## 1 Introduction  
Virtual reality (VR) is increasingly adopted by architects as it allows a design to be visualized in immersive 3D and experienced better than 2D drawings and even miniature models [1]. In the design of landscapes such as urban green spaces (UGS), VR has the potential to improve designs and maximize mental well-being benefits [2]. However, UGS designs in VR may not be valid, as the psychological effects of nature in VR may not be transferable into the real world [3, 4]. For instance, [PERSON] et al. compared participants' preferences for different UGS through either on-site, VR (panorama of landscape viewed through a head-mounted display (HMD)) or photos and found that participants' preference for different types of UGS differed between the on-site and VR conditions [3]. [PERSON] and [PERSON] [4] found that while exposure to virtual nature reduced anxiety, it did not improve directed attention as predicted by the attention restoration theory and as reported in other studies [5, 6, 7]. Thus, the effects of nature and green elements in VR may be different from reality and UGS designs in VR may be sub-optimal when transferred into the real world. Thus, it is important to establish the validity of the mental well-being or psychological benefits of nature in VR. While many studies have established the effectiveness of nature in VR to elicit positive psychological benefits [8, 9, 10, 11, 12, 13, 14, 15], these studies have different premises. These studies are based on the premise of knowing whether experiencing nature through VR can be used as a replacement for physically experiencing nature, for scenarios where physical nature is inaccessible due to distance or due to school or work commitments [12; 16]. Thus, these studies are concerned only with whether experiencing nature through VR can have positive psychological benefits but not whether the experience of nature through VR produces the same psychological benefit as the same nature in the real world, which is the concern when designing nature environments and UGS through VR. The ecological validity of nature in VR can be addressed by studies comparing the psychological effects of nature in VR with the same nature in the real world. While there have been reviews about the psychological benefits of virtual nature [17; 18; 19] and physical nature [20; 21; 22], there is, to our knowledge, no review of studies that explicitly compare virtual nature to real-world nature to establish the ecological validity of virtual nature. Several review articles review the psychological benefits of nature through virtual reality. [PERSON] et al. [17] conducted a systematic review of the psychological benefits of immersion in nature through VR, identifying 21 studies, with some evidence for a decreased negative affect. [PERSON] et al. systematically reviewed the effect of nature in VR on nature connectedness in non-clinical populations. [PERSON] et al. [18] systematically reviewed a range of mental health effects of green experiences through VR and synthesized results from 21 studies. [PERSON] et al. [19] systematically reviewed the stress reduction effects of nature exposure through VR. However, these systematic reviews were concerned with the psychological benefits of nature in VR but not with whether they are valid and correspond with real-world nature. Other reviews have looked at the psychological benefits of physical or real-world nature. For example, [PERSON] [20] reviewed studies that used EEG, fMRI, and fNIRS to measure neurophysiological differences between experiencing urban and natural environments. [PERSON] and [PERSON] [21] reviewed studies of stress relief and relaxation from forests. [PERSON] et al. [22] reviewed studies of the mental health benefits of nature for children and teenagers (0-18 years old).