Timing and reaction time

Because reaction time (RT) tasks are generally repetitive and temporally re gular, participants may use timing strategies that affect response speed an d accuracy. This hypothesis was tested in 3 serial choice RT experiments in which participants were presented with stimuli that sometimes arrived earl ier or later than normal. RTs increased and errors decreased when stimuli c ame earlier than normal, and RTs decreased and errors increased when stimul i came later than normal. The results were consistent with an elaboration o f R. Ratcliff's diffusion model (R. Ratcliff, 1978; R. Ratcliff & J. N. Rou der, 1998; R. Ratcliff, T. Van Zandt, & G. McKoon, 1999), supplemented by a hypothesis developed by D. Laming (1979a, 1979b), according to which parti cipants initiate stimulus sampling before the onset of the stimulus at a ti me governed by an internal timekeeper. The success of this model suggests t hat timing is used in the service of decision making.