The landmark 1980s experiment that purportedly showed that free will doesn't exist among humans has been challenged by a new study.
In 1983, neuroscientist Benjamin Libet asked volunteers wearing scalp electrodes to flex a finger or wrist, which led to a dip in the signals being recorded, called the "readiness potential".
Libet interpreted this RP as the brain preparing for movement, but the RP came a few tenths of a second before the volunteers said they had decided to move.
Thus, he concluded that unconscious neural processes determine our actions before we are ever aware of making a decision.
Since then, scientists 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.
To contradict the interpretation, Jeff Miller and Judy Trevena of the University of Otago in Dunedin, New Zealand, attempted to tease apart what prompts the RP using a similar experiment, with a key twist, reports New Scientist.
Just like Libet, they used scalp electrodes, but instead of letting their volunteers decide when to move, the duo asked them to wait for an audio tone before deciding whether to tap a key.
Had Libet's interpretation been correct, the RP should have been greater after the tone when a person chose to tap the key, said Miller.
But they noticed that while there was an RP before volunteers made their decision to move, the signal was the same whether or not they elected to tap.
Miller concluded that the RP might merely be a sign that the brain is paying attention and does not indicate that a decision has been made.
The researchers also failed to find evidence of subconscious decision-making in a second experiment.
This time they asked volunteers to press a key after the tone, but to decide on the spot whether to use their left or right hand.
As movement in the right limbs is related to the brain signals in the left hemisphere and vice versa, they reasoned that if an unconscious process is driving this decision, where it occurs in the brain should depend on which hand is chosen. But they found no such correlation.