Evaluation of a headphones-fitted EEG system for the recording of auditory evoked potentials and mental workload assessment.

Advancements in portable neuroimaging technologies open up new opportunities to gain insight into the neural dynamics and cognitive processes underlying day-to-day behaviors. In this study, we evaluated the relevance of a headphone- mounted electroencephalogram (EEG) system for monitoring mental workload. The participants (N = 12) were instructed to pay attention to auditory alarms presented sporadically while performing the Multi-Attribute Task Battery (MATB) whose difficulty was staged across three conditions to manipulate mental workload. The P300 Event-Related Potentials (ERP) elicited by the presentation of auditory alarms were used as probes of attentional resources available. The amplitude and latency of P300 ERPs were compared across experimental conditions. Our findings indicate that the P300 ERP component can be captured using a headphone-mounted EEG system. Moreover, neural responses to alarm could be used to classify mental workload with high accuracy (over 80%) at a single-trial level. Our analyses indicated that the signal-to-noise ratio acquired by the sponge-based sensors remained stable throughout the recordings. These results highlight the potential of portable neuroimaging technology for the development of neuroassistive applications while underscoring the current limitations and challenges associated with the integration of EEG sensors in everyday-life wearable technologies. Overall, our study contributes to the growing body of research exploring the feasibility and validity of wearable neuroimaging technologies for the study of human cognition and behavior in real-world settings.

The (Im)perfect Automation Schema: Who Is Trusted More, Automated or Human Decision Support?

OBJECTIVE: This study's purpose was to better understand the dynamics of trust attitude and behavior in human-agent interaction. BACKGROUND: Whereas past research provided evidence for a perfect automation schema, more recent research has provided contradictory evidence. METHOD: To disentangle these conflicting findings, we conducted an online experiment using a simulated medical X-ray task. We manipulated the framing of support agents (i.e., artificial intelligence (AI) versus expert versus novice) between-subjects and failure experience (i.e., perfect support, imperfect support, back-to-perfect support) within subjects. Trust attitude and behavior as well as perceived reliability served as dependent variables. RESULTS: Trust attitude and perceived reliability were higher for the human expert than for the AI than for the human novice. Moreover, the results showed the typical pattern of trust formation, dissolution, and restoration for trust attitude and behavior as well as perceived reliability. Forgiveness after failure experience did not differ between agents. CONCLUSION: The results strongly imply the existence of an imperfect automation schema. This illustrates the need to consider agent expertise for human-agent interaction. APPLICATION: When replacing human experts with AI as support agents, the challenge of lower trust attitude towards the novel agent might arise.

Human behavior and performance in deep space exploration: next challenges and research gaps.

As space exploration missions move from low orbit to distant destinations, including the Moon and Mars, new psychological, behavioral, and team challenges will arise. This manuscript represents an up-to-date white paper developed by European experts invited by the European Space Agency (ESA), mapping unfilled research gaps related to the psychology of space exploration, considering the incoming human missions, and accounting for the available scientific knowledge. ESA created the expert team and facilitated its work, but the team was completely independent in terms of contents. The white paper considers basic issues of adaptation, pre-, during-, and post-mission experiences, and possible countermeasures to be developed and tested. The resulting integrative map provides a guide for researchers that are interested in conducting research in the support of future space exploration endeavors.

A global and local perspective of interruption frequency in a visual search task.

We investigated the impact of frequency of interruptions in a simulated medical visual search task. Participants (N = 150) performed the visual search task during which they were interrupted by a number-classification task in 25, 50, or 75% of all trials, respectively, reflecting the frequency conditions (i.e., low, mid, high). Target presence (i.e., present vs. absent) and interruption (i.e., uninterrupted vs. interrupted) were varied within-subjects, and interruption frequency was varied between-subjects. Globally, on a frequency condition level, participants in the low frequency condition had longer mean response times (RT) for the primary visual search task than in the high condition, but there were no other performance differences between the three frequency conditions. Locally, on the level of specific interruption effects, accuracy decreased directly after interruptions for target present but not for target absent trials. Furthermore, interruptions caused significant interruption costs, reflected in slower overall RTs in interrupted than in uninterrupted trials. The combined findings show that especially for critical visual search tasks as in the medical field, interruptions-regardless of frequency-should be avoided.

