When you feel rewarded by someone else's happiness, your brain starts treating them like a favorite.
That's the surprising takeaway from new research by psychologists at the USC Dornsife College of Letters, Arts and Sciences: Empathy isn't just a fixed trait - it can be trained. In a study published in Psychological Science, researchers found that people began to care more about someone not because of shared experiences or values, but because that person's joy had become emotionally linked to personal reward.
The effect was subtle but meaningful, and it lasted even when no rewards were involved. "It's a social twist on Pavlov's classic experiment," said Leor Hackel, assistant professor of psychology. "Just as a dog learns to salivate when a bell signals food, our brains may learn to feel good when someone else is happy."
To test the theory, the researchers designed a series of experiments in which participants observed a cartoon character experiencing everyday highs and lows, like playing with a dog or falling off a bike. After each scene, participants saw a number on the screen rise or fall, representing a personal gain or loss for them. Over time, those who consistently experienced gains from the character's happy moments began to associate the character's emotions with reward.
Later, when shown new scenes involving the same character, those participants reported stronger empathic feelings, even when no rewards were involved. They also worked harder to earn rewards while viewing that character's positive emotions, suggesting the emotional link had motivational force.
In a final experiment, participants chose digital gift cards for the character, knowing which ones the character would enjoy or dislike. Sometimes, selecting a gift the character liked reduced the participant's point total. Even then, those who had learned to associate the character's happiness with reward were more likely to prioritize the character's preference - or hesitate longer before choosing otherwise - even when it meant losing points. The results suggest that emotional learning shaped not just how participants felt, but how they acted.
The researchers say these findings could help explain why empathy often grows in cooperative environments - like classrooms, families or teams - where one person's success often benefits everyone. In more competitive settings, where someone else's gain means your loss, those emotional bonds may be harder to form.
"Understanding how people form emotional bonds could help us design AI that responds in more humanlike ways," said Yi Zhang, a psychology doctoral student at USC Dornsife and lead author of the study. "But it also reminds us how much empathy depends on our social environment - and how we can shape it."
