## 5 Discussion  
The results showed that perceived cognitive workload increased slightly from the first trial to the second one. However, it decreased significantly from scenario 2 to the last one, which was consistent with previous research [40,41] and highlighted the importance of minimal jerk, interaction types and feedback given to the users in minimising mental effort. The increase in cognitive workload in the second trial could have been due to the high number of changes and manipulations compared with trial number 1. In the third and final scenario, the cognitive workload decreased significantly, as the subject was able to adjust many different functions of the workstation, such as the robot's speed and the type of commands. Perceived autonomy is one of the most important factors that affect intrinsic motivation and lead to a better cognitive experience and well-being [59,60]. These findings appeared to be consistent with the results of the eye-tacker data, which demonstrated a statistically significant difference in the number of fixations across the three different scenarios; the duration of fixations was not significant. The number of fixations decreased sharply from scenario 1 to scenario 2. It increased significantly from scenario 2 to scenario 3, which was consistent with previous results from [29]; a high cognitive load is associated with fewer fixations. One of the most important results showed a strong and negatively significant correlation between NASA-TLX scores and the number of fixations in scenario 1. This could be due to the particular HRC conditions of the workstation for trial 1. Nevertheless, the absence of correlation between the objective and subjective metrics in trials 2 and 3 was quite relevant, and it could have been due to the different content activity and the input-output modality affecting eye movements. The way each individual engages with an interactive system is different and is influenced by the system design, as the content  
Figure 4: The number of fixations and fixation duration mean scores in the three trials. influences the users' fixations [61]. Visual representations of content can influence the location, duration and speed of fixation without cognitive engagement present. According to our results, acceptance did not significantly predict the cognitive workload. As the literature suggests, higher acceptance of the collaborative robot should reduce the use of the cognitive resources used to work with the cobot. However, these results could have been due to other factors present in the scenarios, such as the way the status of the robot was communicated to the user. During the three trials, notifications were displayed on an LCD screen. Visual animations are often used to help users notice changes or to shift their attention [62]. In the present study, the visual alarm may have negatively impacted the user's awareness of the situation. Future studies should integrate auditory notification to create a multi-modal interaction (i.e., conveying information across two or more modalities) [63]. Indeed, auditory cues alert the user to an item that requires immediate attention, regardless of where the user is currently directing their gaze. The possible combination of auditory and visual alerts would improve situational awareness of change, thus somehow reducing the demands of the collaborative task [64]. The results showed that acceptance predicted perceived stress across the three trials. While the results of the third scenario were consistent with previous research [33]--namely, that the introduction of MJTs increased participants' feelings of predictability and familiarity--the results of the first and second scenarios were unexpected. These results suggested that the robot's non-human-like movements did not negatively affect user acceptance. One explanation could be related to the fact that humans were not focused on the robot's movements because they were busy with their work.