Influence of automation level of human-machine system on operators’ mental load

The appropriate automation in armored vehicles is vital for the operational efficiency and personnel security of operators. In this study, fifty subjects conducted over-the-horizon strike and N-back tests at different automation levels based on a virtual simulation system for armored vehicles. Physiological signals and subjective assessments were recorded. The mental load and task performance of operators were related to different automation levels. Results suggested that the mental load decreased with the increase of automation levels. Apart from object destruction time, heart rate and standard deviation of NN intervals (SDNN), other indexes were all significantly affected by the automation level of subtasks (p ​< ​0.01). The NASA-TLX scores, object destruction time, response time of abnormal states, and reaction time in N-back tests decreased by at least 2.9 ​%, 8.2 ​%, 11.2 ​% and 1.3 ​% respectively, while the mean accuracy in N-back tests increased by 0.1 ​%. Furthermore, there existed several automation levels of tasks where the task performance remained almost unchanged under normal operation. The function of task automation on decreasing mental load reduced in the following order: A3-B3-C2-D2-E2, A2-B2-C2-D2-E2, and A3-B3-C1-D1-E1. The main contribution of this research was to provide a qualitative method and framework for the evaluation of influences of automation level on operators’ mental load, and the design of human-machine interaction and adaptive automation in automated systems.