Preparation for action: an ERP study about two tasks provoking variability in response speed.

This study focused on the covariation of response speed and event-related potentials during response preparation and on whether these variations can be brought under experimental control. Two S1-S2 choice response tasks with temporal uncertainty were conducted. In Experiment 1, S1 was 100% informative. Fast subjects showed larger P3s with S1 than slow subjects. The terminal CNV (tCNV) increased intraindividually with response speed. In Experiment 2, 50% of S1s were uninformative and the visual display was designed to attract more attention. Effects of information were found on P3 amplitude, on the topography of tCNV, and on the temporal distribution of response times. Interindividual differences disappeared in Experiment 2. The results suggest that group differences in Experiment 1 were due to different strategies of allocating visual attention. Interindividual variations of strategy showed a pattern of effects different from intraindividual variations of efficiency.