The researchers said the babies who saw an angry outburst were less likely to play with the toy. Even when the person came back at a later time and didn't show anger, the babies still were reluctant to play with the toy.
In a separate experiment, a person who was either showing anger or acting neutrally asked for a turn with a toy. The babies gave the toy to the angry person 69 percent of the time, compared to 46 percent of the time to the neutral person.
"I was so surprised to see the infants give the toys away — it was like they were appeasing or compromising with the adult," researcher Betty Repacholi said in a UW news release. "They didn't want to risk making the previously angry adult mad again. They didn't act this way with the other adult who had not shown anger."
Fellow researcher Andrew Meltzoff added: "The babies are 'emotion detectives.' They watch and listen to our emotions, remember how we acted in the past, and use this to predict how we will act in the future. How long these first impressions last is an important question."
Simmons said she isn't surprised to hear that research points to 15 months as to when babies try to please people. That is about the age Graham was when he began to understand her positive reinforcement, she said.
"He knows when I'm hurt, like if I stub my toe, and he'll come over and give me a hug," she said of the nearly 2-year-old. "He recognizes what is going on for someone else, and he wants to make them happy."