Electrophysiological evidence for the effect of prior probability on response preparation.

We investigated whether prior probability (PP) information modulates preparatory processes at a central premotor level or at a peripheral motor level. We provided parametrically graded probability information during the foreperiod of a precuing paradigm. The Contingent Negative Variation (CNV) and the Lateralized Readiness Potential (LRP) were used as indicators for premotor and motor preparation during the foreperiod, respectively. The CNV amplitude was parametrically modulated by PP. In contrast, the LRP amplitude during the foreperiod differed from baseline only when the precue was reliable. The interval between precue and LRP onset was shortened when probability information was delivered in contrast to noninformative advance information. Furthermore, a source analysis for the foreperiod revealed a dipole in the anterior cingulate cortex. Together, our results suggest that PP modulates preparatory processes at a central premotor level.