Libet’s classifc experiment on the neuroscience of free will tells us more about our intuition than about our actual freedom
It is perhaps the most famous experiment in neuroscience. In 1983, Benjamin Libet sparked controversy with his demonstration that our sense of free will may be an illusion, a controversy that has only increased ever since.
Libet’s experiment has three vital components: a choice, a measure of brain activity and a clock.
The choice is to move either your left or right arm. In the original version of the experiment this is by flicking your wrist; in some versions of the experiment it is to raise your left or right finger. Libet’s participants were instructed to “let the urge [to move] appear on its own at any time without any pre-planning or concentration on when to act”. The precise time at which you move is recorded from the muscles of your arm.
The measure of brain activity is taken via electrodes on the scalp. When the electrodes are placed over the motor cortex (roughly along the middle of the head), a different electrical signal appears between right and left as you plan and execute a movement on either the left or right.
The clock is specially designed to allow participants to discern sub-second changes. This clock has a single dot, which travels around the face of the clock every 2.56 seconds. This means that by reporting position you are reporting time. If we assume you can report position accurately to 5 degree angle, that means you can use this clock to report time to within 36 milliseconds – that’s 36 thousandths of a second.
Putting these ingredients together, Libet took one extra vital measurement. He asked participants to report, using the clock, exactly the point when they made the decision to move.
Physiologists had known for decades that a fraction of a second before you actually move the electrical signals in your brain change. So it was in Libet’s experiment, a fraction of a second before participants moved, a reliable change could be recorded using the electrodes. But the explosive result was when participants reported deciding to move. This occurred in between the electric change in the brain and the actual movement. This means, as sure as cause follows effect, that the feeling of deciding couldn’t be a timely report of whatever was causing the movement. The electrode recording showed that the decision had – in some sense – already been made before the participants were aware of having taken action. The brain signals were changing before the subjective experience of taking a decision occurred.
Had participants’ brains already made the decision? Was the feeling of choosing just an illusion? Controversy has raged ever since. There is far more to the discussion about neuroscience and free will than this one experiment, but its simplicity has allowed it to capture the imagination of many who think our status as biological creatures limits our free will, as well as those who argue that free will survives the challenge of our minds being firmly grounded in our biological brains.
Part of the appeal of the Libet experiment is due to two pervasive intuitions we have about the mind. Without these intuitions the experiment doesn’t seem so surprising.
The first intuition is the feeling that our minds are a separate thing from our physical selves – a natural dualism that pushes us to believe that the mind is a pure, abstract place, free from biological constraints. A moment’s thought about the last time you were grumpy because you were hungry shatters this illusion, but I’d argue that it is still a persistent theme in our thinking. Why else would we be the least surprised that it is possible to find neural correlates of mental events? If we really believed, in our heart of hearts, that the mind is based in the brain, then we would know that every mental change must have a corresponding change in the brain.
The second pervasive intuition, which makes us surprised by the Libet experiment, is the belief that we know our own minds. This is the belief that our subjective experience of making decisions is an accurate report of how that decision is made. The mind is like a machine – as long as it runs right, we are happily ignorant of how it works. It is only when mistakes or contradictions arise that we’re drawn to look under the hood: Why didn’t I notice that exit? How could I forget that person’s name? Why does the feeling of deciding come after the brain changes associated with decision making?
There’s no reason to think that we are reliable reporters of every aspect of our minds. Psychology, in fact, gives us lots of examples of where we often get things wrong. The feeling of deciding in the Libet experiment may be a complete illusion – maybe the real decision really is made ‘by our brains’ somehow – or maybe it is just that the feeling of deciding is delayed from our actual deciding. Just because we erroneously report the timing of the decision, doesn’t mean we weren’t intimately involved in it, in whatever meaningful sense that can be.
More is written about the Libet experiment every year. It has spawned an academic industry investigating the neuroscience of free will. There are many criticisms and rebuttals, with debate raging about how and if the experiment is relevant to the freedom of our everyday choices. Even supporters of Libet have to admit that the situation used in the experiment may be too artificial to be a direct model of real everyday choices. But the basic experiment continues to inspire discussion and provoke new thoughts about the way our freedom is rooted in our brains. And that, I’d argue, is due to the way it helps us confront our intuitions about the way the mind works, and to see that things are more complex than we instinctively imagine.
This is my latest column for BBC Future. The original is here. You may also enjoy this recent post on mindhacks.com Critical strategies for free will experiments
3 thoughts on “Intuitions about free will and the brain”
Gazzaniga proved in the 1960’s during open brain surgery that at least 0.5 up to 1 second pass between action and awareness. Which stanbds to reason, awareness only can come about after various filters have been passed. Awareness is vastly overrated
Where is the mind before children develop language?
Were the students in Libet’s study required to participate as part of the class, or did they volunteer of their own free will?
The question is more important than the answer. It shows that there is a meaningful definition of free will that everyone understands.
It requires no freedom from causation, from oneself, or from reality. Nothing magical or supernatural.
And it is not an “illusion”, because it actually happens within the physiology of a biological organism’s nervous system. Thinking is just as real as walking.
Our experience of the phenomenon is no more complicated than is necessary to get the job of choosing done.
If someone forces us to choose or act against our will, then our will is not free. When we do the choosing for ourselves, it is our own free will.
It is certainly a deterministic process. We make choices for reasons. But they are our own reasons and it is authentically us doing the choosing.
Every decision we make of our own free will is also inevitable. Both facts are true in every decision we make. The only illusion is the imaginary conflict. And that conflict comes from replacing ordinary freedom with an impossible absolute freedom. I suspect that all paradoxes result from such mental errors and subtle frauds.