Libet and Free Will

The Atlantic has an article on free will and Libet’s experiments that has been getting a lot of attention the past few days. It is actually discussing work from several years ago, but which probably has not received sufficient attention outside of neuroscience circles.

In a nutshell, Libet’s experiments involved subjects in a lab doing simple tasks such as deciding when to move their finger (or variations involving other very simple decisions). The subjects reported the time that they made their decision. The popular story that has been told is that brain imaging shows that the decision was actually made substantially earlier than the conscious experience (as indicated by readiness potentials), and so conscious volition can’t be responsible for the action.

What the more recent work cited by The Atlantic shows is that there is a plausible alternative explanation. Any time series data will have troughs and peaks, and often these are just noise. This might be the case with the readiness potentials, and in some situations this noise might be sufficient to attain a threshold towards making a decision:

“Neuroscientists know that for people to make any type of decision, our neurons need to gather evidence for each option. The decision is reached when one group of neurons accumulates evidence past a certain threshold. Sometimes, this evidence comes from sensory information from the outside world…

But Libet’s experiment, Schurger pointed out, provided its subjects with no such external cues. To decide when to tap their fingers, the participants simply acted whenever the moment struck them. Those spontaneous moments, Schurger reasoned, must have coincided with the haphazard ebb and flow of the participants’ brain activity.”

This explanation undermines the idea that the brain decided to move the finger prior to conscious experience of the decision.

The article describes a variant of the Libet experiment that includes a control condition where the subjects do not move:

“To avoid unintentionally cherry-picking brain noise, they included a control condition in which people didn’t move at all. An artificial-intelligence classifier allowed them to find at what point brain activity in the two conditions diverged. If Libet was right, that should have happened at 500 milliseconds before the movement. But the algorithm couldn’t tell any difference until about only 150 milliseconds before the movement, the time people reported making decisions in Libet’s original experiment.”

So in that experiment, the subject’s report of the conscious experience of making a decision corresponds with the detected difference in brain activity.

As an example of reactions to this article and the research it is describing, here is Dan Dennett:

Dennett has criticized these experiments before. Note his comment about dualism. It’s not surprising that someone who is opposed to dualism would be uncomfortable with all this talk about the brain deciding prior to the mind being conscious of it, and particularly if one believes that conscious states are just brain states.

Here is Sam Harris regretting having cited the Libet studies in his work on free will:

I should add that the idea that the Libet experiments disprove free will is one that has been criticized for many years. For one thing, deciding whether or not to wiggle a finger in a controlled lab is very different from complex decision-making such as deciding on a restaurant. For examples of other criticisms of the view that Libet undermines free will, see this article or this book, which dedicates a chapter to covering Libet’s experiments.

Obviously none of this proves that free will exists. I am open to the idea, but think it’s unclear what true libertarian free will would even look like.

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