## 5 Discussion
As a perceptual factor, they focused on visual acuity and speculated that the present results would be obtained if visual acuity was superior in the horizontal and vertical axes. As for the kinematic factor, they speculated that the result was due to the complexity of the movements required to manipulate the oblique method. The neck joint movements can be divided into three categories: Cervical flexion/extension, Cervical rotation, and Cervical side-bending. The head movement in the horizontal and vertical directions can be achieved by any one of the above three movements. However, movement in the oblique direction can include not only the combined movement of theabove three but also may add movement of the lower limbs, i.e., waist and foot joints, which may have increased the overall difficulty of the operation. Although the operability of ARHD by head movement was not as good as that of hand operation as an endoscopic surgical communication support system, the fact that information can be presented directly by the head is still helpful for practical use because AR can be projected onto the real environment, unlike the VR environment. Additionally, since the steering model can be applied, it became clear that improvements using this model will be effective in designing the space in the operating room for using the system in the future, such as the display size of endoscope images and the distance between the surgeon and the display. Once clear performance differences between different angles become apparent, it would be helpful to improve the system so that the operating room can display several virtual monitors adjusted to appropriate angles instead of using a fixed endoscopic surgical image monitor. [PERSON] et al. [25] have developed a system that uses AR to display the monitor as a hologram instead of a conventional monitor, allowing the surgeon to view the endoscopic image in real-time and at any position. In this way, the introduction of a technology to project the endoscope image itself as a hologram at an arbitrary position in the operating room space can be a factor that increases the usefulness of this system. There are various endoscopic surgery techniques, and the technique targeted in this study assumes laparoscopic gastrectomy using five trocars (two for each surgeon and one for the camera) in the field of digestive surgery. However, according to [PERSON] et al. [26], thanks to recent advanced and improved technologies, there have been reports of cases in which laparoscopic gastrectomy with a small number of ports has been safely performed. In such a case, not all of the hands of both surgeons are occupied by the device, and some communication is possible with hands free. However, a recent report [27] also states that most surgeons still use at least five trocars for laparoscopic gastrectomy in the field of digestive surgery. Thus, the proposed system is still valid, although limited. Our studies' immediate goal was not to introduce the communication supporting system for practical use in its current form. Instead, the immediate goal was to evaluate the performance of this prototype as a benchmark for considering whether it could serve as a base idea for future development. Therefore, the prototype system does have some inherent limitations for practical use. Most of all, the use of head-mounted AR glasses does not fit in a clinical environment in terms of the sterilization issues, weight problem, the requirement of hand gesture, and difficulty in using the holographic display in strong light conditions. With recent technological advances, we believe that head-mounted AR glasses will continue to progress in the direction of being lighter and more packaged and that the problems above of weight, sterilization and the need for gestures will not necessarily present in the future.