Are Voluntary Movements Initiated Preconsciously? The Relationships between Readiness Potentials, Urges, and Decisions

Libet's data show that EEG readiness potentials begin before the urge to move is consciously felt. This result has been widely interpreted as showing that spontaneous voluntary movements are initiated preconsciously. This chapter reports two new findings relevant to this conclusion. First, the question of whether readiness potentials (RPs) are precursors of movement per se or merely indicators of general readiness has always been moot. On the basis of both new experimental evidence and an inspection of the literature, it is argued that Libet's type II RPs 1 are neither necessary nor sufficient for spontaneous voluntary movement. Secondly, it argues that RPs often do not occur at all before movements initiated as a result of decisions, as opposed to spontaneous urges. When RPs do occur before decision-based movements, they are much shorter than urge-related RPs, and usually start at the same time as or slightly after the reported decision times. Thus, even if this third, shorter type of RP could be considered to relate specifically to movement rather than to general readiness, movements resulting from conscious decisions (as opposed to spontaneous urges) are unlikely to be initiated preconsciously.