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When simultaneously performing two tasks that share response properties, interference can occur. Besides general performance decrements, performance in the first task is worse when the second task requires a spatially incompatible response, known as the backward crosstalk effect (BCE). The size of this BCE, similar to congruency effects in conflict tasks, is subject to a sequential modulation, with a smaller BCE after incompatible compared to compatible trials. In the present study, we focus on a potential bidirectional interaction between crosstalk (and its resolution) at a lower level of task performance and higher-order processes of task organization. Two questions were of particular interest: First, do participants switch task order more frequently after a conflict-prone incompatible trial than after a compatible trial? Second, does changing task order influence the efficiency of conflict resolution, as indexed by the size of the sequential modulation of the BCE. Across four experiments, we only found marginal evidence for an influence of lower-level conflict on higher-order processes of task organization, with only one experiment revealing a tendency to repeat task order following conflict. Our results thus suggest practical independence between conflict and task-order control. When separating processes of task selection and task performance, the sequential modulation was generally diminished, suggesting that conflict resolution in dual-tasks can be disrupted by a deliberate decision about task order, or, alternatively, by a longer inter-trial interval. Finally, the study found a strong bias towards repeating the same task order across trials, suggesting that task-order sets not only impact task performance but also guide task selection.

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When the performance of two tasks overlaps in time, performance impairments in one or both tasks are common. Various theoretical explanations for how component tasks are controlled in dual-task situations have been advanced. However, less attention has been paid to the issue of how two temporally overlapping tasks are appropriately coordinated in terms of their order. The current study focuses on two specific aspects of this task-order coordination: (1) the potential effects of practice on task-order coordination performance and (2) its relationships with cognitive meta-control mechanisms that adjust this coordination. These aspects were investigated in a visual-auditory dual-task combination with randomly changing task orders across trials after four sessions of dual-task practice (N = 24) and single-task practice (N = 24). The results demonstrated that task-order coordination improves during dual-task practice, and in contrast to the effects of single-task practice. Practice, on the other hand, did not show substantial evidence of an effect on the adjustment of task-order coordination. This practice-related dissociation is consistent with the assumption that (1) task-order coordination and (2) its sequential adjustment are separable sets of processes.

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When two tasks are presented simultaneously or in close succession, such as in the overlapping task paradigm of the psychological refractory period, dual-task performance on those tasks is usually impaired compared with separate single-task performance. Numerous theories explain these emerging dual-task costs in terms of the existence of capacity limitations in the constituent component tasks. The current paper proposes active dual-task coordination processes that work on the scheduling of these capacity-limited processes. Further, there are recent findings that point to a meta-cognitive control level in addition to these active coordination processes. This additional level's responsibility is to adjust the dual-task coordination of capacity-limited stages (i.e., coordination adjustment). I review evidence focusing on the existence of dual-task coordination processes and processes of coordination adjustment. The remainder of the paper elaborates on preliminary findings and points to the separability of these sets of processes, which is a key assumption of the framework of dual-task coordination adjustment.

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An important cognitive requirement in multitasking is the decision of how multiple tasks should be temporally scheduled (task order control). Specifically, task order switches (vs. repetitions) yield performance costs (i.e., task-order switch costs), suggesting that task order scheduling is a vital part of configuring a task set. Recently, it has been shown that this process takes specific task-related characteristics into account: task order switches were easier when switching to a preferred (vs. non-preferred) task order. Here, we ask whether another determinant of task order control, namely the phenomenon that a task order switch in a previous trial facilitates a task order switch in a current trial (i.e., a sequential modulation of task order switch effect) also takes task-specific characteristics into account. Based on three experiments involving task order switches between a preferred (dominant oculomotor task prior to non-dominant manual/pedal task) and a non-preferred (vice versa) order, we replicated the finding that task order switching (in Trial N) is facilitated after a previous switch (vs. repetition in Trial N - 1) in task order. There was no substantial evidence in favor of a significant difference when switching to the preferred vs. non-preferred order and in the analyses of the dominant oculomotor task and the non-dominant manual task. This indicates different mechanisms underlying the control of immediate task order configuration (indexed by task order switch costs) and the sequential modulation of these costs based on the task order transition type in the previous trial.

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BACKGROUND: Dual-tasking procedures often involve the successive presentation of two different stimuli, requiring participants to execute two tasks in a particular order. Performance in both tasks suffers if the order of the tasks is reversed (i.e., switched) compared to the directly preceding trial. This task-order switch cost is reduced, however, if the preceding trial itself involved a task-order switch compared to a task-order repetition (Strobach in Acta Psychol 217:103328, 2021). Theoretical accounts range from assumptions of top-down implementation of a task-order control set, or passive persistence thereof, to priming based on episodic binding of tasks and temporal positions. Here, we tested these accounts by investigating whether the sequential modulation decays as a function of the inter-trial interval. METHODS AND RESULTS: Task-order switch costs were reliably reduced after a task-order switch (compared to after a task-order repetition) and this reduction did not decrease over inter-trial intervals ranging from 350 ms to 1,400 ms. Also replicating previous findings, for reaction times the reduction was driven by selective slowing in task-order repeat trials, suggesting increased response caution. CONCLUSIONS: Our results are consistent with preparatory processes of task-order control or with episodic integration of task-order information but argue against accounts assuming short-lived, decaying task-order sets.

