Tag Archives: Free Won’t

Libet Unreadied

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Benjamin Libet’s famous experiments have been among the most-discussed topics of neuroscience for many years. Libet’s experiments asked a subject to move their hand at a random moment of their choosing; he showed that the decision to move could be predicted on the basis of a ‘readiness potential’ detectable half a second before the subject reported having made the decision. The result has been confirmed many times since, and even longer gaps between prediction and reported decision have been claimed. The results are controversial because they seem to be strong scientific evidence against free will. If the decision had been made before the decider knew it, how could their conscious thought have been effective? My original account (14 years ago, good grief) is here.

Libet’s findings and their significance have been much disputed philosophically, but a new study reported here credibly suggests that the readiness potential (RP) or Bereitschaftspotential has been misunderstood all along.

In essence the RP is a peak of neural activity, which seemed to the original researchers to represent a sort of gathering of neural resources as the precursor of an action. But the new study suggests that this appearance is largely an artefact of the methods used to analyse the data, and that the RP really represents nothing more than the kind of regular peak which occurs naturally in any system with a lot of background noise. Neural activity just does ebb and flow like that for no particular reason.

That is not to say that the RP was completely irrelevant to the behaviour of Libet’s subjects. In the rather peculiar circumstances of the original experiment, where subjects are asked to pick a time at random, it is likely that a chance peak of activity would tip the balance for the unmotivated decision. But that doesn’t make it either the decision itself or the required cause of a decision. Outside the rather strange conditions of the experiment, it has no particular role. Perhaps most tellingly, when the original experiments were repeated with a second group of subjects who were asked not to move at all, it was impossible to tell the difference between the patterns of neural activity recorded; a real difference appeared only at the time the subjects in the first group reported having made a decision.

This certainly seems to change things, though it should be noted that Libet himself was aware that the RP could be consciously ‘over-ruled’, a phenomenon he called ‘Free Won’t’. It can, indeed, be argued that the significance of the results was always slightly overstated. We always knew that there must be neural precursors of any given decision, if not so neatly identifiable as the RP. So long as we believe the world is governed by determined physical laws (something I think it’s metaphysically difficult to deny) the problem of Free Will still arises; indeed, essentially the same problem was kicked around for centuries in forms that relied on divine predestination or simple logical fatalism rather than science.

Nevertheless, it looks as though our minds work the way they seem to do rather more than we’ve recently believed. I’m not quite sure whether that’s disappointing or comforting.

Quando Libet

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New light on Libet’s challenge to free will; this interesting BQO piece by Ari N Schulman focuses on a talk by Patrick Haggard.

Libet’s research has been much discussed, here as well as elsewhere. He asked subjects to move their hand at a time of their choosing, while measuring neural activity in their brain. He found that the occurrence of a ‘Readiness Potential’ or RP (something identified by earlier researchers) always preceded the hand movement. But it also preceded the time of the decision, as reported by subjects. So it seemed the decision was made and clearly registered in brain activity as an RP before the subjects’ conscious thought processes had anything to do with it. The research, often reproduced and confirmed, seemed to provide a solid scientific demonstration that our feeling of having free conscious control over our own behaviour is a delusion.

However, recent research by Aaron Schurger shows that we need to re-evaluate the RP. In the past it has been seen as the particular precursor of intentional action; in fact it seems to be simply a peak in the continuing ebb and flow of neural activity. Peaks like this occur all the time, and may well be the precursors of various neural events, not just deliberate action. It’s true that action requires a peak of activity like this, but it’s far from true that all such peaks lead to action, or that the decision to act occurred when the peak emerged. If we begin with an action and look back, we’ll always find an RP, but not all RPs are connected with actions. It seems to me a bit like a surfer, who has to wait for a wave before leaping on the board; but let’s suppose there are plenty of good waves and the surfer is certainly not deprived of his ability to decide when to go.

This account dispels the impression that there is a fatal difficulty here for free will (of course there are plenty of other arguments on that topic); I think it also sits rather nicely with Libet’s own finding that we have ‘free won’t’ – ie that even after an RP has been detected, subjects can still veto the action.

