How Do Babies Realize They Can Influence the World?

An infant’s aha! moment may hold secrets to the origins of agency

BY ALIZA SLOAN & SCOTT KELSO for Scientific American

Sometimes the simplest questions are the hardest to answer. How, for example, do you decide to wiggle your fingers? Quite a lot is known about the neural structures and muscles involved— the puppet and the strings, as it were—but what about the puppeteer?

Humans act with purpose, but much is still unknown about how we become purposeful agents—that is, how we develop the ability to willfully make things happen. In a recent study to probe agency’s mysterious roots, we tried to catch infants in the act of discovering their own agency. As we reported last September in the Proceedings of the National Academy of Sciences USA, we identified these aha! moments and the events surrounding them, thereby revealing the process of agency formation for the first time.

For more than 50 years, researchers have used a very simple method to investigate learning in infancy. They place a baby into a crib with a mobile suspended above. Then a scientist ties one end of a string to the mobile and the other to the infant’s foot. Now if the baby moves, the toy will, too. By observing babies in this setup in multiple sessions, scientists can watch as the infants learn and recall a simple cause-and-effect interaction: kick a foot and the mobile moves.

We revisited that setup with the intention of identifying the moment when babies first realize they can control the mobile’s motion. We worked with 16 infants who were three to four months of age and measured the movements of both infant and mobile in three-dimensional space using cutting-edge motion-capture technology.

As past baby-mobile experiments had demonstrated, infants kicked significantly more when their foot was tethered to the mobile than when it was not. But did the infants actually know that their movements were propelling the mobile? After all, they were too young to speak for themselves, so we had to consider other possible explanations for what might have been happening.

One clue came when an experimenter pulled the string to make the mobile move instead. Infants moved less in those situations than when the mobile was stationary. That finding rules out the idea that babies simply kick in excitement when they see the mobile moving. In fact, our data showed it was the highly coordinated exchange between the tethered infant and the mobile—foot and mobile moving together—that seemed to prompt a baby’s activity.

Read more here.


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