The effect of warning stimulus novelty on the P300 and components of the contingent negative variation.

Studied 12 male university students to evaluate the effects of stimulus and response probability on the P300 and on components of the contingent negative variation (CNV) in 3 different reaction tasks. In the 1st task the warning stimulus (S1) indicated that the imperative stimulus (S2) would require either a left or right buttonpress response; in the 2 other tasks the S1 indicated that S2 would either require a buttonpress response or not. The a priori probability of S1 and the response to S2 were independently varied. Results show that a novel S1 significantly increased the amplitude and latency of the P300 and early CNV component: the late CNV component, however, increased significantly when a motor response to S2 was required. Early and late CNV components also differed in midline distribution. It is concluded that the early CNV can be viewed as the slow wave part of the event-related potential to S1, while the late CNV is an event preceding shift that strongly relates to the motor requirements of S2. It is suggested that both the P300 and early CNV reflect an orienting response to S1.