For most people, there’s nothing as heartwarming as a baby’s smile.

For moms, smiling games are one of the earliest forms of interaction with their child.

However, this interaction is more than fun and games, according to a study conducted by researchers at the Olin College of Engineering in Needham, Massachusetts.

Using control theory, an approach used in robotics to analyze and synthesize goal-oriented behavior, researchers discovered that by the time infants reach 4 months old, they and their mothers time their smiles in a purposeful, goal-oriented manner.

Moms in the study tried to maximize the time spent in mutual smiling, while their infants tried to maximize mother-only smile time.

Baby Smiles

However, researchers don’t claim that the infants or mothers were aware they were timing their smiles.

Moreover, researchers say these smile games are important for infant social development and act as the foundation for social interaction later on in the infant’s life.

“Everybody likes to talk about a baby’s smile. Is it gas or is it a smile? These are important and fun conversations to have, but there’s much more to a baby’s smile than that,” Dr. Laura Jana, director of innovation at the University of Nebraska Medical Center, told Healthline.

“With our new technology capabilities we’re able to say ‘Look, this is more than soft, fuzzy, feel-good stuff,’” said Jana, a pediatrician. “It’s measurable, and if you combine early interactions with early brain science, we see that building bonds, like the social smile, is really foundational for social emotional development and early brain development, and serves as the key for all the things that people care about down the road like skill development, innovation, and more.”

Read More: When Do Babies Start Laughing? »

Detailed Approach to Study

To validate their findings, researchers observed thirteen infants between 4 and 17 weeks old and their mothers in weekly face-to-face interactions.

They analyzed how both the mother and infant maximized the time of simultaneous smiling; how each maximized the time of mother smiling/infant not smiling; how each maximized the time of mother not smiling/infant smiling; and how each maximized the time of neither smiling.

By timing the different interactions between mother and infant, researchers found that most of the mothers prioritized simultaneous smiling, while most of the infants tried to maximize mother-only smiling.

Researchers concluded that by 4 months of age, infants smile with a purpose.

They also stated in their study that “control theory is a promising technique for analyzing complex interactive behavior and providing new insights into the development of social communication.”

For instance, the discovery of goal-oriented interactive behavior in infants could help in the understanding of the development of typical and atypical social behavior, such as children who are at high risk for developing autism spectrum disorders (ASD).

This may be possible by analyzing if infants who develop ASD have more object-oriented and less socially-oriented goals than infants who don’t develop the disorder.

Jana says the study also brings up the question of what happens when children aren’t engaged socially at an early age.

“We know that early human interaction, such as singing, reading, cooing, smiling, and talking to babies is foundational. Think about what that means for children growing up in homes where this isn’t happening,” said Jana. “The more we understand the importance of foundational development, the more it gets increasingly difficult for anyone to say all children should pull themselves up from their boot straps and get themselves on a good life trajectory. If you don't have the foundation to do that, how is that possible?”

Read More: When Do Babies Sit Up? »

Childlike Robot Programmed to Play Smile Games

Researchers created a childlike robot named Diego-San to help to build on their findings.

Based on information gathered from the infant-mother interaction study, Diego-San was programmed to perceive and produce smiles while interacting with adults.

Undergraduates at the University of California, San Diego, participated in the study by interacting with the robot for three-minute sessions in which the robot was programmed to smile in different ways.

They then tracked the participant’s face using eye and head movements.

The participants had similar preferences to the mothers in the previous study in that they rated their experience with the robot more positively when the robot smiled with them simultaneously.