Two types of between-task conflict trigger respective processing adjustments within one dual-task.

In dual tasking, two different kinds of between-task conflict occur. Because in both cases, Task 2 characteristics affect Task 1 performance, they are commonly referred to as backward crosstalk effects (BCE): One with a conflict at the response selection stage when Task 1 and Task 2 have dimensional overlap (the compatibility-based BCE) and one with a conflict at the motor execution stage when response inhibition resulting from a Task 2 no-go-trial interferes with simultaneous response execution in Task 1 (the no-go BCE). Recent research suggests that these BCEs differ not only in their underlying cognitive processes, but also in how cognitive control is regulated. Here, we investigated whether both can be produced in a single dual-task set up and whether they trigger their respective processing adjustments (i.e., a sequential modulation). In three experiments, participants categorized numbers as smaller or larger than 5 in Task 1. In Experiments 1 and 2, numbers were responded to irrespective of numerical size (go-response) as Task 2. Further, dimensional overlap was provided by (non)corresponding size information in both stimuli, which was strengthened in Experiment 2 by presenting S1 and S2 in the same/different color in compatible/incompatible trials, respectively. In Experiment 3, participants were required to perform a number-size categorization also in Task 2, establishing strong dimensional overlap by activating the same or different response categories in both tasks. In all three experiments, the number 5 served as the no-go stimulus in Task 2 to induce a no-go BCE on Task 1. By and large, our results show that both types of between-task conflicts not only occur within the same type of BCE, but they also trigger their respective sequential modulation.