## 6 Results and Discussion
### Discussion
The requirement of this type of feedback was evident for both interfaces, especially when depth information was unavailable (similar scores, \(\mu_{t}=5.85\), \(\sigma_{t}=1.34\) vs. \(\mu_{i}=5.7\), \(\sigma_{i}=1.38\)). Visual localization of the objects was frequently confirmed through the sense of touch while reaching it. Visual images of the tool in movement enable knowing its position; however, the knowledge of its height can be difficult. To overcome this limitation, some users moved the tip of the tool in contact with the table, refining in this way the reference plane with haptic information provided by arm proprioceptive sensors. Presence Question Q5-Q8 show that the immersive interface easily becomes transparent for the user, letting him/her feel that he/she is naturally perceiving the remote environment. Visual feedback is transparently mediated and, combined with motor-actions, contributes to the sense of telepresence. The findings also show that the performances are better when the task workspace is in front of the user, in opposition to setting it on the right side. A visuomotor task where the natural frame of reference of vision is shifted with relation to the common frame of reference for hand/arm movement increases mental workload and consequently decreases task performance. Operators are required to do mental transformation to compensate for their manipulation inputs with relation to the corresponding tool action observed in the displays. The gesture coordination ends up relying more on visual feedback. For example, in our experiments, the pick-and-place task using a hand gripper (Task 2) with the traditional interface had the workspace on the right side; whereas, in the control experiment, the same task was performed using the traditional setup \"monitor indirect vision (mono biocular) + gripper\" (F5) with the workspace in front of the user. Comparing the mean task-time performance for the traditional interface in both experiments, we found that participants performed faster with the workspace in front than with it on their right side (\(\mu=56.4\), \(\sigma=16.47\) vs. \(\mu_{t}=136.75\), \(\sigma_{t}=61.93\)). It is a significant difference with one-way ANOVA \(F_{1,23}=8.03\) and \(p=0.009^{*}\). Thus, users are used to the consistency between visual, proprioception (sense of body position), kinesthesia (sense of body movement), and vestibular feedbacks, and any inconsistency implies new skills. The research on perceptual factors affecting user's control behavior is useful to improve direct control teleoperation interfaces, minimize control workload, improve task performance, and maximize safety. Additionally, it can contribute to designing semi-autonomous functionalities based on cognitive human-robot interaction architectures to assist operators. For example, during direct interaction such as telesurgery, semi-autonomous systems can prevent dangerous movements of the robotic arm, adapt the responsiveness of the system to the variability of perceptual factors, or adapt the interface to different users. Moreover, the interfaces or robot's behaviors can be adapted to the context.