Escape from Libet

If you brain signals an action before you experience yourself deciding, a clear interpretation is that your subjective feeling of deciding has nothing to do with the actual deciding - that conscious will is an illusion¹.

But this isn’t the only interpretation.

Here are some common, and less common, critiques of the experiment²:

The Disconnect Criticism

The choice required from Libet’s participants was trivial and inconsequential. Moreover, they were specifically told to make the choice without any reason (“let the urge [to move] appear on its own at any time without any pre-planning or concentration on when to act”). A common criticism is that this kind of choice has little to tell us about everyday choices which are considered, consequential or which are actively trying to involve ourselves in.

The timing criticism(s)

Dennett discusses how the original interpretation of the experiment assumes that the choosing self exists at a particular point and at particular time – so, for example, maybe in some central ‘Cartesian Theatre’ in which information from motor cortex and visual cortex come together, but crucially, does not have direct report of (say) the information about timing gathered by the visual cortex. Even in a freely choosing self, there will be timing delays as information on the clock time is ‘connected up’ with information on when the movement decision was made. These, Dennett argues, could produce the result Libet saw without indicating a fatal compromise for free choice.

My spin on this is that the Libet result shows, minimally, that we don’t accurately know the timing of our decisions, but inaccurate judgements about the timing of decisions doesn’t mean that we don’t actually make those decisions.

Spontaneous activity

Aaron Schurger and colleagues have a nice paper in which they argue that Libet’s results can be explained by variations in spontaneous activity before actions are taken. They argue that the movement system is constantly experiencing sub-threshold variation in activity, so that at any particular point in time you are more or less close to performing any particular act. Participants in the Libet paradigm, asked to make a spontaneous act, take advantage of this variability – effectively lowering their threshold for action and waiting until the covert fluctuations are large enough to trigger a movement. Importantly, this reading weakens the link between the ‘onset’ of movements and the delayed subjective experience of making a movement. If the movement is triggered by random fluctuations (observable in the rise of the electrode signal) then there isn’t a distinct ‘decision to act’ in the motor system, so we can’t say that the subjective decision to act reliably comes afterwards.

The ‘only deterministic on average’ criticism

The specific electrode signal which is used to time the decision to move in the brain is called the readiness potential (RP). Electrode readings are highly variable, so the onset of the RP is a statistical artefact, produced by averaging over many trials (40 in Libet’s case). This means we lose the ability to detect, trial-by-trial, the relation between the brain activity related to movement and the subjective experience. Libet reports this in his original paper (‘only the average RP for the whole series could be meaningfully recorded’, p634). On occasion the subjective decision time (which Libet calls W) comes before the time of even the average RP, not after (p635: “instances in which individual W time preceded onset time of averaged RP numbered zero in 26 series [out of 36] – which means that 28% of series saw at least one instance of W occurring before the RP).

The experiment showed strong reliability, but not complete reliability (the difference is described by Libet as ‘generally’ occurring and as being ‘fairly consistent’, p636). What happened next to Libet’s result is a common trick of psychologists. A statistical pattern is discovered and then reality is described as if the pattern is the complete description: “The brain change occurs before the choice”.

Although such generalities are very useful, they are misleading if we forget that they are only averagely true, not always true. I don’t think Libet’s experiment would have the imaginative hold if the result was summarised as “The brain change usually occurs before the choice”.

A consistent, but not universal, pattern in the brain before a choice has the flavour of a prediction, rather than a compulsion. Sure, before we make a choice there are antecedents in the brain – it would be weird if there weren’t – but since these don’t have any necessary consequence for what we choose, so what?

To my mind the demonstration that you can use fMRI to reproduce the Libet effect but with brain signals changing up to 10 seconds before the movement (and an above chance accuracy at predicting the movement made), only reinforces this point. We all believe that the mind has something to do with the brain, so finding patterns in the brain at one point which predict actions in the mind at a later point isn’t surprising.

The power of Libet’s experiment relies as much on our false intuitions about the mind, rather than conclusively demonstrating anything new about freewill.

We all share, to some degree, common but flawed intuitions that our minds are separate from our brains (known as dualism). This makes any result showing a connection between our minds and brains feel surprising. We also share the intuition that our experience of things is accurate, so tend to interpret the experience of when we made a choice as reliable, but that doesn’t mean that when we thing we decided was actually when we decided. If deciding isn’t a think that happens at a fixed point in time, decisions can still be ours, even if some brain activity changes before we realise we’ve decided.³.

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To dive into why thinking of the brain as complex system gives even more reason to believe in a rich sense of free will: COMPLEXITY; direct link complexity

To skip to evidence that reason, argument and evidence have real power to guide our choices: REASONS; direct link reasons

If you’d like to hear some closing words, tweet @ChoiceEngine CLOSE; direct link close

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1: Daniel Wegner expanded this argument with a range of evidence in his (great) book “The Illusion of Conscious Will”

2: Parts of this text taken from a blog post I wrote about criticisms of Libet’s experiment: Critical strategies for free will experiments. For a recent review of Libet’s experiment and research it has inspired see Volition and the Brain – Revisiting a Classic Experimental Study

3: I wrote more about how Libet’s experiment plays on our intuitions about the mind in this BBC Future column