On average, participants reported experiencing a conscious decision to move about 200 milliseconds (one-fifth of a second) before the movement occurred. Although the participants felt that they moved their hands at their own freely-chosen random intervals, Libet found that he could predict their movements in advance!

How is this possible? About half a second before the actual movement, one region of the participants’ brains began to show an increase in electrical activity (called a readiness potential). Participants were not aware of this rise in brain activity, but when Libet saw it, he knew that they were “about to decide to move.”