# Study on Hand-Eye Coordination Area with Bare-Hand Click Interaction in Virtual Reality
## 4 Discussion
Therefore, movement time included not only the visual search time but also the time of the hand movement. Hand movement time is much longer than visual search time [37]. The distance of hand movement was shorter when clicking on the right side because those targets were closer to the starting position of the right hand. As a result, the measured movement time of the targets in the right area was shorter than that of the left area. Click performance was analyzed by movement time, continuous click time, and accuracy, which were found to be significantly affected by target appearance areas. Moreover, the areas with higher scores of subjective preferences acquired a better interactive performance, in terms of movement time and click accuracy This consistency shows the necessity of dividing efficient and interactive areas in a VE. Combining the movement time and click accuracy contour maps, their overlapping area is the best operation area, defined by a high accuracy and a short reaction time. In this experiment, the optimal interactive range of direct clicks with bare hands in virtual space is from \(-25^{\circ}\) on the left side to \(35^{\circ}\) on the right side horizontally and from \(-15^{\circ}\) in the downward view to \(20^{\circ}\) in the upward view vertically, as shown in Figure 10. The sub-optimal interaction area is the range above \(20^{\circ}\) in the vertical direction, except the top left corner. The remaining areas in the FoV supported by the HMD are areas of low click performance. Interaction areas divided for bare-hand interactions in the VE are shown in Figure 11, which includes the optimal interactive range, the sub-optimal interactive range, and the low interactive performance range. According to the results, some design suggestions for the interactive click interface could be proposed as follows to help arrange the layout of interactive components in virtual reality. Firstly, components that need to be clicked frequently and quickly (such as the confirm button and selection button) should be located in the center or slightly rightward area in the FoV. As shown in Figure 4, this is because the movement time contour is partial to the right side and the targets in the right area enable users to produce efficient click behavior. Moreover, since the lower right corner area may be obscured by the arm, the smaller moving distance doesnot make a shorter total interaction time. Therefore, the lower right corner area was not suitable for components requiring quick clicking. Figure 11: Suggested areas for the bare-hand interaction in the VE. Figure 10: Contour map of accuracy and movement time. Moreover, components that require precise control (such as a keyboard) should be located slightly below the horizontal line of sight. It can be seen from the offset heat map (Figures 8 and 9) that the offset in the horizontal and vertical directions is small in the area below the center of the field of view, where operation can reduce the occurrence of wrong clicks. Furthermore, the subjective preference scores of these areas were higher than others, which means a lower psychological load. In addition, notification information (such as warning notification) that needs to attract the attention of users quickly should be placed in the left area, where users can respond quickly to the targets. On the other hand, the information interface component (such as indicators and progress bars) could be located in the marginal area to avoid squeezing the space of interactive components. In VEs, visual target clicking occurs through visual and upper limb movements. As early as 1947, [PERSON] blind touch tests showed that click accuracy in the side area was lower than in the center in the horizontal direction, and that of the right side was higher than that on the left; in the vertical direction, the area below has the highest accuracy, and the middle area has a higher accuracy than that of the upper area [38].