Brain preparation before a voluntary action: Evidence against unconscious movement initiation
ABSTRACT Benjamin Libet has argued that electrophysiological signs of cortical movement preparation are present before people report having made a conscious decision to move, and that these signs constitute evidence that voluntary movements are initiated unconsciously. This controversial conclusion depends critically on the assumption that the electrophysiological signs recorded by Libet, Gleason, Wright, and Pearl (1983) are associated only with preparation for movement. We tested that assumption by comparing the electrophysiological signs before a decision to move with signs present before a decision not to move. There was no evidence of stronger electrophysiological signs before a decision to move than before a decision not to move, so these signs clearly are not specific to movement preparation. We conclude that Libet’s results do not provide evidence that voluntary movements are initiated unconsciously.
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ABSTRACT: In 1983 Libet et al. found that the Readiness Potential (RP) precedes the intention to act by 350ms and the actual movement by 500ms on average. Using our own replication study, we illustrate how seemingly innocuous technical details are actually crucially relevant to the debate surrounding the interpretation of Libet-style experiments. For instance, using one specific method for determining the RP onset actually led to a reversal of Libet's results (i.e., the intention preceded the RP onset) for one of the participants. Claims regarding the causal relation between RP and intention cannot be based on averages, but require individual, case by case analyses, which show no exceptions in the temporal relation between RP and intention. We conclude that, properly speaking, Libet-style results in themselves cannot yet be taken as proof for the type of conclusions that are often formulated regarding the non-existence of free will. Copyright © 2015 Elsevier Inc. All rights reserved.Consciousness and Cognition 02/2015; 33C:300-315. DOI:10.1016/j.concog.2015.01.011 · 2.31 Impact Factor
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ABSTRACT: The idea that intentions make the difference between voluntary and non- voluntary behaviors is simple and intuitive. At the same time, we lack an understanding of how voluntary actions actually come about, and the unquestioned appeal to inten- tions as discrete causes of actions offers little if anything in the way of an answer. We cite evidence suggesting that the origin of actions varies depending on context and effector, and argue that actions emerge from a causal web in the brain, rather than a central origin of intentional action. We argue that this causal web need not be confined to the central nervous system, and that proprioceptive feedback might play a counter- intuitive role in the decision process. Finally we argue that the complex and dynamic origins of voluntary action and their interplay with the brain’s propensity to predict the immediate future are better studied using a dynamical systems approach.Review of Philosophy and Psychology 03/2015; in press. DOI:10.1007/s13164-014-0223-2