Task 1: The first task is a visual tracking task. In each trial, the subject needs to watch a 10-second video where a red arrow and one or more white arrows move in a constant speed, as shown in the left figure. The subjects are informed that the red arrow represents their own UAV, while the white arrows represent intruders. After each video concludes, all arrows disappear and the subject must use the mouse to click on the monitor to indicate all arrows' latest position and heading. The position of an arrow is marked by the first click, and its heading is determined by the subsequent click, indicating the direction in which the arrow was moving. Each click is marked by a blue box containing a number, which indicates the sequence of the clicks. Each pair of clicks is connected by a blue line, enabling subjects to better visualize their indicated heading. An undo button is provided at the top left corner where the subjects can use to undo their clicks if necessary. All things mentioned above are also included in an instruction video, which is played at the beginning of Task 1. We ask the subjects questions after the instruction video to make sure they fully understand what they need to do in this task and how to indicate the position and heading. After the subject finishes making all clicks, they can click the Next button on the bottom and complete the NASA-TLX survey. Completing the NASA-TLX survey represents the end of one trial in Task 1. To control the task complexity, we control the number of intruders in one trial to be 1, 3, or 5. To minimize the learning effect, the order of the videos is random for each subject. In total, there are 30 trials in Task 1. Additionally, a secondary task is added in the last 15 trials to further increase the task complexity. Details about the design of the secondary task are included in the Secondary Task section. 

Task 2: The second task is designed based on the real-world operations utilizing Windracers' cloud control system. In this task, subjects are required to use the cloud control system to: (1) plan a UAV mission from one airport to another by setting waypoints, (2) monitor the UAV during the mission, and (3) set new waypoints to avoid any intruders that may appear during the mission. Each trial lasts between 15 to 20 minutes, depending on the subjects. Prior to the first trial, the subject watches a series of training videos that provide instructions on using the cloud control system. To standardize the subjects' behaviors and facilitate performance assessment, specific guidelines are provided. For instance, the take-off and landing angles must be set between 3 to 5 degrees, and the airspeed must be adjusted to 70 knots during cruising and 45 knots prior to landing. These guidelines are detailed in the training videos and are also available as a hard copy attached to the bottom of the monitor, allowing subjects to reference them as needed. Following the training videos, the subjects are guided through a test session in which they plan and conduct a mission that navigates one UAV around an airport. Trials begin only after we are convinced that the subject has sufficiently mastered the use of the system. To collect the subjects' subjective CL without disrupting the trials, we employ the instantaneous self-assessment (ISA). Once the subject is ready to start the trial, the subject can click the start button. Every minute thereafter, five red boxes, each labeled with a number, appear on the screen, as illustrated in the figure above. The subject needs to click the box that best represents their perceived cognitive load level at that moment. At the end of every trial, the subject needs to complete a NASA-TLX survey (same as the one in Task 1), followed by a 5-minute break. The ISA results serve as the reference label of the subject's CL during the mission, while NASA-TLX survey results are used to assess the subject's overall experience.