The choice is yours

There's an experiment which has been popularly held to discredit free will. Brain activity of subjects shows a very distinct pattern (the Bereitschaftspotential) several seconds ahead of the time before they commit to a decision to press a button. I've argued that there's no way to know when their conscious decision is actually made, and that a "decision" without consequences isn't much of a decision at all and so doesn't need much or any conscious choice. Neither do I think that predictability - e.g. having known preferences - discredits free will either. That someone could I guess I might prefer to see a movie about space werewolves than play a round of golf doesn't in any way mean I didn't have a free choice. And I'd add the habitual behaviour can make it very difficult to distinguish conscious choices, i.e. when you mean to turn left, say, but turn right out of habit instead.

But there may be an even simpler explanation for this particular experimental case - a somewhat subtle and interesting variation on the classic fallacy of correlation not being causation.

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. They would have been more likely to tap their fingers when their motor system happened to be closer to a threshold for movement initiation. 

This would not imply, as Libet had thought, that people’s brains “decide” to move their fingers before they know it. Hardly. Rather, it would mean that the noisy activity in people’s brains sometimes happens to tip the scale if there’s nothing else to base a choice on, saving us from endless indecision when faced with an arbitrary task. The Bereitschaftspotential would be the rising part of the brain fluctuations that tend to coincide with the decisions. This is a highly specific situation, not a general case for all, or even many, choices.

In a new study under review... researchers repeated a version of Libet’s experiment. 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. 

In other words, people’s subjective experience of a decision—what Libet’s study seemed to suggest was just an illusion—appeared to match the actual moment their brains showed them making a decision.

So in this particular case, it appears that the actual and subjective moment of decision coincide. In that other study claiming to predict decisions from MRI scans 10 seconds ahead of time, prediction accuracy is only about 60%. It still seems to me that this gives no grounds for claiming you even know if the decision is truly made, short of actually pressing the button. Even that would be tricky : suppose you were to decide at the last second not to press it but the signal from your brain to stop your finger wasn't fast enough ?

This doesn't mean that we do or don't have free will, of course, but I think determining that by monitoring the brain is going to be at best much more difficult than the earlier experiments suggested. I suspect it's fundamentally impossible to objectively measure what is in inherently subjective experience.

A Famous Argument Against Free Will Has Been Debunked

For decades, a landmark brain study fed speculation about whether we control our own actions. It seems to have made a classic mistake. The death of free will began with thousands of finger taps. In 1964, two German scientists monitored the electrical activity of a dozen people's brains.