What did Libet's experiments show about free will?

Libet's 1983 experiment showed that a brain signal called the readiness potential begins well before people report feeling the urge to move. Libet read this as evidence that voluntary acts start unconsciously. Many researchers now think the data do not support the stronger claim that free will is an illusion, though the timing pattern itself has largely held up. [1] [2]

Participants made a simple hand or wrist movement whenever they chose, while EEG recorded brain activity. They watched a rapidly rotating clock-like spot and noted when they first felt the urge to act. According to the review by Frith and Haggard, the readiness potential began on average 635 ms before the action, whereas the reported urge came only about 200 ms before it. [1] [3]

Because causes must precede effects, Libet argued that the conscious urge could not be what started the readiness potential. He concluded that the brain prepares, or perhaps decides, to act before the person is aware of it. Many people took this to undermine free will, since conscious initiation is often seen as a requirement for it. [3] [1]

Libet left limited room for free will. He suggested that consciousness might veto an impending action, sometimes called free won't. Later studies found that vetoes are also preceded by a readiness potential, and one estimate placed the point of no return near 200 ms before movement, about when Libet thought the veto window opened. Libet also noted that many actions come from deliberation over longer timescales. [4] [3]

One position holds that the result shows decisions begin unconsciously. Frith and Haggard note that this fits a materialist view in which conscious experience follows from brain activity, and that similar timing values have been replicated in several studies. [1]

A second position challenges what the readiness potential means. Jeff Miller's team found the signal appeared both before movements and when no movement occurred, so it was not a consistent marker of movement preparation. Recent models discussed in Trends in Cognitive Sciences suggest the readiness potential may not be a real signal on individual trials, or one that causes action, so its timing cannot show that conscious will is absent. Philosophers add that few decisions where responsibility matters resemble Libet's arbitrary finger movements. [4] [3]

A third concern is the evidence base. A meta-analysis of Libet-style studies found a temporal pattern largely consistent with Libet's, but only six studies measured the key gap between unconscious brain activity and conscious intention, with high uncertainty. The authors concluded that some findings are more fragile than expected. The methods and interpretation have been hotly debated, and I found no source in these results stating a single consensus beyond the criticisms above. [2] [1]