“Free will”: are we all equal? A dynamical perspective of the conscious intention to move

In their seminal (1983) study, Libet and colleagues suggested that awareness of one’s intention to act has a postdictive character in that it occurs long after cerebral activity leading to action has been initiated. Crucially, Libet et al. further suggested that the time window (±200 ms) between the conscious experience of the intention to act and the action itself offers people the possibility of “vetoing” the unfolding action. This raises the question of whether there are individual differences in the duration of this “veto window” and which components of the readiness potential (RP) and the lateralized readiness potential (LRP) explain this variability. It has been reported that some psychiatric diseases lead to shorter intervals between conscious intentions and actions. However, it is unclear whether such patients suffer from impairment of the sense of volition, thus experiencing voluntary movements as involuntary, or whether voluntary inhibition of action is actually reduced, since conscious intention occurs later. We had two aims in the present paper. First, we aimed at clarifying the role of consciousness in voluntary actions by examining the relation between the duration of the veto window and impulsivity. Second, we sought to examine different components of the RP and LRP waveforms so as to attempt to explain observed variability in W judgments. Our results indicate (1) that impulsive people exhibit a shorter delay between their intention and the action than non-impulsive people, and (2) that this difference can hardly be attributed to a difference in time perception. Electroencephalography indicated that the rate of growth of the RP is relevant to explain differences in W judgments, since we observed that the RP at the moment of conscious intention is lower for people with late conscious intention than for people with early conscious intention. The onset and the intercept of these waveforms were less interpretable. These results bring new light on the role that consciousness plays in voluntary action.