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Neuroscience and Philosophy

The Libet Experiments - Four Decades of Research on Free Will



In the early 1980s, the neuroscientist Benjamin Libet decided to make the philosophical claim that people have free will empirically testable. He instructed subjects to freely decide within the next minute or so to make a simple voluntary motor movement, like flexing their hand. He measured the exact time of the onset of muscular acitivity in order to determine the time of the movement (M). He also invented an ingenious device in order to measure the exact time when people first became consciously aware of their decision to execute the movement (W). Lastly, he used EEG to record the exact time of the onset of the Readiness Potential, a neural activity that precedes motor movements (RP).

The findings of Libet's experiments were as follows: RP preceeded M by about 550MS. That is, it apparently takes the brain about half a second to initiate a simple motor movement. However, W preceeded M by about only 200MS. W (the 'conscious will') thus occured only about a third of a second AFTER the brain had already begun to initiate the movement! For that reason, Libet's experiments and others along similar lines have ever since been said to show that "Free Will is an Illusion", that the conscious will simply comes too late for it to have any impact on what we do.

This, of course, has sparked some controversy. Part of the controversy is philosophical. Philosophers have, for example, questioned whether Libet's notion of free will is viable, whether it is the kind of free will worth caring about. Interestingly, however, part of the controversy is also empirical. There are lots and lots of methodological problems with Libet-style experiments that do not throw doubt on the philosophical interpretation of Libet's results, but on the viability of the results themselves.

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