Individual differences fill the uncharted intersections between cognitive structure, flexibility, and plasticity in multitasking.

It has been recently suggested that research on human multitasking is best organized according to three research perspectives, which differ in their focus on cognitive structure, flexibility, and plasticity. Even though it is argued that the perspectives should be seen as complementary, there has not been a formal approach describing or explaining the intersections between the three perspectives. With this theoretical note, we would like to show that the explicit consideration of individual differences is one possible way to elaborate in more detail on how and why the perspectives complement each other. We will define structure, flexibility, and plasticity; describe what constitutes individual differences; will outline selected empirical examples; and raise possible future research questions helping to develop the research field. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Sequential human redundancy: Can social loafing diminish the safety of double checks?

It is often assumed that if two people work on a failure-detection task one after the other, they will observe more failures than when only one person undertakes the task (4-eyes principle). However, human beings have also been found to exert less effort on tasks that they share responsibility for, a phenomenon called social loafing. In the current research, we assessed the effectiveness of sequential human redundancy in light of possible social loafing. In two laboratory experiments, teams of two participants performed a quality-control task in a blinded and in a nonblinded condition, operationally defined by whether or not evaluations of the first checker were forwarded to the second one. In the blinded condition, no social loafing was found, and a near-perfect overall team performance was observed. In contrast, nonblinded redundancy led to a substantial effort reduction of the second checker. However, despite this social-loafing effect at the second position, even nonblinded redundancy led to an overall safety advantage over a single-checker condition. Our research suggests that social loafing in sequential-human-redundancy work settings can occur but does not necessarily reduce the gains in overall reliability. Blinded processes, however, seem to provoke less social loafing than nonblinded processes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Understanding the Impact of Time Pressure and Automation Support in a Visual Search Task.

OBJECTIVE: To understand the impact of time pressure and automated decision support systems (DSS) in a simulated medical visual search task. BACKGROUND: Time pressure usually impairs manual performance in visual search tasks, but DSS support might neutralize this negative effect. Moreover, understanding the impact of time pressure and DSS support seems relevant for many real-world applications of visual search. METHOD: We used a visual search paradigm where participants had to search for target letters in a simulated medical image. Participants performed the task either manually or with support of a highly reliable DSS. Time pressure was varied within-subjects by either a trialwise time-pressure manipulation (Experiment 1) or a blockwise manipulation (Experiment 2). Performance was assessed based on signal detection measures. To further analyze visual search behavior, a mouse-over approach was used. RESULTS: In both experiments, results showed impaired sensitivity under high compared to low time pressure in the manual condition, but no negative effect of time pressure when working with a highly reliable DSS. Moreover, participants searched less under time pressure and when receiving DSS support, indicating participants followed the automation without thoroughly checking recommendations. However, the human-DSS team's sensitivity was always worse than that of the DSS alone, independent of the strength of time pressure. CONCLUSION: Negative effects of time pressure can be ameliorated when receiving support by a DSS, but joint overall performance remains below DSS-alone performance. APPLICATION: Highly reliable DSS seem capable of ameliorating the negative impact of time pressure in complex detection tasks.

Serial and parallel processing in multitasking: Concepts and the impact of interindividual differences on task and stage levels.

In multitasking research, a central question revolves around whether humans can process tasks in parallel. What "in parallel" refers to, however, differs between research perspectives and experimental approaches. From a task-level perspective, parallel processing can be conceived as to whether complete tasks are processed in an overlapping manner and how this impacts task performance. In contrast, a large body of literature solely focuses on the central stage of response-selection and whether it can run in parallel with other processing stages, an approach we refer to as the stage-level perspective. Importantly, although each perspective addresses related topics and highlights interindividual differences, they evolved through independent lines of research. In 2 experiments, we have taken a first step to investigate if individuals' tendencies for an overlapping versus serial processing mode on the task level are related to vulnerabilities for task interference on the stage level. Individual preferences for either task processing mode were assessed in the task switching with preview (TSWP) paradigm. Individuals' vulnerability for task interference was assessed with the backward crosstalk effect (BCE) in a classical dual task. Our results suggest that individuals who prefer overlapping relative to serial task processing at the task level are less vulnerable to task interference during response selection, indicated by a smaller BCE. This difference, however, only emerged in the second experiment with an increased sample size and with task-stimuli that facilitate a bottom-up separation of tasks in the dual-task. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Challenging presumed technological superiority when working with (artificial) colleagues.

