*2.2. Design of the Experimental Conditions* 2.2.1. Levels of Automation (LOA) Modes

The automation design focuses on the *decision* and *action* aspects of the overall process taken either by the robot or the user. This specifies the degree of control the user or robot in the decision of action(s) to be taken and the execution of the actions. It is conditioned in

two levels for this study: (a) Low LOA—the user has autonomy to select the type and order of cubes. The robot

supports the user by bringing the type of cube the user selected via the user interface. (b) High LOA—the robot has autonomy to bring the specific type of cube and in the order preprogrammed in its operation. The user simply demands for a cube through the user interface and the robot brings the type of cube suitable for the specific configuration assembled.

### 2.2.2. Levels of Workload

The workload design focuses mainly on the physical and cognitive workload induced through the selection of the right cubes to assemble in the minimum possible time. This is the main task. Workload is increased in two ways: through a secondary task and by increasing task complexity.

The secondary task influence was depicted through an off-the shelf well known cognitive game, the "RUSH HOUR" (https://www.thinkfun.com/products/rush-hour/, accessed on 30 May 2021) thinking game (Figure 3). It involves arranging toy cars in a way to get a specific car out of a gridlock. There are tabs at each stage showing how to arrange the cars and finding a way to get the required red car out at different stages.

**Figure 3.** "RUSH HOUR" game.

In the main task, where cubes are assembled, the default setting is that the cubes for the assembly differ only by color. The users are required to assemble the cubes to match particular configurations characterized by differences in color pattern (Figure 4a).

**Figure 4.** Sample of cubes configurations in (**a**) without complexity and (**b**) with complexity.

The task complexity influence was depicted by introducing the cubes for the assembly that differ in color and in numbers on a particular side (Figure 4b). The users are required to assemble the cubes in color patterns as done in the low task complexity condition, but in addition, they must ensure that the specific numbers on a particular color of cubes match the required configuration per time. The task complexity is increased by the additional information cue (presence of numbers) and their spatial consideration (position of the number in the configuration). It represents component and coordinative task complexity induced through the number and type of sub-actions to be performed while selecting the right cubes and assembling along with the coordination of the actions in the secondary task.

Four levels of workload were designed using these factors:

