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brain development in children
This drawing of the brain shows where researchers detected greater brain activity for children who engaged in more conversation at home. Credit: Figure 5 of Beyond the 30-Million-Word Gap: Children’s Conversational Exposure Is Associated With Language-Related Brain Function, Psychological Science February 2018

More than 20 years ago, psychologists Betty Hart and Todd Risley discovered what they called the “30 million word gap.” Through family visits, they estimated that children under 4 from lower-income families heard a staggering 30 million fewer words than children from higher-income families. That study was embraced by Hillary Clinton and it spurred a White House conference on the topic, public service announcement campaigns, and the creation of at least two outreach organizations. The clear message:  talk to your babies a lot.

But now a team of scientists from Harvard, the Massachusetts Institute of Technology and the University of Pennsylvania is questioning whether the quantity of words matters much at all. A study they published last month in the journal Psychological Science found that young 4-, 5- and 6-year-olds who engaged in more conversation at home had more brain activity while they were listening to a story and processing language.

“What we found is that the sheer amount of language, the number of adult words, was not related to brain activation or verbal skills,” said Rachel Romeo, lead author of the study and a doctoral student at a joint Harvard and MIT program. “But what was related, strongly related, was the amount of back-and-forth conversation between children and adults. We think this research finding suggests, instead of talking at or to your child, you really need to talk with your child to have meaningful brain development and language development.”

Romeo’s hypothesis is that back-and-forth conversation might actually rewire the brain and cause it to grow. Scientists call this neuroplasticity. But that needs to be tested in a future study that Romeo is planning. All this initial research showed was that kids in the study who experienced more conversation at home had greater brain activity and verbal aptitude. We don’t know yet if conversation is really causing those changes in brain development and verbal skill.

In the study, the benefits of conversation were just as strong for low-income children as they were for high-income children. Children who experienced high amounts of conversation scored 12 percent higher on standardized language assessments.

But low-income children tended to experience far less conversation at home, the study documented. Researchers compared a peak hour of conversation for each child. A child in a high-income household had 50 more conversational turns in a single hour than a child in a low-income household. A turn is when an adult speaks and the child responds, or vice versa. A single turn could be as short as this: “Eat.” “No!”

The implications of this study are important. Many programs targeted at low-income mothers have emphasized the importance of talking to babies from birth through 3 years old. “Some parents or even educators interpret this to mean, just get the words in, it doesn’t matter how, what, or where, just talk, talk, talk,” said Romeo. “It’s not that the amount doesn’t matter. But the engagement, the social exchange, is what seems to be important.”

To be sure, Hart and Risley’s 30-million-word-gap study never made the point that only quantity was important. They also wrote about the importance of exposing babies to a range of vocabulary and offering more positive, encouraging feedback than negative prohibitions.

Romeo advises parents to ask questions and wait for responses instead of just rattling off shopping lists or narrating the day. Admittedly, engaging in intellectual discourse with a 6-month-old is a challenge. With infants, Romeo suggests exchanging coos or silly faces. For many parents, that might be easier than sustaining an hour of narration.

Conducting a monologue may be annoying (to me, at least) but it certainly isn’t harmful. Romeo suspects that the parents who do it are also incidentally engaging in back-and-forth conversation and exposing their children to a lot of vocabulary and grammatical complexity. And that might explain why the parents who talk more tend to produce more verbally skilled children.

Romeo and her colleagues began their study in an MIT laboratory where 36 Boston-area children, ages 4 to 6, were tested to measure their verbal and reasoning skills. Then, each kid entered a brain scanner, which produced MRI images of brain activity while the child listened to audio stories. Afterward, families were sent home with a lightweight digital voice recorder that could fit in the child’s pocket and were told to turn it on during the child’s waking hours for an entire weekend. Algorithms analyzed the recordings, counting words spoken by adults and conversational turns. The algorithms were able to discern real, live human voices and discard words that the child heard from the television or other devices. If the recorder picked up a caretaker talking on the cellphone, that would be categorized as adult speech and the words counted.

Finally, the researchers compared the children’s test scores and brain images in the laboratory with the audio patterns at home. They found for every 11 conversational turns, a child’s verbal test score increased by one point. And they saw that the part of the brain involved in language processing lit up more for children who had experienced more conversation at home. The researchers saw no such connections for the number of words spoken.

This is only a small study and it needs to be replicated. We will need more studies to prove that conversation is the key to language development in the brain. But this neuroscience study confirms 2009 research from psychologists who weren’t conducting brain scans, and were beginning to discern what kinds of language exposure in early childhood are most important. I was also surprised to learn, in the process of researching this piece, that Hart’s and Risley’s landmark study wasn’t much larger than this one, tracking only 42 kids. It shows how a small study can have a huge impact.

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