Technological advancements are ubiquitously supporting or even replacing humans in all areas of life, bringing the potential for human-technology symbiosis but also novel challenges. To address these challenges, we conducted three experiments in different task contexts ranging from loan assignment over X-Ray evaluation to process industry. Specifically, we investigated the impact of support agent (artificial intelligence, decision support system, or human) and failure experience (one vs. none) on trust-related aspects of human-agent interaction. This included not only the subjective evaluation of the respective agent in terms of trust, reliability, and responsibility, when working together, but also a change in perspective to the willingness to be assessed oneself by the agent. In contrast to a presumed technological superiority, we show a general advantage with regard to trust and responsibility of human support over both technical support systems (i.e., artificial intelligence and decision support system), regardless of task context from the collaborative perspective. This effect reversed to a preference for technical systems when switching the perspective to being assessed. These findings illustrate an imperfect automation schema from the perspective of the advice-taker and demonstrate the importance of perspective when working with or being assessed by machine intelligence.

Effects of complexity and similarity of an interruption task on resilience toward interruptions in a procedural task with sequential constraints.

The goal of the present study was to examine effects of complexity and similarity of an interruption task on postinterruption performance in an 8-step procedural task with sequential constraints. In Experiment 1, the primary task was interrupted between different steps with 1 of 4 versions of n-back task, which differed in complexity (simple, complex) and similarity in processing codes (verbal, spatial) to the primary task. After the interruption, participants (N = 44) had to resume the primary task as quickly as possible with the next correct step, that is, the 1 following the step after which the interruption occurred. Postinterruption performance in terms of resumption times, sequence errors and nonsequence errors was assessed. Results of Experiment 1 revealed longer resumption times and more sequence errors after complex interruptions compared to the simple ones. However, effects of processing-code similarity were less clear. For assessing the effects of similarity in processing codes again in Experiment 2, participants (N = 41) performed the same primary task and were interrupted with a verbal or a spatial classification task. The results revealed no significant effect of processing code on the postinterruption performance. Moreover, a posthoc analysis revealed that 1-back (sequential) interruption led to longer resumption times compared to the classification (nonsequential) interruption. Overall, our results revealed strong and consistent detrimental effects of interruption complexity on the postinterruption performance and no effect of similarity in processing codes. Finally, we provide preliminary evidence that similarity in sequential structure between the tasks can influence the resilience toward interruptions. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Human Performance Consequences of Automated Decision Aids: The Impact of Time Pressure.

OBJECTIVE: The study addresses the impact of time pressure on human interactions with automated decision support systems (DSSs) and related performance consequences. BACKGROUND: When humans interact with DSSs, this often results in worse performance than could be expected from the automation alone. Previous research has suggested that time pressure might make a difference by leading humans to rely more on a DSS. METHOD: In two laboratory experiments, participants performed a luggage screening task either manually, supported by a highly reliable DSS, or by a low reliable DSS. Time provided for inspecting the X-rays was 4.5 s versus 9 s varied within-subjects as the time pressure manipulation. Participants in the automation conditions were either shown the automation's advice prior (Experiment 1) or following (Experiment 2) their own inspection, before they made their final decision. RESULTS: In Experiment 1, time pressure compromised performance independent of whether the task was performed manually or with automation support. In Experiment 2, the negative impact of time pressure was only found in the manual but not in the two automation conditions. However, neither experiment revealed any positive impact of time pressure on overall performance, and the joint performance of human and automation was mostly worse than the performance of the automation alone. CONCLUSION: Time pressure compromises the quality of decision-making. Providing a DSS can reduce this effect, but only if the automation's advice follows the assessment of the human. APPLICATION: The study provides suggestions for the effective implementation of DSSs in addition to supporting concerns that highly reliable DSSs are not used optimally by human operators.

Visual search behavior and performance in luggage screening: effects of time pressure, automation aid, and target expectancy.

