Effects on contingent negative variation of set created by anticipating variable foreperiods.

The influence of set on a simple reaction time task was examined by comparing the differences of psychological factors between a group of subjects who expected and experienced a fixed foreperiod Control condition: 12 subjects) and another group of subjects who were instructed to expect variable foreperiods but experienced the same fixed foreperiod (Instruction condition: 11 subjects), using the index of contingent negative variation (CNV). The foreperiod of simple reaction time task in each condition was fixed at 3 sec. Subjects were required to respond to 2 blocks of 24 trials, and each instruction was presented between blocks. On the second block CNV amplitudes were higher in the instruction condition as was every CNV component (early late, and whole component). The set created by anticipating variable foreperiods seems to increase cerebral activity, arousal, and attention during simple reaction time tasks.