Benjamin Libet’s experiments have convinced many people that we lack free will. These experiments seem to show that physical processes in the brain that cause our hands to move happen before we make the conscious decision to move our hands. In other words, our brains decide what we are going to do before we do. Libet himself, however, does not draw this conclusion. He believes our actions are free because we have the ability to veto the decisions that our brains make.
The experiments measure two things:
Readiness Potential (RP): electrical signals in the brain that precede voluntary acts.
When someone is aware (i.e. conscious) of having decided to act.
The subjects in the experiment are put in a device that measures electrical activity in their brains. While they are in the device, they can see a clock that measures time in milliseconds (msec).
They are told to move their hand whenever they want to and mark the time when they make the decision.
What the experiments show is that the electrical activity that precedes voluntary movements happens about 400 milliseconds before the subjects think they made the decision to move their hands.
You might ask how the timing could possibly be accurate. No one can track milliseconds on a clock, after all.
They thought of this. There is one more measurement. The subjects were asked to report the timing of a stimulus to their skin made by the experimenters. The experimenters know exactly when the stimulus happened and so they can easily calculate the difference between when the subjects report being aware of something, like the stimulus to the skin, and when it actually happened. The difference is about 50 milliseconds.
They assume that the gap between making a decision to move your hand and reporting being aware of that decision will have the same gap. So they add 50 milliseconds from the reported time to get what they believe is the actual time the subject was aware of having made a decision (Libet 1999, 50–51).
On the face of it, these experiments suggest that we do not have free will. Our brains start preparing for action before we are aware of deciding to act. What we think of as our decision to do something seems irrelevant to the movement of our bodies. The conscious decision comes well after the brain has already started taking the steps to make the body move, after all.
Libet, however, believes there is more to the story. He thinks his experiments have shown that we have the ability to exercise a conscious veto. A subject can have the readiness potential that normally precedes voluntary action but prevent action by making a conscious decision not to act (Libet 1999, 52).
If we do not have free will, maybe we have free won’t?1
Seriously, though, this would be a revisionist account of free will. Instead of initiating our actions, our role as free agents lies in serving as a gatekeeper who prevents the brain from completing some of the actions that it initiates. That said, Libet asserts this is all consistent with ordinary understandings of moral responsibility (Libet 1999, 54).
More broadly, Libet regards determinism as unproven. Since there is some experimental evidence that suggests the conscious mind can control the physical brain, he thinks libertarianism is the best position (Libet 1999, 55–57).
Libet is clearly putting a lot of weight on the assumption that conscious decisions, that is, decisions we are aware of making, are essential to free will. Here is how he puts it.
a free will process implies one could be held consciously responsible for one’s choice to act or not to act. We do not hold people responsible for actions performed unconsciously, without the possibility of conscious control. For example, actions by a person during a psychomotor epileptic seizure, or by one with Tourette’s syndrome, etc., are not regarded as actions of free will. (Libet 1999, 52)
It is not obvious to me that this is correct.
You should be familiar with these points from today’s class.
Also, it would not hurt to have an opinion about the role the conscious decisions play in free will.
Not my joke, unfortunately.↩︎