For sleep-deprived parents, babies’ babbling and squeals can quickly turn from cute to obnoxious. But a new study by a Duke researcher shows that infants understand more about language than previously thought. 

Elika Bergelson, assistant professor of psychology and neuroscience, recently authored a report revealing that infants can recognize that the meanings of some words are more alike than others. It was published Nov. 20 in the journal “Proceedings of the National Academy of Sciences.”

“In this study, we wanted to get a little bit of a better sense about what babies know when they first start to understand words,” she said. “Previous work shows babies can understand a little bit of what words mean by six months.”

Bergelson’s team had babies and their caregivers visit a lab with a computer screen, which showed the infants pairs of images that were related—like a car and stroller—as well as unrelated pictures—like a car and juice. Babies were then directed to look at one of the images. 

The researchers used an eye tracker that monitored positions over time with infrared. Analysis of this showed that babies did a better job looking at the right image when the two were related than when they were not related. 

“I think the most surprising part of the findings themselves is how intelligent babies as young as six months are, and how much of a vocabulary they’ve already developed,” said junior Micaela Brewington, a research assistant in the lab.

The team also investigated how the words babies hear at home could influence this knowledge of language. Bergelson gave each caregiver a colorful baby vest that included a small audio recorder to document the day-long speech of the infant. In addition, the caregivers received a baby hat with a small video recorder to film an hour-long video of the infant’s interactions with his or her caregiver. 

Once the team received the recordings, they analyzed the kinds of speech the babies overheard, such as which objects were named, who said them and whether the objects were actually present when they were being discussed, Brewington explained. 

They found that the proportion of time the caregivers talked about an object when it was present correlated with the infants’ comprehension of it. 

“The more parents talked about things that were actually there, the better babies did on the lab tests,” Bergelson said. 

She noted that all of the babies involved in the study were from monolingual, English families with no known hearing or vision problems. None of them had been born premature. When the babies came into her lab for the eye tracking study, they were also invited to participate in the home visit portion of the research. 

“This research lets us take a few more steps in figuring out how infants are learning from the world around them,” Bergelson said. 

She explained that the results could be useful for future work on language delays and deficits in infants. 

Babies that are raised in families in poverty often have delays in developing their speech, which researchers do not yet fully understand. Knowing more about how language develops can contribute to improved diagnosis and intervention, Bergelson noted. 

She added that studying babies’ language use is important because it can provide insight into how infants’ brains work. 

“They’re very good at [language], and we don’t know how they do it,” Bergelson said. “Within a year or two, they’ve figured out a lot about the language that will become their native language.” 

Brewington noted that this work is especially interesting because it incorporates the home environment, which is a major factor in babies’ language acquisition. 

“The research could point us towards the most important factors for ensuring the best learning,” she said. 

In the future, Bergelson plans to continue tracking the same set of babies to examine how their settings have impacted their development.

“We’re trying to get a bigger, broader picture of how home environment and social interaction come together,” she said.