Visual inspection of luggage using X-ray technology at airports is a time-sensitive task that is often supported by automated systems to increase performance and reduce workload. The present study evaluated how time pressure and automation support influence visual search behavior and performance in a simulated luggage screening task. Moreover, we also investigated how target expectancy (i.e., targets appearing in a target-often location or not) influenced performance and visual search behavior. We used a paradigm where participants used the mouse to uncover a portion of the screen which allowed us to track how much of the stimulus participants uncovered prior to their decision. Participants were randomly assigned to either a high (5-s time per trial) or a low (10-s time per trial) time-pressure condition. In half of the trials, participants were supported by an automated diagnostic aid (85% reliability) in deciding whether a threat item was present. Moreover, within each half, in target-present trials, targets appeared in a predictable location (i.e., 70% of targets appeared in the same quadrant of the image) to investigate effects of target expectancy. The results revealed better detection performance with low time pressure and faster response times with high time pressure. There was an overall negative effect of automation support because the automation was only moderately reliable. Participants also uncovered a smaller amount of the stimulus under high time pressure in target-absent trials. Target expectancy of target location improved accuracy, speed, and the amount of uncovered space needed for the search.Significance Statement Luggage screening is a safety-critical real-world visual search task which often has to be done under time pressure. The present research found that time pressure compromises performance and increases the risk to miss critical items even with automation support. Moreover, even highly reliable automated support may not improve performance if it does not exceed the manual capabilities of the human screener. Lastly, the present research also showed that heuristic search strategies (e.g., areas where targets appear more often) seem to guide attention also in luggage screening.

Individual preferences for task coordination strategies in multitasking: exploring the link between preferred modes of processing and strategies of response organization.

Recent investigation of individual differences in multitasking revealed evidence for individual preferences for modes of task processing (serial vs. overlapping) in a task switching with preview (TSWP) paradigm and different strategies of response organization (blocking, switching, and response grouping) in a free concurrent dual-tasking (FCDT) paradigm. However, this research on individual differences at the levels of cognitive task processing and behavioral response organization has been pursued separately, thus far, by testing independent samples of participants. In the current study, we investigated whether these two levels of task coordination were linked intra-individually. As individuals preferring an overlapping task processing mode can generate time gains particularly at task switches, we predicted that they prefer a switching strategy of response organization. In contrast, individuals preferring a serial processing mode are expected to prefer a blocking strategy to reduce dual-task demands. These predictions were confirmed in an experiment based on n = 70 participants. Indeed, most serial processors preferred a blocking strategy, whereas overlapping processors predominantly preferred to switch between the tasks. This finding suggests a strong correspondence between individual preferences emerging in both aspects of task coordination, which might reflect a common basic difference in the preferred style of cognitive control (flexible vs. persistent). Moreover, in case the preferred modes of task processing and strategies of response organization did not correspond to each other, the overall multitasking efficiency was comparably low. Thus, the distinction between the preferences for both aspects of multitasking seems to be an important aspect of understanding multitasking performance and should be considered in future studies.

Moving-horizon versus moving-aircraft: Effectiveness of competing attitude indicator formats on recoveries from discrete and continuous attitude changes.

The present research revisits the old issue whether attitude information is best conveyed to pilots in a moving-horizon format or in a moving-aircraft format. Previous research has suggested that the moving-aircraft format might not be beneficial for flight path tracking but recoveries from unusual attitudes, although the result are not fully consistent. A limitation of studies to date is that the recovery task usually did not involve progressive attitude changes of the aircraft but only sudden discrete changes. Compared with a discrete stimulus, the continuous dynamics might increase the perceived time pressure to respond, which in turn can be expected to amplify the error proneness with a less intuitive format. Two experiments were conducted where flight novices and experienced pilots performed tracking and recover tasks with both formats. Recoveries were performed from both, sudden (discrete) and continuously developing attitude changes. Independent of whether novices or pilots were considered, the general superiority of the moving-aircraft format was confirmed. As expected, the benefits of this format became even more evident with progressive attitude changes. No differences were found for tracking. The results add to the evidence favoring the moving-aircraft over the moving-horizon format for both novices and pilots. The moving-aircraft format of the attitude indicator should at least be considered as a standard for new applications, such as ground control stations of unmanned aerial vehicles. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Multitasking strategies make the difference: Separating processing-code resources boosts multitasking efficiency when individuals prefer to interleave tasks in free concurrent dual tasking.

