Once the robot was programmed, 32 undergrad students interacted with it during a series of three-minute sessions. Using a robotics tool called optimal control theory, it was possible for the scientists to essentially reverse-engineer the behavior – they could establish what the babies’ goals were, based on the modeled behavior.

 

Essentially, it was found that babies (and the robot) carefully timed their smiles, in order to get smiles back from the mothers or students. In situations where the chances of getting a return smile were slim, the infants tended not to bother smiling in the first place. That said, it’s not at all clear if the infants were doing so knowingly.
via Gizmag