The time course of effort mobilization and strategic adjustments of response criteria

In two-choice reaction time experiments, participants were instructed within a variable precueing interval to speed up responding in 20% of trials and to maintain their basic level of performance in the remaining trials. The achievement of this goal was rewarded by a monetary bonus. The requirement to speed up was signaled at varying intervals before the onset of the imperative stimulus. The main questions to be answered were whether participants would be able to dynamically adjust their response speed, and if so, whether a speed up would be due to enhanced effort with a genuine improvement of performance or due to an adjusted response criterion, accompanied by a speed-accuracy trade-off. The data of both experiments suggest that participants were able to invest some extra effort, the amount of which varied as a function of the length of the precueing interval. This speed-up was evident already in the fastest bins of the reaction time distribution, indicating a continuous modulation of processing efficiency. Only in the first experiment was there clear evidence for a speed-accuracy trade-off in addition to effort mobilization.