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If you’re happy and you know it, clap someone else’s hands. A muscle stimulation system aims to evoke empathy by triggering involuntary hand gestures in one person in response to mood changes in another.

“If you’re moving in the same way as another person you might understand that person better,” says Max Pfeiffer at the University of Hannover in Germany.

Pfeiffer and his team wired up four people to an EEG machine that measured changes in the electrical activity in their brain as they watched film clips intended to provoke three emotional responses: amusement, anger and sadness. These people were the “emotion senders”. Each sender was paired with an “emotion recipient” who wore electrodes on their arms that stimulated their muscles and caused their arms and hands to move when the mood of their partner changed.


The gestures they made were based on American Sign Language for amusement, anger and sadness. To express amusement, volunteers had their muscles stimulated to raise one arm, to express anger they raised an arm and made a claw gesture, and to express sadness they slowly slid an arm down their chest. These resemble natural movements associated with the feelings, so the team hypothesised that they would evoke the relevant emotion. Asked to rate how well the gestures corresponded to the emotions, the volunteers largely matched the gestures to the correct mood.

Emotionally connected

The system could be used to emotionally connect couples in long-distance relationships, says Pfeiffer. It could even be linked with a person’s social media profile, he says, so that multiple friends could experience their emotions at the same time. The researchers will present their work at the Conference on Human Factors in Computing Systems (CHI) in Denver, Colorado, in May.

Ernst Kruijff at the Bonn-Rhein-Sieg University of Applied Sciences in Germany says the idea could open up a new way of communicating. “It’s important to explore the boundaries of what is possible with the human body within the frame of human-computer interaction,” he says.

But Brian Parkinson at the University of Oxford is sceptical that simple gestures can evoke a single emotion in this way. He uses the example of a clenched fist being associated with anger. “Imagine that you are trying to hold onto a small feather in your hand to stop it blowing away,” he says. “Would that make you more angry?”

It’s also not necessarily always desirable to experience the same emotions as the person you’re communicating with, says Parkinson. “Sometimes a more detached form of sympathy is better for communication.”

Next, Pfeiffer plans to use electrical muscle stimulation to make the arm movements of one person mimic those of their partner. In the future, he says, electrodes woven into clothing could let couples subtly share experiences using muscle stimulation.