Experiment #30 · Scientific experiment

Libet's Free Will Experiments

The brain decides before "you" do

Benjamin Libet · 1983 · Neuroscience, philosophy of mind

First published: B. Libet et al., "Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential)", *Brain* 106 (1983): 623–642.

A readiness-potential builds in the motor cortex hundreds of milliseconds *before* the subject reports deciding to act.

Libet asked subjects to flex a finger whenever they felt the urge, while watching a rotating dot on an oscilloscope to record the moment they were conscious of the urge. EEG recorded the *readiness potential*, a slow buildup of cortical activity preceding voluntary movement. The readiness potential began ~550 ms before the movement; the reported moment of conscious decision came only ~200 ms before. By the time "I" decided, the brain had been preparing for a third of a second. Libet himself thought conscious free will survived as a *veto* power; later researchers (Wegner, Haggard, Soon) argued the result generalises into a deeper threat to libertarian free will. The case is the central empirical reference point for contemporary philosophy of action.

Formulation

Subject watches clock-like display, freely chooses moment to flex wrist, reports clock position at moment of conscious urge. EEG measures readiness-potential onset. Times (approximate): readiness-potential onset, t = −550 ms; reported conscious urge, t = −200 ms; movement, t = 0. Replicated with refinements (Soon et al. 2008: predictive classifiers can guess the choice up to 7 s in advance from fMRI).

Compare this experiment

Dimensions Engaged

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Observer

Strikes Observer · Agency and Metaphysical Agency: if cortical activity reliably predicts "voluntary" choice before consciousness reports it, the conscious self may not be the locus of agency it takes itself to be.

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Time

Bears on Time · Freedom: in the standard libertarian reading, a choice is free only if it is undetermined by antecedent state. The readiness-potential is an antecedent state that predicts the choice.

Responses — How Schools Engage

Affirms / takes the bait 1

Determinism

A canonical empirical confirmation: "free choices" are preceded by neural activity that determines them. Libertarian free will is a folk-psychological illusion now subject to neuroscientific refutation.

Denies / rejects the premise 2

Existentialism

The experimental setup — flex a finger at a randomly-chosen moment — measures something far from existentially relevant choice. Authentic freedom is a structure of how one inhabits a life, not a single motor decision.

Phenomenology

The "moment of conscious decision" assumed by the protocol is itself a phenomenological fiction. Volition is not a punctate inner event timeable against an external clock; the Libet design misdescribes its subject.

Reframes the question 2

Naturalism

Compatibilist naturalism: the readiness-potential is part of what *choosing* is; the time-lag is a red herring once we drop the dualist picture of an agent who acts on the brain rather than as the brain.

Dualism

A dualist can grant the result without surrendering the soul's agency: the readiness-potential may be the body's preparation, but the conscious self retains final assent. Libet himself defended this kind of "veto" reading.

Holds it inconclusive 1

Analytic Metaphysics / Logical Atomism

Modern reanalyses (Schurger 2012) argue the readiness-potential is largely noise that crosses a threshold rather than a deterministic causal chain. The case is empirically alive; metaphysical morals are premature.