The Effect of Prior Task Loading on Mental Workload: An Example of Hysteresis in Driving

Objective: This study examined how transitions in task demand during a driving and navigation task manifested themselves as delayed adaptation in driver mental workload. Background: A delayed reaction to changes in demand levels, termed hysteresis, has been identified in a number of settings. However, little research has specifically examined the driving task for hysteresis effects. Method: A total of 32 drivers completed drives while using a navigation system that would fail within the drive. Subjective mental workload was recorded prior to and following system failure as well as at the conclusion of the drive. Results: Results indicated that a gradual reduction in overall mental workload across trials and a lagged recovery to reduction in task demand was present within trials. Analysis of the mental workload subscales within trials indicated that this effect was produced by the mental effort component of workload. Conclusion: A moderate hysteresis effect is present in mental workload transitions within the driving task. Although subjective mental workload decreases across trials, the magnitude of the lagged recovery within trials remains unchanged. Application: Scaling of in-vehicle information is beneficial with respect to driver mental workload. Display and communication technologies designers should consider not only the immediate task demand but also the driver’s task demand history when determining what and how to provide information.