Dual-tasking often requires prioritizing one task over the other. For example, in the psychological refractory period (PRP) paradigm, participants are instructed to initially respond to Task 1 (T1) and only then to Task 2 (T2). Furthermore, in the prioritized processing paradigm (PP), participants are instructed to perform T2 only if T1 was a no-go trial—requiring even more prioritization. The present study investigated the limits of task prioritization. Two experiments compared performance in the PRP paradigm and the PP paradigm. To manipulate task prioritization, tasks were rewarded differently (e.g., high reward for T1, low reward for T2, and vice versa). We hypothesized (a) that performance will improve for the highly rewarded task (Experiments 1 and 2) and (b) that there are stronger reward effects for T1 in the PRP than in the PP paradigm (Experiment 2). Results showed an influence of reward on task prioritization: For T1, high reward (compared to low reward) caused a speed-up of responses that did not differ between the two paradigms. However, for T2, reward influenced response speed selectively in the PP paradigm, but not in the PRP paradigm. Based on paradigm-specific response demands, we propose that the coordination of two motor responses plays a crucial role in prioritizing tasks and might limit the flexibility of the allocation of preparatory capacity.
