Davide Rigoni and his colleagues, who made the finding, aren't sure what the precise mechanism for this effect is, but they speculated that bursting the free will bubble somehow causes people to put less intentional effort into their movements.
Rigoni's team tested thirty participants on a version of Benjamin Libet's classic task from the 1980s. This requires that participants watch a dot proceed round a clock face, that they make a voluntary finger movement at a time of their choosing (the current study had participants press a button), and then make a mental note of the position of the clock at the time they made their decision to move. Libet's controversial discovery, replicated here, was that the brain begins preparing for the finger movement several hundred milliseconds prior to the conscious decision to move, as revealed by electrical activity recorded via electrodes on the scalp. The finding implies that free will is illusory.
For Rigoni's task, an additional detail was that half the participants read a passage debunking our sense of free will (see comments for the text) before they completed the Libet task. The other half acted as controls and read a passage about consciousness that didn't mention free will.
The new finding was that the earliest phase of preparatory brain activity known as "the readiness potential" differed between the two groups. This early component (around 1300 to 400 ms prior to the voluntary movement) was weaker in the brains of the participants who'd had their belief in free will diminished. Moreover, a questionnaire administered afterwards showed that this effect on brain activity was greater among the participants who reported having less belief in free will. In contrast, later phases of the brain's preparatory brain activity were not correlated with belief in free will.
What do we know about the early phase of preparatory brain activity that was affected? Quoting Lang (2003), Rigoni and his colleagues said that this early phase is associated specifically with movements that are executed with the "introspective feelings of the willful realisation of the intention to move at a particular time." In English, this means the early phase of preparatory brain activity is associated with just the kind of movement under study - a deliberate movement initiated at a consciously chosen time. The implication is that undermining someone's sense of free will leads them to invest less intention into an intentional movement. Exactly how one does that, and what it means, remains unclear. Rigoni's team conceded in their conclusion: "How disbelief in free will affects intentional effort is an open question."
They added: "In sum, our results indicate that beliefs about free will can change brain processes related to a very basic motor level, and this suggests that abstract belief systems might have a much more fundamental effect than most people would expect."
The study builds on past research showing how undermining people's belief in free will affects their social behaviour, for example encouraging them to cheat.
Rigoni, D., Kuhn, S., Sartori, G., and Brass, M. (2011). Inducing Disbelief in Free Will Alters Brain Correlates of Preconscious Motor Preparation: The Brain Minds Whether We Believe in Free Will or Not. Psychological Science, 22 (5), 613-618 DOI: 10.1177/0956797611405680
Previous Digest reports featuring Libet's classic task: Libet Redux: Free will takes another hammering and Exposing some holes in Libet's classic free will study.
This post was written by Christian Jarrett for the BPS Research Digest.