## 4 Discussion
Generally, distance judgment in HMD condition tends to be underestimated as target distance increases, while distance judgment tends to be more overestimated in the SWDs (Figure 7b). The overestimation in the SWDs might be because of the negative parallax condition used in the experiment, where previous studies have reported that the distance judgment can be overestimated for the targets displayed at negative parallax [38; 39], where targets are viewed floating in front of the screen. Figure 7: A representative sample result of two participants showing how the estimates with respect to the reference at 65 cm distance from participants were observed. The positions judgment (**a**) in the HMD, a systematic shift to the right or to the left was observed. The way the HMD lens fit to the to the participant’s eye might be the possible reason for the observed result. However, (**b**) in the SWD, there was no systematic shift to any of the directions, instead, consistent estimates and overestimations were observed. The previously discussed studies in peripersonal space have revealed that distance estimation was more accurate when the target was positioned nearer to the observer. For instance, [PERSON] and [PERSON] [6] reported, as the target distance lengthened, the accuracy of distance judgment was found to endure more in the SWDs. However, the findings of the current study did not bolster this, and the overall exocentric distance judgment accuracy was low at 65 cm (Figure 4a) when compared to 100 and 150 cm. [PERSON] [23] suggested that several factors that affect spatial perception are likely to affect exocentric distances judgments. Thus, this phenomenon might be explained by accommodation convergence conflict as it was reported to be one of the possible reasons for the scrutinized impact [11; 32] at the nearest target distance. Similarly, [PERSON] et al. [40] and [PERSON], [PERSON], [PERSON] and [PERSON] [39] elucidated that the user's visual framework is stood up to conflicting visual information for targets closer to the participant as the highest accommodation-convergence mismatch observed. Another issue considered in this study was the position accuracy, and the result showed the significant effects of the displays on estimating the position of targets in the horizontal direction of the frontal plane. In the X direction (horizontal position), the position accuracy (Figures 5a-c and 8a,b) in the SWDs was seen to be better than in the HMDs, with the accuracies of about 91.6% and 86.3% respectively. However, in the Y direction (vertical position), the position accuracy (Figure 6a) was not significantly different between the SWDs and HMDs, with the accuracy of about 90.3% and 91.3% respectively. To the best of our knowledge, none of the past related investigations have reported position accuracy comparing different VR displays. However, for example, [PERSON] and [PERSON] [6] compared position accuracy in the frontal plane of real and stereoscopic environments, founded that the real environment (94% accuracy) was better than the position judgment in SWDs (89% accuracy), which was similar to the result reported in the present study. Additionally, the position accuracy was significantly higher at both 65 and 100 cm than at 150 cm. The finding is in concurrence with the past investigations, for example, [PERSON] and [PERSON] [6] reported that position accuracy decreases as egocentric distance increases. Similarly, the effect of the exocentric distance was significant, where precision declines as an exocentric distance increases (Figures 5d and 6b), and it might be explained by [PERSON]'s law that, as the exocentric distance increases, the error of estimation also increases [8; 37]. In addition, as shown in Figures 9-11, the position estimations of both VR displays were slightly shifted to the right side. We suspect that this might be because of the position estimations for the left sides of participants were blocked since all the participants were right-handed.