Is multitasking efficient? Different metrics, different conclusions

Jung, A.; Janczyk, Markus; Manzey, Dietrich; Fischer, Rico · 2026 · OpenAlex-citations

DOI: 10.1007/s00426-026-02281-x

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Summary

This study investigates whether multitasking is efficient by comparing two distinct metrics: Total Reaction Time (TRT), which sums the reaction times of individual tasks, and Time on Task (ToT), which measures the total duration from the onset of the first stimulus to the completion of the second response. While traditional research emphasizes the costs of multitasking due to central processing bottlenecks, the authors argue that ToT captures potential benefits of parallel peripheral processing. The study tests the hypothesis that overlapping task execution is more efficient than sequential execution when measured by ToT, despite known central processing delays. The researchers conducted two experiments using dual-task paradigms. Experiment 1 (N = 18) employed a Psychological Refractory Period (PRP) design with distinct tasks: an auditory pitch-categorization task (Task 1) and a visual number-categorization task (Task 2). Participants performed these tasks either sequentially or with overlapping stimuli at short (50 ms) and long (500 ms) stimulus onset asynchronies (SOAs). Experiment 2 (N = 32) used identical task sets (visual number categorization for both tasks) to maximize between-task interference and crosstalk, with simultaneous stimulus presentation. Both experiments measured ToT and percent error (PE) to assess speed-accuracy trade-offs. Experiment 2 additionally assessed subjective effort, arousal, and mood. Results from both experiments demonstrated that ToT was significantly shorter in overlapping conditions compared to sequential conditions. In Experiment 1, ToT was 1230 ms for the 50 ms SOA and 1326 ms for the 500 ms SOA, compared to 1516 ms for the sequential condition. This efficiency gain occurred without significant reductions in accuracy; total error rates remained low and comparable across conditions. Experiment 2 replicated these findings, showing shorter ToT for overlapping processing despite high dimensional overlap between tasks. The data indicate that the time saved by parallel peripheral processing outweighs the delays caused by central response selection bottlenecks. The findings challenge the conventional view that multitasking is inherently inefficient. The study concludes that the assessment of multitasking efficiency depends critically on the chosen metric: TRT suggests sequential processing is superior, while ToT reveals overlapping processing is faster. The authors argue that ToT provides a more holistic measure of efficiency by accounting for both central costs and peripheral benefits. These results imply that individuals may engage in multitasking not due to cognitive fallacies, but because it allows for higher task throughput in a given time frame. The study underscores the importance of selecting evaluation metrics that align with research goals and considering multiple performance indicators, including speed, accuracy, and effort, to fully understand multitasking dynamics.

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Topics

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• dual task multitasking
• dual task performance