Given the strong link between free will and systems of moral and legal responsibility, like punishment, the stakes are high not just for our conception of human nature, but also for our everyday practices that matter.
You may like to watch this video of Libet’s experiment on free will and illusion:
The current neuroscience of free will traces its lineage back to an influential experiment by Benjamin Libet and his colleagues. The majority of our actions begin with bodily movements, and most of us think that when we decide to move (e.g., decide to pick up my cup of tea), first I, the agent or person, decides and then I hand off control, so to speak, to the brain circuits for motor control to execute the action.
It was known since the 1960s from work by Kornhuber and Deecke that there is a slow buildup of negative brain activity in the supplementary motor area (SMA) and pre-SMA measurable by electroencephalography (EEG) just prior to voluntary (i.e., movement initiated by the participant) bodily movement.
This brain activity, called the readiness potential (RP), was taken to be neural preparation to move for spontaneous movements and starts about a half-second before the time of the movement (here).
So Libet and his fellow researchers ask when does the agent appears in relation to the RP? The agent’s decision has to be something measurable in the lab, so Libet asked participants to make movements (of the finger or wrist) at a time of their choosing and then report after the fact when they were first aware of their decision or urge to move using a modified clock (termed ‘W time’).
Libet found, contra the commonsense expectation, that the average reported time of first awareness of the decision to move, W-time, occurred almost a third of a second after the start of the RP. So Libet (and select others since) concluded that the RP is the brain’s unconscious decision to move with the agent’s decision occurring later (here).
Libet took this as evidence that the conscious agent or self doesn’t initiate, or kick off, preparation to act, the unconscious brain does. He argued that this result is representative of how all of our voluntary movements are produced, and, if so, then the agent’s conscious decision to act doesn’t initiate the process leading to movement. But if the agent doesn’t play this initiating role in acting, how can it be up to me how I act?
These results have worried a lot of folks and inspired a booming research enterprise in cognitive neuroscience and philosophy. One shouldn’t jump to the depressing conclusion, though, that we don’t act freely or don’t really deserve any of the moral reactions others have to our actions; there is a healthy discussion on how the original Libet results can be interpreted as consistent with that picture of us humans as self-governing and free and moral persons.
W-time is taken to indicate the moment of awareness of a decision. Can we capture “moments of conscious awareness” scientifically?
Since the initial publication of Libet and colleagues’ study, worries about whether we could measure the time of conscious awareness have been voiced. After all, we are talking here about the timeframe of milliseconds.
What does the study reveal?
In these studies, all of the events measured prior to movement in the lab are happening within one second before the participant wiggles a finger or hand (now button presses are the preferred movement). Libet argued that W-time within a reasonable range was reliable since we can see how accurately participants in the lab estimate the time of other events, such as skin shocks. The reliability of W-time has recently been challenged yet again with a new study that concludes that depending on the order in which participants complete certain tasks in the experiment, W-time can be strikingly different (i.e., there is an order effect; see here).
Other researchers are currently exploring alternative ways to measure a decision to move in the lab, including work by Parés-Pujolràs and co-authors, who have been using an online (i.e., pre-movement) measure of the agent’s awareness of a decision to move (here).
In these studies, participants watch a continuous stream of letters on a computer while spontaneously pressing a button. Every now and then, though, the letters change color. When this happens participants are told to press the button just then if they were already aware of their preparing to press the button soon. These kinds of online measures of awareness may yet prove to be more reliable ways of getting at whether people have conscious intentions to act in the lab.
What’s the latest work on the neuroscience of free will?
Two of the hottest topics seem to be, first, what exactly the RP, that negative build-up of brain activity pre-movement, really signifies and, second, how we can make our voluntary actions in the lab more ecologically valid.
As to the first, the past decade has seen researchers investigating if we have evidence that the RP really does stand for a decision to move or, alternatively, if the RP just is the brain’s being biased to move in some way (say, left, instead of right) without the commitment to do so.