Black and white portrait of a parent lovingly cradling a newborn baby. Image credit: Natalia Olivera (CC0)
When we remember events, we often do not just recall what happened, but also where and when it was, and who was there. This is because human memory tends to merge different features of experiences into whole episodes rather than store them as separate items. Combining all these features is what makes memories stronger and easier to remember in the long term, shaping who we are and how we act.
Our earliest episodic memories probably go back to the first years of life. But linguistic memory may develop earlier. Infants start learning a language before they can speak. By four months, they can respond to their own name and by six months, they can recognise common words. This suggests that they already possess the ability to store and retrieve linguistic information. But what is the nature of these earliest memories, and when are they first formed?
To find out more, Visibelli et al. tested brain signatures of episodic-like, linguistic memories in infants a few hours after birth. They designed a task to examine verbal memory formation in the presence of different speakers. Newborns, while lying in their hospital cribs, were exposed to a word pronounced by one speaker and then listened to the same or a different word three minutes later, after having been exposed to interfering words pronounced by another speaker.
Visibelli et al. investigated whether a change in who produces the words (the who) helps newborns create separate, retrievable memory traces for the words (the what). The researchers used a non-invasive method known as functional Near-Infrared Spectroscopy, which uses near-infrared light to monitor changes in brain oxygenation.
The recordings showed that newborns’ brains responded differently to a word they had heard before than to one they had not. This difference in response indicates that the brain distinguishes the familiar word from a new one - a sign that a memory had been stored and retrieved. Crucially, these memories were maintained only when different speakers produced both the familiar and interfering words. When recognition was successful, brain regions involved in speech and voice processing became active, suggesting that infants were not only processing the words themselves, but also who was speaking. This suggests that, at birth, newborns readily link words to speaker identity, encoding both what is being said and who is speaking.
The findings of Visibelli et al. open new directions for understanding memory and language development from the very first hours of life. The data suggest that speaker identity is a key feature of speech, enabling episodic-like memories of word sounds from birth and offering evolutionary advantages at the outset of human communication. They also raise the possibility that difficulties with feature binding (when the brain combines different attributes of an object or sound) may be detectable at a very early stage – before any language difficulties become apparent – thereby creating new opportunities for early identification and intervention.
