Effects of Shared Secondary Controls and Operational Modes on Performance and Perceived Workload during a Simulated Driving Task

During a simulated driving task, subjects were prompted to actuate specific shared (mode-based) secondary controls, which required subjects to ensure that the proper mode was active before actuating the control. The independent variables were number of controls, number of operational modes, and number of functions assigned to a control. The dependent variables included performance time, speed and lane deviations, error measures, and subjective ratings. Subjects perceived higher workloads and took longer to complete the secondary task as the number of controls and number of functions increased. The number of operational modes had no effect on secondary control performance while subjective ratings indicated little or no significant differences between multiple and single mode systems. Comparing systems with identical number of functions, a system that reduces the number of controls by assigning a set of functions (in which each function belongs to a different mode) to each control may be preferable to a system that dedicates each function to a single control.