Babies are more clever than we give them credit for. They’re secretly manipulating us into beaming joyfully at them! 

According to a new study in the journal PLOS ONE, infants begin timing their facial expressions to garner smiles from their mothers by just four months of age. How did researchers figure this out? They created a creepy baby robot. 

To get at the root motivations of a baby’s smiles, the researchers first brought 13 mothers and their babies into the lab to observe how they interacted. They found that babies used “sophisticated timing” to ensure that their mother spent a maximum amount of time smiling at them, but the babies didn’t necessarily want to be smiling back—they seemed to time their smiles (often only a second long) so that their mother would smile at them for the longest amount of time, not so that they would both be smiling at each other.  

Image Credit: Ruvolo et al. ,PLOS ONE (2015)

In order to prove this hypothesis, the researchers then programmed a robot child, Diego-San, to smile in the same patterns as the real infants in the study. The mother substitutes, in this case, were 32 undergraduate students who interacted with the creepy creation. Each student interacted with the robot in a series of four three-minute periods, during which the robot smiled in different configurations (sometimes it mimicked the smile observation data from the infants, sometimes it mirrored the person’s expression, and sometimes it smiled in a pattern that had nothing to do with the person’s facial expressions).

They found that the undergraduates “appeared to have similar preferences to the ones we had previously found in mothers: they rated their experience with the robot more positively when the robot simultaneously smiled with them.” And when the robot mimicked the observed infant behavior, it had the intended effect that the researchers believed babies were looking for—it maximized the amount of time the “mother” spent as the only one smiling. 

The researchers don’t argue that babies are conscious of this behavior. And it’s not entirely clear what the purpose is. Perhaps babies want the positive attention of a smile, and learn that if they smile, their mother will—but once their mom beams, the baby has what she wants and no longer needs to smile herself. Or it may be something else. Bring more smiley babies to the lab, stat!

[h/t: IEEE Spectrum]