The “everyone does” vs. “some do and some don’t” perspective on multitasking: Constraining explanations for dual-tasking effects by analyzing their interindividual variability through the lens of mixture modeling

• Applicant: Dr. Christoph Naefgen
• Subject Area: General, Cognitive and Mathematical Psychology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 552515799

In research on dual-task performance there are several phenomena with competing explanations that assume either structural and inflexible or adaptive and flexible underlying mechanisms. Because they aim to explain the same phenomena and cognitive capacities, the theoretical models in question tend to have very similar sets of predictions, making them hard to differentiate empirically. One example here is the psychological refractory period (PRP), in which a decrease in the delay between the presentation of two stimuli corresponds to an increase in the reaction time to the second stimulus. One explanation for this that assumes structural and inflexible mechanisms is the theory of the structural cognitive bottleneck. It posits that in the cognitive processing of a stimulus, there is a central phase of which only one can be processed at a time. The second task’s central phase has to „wait” for the first task’s phase to finish processing. An alternative explanation that is adaptive and flexible is the capacity sharing theory. It posits that multiple central phases can be processed at the same time but that the capacity for such processing is limited and has to be distributed among the tasks. Regarding reaction times and error rates, both types of theories make very similar predictions, as both are supposed to explain the PRP effect. However, it is possible to make contrasting predictions based on the assumed differences in flexibility: A structural and thus inflexible mechanism should always and for everyone lead to the emergence of the effect (here: the PRP effect), while an adaptive mechanism allows for variability. If at least some people do not show the effect at least sometimes, this favors the adaptive and flexible explanation for it over the structural and inflexible one. One challenge here is that the statistical variance and substantive variability of effects look very similar through the lens of population mean-oriented statistical methods that are often used in this context. Recently, Haaf and Rouder (2019) applied a method based on hierarchical Bayesian modeling in the context of cognitive psychology that is supposed to deal with exactly this issue. Among other scenarios, this approach allows differentiating whether an effect emerges always and for everyone or whether it only appears for a part of the population. The goals of this project are to establish this approach in the field of dual-task research, use it to test between theories that predict flexible result patterns and those that predict inflexible patterns. These phenomena include the PRP effect, the backward crosstalk effect, a congruence bias in free choice tasks, action effect monitoring, and the common encoding of task episodes. Alternative explanations of these contrasts are explored by using experimental manipulations.

• DFG Programme: Research Grants