Previous research has shown that individuals differ with respect to their preferred strategies in self-organized multitasking: They either prefer to work on one task for long sequences before switching to another (blocking), prefer to switch repeatedly after short sequences (switching), or prefer to respond almost simultaneously after processing the stimuli of two concurrently visible tasks (response grouping). In two experiments, we tested to what extent the choice of strategy and related differences in multitasking efficiency were affected by the between-resource competition (Wickens, 2002) of two tasks to be performed concurrently in a self-organized manner. All participants performed a set of dual tasks that differed with respect to the kind of stimuli (verbal vs. spatial) and/or responses (manual vs. vocal). The choice of strategy was hardly affected as most individuals persisted in their response strategy independent of the degree of resource competition. However, the efficiency of individuals preferring a switching or response-grouping strategy increased especially when the reduction in resource competition was response related (manual vs. vocal), leading even to considerable dual-tasking benefits under these circumstances. In contrast, individuals who preferred to block their responses did not achieve any considerable benefits (or costs) with either of the different dual tasks. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Absence of DOA Effect but No Proper Test of the Lumberjack Effect: A Reply to Jamieson and Skraaning (2019).

OBJECTIVE: The aim was to evaluate the relevance of the critique offered by Jamieson and Skraaning (2019) regarding the applicability of the lumberjack effect of human-automation interaction to complex real-world settings. BACKGROUND: The lumberjack effect, based upon a meta-analysis, identifies the consequences of a higher degree of automation-to improve performance and reduce workload-when automation functions as intended, but to degrade performance more, as mediated by a loss of situation awareness (SA) when automation fails. Jamieson and Skraaning provide data from a process control scenario that they assert contradicts the effect. APPROACH: We analyzed key aspects of their simulation, measures, and results which we argue limit the strength of their conclusion that the lumberjack effect is not applicable to complex real-world systems. RESULTS: Our analysis revealed limits in their inappropriate choice of automation, the lack of a routine performance measure, support for the lumberjack effect that was actually provided by subjective measures of the operators, an inappropriate assessment of SA, and a possible limitation of statistical power. CONCLUSION: We regard these limitations as reasons to temper the strong conclusions drawn by the authors, of no applicability of the lumberjack effect to complex environments. Their findings should be used as an impetus for conducting further research on human-automation interaction in these domains. APPLICATIONS: The collective findings of both Jamieson and Skraaning and our study are applicable to system designers and users in deciding upon the appropriate level of automation to deploy.

Do We Really Need More Stages? Comparing the Effects of Likelihood Alarm Systems and Binary Alarm Systems.

OBJECTIVE: This research investigates the potential behavioral and performance benefits of a four-stage likelihood alarm system (4-LAS) contrasting a 3-LAS, a binary alarm system with a liberal threshold (lib-BAS), and a BAS with a conservative threshold (con-BAS). BACKGROUND: Prior research has shown performance benefits of 3-LASs over conventional lib-BASs due to more distinct response strategies and better discriminating true from false alerts. This effect might be further enhanced using 4-LASs. However, the increase in stages could cause users to reduce cognitive complexity by responding in the same way to the two lower and the two higher stages, thus treating the 4-LAS like a con-BAS. METHOD: All systems were compared using a dual-task paradigm. Response strategies, number of joint human machine (JHM) false alarms (FAs), misses, and sensitivity were regarded. RESULTS: Compared with the lib-BAS, JHM sensitivity only improved with the 4-LAS and the con-BAS. However, the number of JHM misses was lowest for the con-BAS compared with all other systems. CONCLUSION: JHM sensitivity improvements can be achieved by using a 4-LAS, as well as a con-BAS. However, only the latter one may also reduce the number of JHM misses, which is remarkable considering that BASs with conservative thresholds a priori commit more inbuilt misses than other systems. APPLICATION: Results suggest implementing conservative BASs in multi-task working environments to improve JHM sensitivity and reduce the number of JHM misses. When refraining from designing systems which are miss prone, 4-LASs represent a suitable compromise.

The Impact of a Mnemonic Acronym on Learning and Performing a Procedural Task and Its Resilience Toward Interruptions.

