How babies learn words for objects they've never seen

Babies don’t need to see everything to start learning what things mean. Even before they can talk, they’re already picking up new words by simply listening to people around them.

Picture a baby on the floor surrounded by toys while adults chat nearby. Even if the topic is something unfamiliar – like kumquats – the baby might still start piecing together what the word refers to, without ever laying eyes on the fruit.

That surprising ability was at the center of a study led by scientists from Northwestern and Harvard Universities. The researchers found that 15-month-old babies can learn about objects they’ve never seen, just by hearing others talk about them. In contrast, 12-month-olds don’t yet show the same skill.

The findings reveal how quickly babies begin to understand the world through language, even when the objects in question are completely hidden.

Babies learn words through sound

The team wanted to explore how early humans start forming mental pictures of things they’ve only heard about. To test this, they recruited 134 infants – half were 12 months old and the other half were 15 months.

The task was simple but clever. First, the babies heard familiar words like “apple” or “banana,” and saw matching images of those fruits.

Then, they were introduced to a new word, like “kumquat,” but without seeing any image – just hearing the word while the matching object stayed out of sight. Later, two new items appeared, for example, a kumquat and a whisk. The researchers asked, “Where is the kumquat?”

Babies form mental representations

The results were striking. Fifteen-month-olds looked longer at the kumquat, even though they had never seen one before. They didn’t need the object to be present – the language alone gave them enough clues to identify which item matched the new word.

“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,” said senior author Sandra Waxman.

“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.”

Babies use context to learn words

At 12 months, babies didn’t yet show this ability. The researchers believe this may be because younger infants haven’t heard enough familiar words in conversation to grasp what a new one might mean. For instance, if they don’t yet recognize words like “apple” or “banana,” then “kumquat” just sounds like more noise.

“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!’),” Waxman explained. “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.”

“We’re asking whether infants, too, can use the conversational contexts in which a word occurs to begin to learn their meaning.” The answer, at least for 15-month-olds, is yes.

Understanding the world through language

The experiment offered a unique window into how language itself shapes a child’s understanding of the world. By designing a test where the object stayed out of sight until later, the researchers could see just how much infants rely on context to learn.

This also reflects everyday life. Infants constantly hear adults talking about things they can’t see – while reading books, walking through the grocery store, or chatting during dinner.

The study shows that these moments still matter. Even if a baby doesn’t yet know the word “kumquat,” they’re already forming ideas about what it might be.

“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,” said Waxman. “We now know this is also true about tiny babies.”

The research sheds light on one of the earliest building blocks of human language and thought: our ability to understand the world not just through what we see, but through what we hear. And for babies, it seems that the process begins even earlier than many people might think.

The full study was published in the journal PLOS One.

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