In fact, in many cases the participants were able to cancel the nonconscious preparatory brain activity and stop their foot movement before it even began.

Now, there was a point of no return — red lights that appeared too close (less than about one-quarter of a second) to the beginning of a foot movement could not be completely inhibited — there simply wasn’t time for the new cancellation signal to overtake the earlier command to move. But still, the principle stands — these results suggest at least some of the activity identified by Libet can, in fact, be vetoed by conscious will.

    Christian JarrettNeuroscience and Free Will Are Rethinking Their Divorce