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

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.TU Berlin, Open-Access-Mittel – 202

Individual processing preferences in multitasking

Concurrent multitasking will often be a challenge for human information processing. Dealing with that, several tasks that are visible at the same time could be processed either in a rather separated or in a rather integrated or even parallel manner. Only a few studies have investigated individual strategies when working in a concurrent multitasking situation so far, although some evidence clearly suggests individual differences in coping behavior. The thesis describes an extended version of a task switching paradigm making it possible to process two tasks at the same time. With the help of that we could specifically investigate the prevalent processing strategy on an individual level. In study A we could demonstrate individual preferences for serial or parallel processing when task switches were predefined. Both frequency and complexity of tasks influenced the individually prevalent processing mode. Analog to previous task switching studies, serial processing led to performance decrements. Decrements decreased significantly with a parallel processing mode. Some participants could even realize performance benefits from the multitasking situation. When task switches were optional in studies B–D, giving the participants more degrees of freedom for their strategy, almost no performance differences between strategy subgroups were present. Apparently, the response organization level of the strategy was adapted by persons with a serial processing preference so that task switches were avoided, while persons with a preference for task integration switched rather often between tasks. Both strategy types presumably led to an individual optimization of performance. Those two strategy types that could primarily be observed in the reported studies can be considered in the light of the stability-flexibility-dilemma of cognitive control. The individually applied strategy might be a manifestation of an either persistent, task focusing control mode or a flexible, task integrating control mode. In accordance with the meta-control state model of Hommel (2015) the results of this thesis suggest that every human might have an individual default value for a cognitive control type that can be biased toward the persistence or the flexibility pole of cognitive control. The actually applied control mode leads to a corresponding processing strategy that can be either task separating or task integrating and that seems to be situatively adaptable. However, such adaptions are supposed to be limited within a certain individual range. This thesis offers new methodical approaches and first evidence serving as a basis for further investigations regarding individual preferences in multitasking. Subsequent research seems to be highly relevant for both applied and basic psychological perspectives. Furthermore, due to the fact that analyses on the level of group averages can cover the behavior that is actually taking place, the thesis demonstrates the relevance of individual analyses of strategies when dealing with multitasking.Konkurrierendes Multitasking stellt eine in der Realität sehr häufig anzutreffende Herausforderung für die menschliche Informationsverarbeitung dar. Dabei können mehrere Aufgaben, die gleichzeitig sichtbar sind, entweder eher separiert voneinander oder eher integriert bzw. sogar parallel bearbeitet werden. Nur wenige, ältere Studien haben bisher gezielt die angewendeten Bearbeitungsstrategien beim konkurrierenden Multitasking untersucht, obwohl einige Befunde darauf hinweisen, dass es hier deutliche individuelle Verhaltensunterschiede gibt. Im Rahmen der vorliegenden Arbeit wurde das Aufgabenwechsel- Paradigma so weiterentwickelt, dass grundsätzlich zwei Aufgaben gleichzeitig bearbeitet werden können. So war die gezielte Untersuchung der jeweils vorherrschenden Bearbeitungsstrategie der Probanden auf individueller Ebene möglich. In Studie A konnte zunächst bei vorgegebenen Aufgabenwechseln eine starke individuelle Präferenz für serielle oder parallele Verarbeitung nachgewiesen werden. Sowohl die Häufigkeit der Aufgabenwechsel als auch die Aufgabenkomplexität wirkten sich dabei auf den angewandten Verarbeitungsmodus aus. Hinsichtlich der Leistung kam es, analog zu bisherigen Befunden aus Aufgabenwechsel-Studien, bei serieller Verarbeitung zu hohen Leistungseinbußen. Wurde jedoch parallel gearbeitet, fielen diese deutlich geringer aus. Teilweise konnten sogar Leistungsvorteile durch die Aufgabenwechsel erzielt werden. Bei freigestellten Aufgabenwechseln in den Studien B–D, und somit mehr Freiheitsgraden für die Ausbildung einer Bearbeitungsstrategie, traten demgegenüber kaum Leistungsunterschiede zwischen den Strategiegruppen mehr auf. Offenbar wurde hier auf der Ebene der Handlungsorganisation die Bearbeitungsstrategie so ausgestaltet, dass Personen mit einer seriellen Verarbeitungspräferenz Aufgabenwechsel vermieden, während Personen mit einer Präferenz für aufgabenintegrierendes Arbeiten häufige Aufgabenwechsel durchführten, um insgesamt ihre Leistung zu optimieren. Die beiden hier vorrangig gefundenen unterschiedlichen Strategietypen lassen sich im Rahmen des Stabilität-Flexibilität-Dilemmas der kognitiven Kontrolle als Manifestation eines eher persistenten, aufgabenfokussierenden Kontrollmodus oder eines eher flexiblen, aufgabenintegrierenden Kontrollmodus deuten. Im Einklang mit Hommels Modell einer Meta- Kontroll-Richtlinie (Hommel, 2015) weisen die Befunde dieser Arbeit darauf hin, dass jeder Mensch über einen individuellen Richtwert eines kognitiven Kontrollmodus verfügt, der eher persistent oder eher flexibel ausgerichtet sein kann. Der tatsächlich angewandte Kontrollmodus führt zu einer entsprechend überwiegend aufgabenseparierenden oder aufgabenintegrierenden Bearbeitungsstrategie und scheint situationsbezogen anpassbar zu sein. Eine Anpassung kann jedoch offenbar nur in einem gewissen Rahmen erfolgen. Die vorliegende Arbeit bietet mit ihren methodischen Ansätzen sowie ihren Befunden eine Grundlage für die weitere Erforschung individueller Präferenzen für die Bearbeitung beim Multitasking. Weitere Forschungsarbeiten hierzu erscheinen sowohl aus anwendungs- orientierter als auch kognitionswissenschaftlicher Sicht in hohem Maße relevant. Die Arbeit belegt zudem die besondere Wichtigkeit einer individuellen Betrachtungsweise bei der Untersuchung von Strategien beim Multitasking, da eine reine Betrachtung auf der Ebene von Gruppenmittelwerten tatsächlich vorliegende Verhaltensweisen verdecken kann