Brain Might Not Stand in the Way of Free Will
Advocates of free will can rest easy, for now. A 30-year-old classic experiment that is often used to argue against free will might have been misinterpreted.
In the early 1980s, Benjamin Libet, a neuroscientist at the University of California in San Francisco, used electroencephalography (EEG) to record the brain activity of volunteers who had been told to make a spontaneous movement. With the help of a precise timer that the volunteers were asked to read at the moment they became aware of the urge to act, Libet found there was a 200 millisecond delay, on average, between this urge and the movement itself.
But the EEG recordings also revealed a signal that appeared in the brain even earlier, 550 milliseconds, on average, before the action. Called the readiness potential, this has been interpreted as a blow to free will, as it suggests that the brain prepares to act well before we are conscious of the urge to move.
This conclusion assumes that the readiness potential is the signature of the brain planning and preparing to move. “Even people who have been critical of Libet’s work, by and large, haven’t challenged that assumption,” says Aaron Schurger of the National Institute of Health and Medical Research in Saclay, France.
One attempt to do so came in 2009. Judy Trevena and Jeff Miller of the University of Otago in Dunedin, New Zealand, asked volunteers to decide, after hearing a tone, whether or not to tap on a keyboard. The readiness potential was present regardless of their decision, suggesting that it did not represent the brain preparing to move. Exactly what it did mean, though, still wasn’t clear.
Crossing a threshold
Now, Schurger and colleagues have an explanation.