Direct-current Potentials in the Human Brain evoked during Timed Cognitive Performance

Abstract

WALTER et al.¹ observed that when a human subject is presented with two sequentially paired stimuli so that the first serves to signal the occurrence of the second, a negative d.c. shift occurs during the interval between the stimuli in an averaged scalp EEG recording; he termed this phenomenon the “contingent negative variation” (CNV). CNV is frequently elicited with fixed foreperiod decision tasks, which may be said to include a “hold” phase, from the warning signal (WS) to the task stimulus (TS), and an “operate” phase, following the TS and terminating with the subject's response (R) to the TS (Fig. 1). CNV definitely occurs during the hold phase, so long as the subject is motivated and the task is sufficiently difficult^2–6, but it has not been demonstrated that CNV is present during the operate phase. The tasks used in previous experiments have been so simple that TS and R occurred virtually simultaneously, and it could not be determined whether the termination of CNV covaries with the TS (the end of the hold phase) or with R (the end of the operate phase). In these experiments CNV was averaged during several complex cognitive tasks with considerably longer operate phases, and found to persist throughout the operate phase, for periods ranging up to 8 s after the TS.