Effects of a neutral warning signal on spatial two-choice reactions.

Posner et al. reported that, at short fixed foreperiods, a neutral warning tone reduced reaction times (RTs) in a visual two-choice task while increasing error rates for both spatially compatible and incompatible stimulus-response mappings. Consequently, they concluded that alertness induced by the warning does not affect the efficiency of information processing but the setting of a response criterion. We conducted two experiments to determine the conditions under which the trade-off occurs. In Experiment 1, participants performed the same two-choice task as in Posner et al.'s study without RT feedback. Results showed that the warning tone speeded responses with no evidence of speed/accuracy trade-off. In Experiment 2, RT feedback was provided after each response, and a speed/accuracy trade-off was found for the 50-ms foreperiod. However, better information-processing efficiency was evident for the 200-ms foreperiod. We conclude that the foreperiod effect of a 50-ms foreperiod is a result of response criterion adjustment and that providing trial-level RT feedback is critical for replicating this pattern. However, fixed foreperiods of 200 ms or longer benefit both speed and accuracy, implying a more controlled preparation component that improves response efficiency.