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In situations requiring the execution of two tasks at around the same time, we need to decide which of the tasks should be executed first. Previous research has revealed several factors that affect the outcome of such response order control processes, including bottom-up factors (e.g., the temporal order of the stimuli associated with the two tasks) and top-down factors (e.g., instructions). In addition, it has been shown that tasks associated with certain response modalities are preferably executed first (e.g., temporal prioritisation of tasks involving oculomotor responses). In this study, we focused on a situation in which task order has to be unpredictably switched from trial to trial and asked whether task-order representations are coded separately or integrated with the component task sets (i.e., in a task-specific manner). Across three experiments, we combined two tasks known to differ in prioritisation, namely an oculomotor and a manual (or pedal) task. The results indicated robust task-order switch costs (i.e., longer RTs when task order was switched vs. repeated). Importantly, the data demonstrate that it is possible to show an asymmetry of task-order switch costs: While these costs were of similar size for both task orders in one particular experimental setting with specific spatial task characteristics, two experiments consistently indicated that it was easier for participants to switch to their prioritised task order (i.e., to execute the dominant oculomotor task first). This suggests that in a situation requiring frequent task-order switches (indicated by unpredictable changes in stimulus order), task order is represented in an integrated, task-specific manner, bound to characteristics (here, associated effector systems) of the component tasks.

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Performing two tasks simultaneously involves the coordination of their processing. Task coordination is particularly required in dual-task situations with varying order of the component tasks. When task order switches between subsequent trials, task-order coordination leads to order switch costs in comparison to task order repetitions (i.e., worse performance in trials associated with an order switch compared to an order repetition). However, the adaptive characteristics of task-coordination processes and order switch costs are underspecified so far. For example, studies on conflict control have shown that these coordination processes can be modulated in response to changes in task demands. The present study investigated therefore whether task-order coordination processes are modulated by the previous experience of a task-order switch. To investigate order switch costs in a dual-task situation with two sensorimotor tasks with variable task-order, we analyzed performance in current trials with task-order switches and with task-order repetitions following task-order switches and task order repetitions in the preceding trial. The data of four different experimental conditions showed that order switch costs were reduced in trials following task-order switches compared to task-order repetitions; resembling the Gratton effect commonly observed in conflict adaptation paradigms. We discussed the present results in the context of task-order set representations, cognitive control theories, and dual-task models.

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When humans are required to perform two or more tasks concurrently, their performance declines as the tasks get closer together in time. Here, we investigated the mechanisms of this cognitive performance decline using a dual-task paradigm in a simulated driving environment, and using drift-diffusion modeling, examined if the two tasks are processed in a serial or a parallel manner. Participants performed a lane change task, along with an image discrimination task. We systematically varied the time difference between the onset of the two tasks (Stimulus Onset Asynchrony, SOA) and measured its effect on the amount of dual-task interference. Results showed that the reaction times (RTs) of the two tasks in the dual-task condition were higher than those in the single-task condition. SOA influenced the RTs of both tasks when they were presented second and the RTs of the image discrimination task when it was presented first. Results of drift-diffusion modeling indicated that dual-task performance affects both the rate of evidence accumulation and the delays outside the evidence accumulation period. These results suggest that a hybrid model containing features of both parallel and serial processing best accounts for the results. Next, manipulating the predictability of the order of the two tasks, we showed that in unpredictable conditions, the order of the response to the two tasks changes, causing attenuation in the effect of SOA. Together, our findings suggest higher-level executive functions are involved in managing the resources and controlling the processing of the tasks during dual-task performance in naturalistic settings.

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Task preparation in dual-tasking is more complex than preparation for single tasks and involves additional factors such as task prioritization. Utilizing event-related potentials, we sought to disentangle preparatory processes involving preparation on the subtask level and the superordinate dual-task level. Participants worked on a psychological refractory period paradigm in which two temporally overlapping tasks have to be completed in a specified order. Whereas dual-task-related preparation was measured by comparing task-order switches and repetitions, subtask preparation was isolated through error precursors for the individual subtasks. We found that a switch-related posterior positivity was linked to the preparation of the superordinate dual-task set. In contrast, an early frontal modulation and a stimulus-preceding negativity were markers of subtask preparation of Task 1 and Task 2, respectively. Our study provides neural evidence for a hierarchical system of control processes in dual-tasking and confirms assumptions from earlier behavioral and computational studies on strategic task prioritization.

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Using an original conflict task paradigm, Nassauer and Halperin (2003) argued that inhibition ability can be classified into two distinct perceptual and motor inhibitory processes. The current study examined the robustness of this paradigm by raising two major methodological points: the amount of information that needs to be processed and the task order (fixed vs. random). Sixty young adults performed the original or modified tasks. Overall, a decrease in the amount of information had the effect of removing the stimulus conflict on some subtests. Therefore, no more inhibition performance could be assessed. Even if the findings can be interpreted as a change in response-related complexity that relates reaction time performance to the informational processing load, the discrepancies in terms of the amount of information originally designed are necessary to induce inhibitory conflicts. Additionally, unlike previous recommendations, the fixed task order initially adopted cannot be considered an essential methodological requirement.

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