Recently, Ping-Pong players faced off against a surprising opponent: a robot. Scientists from the University of Florida wanted to see if people’s brains behaved differently while competing against a machine.

Volunteers swatted balls served by either a human or robotic opponent. Each volunteer wore a special cap that contained more than 100 electrodes. The high-tech headgear measured electrical activity between their brains’ neurons, or nerve cells.

The scientists found that people’s brains worked harder—seemingly paying more attention—when playing against the robot. That may be because humans provide visual cues about how they’re going to move and serve the ball. But “with a robot, you’re guessing,” says Amanda Studnicki, an engineer who designed the study.