Bivalent task switching and memory load: Similar costs on reaction times, different costs on concurrent timing

Some studies suggest that time estimation involves executive control resources. This proposition was challenged recently, however, by results showing simultaneous performance of executive and timing tasks with no cost. The present study examined whether bivalent switching, in which targets may be relevant in more than one task, would interfere with timing. In Experiment 1, the effect of switching between memory search and a classification task was compared with the effect of varying load in memory search. Effects of task switching and of increasing load were similar on reaction times (RTs) in an RT control condition, but drastically different on concurrent timing: Time productions were affected by memory search only. In Experiment 2, the effect of task switching preparation, which involves advance reconfiguration in the switching paradigm, was examined. Preparation to a switch and timing could be performed simultaneously with no cost. These results reveal a fundamental difference between memory search and task switching in terms of dual-task costs, and show that timing and some executive control tasks do not share cognitive resources.