Infants as young as 15 months can learn new words for unseen objects

Human language allows us to learn new words for things we’ve never witnessed directly. We do this seamlessly, for example, in conversations, using clues from the overall context to infer a new word’s meaning.

But how early does this ability become available? And what makes it possible to create a new mental representation of an object or event that we cannot see directly?

A new study by developmental scientists at Northwestern University and Harvard University offers the first evidence that infants as young as 15 months can identify an object they have learned about from listening to language—even if the object remains hidden.

The paper “Semantic priming supports infants’ ability to learn names of unseen objects” is published in PLOS One.

Imagine an infant playing with blocks on the floor while listening to parents talk about kumquats in a conversation about more familiar fruits like apples and bananas. Might the infant form an initial representation, or gist, about what kumquat means—something edible, likely a fruit? Can they then use this initial gist later when the infant first sees a novel fruit? These are the questions the researchers sought to answer.

“Many people believe that success in word learning requires that the infant ‘map’ a new word to an object that is physically present (e.g., ‘Look at the kumquat!’). But in the natural course of a day, it is very common for us—and for infants—to hear words when the objects to which they refer to are not available to our immediate perception,” said senior author Sandra Waxman.

“We’re asking whether infants, too, can use the conversational contexts in which a word occurs to begin to learn their meaning.”

Waxman is the Louis W. Menk Professor of Psychology, director of the Infant and Child Development Center and an Institute for Policy Research Fellow at Northwestern. The study’s co-author is Elena Luchkina, formerly a postdoctoral fellow at Northwestern, and now a research scientist at Harvard.

The researchers engaged 134 infants, 67 each at 12 months and 15 months in a three-part task. First, the researchers presented infants with words they understand, paired with an image of the object to which it referred (e.g., apple, banana, grapes).

Next, infants heard a new word while the image of a novel object (e.g., a kumquat) was hidden from their view. Finally, two novel objects appeared (e.g., a kumquat and a whisk) and infants were asked, e.g., “where is the kumquat?”

Fifteen-month-olds, but not 12-month-olds, looked longer at the novel fruit (e.g. kumquat) than the novel artifact (e.g., whisk). Although they had never seen any object paired with that novel word, 15-month-olds nevertheless used the context clues to identify which object was most likely the one to which the novel word referred.

“The study shows that even babies who are just beginning to say their first words learn from the language they hear, even if the objects or events being discussed are not present,” Waxman said. “Babies take in what they hear, and even if no object is present, they form a mental representation, or ‘gist’ of the new word’s meaning, one that is strong enough for them to use later when its referent object does appear.”

Waxman suggested that at 12 months, infants may not yet know enough of the familiar words they heard in the context to begin to form a representation or gist of the new word’s meaning (e.g., that it is likely another fruit).

Gleaning the meaning of kumquat

By introducing infants to novel words in the absence of any visible object, the researchers devised a powerful test of how much infants can learn about the meaning of a novel word based on language input alone.

The study provides new insight for the developmental origins of the human capacity to learn about things that are not perceptually present. It also begins to address how, and how early, the human mind can create mental representations of objects and events never witnessed directly.

This new work also highlights the power of language in infants’ daily lives. In listening to conversations and in book-reading, infants often hear words that they don’t yet understand, and that they cannot ‘map’ immediately to an object or event. The results of this study show that by 15 months, infants spontaneously use the linguistic context in which a new word occurs to build a gist of its meaning that will support subsequent learning.

“When we hear new words, like ‘kumquat’ in conversation when there are no kumquats around, we don’t waste the opportunity to home in its meaning,” Waxman said. “We now know this is also true about tiny babies.”