The Residual Costs of Multitasking

Objective: The cognitive workload of three Smartphone Digital Assistants (SDA) was manipulated in an on-off manner while participants drove an instrumented vehicle in order to measure the costs associated with intermittent dual tasking. Background: Previous research has shown costs in productivity when switching between two discrete tasks; however, similar costs have not yet been examined using intermittent, continuous dual tasks. Methods: Participating drivers completed 5 conditions: baseline driving, 3 SDA conditions, and a cognitively demanding math-memory operation span (OSPAN) task, each while responding to Detection Response Task (DRT) stimuli. Within the SDA conditions, on- and off-task DRT performance was compared to baseline driving and to the OSPAN task performance. Results: The on-task periods of the SDA conditions resulted in similar RTs as the OSPAN condition, while the off-task periods did not immediately return to baseline driving performance. Post hoc analyses of the on-off transitions within the SDA conditions revealed a gradual return to baseline driving performance over the course of 18 seconds. Conclusions: The delays in returning to baseline driving performance after completing a secondary task raise concerns about the usage of in-vehicle devices while driving as the effects of the delays last beyond the cessation of the SDA interaction.