Libet-style experiments, neuroscience, and libertarian free will

Abstract

People have disagreed on the significance of Libet-style experiments for discussions about free will. In what specifically concerns free will in a libertarian sense, some argue that Libet-style experiments pose a threat to its existence by providing support to the claim that decisions are determined by unconscious brain events. Others disagree by claiming that determinism, in a sense that conflicts with libertarian free will, cannot be established by sciences other than fundamental physics. This paper rejects both positions. First, it is argued that neuroscience and psychology could in principle provide support for milder deterministic claims that would also conflict with libertarian free will. Second, it is argued that Libet-style experiments—due to some of their peculiar features, ones that need not be shared by neuroscience as a whole—currently do not (but possibly could) support such less demanding deterministic claims. The general result is that neuroscience and psychology could in principle undermine libertarian free will, but that Libet-style experiments have not done that so far.

Keywords:

• Benjamin Libet
• determinism
• free will
• libertarianism
• neuroscience

Acknowledgements

For comments, I thank Gilberto Gomes, Alfred Mele, Frank Sautter, Rogério Severo, and four anonymous referees. Thanks also to Eddy Nahmias and Adina Roskies for their comments at the 2015 Minds Online Conference, and to Ricardo di Napoli, Gilson Olegario, Danilo Dantas, Lucas Roisenberg, Márlon Teixeira, Cristina Nunes, Lucas Dalsotto, and Rafael Cortes for discussion. This work has been financially supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) [grant number BEX 4789/15-6], and by Fulbright Brasil.

Notes

1. This information refers only to what Libet calls “type II” RP, that is, RPs preceding movements for which subjects reported no previous planning of when to move. For other conditions, see Libet and colleagues (1982, 1983). It is worth noting that both the specific measurements and the implications for free will of Libet’s results are a matter of dispute. On the former, mentioned difficulties include the effects of instructions and training during the experiments, and subjects’ ability to accurately report the time of decisions (see Banks & Isham, 2011; Gomes, 1998; Maoz et al., 2015). Questions related to the latter point include the representativeness and significance of finger flexions for free will, the precise nature of the mental phenomena investigated, and various others (see Mele, 2006, 2009 and the essays in Mele, 2015; Pockett, Banks, & Gallagher, 2006, part 2; Sinnott-Armstrong & Nadel, 2011; and most of what is discussed below).

2. This is a modified and simplified version of an analysis of causal laws developed by Davidson (2001, p. 158).

3. Strictly speaking, the subject would be unable not to choose to push the given button. The logical possibility (whatever its empirical plausibility) remains that the subject could simultaneously make other, unrelated decisions. What is usually taken to be relevant in the free will debate, however, is the possibility of not choosing in a particular way. For example, it could be that the murderer in Chisholm’s example could choose both to shoot and to shoot with a black (rather than, say, a gray) gun. But this additional choice would not make the shooting free on his account. The relevant possibility for free will would still be that of not choosing to shoot.

4. Pockett and Purdy say that “waveforms that look like RPs have been known for decades to occur before a variety of expected events that are not movements” (2011, pp. 36–37). This suggests that RPs in fact are not uniquely related to decisions to “flex now.” It should also be mentioned that Libet’s experiments on “veto” conditions—when subjects were instructed to prepare to move at a prearranged time and, shortly before, block that preparation—indicated that a great initial portion of an RP of type I may not be followed by actual movement (see Libet, 1985, pp. 537–538, especially figure 2).

5. As I have noted earlier, controversies remain in the philosophical debate on compatibilism versus incompatibilism, as well as in the experimental research on laypersons’ beliefs about free will. On the latter, see Andow and Cova (in press); Deery, Davis, and Carey (2014); Feltz and Cova (2014); Nahmias, Coates, and Kvaran (2007); Nahmias, Morris, Nadelhoffer, and Turner (2006); Nahmias (2014a); Nichols and Knobe (2007); and Rose and Nichols (2013).