## 3 The Human Role in Teleoperation
### Field of View  
The field of view (FOV) refers to the size of the visual field observed. Manipulation studies typically compare narrow viewpoints with wide panoramic views, revealing that narrow FOVs result in difficult navigation [81]. For example, they can limit the acquisition of contextual information about the space around a rover, compromising the perception of distance, size, and direction, having difficult cognitive map formation, and being more demanding of operator memory and attention. In [51], the FOV had a significant impact on rover teleoperation tasks. Different horizontal FOVs were tested, 40\({}^{\circ}\), 60\({}^{\circ}\), 120\({}^{\circ}\), and 200\({}^{\circ}\), and it was found that an horizontal field of view (HFOV) of 200\({}^{\circ}\) allowed average speeds 40% higher than with an HFOV of 40\({}^{\circ}\). The average stopped time with an HFOV of 40\({}^{\circ}\) was two times greater than with an HFOV of 120\({}^{\circ}\). Path decisions were compromised at lower FOVs, and operators reported that a wide field of view benefited the situational awareness while enabling higher speeds. In [82], the field of view was manipulated at two levels, 30\({}^{\circ}\) (narrow FOV) and 60\({}^{\circ}\) (wide FOV), while navigating a virtual UGV. Widening the FOV resulted in a superior performance benefit, leading to lower times to complete obstacle navigation tasks, decreasing the number of collisions and the number of turnarounds, and having higher piloting comfort. In [83], three different levels of FOV (48\({}^{\circ}\), 112\({}^{\circ}\), and 176\({}^{\circ}\)) wearing an HMD while walking, avoiding obstacles, estimating distances, and recalling spatial characteristics were analyzed. He reported that users' walking was more efficient with a wider FOV, but did not find significant effects on distance estimation (spatial understanding), on user's balance, nor on recalling the characteristics of the environment (i.e., memory recall). Wider to moderate fields of view tend to contribute positively to performance. Subjectively, FOV significantly improves teleoperators' situational awareness and perception of robot position and motion. However, moderation is advised as a wider FOV can increase motion sickness [81; 84; 85]. The causes of motion sickness can be related to the fact that a wider FOV increases ocular stimulation and motion in operators' peripheral vision. Video cameras have been used in robot navigation to perceive the environment, although this process can suffer from the \"keyhole\" effect [8; 86]. This means that just part of the environment can be acquired and presented to the human operator. Usually, the operator overcomes this situation with extra effort, manipulating the cameras to survey the environment and gaining similar scene awareness to direct viewing. Human eyes provide a horizontal field of view of 210\({}^{\circ}\) by 135\({}^{\circ}\) in the vertical [37]; however, stereo central vision relies on the overlap of the FOV of both eyes, and it is around 114\({}^{\circ}\). Thus, as a result of 210\({}^{\circ}\)/2 + 114\({}^{\circ}\)/2, an ideal HMD should provide a view of 162\({}^{\circ}\) horizontally for each eye [38]. Robotic remote operations include remote spatial and motion perception, navigation, and remote manipulation. A limited field of view (FOV) degrades the remote perception in several ways; however, it affects tasks differently. Tasks like navigation, self-location identification in space, and target detection are negatively affected due to the video feedback constraints [87]. Manipulation tasks involving action in a limited space can overcome the FOV limitation by gathering new points of view of the scene with more or less extra effort. Operators that perform navigation tasks based on a fixed camera mounted on a mobile robot tend to perceive the environment through a stack of images for which the points of view correspond uniquely to the robot's path.