ABSTRACTTwo experiments were performed to explore further the relationship between the cortical slow potential change known as the “contingent negative variation” (CNV) and the concept of “expectancy.”In Experiment I, 24 maleSs were presented click pairs, with inter‐click intervals of 800, 1600 and 4800 msec (2 blocks of 10 trials each, counterbalanced betweenSs for order), and instructed to press a key after the second click. Interval by order by trials analysis of variance showed interval to be the only significant factor: CNVs were lower and RTs longer as interval increased.In Experiment II, 8 femaleSs given 60 pairs of clicks, 30 each with separations of 1200 and 2400 msec, were instructed to respond as in Experiment I, and were asked to make a pretrial prediction of the interval they would next receive. Analysis of variance of RTs showed thatSs responded slower when the interval was other than that predicted. Prediction by reception by subjects analysis of variance of CNV amplitude at the 1200 msec point gave a significantFonly for prediction, mean amplitude forshortbeing higher than forlong. A similar design applied to CNV amplitudes at both the 1200 and 2400 msec points whenSs received thelonginterval yielded a significant measurement point by interval predicted interaction; at the 1200 msec point,shortpredictions were followed by higher CNVs than werelongpredictions; at 2400 msec, the opposite was found.These data combine with those already in the literature to indicate that the relationship between “expectancy” and the CNV is far from simple, and that cognitive and motivational factors play a significant role in determining