2.7. Experimental Setup and Procedure
The study was conducted in the Industrial Engineering Department’s maintenance lab. The temperature, humidity, and light intensity at the center of the table in the laboratory were 21.4 °C, 18.2%, and 392.5 lux, respectively. The experimental zone was secure from vibrations or strong odors during the task’s execution. To attract participants, an announcement and invitation were issued and distributed at King Saud University. The participants were invited to participate in a pre-test session as well as two test sessions ranging from 1 to 4 h. Upon participant arrival, the purpose of the experiment was explained in detail, and the screening process was completed. The results of the health survey were reviewed and approved; if acceptable, the participant was asked to sign a consent form and fill out a demographic questionnaire. In addition, the participants were requested to provide background information and answer questions related to their existing AR experience. After that, their anthropometric data was collected.Next, participants were randomly assigned into two groups and given a briefing on how to use the instruction method assigned to their group. The first group received AR-based instructions, in which a Microsoft HoloLens1 was used to display relevant maintenance instructions and guide the participant to perform the maintenance tasks. In the AR-based instruction group, participants were given 10 to 15 min to familiarize themselves and learn how to handle, adjust, the HoloLens and interact with it [The participant returned to the lab the next day to perform the maintenance tasks with the help of the assigned instruction method from the previous day (AR-based or paper-based instructions). On this day, for example, participants in group 1 (the AR-based instruction group) were randomly assigned to perform the high- or low-demanding task with AR instructions. These tasks were randomly allocated to the participants in different sequences using a counterbalancing method to avoid the ordering effect of the tasks. The AB or BA sequences (A and B refer to high- and low-demanding tasks, respectively) were applied. In the AB sequence, half of the participants within group 1 were asked to perform a highly demanding task first (repairing a piston pump’s gearbox). The remaining participants were assigned to the BA sequence and were asked to perform the least-demanding task first. Two days later, participants returned to the lab to start the other half of the experiment, which is the task that was not performed in the first half (i.e., a low or high-demanding task), with AR instructions. Participants in group 2 (who used paper-based instructions) followed the same procedures as group 1.Before the performance of each training task, the EEG electrodes were placed on the participants’ skin. After that, three minutes of EEG signals were recorded at resting postures to be used as baseline data. During the training tasks, EEG signals were recorded. After the training tasks were completed, the signals were recorded again for three minutes, and the training time was recorded. Total training time is the time taken to complete the task while following the instructions. The camera system and stopwatch were used to record this time. Upon completing the task, the electrodes were removed, and the participants were requested to complete questionnaires to measure their subjective perception of the task and the technique of completing it in terms of perceived workload.