Brain preparation before a voluntary action: Evidence against unconscious movement initiation. Consciousness and Cognition, 19, 447-56
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.
- SourceAvailable from: Yudai Takarada
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- "We assumed that the brain activity specific for hypnosis would be reflected as an observable increase in the excitability of M1. No facilitatory effect on corticospinal excitability was found in the TS condition, despite the fact that conscious motor intention emerges as a result of neural computations carried out within a parietal-motor network (Desmurget and Sirigu, 2009; Trevena and Miller, 2010), and that motor imagery facilitates corticospinal excitability (Kasai et al., 1997; Facchini et al., 2002). One plausible explanation is that cognitive inhibitory action might be exerted on the motor system (for a review see Aron et al., 2004): the right inferior frontal cortex suppressed electrical activity not only in the basal ganglia (Burman and Bruce, 1997), but also in the motor cortex (Sasaki et al., 1989). "
ABSTRACT: Hypnosis often leads people to obey a suggestion of movement and to lose perceived voluntariness. This inexplicable phenomenon suggests that the state of the motor system may be altered by hypnosis; however, objective evidence for this is still lacking. Thus, we used transcranial magnetic stimulation of the primary motor cortex (M1) to investigate how hypnosis, and a concurrent suggestion that increased motivation for a force exertion task, influenced the state of the motor system. As a result, corticospinal excitability was enhanced, producing increased force exertion, only when the task-motivating suggestion was provided during hypnotic induction, showing that the hypnotic suggestion actually altered the state of M1 and the resultant behavior.Neuroscience Research 06/2014; DOI:10.1016/j.neures.2014.05.009 · 2.15 Impact Factor
- "Investigations of free will have recently garnered widespread popular and scientific attention. These studies, however, often focus on some variation of the Libet experiments (Filevich, Kühn, & Haggard, 2013; Haggard, 2011; Lau, Rogers, Haggard, & Passingham, 2004; Libet, Gleason, Wright, & Pearl, 1983; Schurger, Sitt, & Dehaene, 2012; Trevena & Miller, 2010) or on probing people's intuitions regarding whether free will and moral responsibility are compatible with determinism (e.g., Nahmias, Morris, Nadelhoffer, & Turner, 2005; Nichols & Knobe, 2007). Empirical investigations into people's conceptualization of free will itself are virtually non-existent. "
Chapter: Free Will Without Metaphysics[Show abstract] [Hide abstract]
ABSTRACT: Free will is the ability to transform thoughts and desires into actions, and this ability to act freely is presumed to underlie people's practice of moral praise and blame as well society's practice of legal punishment. However, many scholars believe that people's concept of free will is hopelessly corrupted by metaphysical assumptions, such as a belief in the soul or a belief in magical causation. Because science contradicts such metaphysical assumptions, science may also invalidate the ordinary concept of free will and thereby unseat a key requisite for moral and legal responsibility. Such a concern, however, turns on the exact content of people's concept of free will. Here we discuss a program of research that seeks to clarify the folk concept of free will and its role in moral judgment. Our data show that people have, not a metaphysical, but a psychological concept of free will: they assume that "free actions" are based on choices that fulfill one's desires and are relatively free from internal and external constraints. Moreover, we argue that these components—choice, desires, and constraints—lie at the heart of people's moral judgments. Once these components are accounted for, the abstract concept of free will contributes very little to people's moral judgments. What does it mean to have free will? When asked, people widely believe that they have free will (Baumeister, Crescioni, & Alquist, 2010), and free will is commonly asserted as a critical underpinning for moral and legal responsibility (Greene & Cohen, 2004). But for such a seemingly widespread and important concept, there is remarkable confusion over its definition and use. Philosophers and theologians have debated the question of free will for millennia. Today, neuroscientists and psychologists have joined philosophers in trying to answer some nagging questions about free will: Is it an illusion (Wegner, 2002)? Is it incompatible with determinism (Nichols, 2011)? Can people be morally responsible without it (Greene & Cohen, 2004)? However, what is the "it" in each of these questions? The "it" is the folk concept of free will. It is this concept that is suspected to be an illusion, incompatible with determinism, and required for moral responsibility. Unfortunately, scholars know very little about what constitutes this ordinary concept of free will. We therefore need clarity both on the concept and the underlying phenomenon, and in doing so we must go beyond philosophers' and scientists' intuitions. We must empirically examine ordinary people's conceptualization of free will and their application of this concept in everyday life. Without taking seriously the actual folk concept of free will, any theory of free will is at "risk of having nothing more than a philosophical fiction as its subject matter" (Mele, 2001, p. 27). Science and philosophy might discover facts that suggest revisions to the folk concept of free will; but without knowing what the concept is we can hardly revise it. * This chapter was made possible through the support of a grant from the Big Questions in Free Will project, funded by the John Templeton Foundation. The opinions expressed here are our own and do not necessarily reflect the views of the John Templeton Foundation.Surrounding Free Will, Edited by Alfred Mele, 01/2014: chapter Free will without metaphysics; Oxford University Press.
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- "(2) Unlike initially thought, DC potentials similar to the BP can also occur before externally cued movements (Thickbroom et al., 1985; Keller and Heckhausen, 1990; Jahanshahi et al., 1995; Herrmann et al., 2008). Furthermore, they can be observed before expected external stimuli without movements (Brunia, 1988) or even before participants decide not to move (Trevena and Miller, 2010). In these latter cases, the DC potentials are usually not named BP but contingent negative variation (CNV) or stimulus preceding negativity (SPN), due to the different context of occurrence. "
ABSTRACT: Since Libet's seminal observation that a brain potential related to movement preparation occurs before participants report to be aware of their movement intention, it has been debated whether consciousness has causal influence on movement decisions. Here we review recent advances that provide new insights into the dynamics of human decision-making and question the validity of different markers used for determining the onset of neural and conscious events. Motor decisions involve multiple stages of goal evaluation, intention formation, and action execution. While the validity of the Bereitschaftspotential (BP) as index of neural movement preparation is controversial, improved neural markers are able to predict decision outcome even at early stages. Participants report being conscious of their decisions only at the time of final intention formation, just before the primary motor cortex starts executing the chosen action. However, accumulating evidence suggests that this is an artifact of Libet's clock method used for assessing consciousness. More refined methods suggest that intention consciousness does not appear instantaneously but builds up progressively. In this view, early neural markers of decision outcome are not unconscious but simply reflect conscious goal evaluation stages which are not final yet and therefore not reported with the clock method. Alternatives to the Libet clock are discussed that might allow for assessment of consciousness during decision making with improved sensitivity to early decision stages and with less influence from meta-conscious and perceptual inferences.Frontiers in Human Neuroscience 07/2013; 7:385. DOI:10.3389/fnhum.2013.00385 · 2.90 Impact Factor