Abstract
By means of a new visuo-motor synchronization paradigm we test the frequently made proposition that one's feeling of having voluntarily made a decision to act is in fact postdictively established contingent on the outcome of his action rather than on its aim. Subjects had to (1) synchronize a key-press with the end of a random synchronization interval (SI) shorter or longer than their reaction time (RT) and (2) judge thereafter whether (Q1) SI had been long enough to allow synchronization, (Q2) their motor response had been “reactive” (i.e., close to their RT) or delayed, or (Q3) whether SI was short or long. SI was denoted by the filling-up time of an annular “gauge.” In principle, the “synchronization” key-press should be reactive for SI ≤ RT and delayed in proportion with SI for SI > RT. Instead, response time distributions were bimodal for the shortest (0 ms) and longest (500 ms) SIs and widely spread for intermediate SIs. To all three questions asked, subjects’ responses strongly correlated with SI itself (r = 0.62−0.76) and barely with their actual response times (r = 0.03−0.42). Hence subjects’ introspective judgments on their trial-by-trial potential capability to synchronize their motor response (Q1) and on their reactive vs. delayed response mode reflected the objective cause of their action rather than being “corrupted” by its outcome (namely their actual response time). That subjects could not reliably decide whether their motor response was reactive or delayed implies that they did not have retrospective access to (or did not remember) their motor decisions which amounts to say that they could not decide on the intentionality of their actions.
Highlights
There are claims in the field of voluntary action that the sense of agency and of volition relies on a post-hoc evaluation of performed actions rather than on predictive mental processes
While the source of this bimodality is of critical interest in understanding the synchronization process, it is of little relevance for the present topical issue
That the means of the fastest response time (RsT) distributions averaged over the five subjects for synchronization interval (SI) = 0 (249 ± 29.8 ms) are close to and not significantly different from their mean reaction time (RT) assessed in the two preliminary (RT) experiments (230.6 ± 13 and 242.6 ± 12.1 ms)
Summary
There are claims in the field of voluntary action that the sense of agency and of volition relies on a post-hoc (i.e., non-causal) evaluation of performed actions rather than on predictive mental processes (see reviews by Wegner and Wheatley, 1999; Wegner, 2002; Haggard, 2005, 2008, 2009; Knoblich and Sebanz, 2005; Hallett, 2007). Most of the empirical approaches to the predictive–postdictive debate capitalized on the comparison between the introspected timing of the decision/intention to act and the timing of that action’s precursory neural activity (Libet, 1993; Lau et al, 2007; Haggard, 2008, 2009) This literature consistently showed that the introspected decision timing trails (sometimes by seconds; Soon et al, 2008) the timing of premotor activity. The method capitalizes on subject’s retrospective judgments on the feasibility of a just executed synchronization motor task and on whether this task had been executed in a speeded/“reactive” or delayed/“intentional” mode Such distinction is not more conceptually debatable (Pashler, 1998; Nachev et al, 2008; Haggard, 2009) than the notion of volition/free will itself, an introspective belief. The present data show that they do not
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