these factors might contribute to why you can't remember a lot about your life before 2.

The conversation published this article. The original article is worth a read.