Haynes's 2008 study modernized Libet's earlier experiment: where Libet's EEG technique could look at only a limited area of brain activity, Haynes's fMRI set-up could survey the whole brain; and where Libet's participants decided simply on when to move, Haynes's test forced them to decide between two alternatives. But critics still picked holes, pointing out that Haynes and his team could predict a left or right button press with only 60% accuracy at best. Although better than chance, this isn't enough to claim that you can see the brain making its mind up before conscious awareness, argues Adina Roskies, a neuroscientist and philosopher who works on free will at Dartmouth College in Hanover, New Hampshire. Besides, "all it suggests is that there are some physical factors that influence decision-making", which shouldn't be surprising. Philosophers who know about the science, she adds, don't think this sort of study is good evidence for the absence of free will, because the experiments are caricatures of decision-making. Even the seemingly simple decision of whether to have tea or coffee is more complex than deciding whether to push a button with one hand or the other.
Haynes stands by his interpretation, and has replicated and refined his results in two studies. One uses more accurate scanning techniques3 to confirm the roles of the brain regions implicated in his previous work. In the other, which is yet to be published, Haynes and his team asked subjects to add or subtract two numbers from a series being presented on a screen. Deciding whether to add or subtract reflects a more complex intention than that of whether to push a button, and Haynes argues that it is a more realistic model for everyday decisions. Even in this more abstract task, the researchers detected activity up to four seconds before the subjects were conscious of deciding, Haynes says.
Some researchers have literally gone deeper into the brain. One of those is Itzhak Fried, a neuroscientist and surgeon at the University of California, Los Angeles, and the Tel Aviv Medical Center in Israel. He studied individuals with electrodes implanted in their brains as part of a surgical procedure to treat epilepsy4. Recording from single neurons in this way gives scientists a much more precise picture of brain activity than fMRI or EEG. Fried's experiments showed that there was activity in individual neurons of particular brain areas about a second and a half before the subject made a conscious decision to press a button. With about 700 milliseconds to go, the researchers could predict the timing of that decision with more than 80% accuracy. "At some point, things that are predetermined are admitted into consciousness," says Fried. The conscious will might be added on to a decision at a later stage, he suggests.
Thursday, September 08, 2011
Free Will: Neuroscience vs. Philosophy
Kerri Smith offers (PDF here) an update on the perennial debate between neuroscientists and philosophers over free will, it covers findings I've mentioned in previous posts...Haynes and coworkers finding that brain activity in motor cortex areas can be observed one to seven seconds before a subject is aware of willing an action to occur, and Fried et al. making even more compelling observations.