Multitasking: does task-switching add to the effect of dual-tasking on everyday-like driving behavior?

It is well established that performing multiple tasks simultaneously (dual-tasking) or sequentially (task-switching) degrades performance on one or both tasks. However, it is unknown whether task-switching adds to the effects of dual-tasking in a single setup. We investigated this in a simulated everyday-like car driving scenario. We expected an additive effect of task-switching on dual-tasking, leading to a stronger deterioration of driving performance due to the increased cognitive load required to handle multiple task-sets. Forty-five young adults aged 18 to 30 years (age: 23.62 ± 2.51, 28 females) were instructed to follow a lead car driving at a constant speed of 70 km/h through a rural landscape while concurrently performing additional tasks. The additional tasks were typing and arguing, in response to stimuli presented visually or auditorily. The tasks were presented either in separate blocks or in intermixed order (conditions: repetitive vs. switching). Driving performance was assessed by use of the average velocity and the standard deviation of lateral position, and performance in the additional tasks was assessed by reaction time. Linear-mixed effect models revealed better performance in the repetitive, compared to the switch condition only for the standard deviation of the lateral lane position while performing the additional typing task. This provides limited evidence for the view that task-switching adds to the challenges of dual-tasking. We therefore posit that already dual-tasking alone involves processing demands that are not substantially increased by adding switching demands.