[I]t is for his experiment on free will that he will mostly be remembered. In this experiment he wanted to find the cause of our spontaneous, deliberate actions. Certainly we feel as though we consciously decide to act and then do so. Yet philosophers and scientists for hundreds of years have argued that the brain does not need a magical conscious self to start actions off, and free will must be an illusion. Unlike all the thousands of people who have argued around this point, Libet actually found a way to test it.
He asked subjects in the laboratory to hold out their arm and, whenever they felt like it and of their own free will, to flex their wrist. He then measured three things - the time at which the movement began, the time at which the "readiness potential" in the brain began (signalling the brain starting to organise the coming movement) and then, most tricky of all, the time at which the subject made the decision to move.
This really is tricky because there is, by definition, no physical activity in the brain or anywhere else that corresponds to this. He was trying to measure something purely mental - the free decision, or thought, of wanting to act. Finding a way to do this is probably why the experiment became so famous. What he did was this. He had a spot revolving on a screen, like a clock face, and he asked the subjects to call out where the spot was at the exact moment that they decided to act. In other words, they were, after the fact, making a judgement about where the spot was at the time, and that could be used to accurately time the decision to act.
And his results? They were quite consistent and have since been repeated many times. The brain activity comes first, then the decision to act, and then finally the action itself. Not only does the decision to act happen after the brain is already getting ready to set off the action, but it comes nearly half a second later. It looks as though our conscious decision to act cannot, however strongly it feels that way, be the cause of our actions.
Oh dear! Free will seems to be disproved. But it's not that simple. Libet himself did further experiments that seemed to show that we may not be able to start actions consciously, but we can veto them once they have begun - saving at least some role for free will. But even that does not end the issue. Literally hundreds of academic articles, and several whole books, have been written about this experiment and how to interpret it. This is why I say it is the most famous experiment on consciousness ever done.
In a way the whole furore is bizarre. Most scientists claim to be materialists. That is, they don't believe that mind is separate from body, and firmly reject Cartesian dualism. This means they should not be in the least surprised by the results. Of course the brain must start the action off, of course the conscious feeling of having made it happen must be illusory. Yet the results created uproar. I can only think that their materialism is only skin deep, and that even avowed materialists still can't quite accept the consequences of being a biological machine.
Libet, unlike so many others, was wonderfully open about this. He really did believe that mind can affect body, that consciousness is some kind of power of the "non-physical subjective mind" or "conscious mental field", and even that we might consciously survive death. Indeed, this was what inspired his experiments in the first place.
Read it all here.
I will give the last word to Dr. Lisbet, who explains that this "free don't"--the fact that we stop actions that our brian commenses, as opposed to initiating them in the first place--is really an aspect of free will:
That veto power may not seem like much, he wrote in a 1999 essay, but it is enough to satisfy ethical standards. "Most of the Ten Commandments are 'do not' orders," he wrote.
(From the Los Angeles Times obituary.)