Psychology Professor Casey Lew-Williams Seeks to Understand Babies’ Brains

Thanks to two college jobs — one at an emergency shelter for foster children and another at a preschool across the street from his dormitory — Casey Lew-Williams saw firsthand the deep impact a child’s social surroundings have on their development.“ I was captivated by how much children were shaped by their environments,” Lew-Williams says. Lew-Williams went on to earn his Ph.D. in psychology from Stanford and in 2014 founded the Princeton Baby Lab, which uses a combination of experimental, descriptive, computational, and social neuroscience approaches to understand how daily life impacts learning in young children.

“What can we learn about the dynamics of home environments through speech, interactions, communications, and emotions to get a window into variation across families, and how does that variability shape children’s learning?” In 2016, Lew-Williams co-founded, along with a team of developmental scientists, the ManyBabies consortium, a collaborative group of nearly 700 developmental scientists around the world who are committed to sharing research and best practices. “We’re using this to diversify our research questions, diversify our research participants, and even diversify our scholars.”

Quick Facts

Title
Professor of Psychology 

Time at Princeton
11 years

Recent Class
Developmental psychology 

Lew-Williams Research: A Sampling

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Mikel Casal

Early Word Learning

Parents often expect a baby’s first words to be concrete nouns like “mama,” “dadda,” “ball,” or “shoe.” But up to half of many babies’ early vocabularies consists of intangible concepts like “uh-oh,” “wow,” and “shhh.” Lew-Williams wanted to understand how babies absorb these concepts without visual clues. He and his graduate student Kennedy Casey tracked the contexts in which they are spoken and found that situational consistency seems to facilitate the learning. We say “uh-oh,” for example, when something falls or malfunctions. They also discovered that young children tend to learn words that are spoken with more variation — such as “dog,” which becomes “doggy,” “pup,” or “woof-woof”— earlier than those with little to no variation, such as “watch.” 

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Mikel Casal

Babies in Charge

You might assume that parents are the ones who lead interactions and babies follow. But in fact, babies are often the ones choosing what to do and focus on, and parents follow. Lew-Williams, his former postdoc Elise Piazza, and his Princeton colleagues Uri Hasson and Liat Hasenfratz tracked how babies’ and parents’ brains responded to one another during natural play. They found that, on average, babies’ brain activity tended to lead parents’ brain activity by about 3 to 5 seconds, particularly in the prefrontal cortex, which is associated with complex behaviors such as decision making, reasoning, and personality expression.  “It’s just not the case that babies are passive, sponge-like recipients of information. They are active learners who shape the social environment around them, including their parents’ brains.”

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Mikel Casal

Communicating Without Speaking

Across families, children learn in many more ways than through language alone.  “We are gaining a lot of texture and dimensionality by looking beyond just speech,” Lew-Williams says. “Parents communicate with babies using gestures, emotions, actions, and touch, and these are all important for babies’ uptake of the world around them.” Among the insights he and his team have unearthed is that children are more likely to learn words used by parents during positive emotional states and high arousal, meaning parents are alert and engaged.