## 5 Discussion  
All 12 unimpaired subjects and the two subjects with SCI completed the entire experimental protocol, demonstrating an overall robustness and accessibility of the system. The primary goal of the data analysis was to assess whether a general improvement could be observed between pre-training and post-training tests to evaluate the effectiveness of the training and the usability of the system. Interestingly, SCI participants achieved performances comparable to those of unimpaired subjects, especially in terms of time, touch accuracy, task completion, and success rate, highlighting the potential of this robotic system to support users with different levels of motor function. Their performance and success rates were evaluated individually, with the results analyzed separately. This approach allows us to conclude that, for these two subjects, results appear promising, as improvements between the pre-training and the post-training phases are evident, even though the performance of SCI 2 seems poor if compared to the others. The three main performance metrics--Distance Accuracy, \(A\), Time, \(\bar{t}\) and Touch Accuracy, \(A_{t}\)--provided valuable insights into the impact of training on users' interactions with the system. Statistical analysis revealed that participants became significantly more precise in navigating the robot toward the targets following the training sessions. Similarly, improvements were observed in the third metric, touch accuracy. However, the time metric did not show a statistically significant change, indicating that participants prioritized achieving higher precision over reducing the time to reach the targets. Figure 12: Pose of the user’s right upper arm, \(x_{c}\), during **Test 1** before (blue) and after (magenta) training. Additionally, the success rates achieved during both tests demonstrated marked improvements post-training. Nevertheless, the fact that some participants did not reach the final target can be attributed to the limited maximum time available for completing the task. This variability suggests that, while some participants were comfortable engaging with robots on an emotional level, others were less so, reflecting diverse attitudes toward the social and affective dimensions of human-robot interaction. Overall, participants had a positive attitude toward robots in the first two sub-scales (S1 and S2), with slight decrease in the second. The third sub-scale (S3) revealed more distributed opinions. Regarding the algorithm validation and system kinematics, the results confirm the overall correct functioning of the control algorithm, as it effectively translates the user's residual motions into corresponding robot movements. This process generally leads to the convergence of both errors, \(e_{e}\) and \(e_{c}\), toward zero. To illustrate this, our analysis focused on the tetraplegic subject, who successfully reached all targets both before and after the training sessions. The results show a significant reduction in the time required to complete the tasks post-training, demonstrating the effectiveness of the training steps for the subject. Additionally, the analysis of residual motions highlights the subject's learning process. During the pre-training phase, the subject tended to explore the task by performing more pronounced movements. However, after learning the strategy, post-training movements became minimal. The subject relied primarily on small displacements of the right arm, reserving arm orientation adjustments for the final phase of the task, specifically when the robot's arm needed to be raised. Nevertheless, the results from the pilot study involving SCI subjects highlight the potential of this control strategy. Although additional SCI participants are needed to fully assess the learning process during training sessions, this pilot study suggests its promising effectiveness. Furthermore, involving more SCI subjects will require a more detailed investigation to enable the system to better discriminate between voluntary and involuntary motions.