For example, the RP may be related to and modulated by anticipation of the sensory and/or somatosensory consequences of the action and by awareness of movement intention. Numerous studies linking the RP to a variety of phenomena and experimental manipulations complicate its interpretation, especially as a phenomenon indicative of volition. Recent work suggests that the RP may be more prominent in arbitrary versus reason-based decisions.
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The spatial focus and amplitude of the RP are dependent on particulars of the experimental task, including movement effector, limb dominance, attention to timing of movement or the intention to move, and other task factors, including possibly beliefs in free will. The early component (~1500–400 ms prior to movement onset) is a slow but gradual increase in negativity, symmetrical between the two hemispheres, that has been attributed to activity in the supplementary motor area and premotor cortex, whereas the late component (~400–0 ms) is generated by activity in the primary motor cortex. The RP is commonly characterized as having an early and a late component. Libet’s classic study distinguished between two types of RPs: type I RPs, involving ‘preplanning’, had significantly earlier onsets (approximately 1000 ms prior to movement) than type II RPs, associated with spontaneous movement (approximately 500 ms prior), but cf who found the opposite to be true with a larger cohort of subjects. The empirical literature on the RP is vast and varied and difficult to fit under a single theoretical account. The Readiness Potential, Past and Present We review this recent literature and offer a reinterpretation of the nature of the signal that undermines its relevance for classic arguments against free will.
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However, recent literature raises questions about the RP’s ontological status as a real signal in the brain, its relation to action, its significance for arguments about volition, and its implications for free will. The RP has traditionally been interpreted as a sign of planning and preparation for movement and it is well-established as a reliable signal that precedes self-initiated movement in the group average.
In experiments that average data from multiple subjects making self-paced movements, the RP is highly replicable. The RP is prominent at central electrode sites located above mesial motor cortical areas and peaks contralateral to the moving limb. When EEG traces, recorded during such a task, are time-locked to movement onset and averaged together, a slow negative-going electrical potential is evident leading up to movement onset ( Box 1). Originally identified by Kornhuber and Deeke, the RP emerges from the analysis of electroencephalogram (EEG) data recorded during experimental tasks involving spontaneous or self-paced movements. Its existence has been used to argue against the possibility of free will. The readiness potential (RP) (see Glossary) or Bereitschaftspotential (BP) is a brain signal linked to voluntary movement.
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