The present study examines the potential impact of a mnemonic acronym on the learning, the execution, the resilience toward interruptions, and the mental representation of an eight-step procedural task with sequential constraints. 65 participants were required to learn a sequential task, including eight different steps which had to be carried out in a predefined sequence. 33 participants were provided with the acronym "WORTKLAU" as a mnemonic to support the learning and execution of the task and the other 32 participants had to learn and execute the task without such support. Each letter of the acronym coded one step of the task, involving a binary decision about a certain property of the complex stimulus. In 60 out of 72 trials of the task, participants were interrupted between different steps, and had to perform a 2-back interruption task for 6 or 30 s, after which they had to resume the procedural task as quickly as possible at the correct step. Learning times, performance in uninterrupted trials, and post-interruption performance measures were analyzed. Results of Experiment 1 suggest that the mnemonic acronym enhanced learning of the task sequence, and provide some evidence for a hierarchical mental representation of the task, resulting in faster resumption times at certain steps of the procedure after an interruption. In Experiment 2 the internal structure of the acronym was even emphasized by a hyphen at the borders of the two words included in the acronym (WORT-KLAU). This improved the resilience toward interruptions at the border step of the procedure significantly. Our results provide evidence for beneficial effects of mnemonic acronym particularly for the learning of a sequential procedural task. In addition, they suggest that the structure of mnemonic acronym directly impacts the mental representation of a task. Finally, they show that mnemonic acronyms could be used to improve the resilience toward detrimental effect of interruptions, at least at certain task steps of a procedural task.

Flexibility of individual multitasking strategies in task-switching with preview: are preferences for serial versus overlapping task processing dependent on between-task conflict?

The prevalence and the efficiency of serial and parallel processing under multiple task demands are highly debated. In the present study, we investigated whether individual preferences for serial or overlapping (parallel) processing represent a permanent predisposition or depend on the risk of crosstalk between tasks. Two groups (n = 91) of participants were tested. One group performed a classical task switching paradigm, enforcing a strict serial processing of tasks. The second group of participants performed the same tasks in a task-switching-with-preview paradigm, recently introduced by Reissland and Manzey (2016), which in principle allows for overlapping processing of both tasks in order to compensate for switch costs. In one condition, the tasks included univalent task stimuli, whereas in the other bivalent stimuli were used, increasing risk of crosstalk and task confusion in case of overlapping processing. The general distinction of voluntarily occurring preferences for serial or overlapping processing when performing task switching with preview could be confirmed. Tracking possible processing mode adjustments between low- and high-crosstalk conditions showed that individuals identified as serial processors in the low-crosstalk condition persisted in their processing mode. In contrast, overlapping processors split up in a majority adjusting to a serial processing mode and a minority persisting in overlapping processing, when working with bivalent stimuli. Thus, the voluntarily occurring preferences for serial or overlapping processing seem to depend at least partially on the risk of crosstalk between tasks. Strikingly, in both crosstalk conditions the individual performance efficiency was the higher, the more they processed in parallel.

Serial or overlapping processing in multitasking as individual preference: Effects of stimulus preview on task switching and concurrent dual-task performance.

Understanding the mechanisms and performance consequences of multitasking has long been in focus of scientific interest, but has been investigated by three research lines more or less isolated from each other. Studies in the fields of the psychological refractory period, task switching, and interruptions have scored with a high experimental control, but usually do not give participants many degrees of freedom to self-organize the processing of two concurrent tasks. Individual strategies as well as their impact on efficiency have mainly been neglected. Self-organized multitasking has been investigated in the field of human factors, but primarily with respect to overall performance without detailed investigation of how the tasks are processed. The current work attempts to link aspects of these research lines. All of them, explicitly or implicitly, provide hints about an individually preferred type of task organization, either more cautious trying to work strictly serially on only one task at a time or more daring with a focus on task interleaving and, if possible, also partially overlapping (parallel) processing. In two experiments we investigated different strategies of task organization and their impact on efficiency using a new measure of overall multitasking efficiency. Experiment 1 was based on a classical task switching paradigm with two classification tasks, but provided one group of participants with a stimulus preview of the task to switch to next, enabling at least partial overlapping processing. Indeed, this preview led to a reduction of switch costs and to an increase of dual-task efficiency, but only for a subgroup of participants. They obviously exploited the possibility of overlapping processing, while the others worked mainly serially. While task-sequence was externally guided in the first experiment, Experiment 2 extended the approach by giving the participants full freedom of task organization in concurrent performance of the same tasks. Fine-grained analyses of response scheduling again revealed individual differences regarding the preference for strictly serial processing vs. some sort of task interleaving and overlapping processing. However, neither group showed a striking benefit in dual-task efficiency, although the results show that the costs of multitasking can partly be compensated by overlapping processing.