Smile baby smile! We too will!
Babies smile in order to make those they are interacting with smile back using sophisticated timing much like comedians who time their jokes to maximise audience response, researchers have found.
In the study, researchers programmed a toddler-like robot to behave like the babies they studied and had the robot interact with 32 undergraduate students.
They found that the robot got the undergraduates to smile as much as possible, while smiling as little as possible.
"If you've ever interacted with babies, you suspect that they're up to something when they're smiling. They're not just smiling randomly," said Javier Movellan, a research scientist in the Machine Perception Laboratory at the University of California, San Diego, and one of the study's authors.
"But proving this is difficult," Movellan said.
To find out what babies are really up to, researchers turned to optimal control theory, a tool often used in robotics.
The method allows researchers to design and programme robots to perform a specific behaviour based on specific goals. In this study, the researchers used the method to reverse engineer what the babies' goals were based on their behaviour.
Researchers used data from a previous study that observed the face to face interactions of 13 pairs of mothers and infants under the age of four months, including when and how often the mothers and babies smiled.
After running the data through their reverse-control theory algorithms, researchers were actually surprised by the findings, said Paul Ruvolo, a professor at Olin College of Engineering and an alumnus of the Jacobs School of Engineering at UC San Diego.
"We thought either the babies had no goal or it was about mutual smiling," he said.
Researchers point out that they can't determine if the babies are conscious of what they are doing.
"We are not claiming that a particular cognitive mechanism, for instance conscious deliberation, is responsible for the observed behaviours," Ruvolo said.
Even though the sample size was small, the findings were statistically strong, said Movellan. The control theory data analysis found that 11 out of the 13 babies in the study showed clear signs of intentional smiling.
The researchers then developed a programme that mimicked the babies' actions and transferred it onto Diego San, a toddler-like robot.
Diego San interacted with 32 UC San Diego undergraduates individually during three-minute sessions where it displayed one of four different behaviours.
When Diego San behaved like the babies in the study, the undergraduate students behaved like the babies' mothers: they smiled a lot even while the robot did not have to smile that much.
The study is published in the journal PLOS ONE.