## 5 Conclusions  
In this study, we have shown the effects of VR displays on exocentric distance judgment and position accuracy, in a frontal plane. The effects of target distance, exocentric distance, and target size were also explained.  
The results showed that participants were more accurate in exocentric distance estimation while using an HMD than using an SWD. In addition, a significant effect of target distance on exocentric distance judgment accuracy was observed in the SWDs, where accuracy was lower at a target distance of 65 cm from the participant than for the targets displayed at 150 cm from the participant. However, exocentric distance judgment was not affected by the exocentric distance and the target size. Furthermore, the distance judgment appears to be underestimated in the HMDs, whereas distance judgment was overestimated in the SWDs.  
Similarly, the horizontal position accuracy in the SWD was seen to be better than in the HMD, whereas no significant difference was observed in the Y-position accuracy. The horizontal position accuracy was worsened as the exocentric distance increased, while the effect of exocentric distance on the vertical position accuracy was not significant. It seems that the HMD was superior to the SWD with respect to exocentric distance judgment, which, on the other hand, suffered from the systematic shift that made the horizontal position accuracy less accurate. Further studies are necessary to conclude whether the systematic shift in HMD was because of either an error in fitting the center of the lens of the displays to the center of the eyes of participants or interpupillary distance.  
Current trends in commercial technology, though, are likely to result in VR displays for environments that have several shortcomings. The results also confirmed that VR displays have yet to be improved to provide proper space visualization of the environment. Accordingly, the findings are of great significance since the result can give information how VR displays affect the overall accuracy of exocentric distance judgment, and how size, target distance, and exocentric distance influence the accuracy of distance judgment. The results also can help to choose VR displays for a specific application. Quite possibly, the study is one of the first to report exocentric distance accuracy in virtual environments, especially focusing on a comparison between HMD and SWD.  
This paper concentrated on exocentric distance judgment in the frontal plane under three target distance (depth) conditions, which may have restricted the full explanation to just the frontal plane. Furthermore, a fixed chinrest was employed to avoid head movement, which presumably would not be expected in real-world applications. Along these lines, further study will be required to address the influences of displays on exocentric distance judgment in the sagittal and transverse planes.  
Conceptualization, C.J.L. and B.H.W.; methodology, B.T.A., D.C. and B.H.W.; software, B.T.A., D.C. and B.H.W.; data collection, B.T.A. and D.C.; statistical analysis, B.T.A.; writing--original draft preparation, B.T.A.; writing--review and editing, B.T.A., C.J.L. and B.H.W.; supervision, C.J.L. and B.H.W: funding acquisition, C.J.L. and D.C. All authors have read and agreed to the published version of the manuscript.  
This paper was partially funded by the Ministry of Science and Technology, Taiwan grant number MOST-107-2218-E-011-019-MY3 and the APC was funded by [PERSON] and [PERSON].  
The authors declare no conflict of interest.