The Late CNV Wave: Preparation Versus Expectancy

Abstract

ABSTRACT Slow EEG potentials were recorded from different sites along the midline (F z , C z , P z ) in the S 1 ‐S 2 interval of a reaction time task. The effects of expectancy on the contingent negative variation (CNV) were investigated by varying the probability that S 2 would be presented. This probability which was indicated by S 1 , was either 0.9, 0.5, or 0.0. This was done under instructions governing the trade‐off between speed and accuracy. The combined effects of S 2 probability and instructions support the view that the early component of the CNV is a cortical component of the orientation reaction, whereas the late component is mainly determined by the level of motor preparation. The topographical distribution of the early CNV was more anterior than that of the late CNV, which corroborates earlier results.