Libet’s freewill experiments

The most famous experiment on freewill was done by Benjamin Libet¹. Libet’s experiment ingeniously combined the subjective experience of choosing with objective measurement of how a choice develops in the brain. Participants in Libet’s experiment² were instructed to flex their wrist at any time they felt like doing so, not to preplan but to let the act appear on its own. While they were letting a decision to act arise within them they watched a specially designed clock, in which a spot took 2.56 seconds to move once around the clock face. By designing a clock on which the ‘hand’ position indicates subseconds rather than subjects, Libet created a device with which he believed participants could, by observing position, very precisely report the time the decision to act arose within them. Whilst they were doing this, Libet attached electrodes to the scalp above the motor cortex, allowing him to record a signal called the ‘lateralised readiness potential’. This is a change in the electrical activity which occurs when you move.

Here’s the result: Libet’s participants reported that they decided to move in between the time that the electrical activity in their brains showed that they had started preparing to move and the time that they actually moved. The brain changed before people felt that they had choosen.

If your feeling of deciding comes after the brain activity involved in deciding, then - the argument goes - your feeling of deciding cannot play a role in actually deciding. Causation happens forward in time. Something about your brain activity implements deciding, and only then is your subjective sense of making this decision informed, and then after that you actually move. All this happens in fractions of sections, but the order these things happens puts a hard constraint on the role your feeling of deciding can play in the decision.

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Why this doesn’t mean that your brain makes your choices for you LIBET-Y; direct link libet2

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1: I am following his book “Mind time: The temporal factor in consciousness” here for details.

2: See the original report from one of the early papers here: Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential): the unconscious initiation of a freely voluntary act