Benjamin Libet’s Experiments on Free Will

In class the last couple of weeks, we have been discussing the free will debate. In this post, I would like to bring to light an old research study pertaining to free will. Benjamin Libet was a famous 20th century neuroscientist who conducted groundbreaking research on the neurobiology of consciousness. In one of his classic experiments, Libet taped electrodes to the intact scalp of his study volunteers in an attempt to measure the correspondence of electrical signals from their brains. His goal was to measure this correspondence of electrical signals when the volunteers moved their wrists. The volunteers were required to look at a moving clock and take note of the precise time (to the millisecond) that they consciously decided to move their wrist. Following data collection, Libet compared the timing of brain activity with the timing of the volunteers’ decisions to move their wrist. His results showed that the volunteers’ brain activities preceded their conscious awareness of the decision to move their wrists by ~200 milliseconds.

Libet’s results sparked a debate about whether the volunteers’ decisions to move their wrists was predetermined or an act of free will. Those supporting the former claimed that because the volunteers’ brain activities preceded their decisions, it was in essence “predetermined” that the volunteers would subsequently move their wrist. On the other hand, those arguing for the free will side such as Libet himself claimed that there was a possibility for the volunteers to override the brain’s “proposal” to move the wrist at a given time. For instance, Libet argued that there was a brief period between the initiation of brain activity and the volunteers’ awareness of the intention to act during which they could “veto” the brain’s decision to initiate movement a moment after. If they did so, then they would prolong the initiation of movement. In this way, Libet argued that the volunteers exercised free will in deciding to veto the brain activity.

Libet’s justification reminds me of Kane’s businesswoman example in his article about free will, in which she has two conflicting decisions but ends up choosing one voluntarily (out of free will). In the same way, I feel that Libet’s volunteers must have had this internal conflict (whether to initiate movement a moment after as the brain specified or veto the brain’s decision), but consciously chose one (to veto the brain’s decision) over the other as an act of free will. As such, I feel that the free will defense of Libet’s experiments is more plausible than the determinism defense.


5 thoughts on “Benjamin Libet’s Experiments on Free Will

  1. This is very interesting! While I see that the way the study is described, it seems like the wrist movement is predetermined by the brain movement, I also wonder what was going on in the mind of the participant. If the participant was supposed to record when they moved their wrists, then they would know that they are supposed to move their wrists. Their conscious thoughts about moving their wrists could have an effect on how long it took them to actually move their wrists, which would skew the results.

  2. This is very interesting research on the connection between brain movement and thought processes. I imagine that there is some degree of error that is difficult to measure when a persons thoughts occur versus the electrical impulses.

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