Influences between the contingent negative variation and the preceding readiness potential.

Contingent negative variation (CNV) is a slow negative shift in the potential, developing in the period of association between the warning and the imperative stimulus. The readiness potential (RP) resembles the CNV in morphology and amplitude and appears before the performance of a voluntary action. When RP precedes the appearance of the warning stimulus, CNV amplitude reaches considerably lower values. This phenomenon could be explained with the assumptions about a common neuronal pool of McAdam (1971) and with the "ceiling" hypothesis of Hamilton et al. (1973). The aim of the present study is to examine the effect of time intervals with different duration between RP and CNV. A decrease in the amplitude of CNV following RP has been found, without statistically significant differences depending on the interval between them. A more significant influence is observed on CNV morphology: in addition to a decrease in the amplitude, there is also a transition from type B to type A CNV when it is preceded by RP. Under conditions of a more complicated task involving combination with CNV, the RP itself shows lower values compared with the case of independent generation. This gives grounds for the conclusion that the complexity and the complex requirements of the task determine the value of the negatively directed slow-potential changes.