## 5 Discussion  
This study was designed to better understand how variability across environments in the presence of familiar spatial cues can influence spatial perception ability. Specifically, we investigated participants' ability to determine the absolute distance and relative size of stimuli under three environmental conditions. Results confirmed difficulties in distance and size estimation, in particular under the moderate visual cues environment (environment 2: space scape). However, even with maximum visual cues (environment 1: cityscape), perceived distance significantly deviated from the actual distance, and was consistently underestimated. Distance compression could be due to the VR platform. Existing studies have shown that distance estimation is regularly underestimated in a VE when compared to the real world [42; 43; 44; 45; 46; 47; 48]. [PERSON] et al. [35], for example, compared absolute distance judgment in the real world with varying quality VR environments (e.g., low-quality graphics and wireframe graphics). They showed that distance judgment in VR was significantly underestimated. For this study, we evaluated relative distances to mitigate this underestimation. Virtual environments may also not be able to represent the real physical environments exactly. There may also be perceived dilations and compressions of space as found by [PERSON] [49] in a study of lenses that may influence the field of view aspect of computer graphics and VR. We found that the absolute distance to the target was underestimated in maximum (environment 1: cityscape) and minimum (environment 2: space scape) spatial cue conditions, whereas it was overestimated in the moderate cue (environment 3: outer space) condition. We attribute more accurate perceptual judgments in environment 1 to the present's recognizable objects. These objects serve as key frames of reference to determine the distance and size of other objects [50]. This was also expressed in several participants' comments. When judging a target's absolute distance in environment 1: cityscape, the maximum visual cue environment, participants noted that they used the uniform tiles on the floor or standard height street poles to measure the relative distance and size of the virtual objects. In contrast to our expectation that environment 3 (outer space), which had the least amount of visual cues, would yield the highest relative error, it was in fact environment 2 (space scap), the moderate visual cue condition, that produced the highest relative error. The reason for this is unclear, but one may speculate that unfamiliar visual cues in the presence of other familiar cues such as gravity, could lead to misjudgments regarding distance and size. This partially replicates previous findings that show the deceptive nature of surfaces, and that the absence of familiar objects hinders distance judgment [51; 52; 53; 54]. Participants also reported difficulties in estimating distance in environment 2 (space scap), the moderate spatial cue condition, due to the presence of unfamiliar spatial features, such as mountains, valleys, and craters. Some participants reported it was challenging to determine whether the mountain on the Mars-like terrain was a big mountain far away or a small sandpile close by, because of the deceptive nature of the altered environment's surface. Therefore, distance judgment varied considerably between participants. One participant estimated a target at an actual distance nine meters from the standing point as being one meter away, while another judged the same 9-m target to be 356 m away. [PERSON], a former Apollo 14 astronaut, remarked in On the Moon: The Apollo Journals, that \"It's crystal clear up there-there's no closeness that you try to associate with it in Earth terms-it just looks a lot closer than it is\" ([55], as cited in [51]). In the size estimation task, a tendency to underestimate depth was observed. This resonates with previous studies [23; 24; 56].