Evaluation of mental workload accompanying the cognitive task of in-vehicle information devices

The driver's mental workload, constituted of visual cognition, has recently increased with the rapid spread of car navigation systems and other in-vehicle information devices accompanying the progress of Intelligent Transport Systems (ITS). Under such circumstances, accurate evaluation of the driver’s mental workload is important in order to develop in-vehicle information devices that do not jeopardize safety. In this study , an experiment was conducted to evaluate the workload in response to a visual cognition task. The task asked that the subject identify how many characters memorized in advance were contained in a character group shown on a CRT display. In the experiment, mental workload was estimated synthetically from a combination of psychological, behavioral, and physiological viewpoints. When the difficulty of the task increased, the increase in diastolic pressure and beta-1 power ratio of electroencephalogram (EEG) became larger. In conjunction with task execution, parasympathetic nervous activity derived from heart rate variability (HRV) decreased. This result suggests that mental workload could be reflected by several physiological indices such as diastolic blood pressure, EEG beta-1 power ratio, and HRV. In conclusion, it appears that mental workload can be presented to a driver immediately, based on measuring the physiological indices while he or she is actually driving, and safety can be maintained.