*2.1. Experimental System*

The experimental system included a 4 degree of freedom DOBOT Magician robotic arm (https://www.dobot.cc/dobot-magician/product-overview.html, accessed on 30 May 2021) equipped with a suction gripper, user interface (presented on a computer), cubes to be assembled and the human operator (Figure 1). The DOBOT Magician (135 mm high, 158 mm wide with a 320 mm radius and 500 g payload) connects to the computer through a USB connection and was programmed for the two LOA modes using the Python programming language.

**Figure 1.** The experimental system.

The HRC assembly task simulates a work scenario where participants are expected to assemble blocks made from cubes brought to them by a robot according to a configuration presented to them through a user interface. The task was performed in two LOA modes, at four workload levels. The workload levels, detailed below, are composed of different combinations of a secondary task and task complexity.

The user communicates with the robot through a user interface implemented on a GUI screen (Figure 2). This was designed to be friendly to promote ease of use as the human interacts with the robot through the GUI [34–36]. The configuration to be assembled is displayed on the GUI screen when starting the task. The robot brings the cubes in a sequence one after another from a predetermined place according to the specific LOA the robot is operating in. The robot releases the cube when it reaches the front of the participant. The participants are expected to assemble the cubes when received from the robot and place these cubes in a marked area on the desk in front of them.

**Figure 2.** The GUI screen.
