Endogenous control of task-order preparation in variable dual tasks.

Dual-task performance typically leads to performance impairments in comparison to single tasks (i.e., dual-task costs). The literature discusses the contribution to these dual-task costs due to (1) bottleneck limitations in the dual-component tasks and (2) executive control processes regulating access to this bottleneck. Previous studies investigated the characteristics of executive control processes primarily triggered by external stimulus information. In the present study, however, we investigated the existence as well as the characteristics of internally triggered and driven endogenous control processes to regulate bottleneck access. In detail, we presented dual-task blocks with varying task orders and informed participants in advance about repetitions of the same task order as well as switches between different task orders (i.e., task-order repetitions and switches were predictable). Experiment 1 demonstrated that task-order information and an increased preparation time generally increase the efficiency for endogenous task-order control and improves preparation for task-order switches. This finding is basically consistent with the assumption of the existence of endogenous control processes. Experiment 2, however, did not provide evidence that this endogenous control is related with working-memory maintenance mechanisms. Experiment 3 showed that endogenous control does not only fully complete task-order preparation but also requires exogenous, stimulus-driven components.