Between- and within-subject covariance perspectives matter for investigations into the relationship between single- and dual-tasking performance

We expand the usually cross-sectional perspective on dual-tasking performance to include both intra- and interpersonal variability, which should capture within-person dynamics and psychological processes better. Two simple tasks, first as single-, then as dual-tasks, were performed by 58 participants over 20 sessions. We found positive relationships between (1) single- and dual-tasking performance and (2) the dual-task component tasks both inter- and intrapersonally. Better single-taskers were better dual-taskers and better single-tasking sessions were better dual-tasking sessions. This implies shared capacities that covary both inter- and intraindividually. We conclude that taking intra- and interpersonal variability into account is a promising future perspective.