If the sobbing continued, the children usually shifted gears and came forward  to deliver a hug.

Re-armed and newly sensitive, RUBI was ready to test as a teacher. In a paper published last year, researchers from the University of California, San Diego, the Massachusetts Institute of Technology and the University of Joensuu in Finland found that the robot significantly improved the vocabulary of nine toddlers.

After testing the youngsters’ knowledge of 20 words and introducing them to the robot, the researchers left RUBI to operate on its own. The robot showed images on its screen and instructed children to associate them with words.

After 12 weeks, the children’s knowledge of the 10 words taught by RUBI increased significantly, while their knowledge of 10 control words did not. “The effect was relatively large, a reduction in errors of more than 25 percent,” the authors concluded.

Researchers in social robotics  a branch of computer science devoted to enhancing communication between humans and machines  at Honda Labs in Mountain View, Calif., have found a similar result with their robot, a three-foot character called Asimo, which looks like a miniature astronaut. In one 20-minute session the machine taught grade-school students how to set a table  improving their accuracy by about 25 percent, a recent study found.

At the University of Southern California, researchers have had their robot, Bandit, interact with children with autism. In a pilot study, four children with the diagnosis spent about 30 minutes with this robot when it was programmed to be socially engaging and another half-hour when it behaved randomly, more like a toy. The results are still preliminary, said David Feil-Seifer, who ran the study, but suggest that the children spoke more often and spent more time in direct interaction when the robot was responsive, compared with when it acted randomly.

Making the Connection

In a lab at the University of Washington, Morphy, a pint-size robot, catches the eye of an infant girl and turns to look at a toy.

No luck; the girl does not follow its gaze, as she would a human’s.

In a video the researchers made of the experiment, the girl next sees the robot “waving” to an adult. Now she’s interested; the sight of the machine interacting registers it as a social being in the young brain. She begins to track what the robot is looking at, to the right, the left, down. The machine has elicited what scientists call gaze-following, an essential first step of social exchange.