Abstract
A gradual buildup of electrical potential over motor areas precedes self-initiated movements. These “readiness potentials” (RPs) could simply reflect stochastic fluctuations in neural activity. We operationalised self-initiated actions as endogenous ‘skip’ responses while waiting for target stimuli in a perceptual decision task. Across-trial variability of EEG decreased more markedly prior to self-initiated compared to externally-triggered skip actions. This convergence towards a fixed pattern suggests a consistent preparatory process prior to self-initiated action. A leaky stochastic accumulator model could reproduce these features of the data, given the additional assumption of a decrease in noise level at the input to the accumulator prior to self-initiated, but not externally-triggered actions. The assumed reduction in neural noise was supported by analyses of both within-trial EEG variability and of spectral power. We suggest that a process of noise reduction is consistently recruited prior to self-initiated action. This precursor event may underlie the emergence of RP.
Footnotes
NK is currently at Department of Experimental Psychology, University of Oxford, Oxford, UK AD is currently at Laboratoire Psychologie de la Perception, Universite Paris Descartes & CNRS (UMR 8242), Paris, France