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

Abstract

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.