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11/9/10

Free will not an illusion after all

"Champions of free will take heart. A landmark 1980s experiment that purported to show free will doesn't exist is being challenged.

In 1983, neuroscientist Benjamin Libet asked volunteers wearing scalp electrodes to flex a finger or wrist. When they did, the movements were preceded by a dip in the signals being recorded, called the "readiness potential". Libet interpreted this RP as the brain preparing for movement.

Crucially, the RP came a few tenths of a second before the volunteers said they had decided to move. Libet concluded that unconscious neural processes determine our actions before we are ever aware of making a decision (Brain, vol 106, p 623).

Since then, others have quoted the experiment as evidence that free will is an illusion - a conclusion that was always controversial, particularly as there is no proof the RP represents a decision to move." More (Requires a subscription)

A synopsis of the full article:

Jeff Miller and Judy Trevena of the University of Otago in Dunedin, New Zealand, experimented to determine what prompts the Readiness Potential (RP).

Like Libet, they used scalp electrodes, but with a difference. Volunteers did not decide when to move. Miller and Trevena had them wait for an audio tone. Upon hearing it they could decide whether or not to tap a key.

Given Libet's view of the RP, Miller and Trevena held that it should be greater after the volunteer chose to tap the key.

What did they find out? The RP was the same, both before and after the decision to move. For that reason, they posit that the RP may merely be a sign that the brain is paying attention and does not indicate that a decision has been made.

What about Libet's view that decision-making is subconscious? In a second experiment, they failed to find evidence for it. In this experiment, volunteers pressed a key after the tone, but had to decide whether to use their left or right hand.

This is revealing because movement in the right limbs relates to left hemisphere brain signals; the left side, to the right. If an unconscious process is driving this decision, brain location should depend on choice of hand. Choice did not correlate.

The findings do not refute Libet's experiments but they do undermine them.

The original experiments by Benjamin Libet can be read about in Mind Shadows here.

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