What Libet did was to measure electrical changes in people's brains as they flicked their wrists. And what he found was that a subject's ''readiness potential'' - the brain signal that precedes voluntary actions - showed up about one-third of a second before the subject felt the conscious urge to act. The result was so surprising that it still had the power to elicit an exclamation point from him in a 1999 paper: ''The initiation of the freely voluntary act appears to begin in the brain unconsciously, well before the person consciously knows he wants to act!''
Then the experimenters would use magnetic stimulation in certain parts of the brain just at the moment when the subject was prompted to make the choice. They found that the magnets, which influence electrical activity in the brain, had an enormous effect: On average, subjects whose brains were stimulated on their right-hand side started choosing their left hands 80 percent of the time. And, in the spookiest aspect of the experiment, the subjects still felt as if they were choosing freely.
Which makes sense; if cognition is a physical process, then so would be decision-making. And it could be that the conscious mind is a very small part of the processes of the brain.
I've suspected for a while that our conscious minds don't so much do the thinking as weave together a coherent internal narrative from the myriad of subconscious processes in our heads, providing a serial stream of consciousness essential to having the sense of self and the ability to introspection. So it could be that we don't consciously make any decisions, only rationalise what the physical processes in our brains do.