Haggard, who has done extensive work in this area, accepts that RPs need another look; but he contends that we can find more reliable precursors of action. His own research analysed neural activity and found significantly lowered variability before actions, rather as though the disorganised neural activity of the brain pulled together just before an action was initiated.

Haggard’s experiments were designed to address another common criticism of Libet’s experiments, namely the artificiality of the decision involved. Being told to make your hand for no reason at a moment of your choosing is very unlike most of the decisions we make. In particular, it seems random, whereas it is argued that proper free will takes account of the pros and cons. Haggard asked subjects to perform a series of simple button-pushing tasks; the next task might follow quickly, or after a delay which could be several minutes long. Subjects could skip to the next task if they found the wait tedious, but that would reduce the cash rewards they got for performing the tasks. This weighing of boredom against profit is much more like a real decision.

Haggard persuasively claims that the essence of Libet’s results is upheld and refreshed by his results, so in principle we are back where we started. Does this mean there’s no free will? Schulman thinks not, because on certain reasonable and well-established conceptions of free will it can ‘work in concert with decisional impulses’, and need not be threatened by Haggard’s success in measuring those impulses.

For myself, I stick with a point mentioned by Schurger; making a decision and becoming aware of the decision are two distinct events, and it is not really surprising or threatening that the awareness comes a short time after the actual decision. It’s safe to predict that we haven’t heard the last of the topic, however.

Limits of Free Won’t

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Another strange side light on free will. Some of the most-discussed findings in the field are Libet’s celebrated research which found that Readiness Potentials (RPs) in the brain showed when a decision to move had been made, significantly before the subject was aware of having decided. Libet himself thought this was problematic for free will, but that we could still have ‘Free Won’t’ – we could still change our minds after the RP had appeared and veto the planned movement.

A new paper (discussed here by Jerry Coyne) follows up on this, and seems to show that while we do have something like this veto facility, there is a time limit on that too, and beyond a certain point the planned move will be made regardless.

The actual experiment was in three phases. Subjects were given a light and a pedal and set up with equipment to detect RPs in their brain. They were told to press the pedal at a time of their choosing when the light was green, but not when it had turned red. The first run merely trained the equipment to detect RPs, with the light turning red randomly. In the second phase, the light turned red when an RP was detected, so that the subjects were in effect being asked to veto their own decision to press. In the third phase, they were told that their decisions were being predicted and they were asked to try to be unpredictable.

Detection of RPs actually took longer in some instances than others. It turned out that where the RP was picked up early enough, subjects could exercise the veto; but once the move was 200ms or less away, it was impossible to stop.

What does this prove, beyond the bare facts of the results? Perhaps not much. The conditions of the experiment are very strange and do not resemble everyday decision-making very much at all. It was always an odd feature of Libet’s research that subjects were asked to get ready to move but choose the time capriciously according to whim; not a mental exercise that comes up very often in real life. In the new research, subjects further have to stop when the light is red; they don’t, you notice, choose to veto their move, but merely respond to a pre-set signal. Whether this deserves to be called free won’t is debatable; it isn’t a free decision making process. How could it be, anyway; how could it be that deciding to do something takes significantly longer than deciding not to do the same thing? Is it that decisions to move are preceded by an RP, but other second-order decisions about those decisions are not? We seem to be heading into a maze of complications if we go that way and substantially reducing the significance of Libet’s results.

Of course, if we don’t think that Libet’s results dethrone free will in the first place, we need not be very worried. My own view is that we need to distinguish between making a conscious decision and becoming aware of having made the decision. Some would argue that that second-order awareness is essential to the nature of conscious thought, but I don’t think so. For me Libet’s original research showed only that deciding and knowing you’ve decided are distinct, and the latter naturally follows after the former. So assuming that, like me, you think it’s fine to regard the results of certain physical processes as ‘free’ in a useful sense, free will remains untouched. If you were always a sceptic then of course Libet never worried you anyway, and nor will the new research.