Quantity and thumbnail display effects on semi-autonomous ground vehicle operators' performance and mental workload: the moderating role of spatial ability.

Semi-autonomous unmanned ground vehicles (S-UGVs) can improve search and rescue (SAR) operations. However, the optimal vehicle quantity and thumbnail display for operator monitoring and commanding remain unclear. This study investigated how S-UGV quantity (2/4/6) and thumbnail display (with/without) influence operators' performance and mental workload in SAR scenarios. Thirty participants completed the simulated SAR task and were divided into high and low spatial ability (SpA) groups. Results show that increasing S-UGV quantity reduced task completion time but prolonged reaction time and increased workload. Correctly identified targets declined further when the quantity increased from four to six. The High SpA group completed tasks faster and reported lower workload with the thumbnail interface. While the thumbnail interface prolonged reaction time, it enabled the high SpA group to achieve shorter task completion time when operating six S-UGVs. These findings may provide insights into hardware and thumbnail display design in semi-autonomous systems.