British researchers have figured out a way to use brain waves to tell if someone is about to make a mistake.

The size of the P300 brain wave, which is generated when the brain encounters a stimulus, varies according to the response the stimulus calls for. It is larger when there is a need to inhibit action. In an experiment, the size of the P300 waves proved to be a good predictor of performance. When they fell by a third, mistakes increased by about a third. And people whose P300 waves were always smaller than the group’s average consistently made more mistakes.