This study obtains scientific evidence on landscape perception by measuring and analyzing it using the physiological response index to make the assessment objective. To determine the change in psychological and physiological effects due to the difference in views by height of high-rise residential facilities, we selected apartments at least 25 stories high built in the last 5 years in P city, Gyeonggi-do where there is rapid urban development. We classified buildings located relatively on the inner side of the apartment complex into low floors (1–5 floors; approximately 2–12m), middle floors (11–15 floors; approximately 28–38m), and high floors (21 floors and above; approximately 54m and above) and prepared visual images by taking shots of the outside view on each floor. The photos are taken when looking at the window squarely at a horizontal angle from the inside of the apartment (Fig. 1). The experiment was conducted in a lab where temperature and humidity can be controlled, and visual images were presented in the size of 1.5 m × 2.4 m that is similar to the actual landscape size through an image playback device. The photos of each floor are grouped with 10 images and presented continuously for 280 seconds, and the order of presenting the groups with different heights was random by participant to offset the order effect.

We selected 22 participants (11 male, 11 female) out of healthy men and women without any medical history such as cardiovascular or mental diseases who expressed the voluntary will to participate. We explained in detail the purpose and contents of this study before the experiment and obtained consent in writing. They were to move on a wheelchair to minimize physical movements that may affect physiological responses during the experiment. This study was approved by the Institutional Review Board (P01-202009-12-002).

To determine the difference in psychological responses depending on the difference in views by height, we used two types of psychological questionnaire to assess the impression of the landscape, change in mood states, anxiety level, etc. Semantic differential (SD) was first used to assess the impression of the difference in views by height. This study rated items using 9 symmetrical adjectives such as ‘artificial-natural’, ‘closed-open’, ‘complex-simple’, ‘depressedlively’, ‘incongruous-harmonious’, ‘unfamiliar-friendly’, ‘unstablestable’, ‘desolate-comfortable’, and ‘cold-warm’ on a 7-point Likert scale with reference to similar studies (Lee, 2017; Lee and Lee, 2018). The Profile of Mood States (POMS) was used to measure the change in mood states and subjective emotions depending on the view (Yeun and Shin-Park, 2006). By rating 30 items on a 5-point Likert scale, we quantified and analyzed the moods in 6 subscales such as ‘tension-anxiety (T-A)’,‘anger-hostility (A-H)’, ‘depression (D)’, ‘vigor (V)’, ‘fatigue (F)’, and ‘confusion (C)’.

We measured autonomic nervous system activity as an indicator of physiological responses toward the views. We measured heart rate variability (HRV) data widely used in landscape studies by sensitively reflecting the change in environmental stress. We converted R-R intervals of heart rate data into frequency and classified it into low frequency (LF) ranging from 0.04 to 0.15 Hz and high frequency (HF) ranging from 0.15 to 0.40 Hz. In general, HF is used as an indicator of parasympathetic nervous system activation, and LF/HF as an indicator of sympathetic nervous system activation (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). HRV was continuously measured while the participants looked at the visual images and recorded using Mybeat (UNION TOOL Co., Japan). We also measured blood pressure and pulse rate as the typical indicators of autonomic nervous system activity, which we measured 2–3 times on the upper right arm using a sphygmomanometer HEM-1000 (OMRON, Japan) after looking at the views, and recorded the means.

As a result of analyzing the impression evaluation on the difference in views by height of high-rise apartments, there was a significant difference in 8 out of total 9 items excluding ‘complex-simple’ (Fig. 2). Overall, naturality (0.77 ± 0.24) and openness (0.41 ± 0.32) were high in low floor views of green space outside, and openness (0.45 ± 0.33) and stability (0.45 ± 0.23) were relatively high in high floor views. Spatial openness of an apartment complex is greatly affected by the height of the housing (Kang and Park, 2006), which is why low-rise buildings were expected to seem more closed compared to mid-rise or high-rise buildings, but they actually showed a similar level of openness as high floor views. A previous study (Kim et al., 2021) reported that people may feel greater spatial openness when there are plants even if the size of the space is the same. The psychological response shown in this experiment can be interpreted in this context. On the contrary, middle floor views that mostly show the apartment building on the other side showed a remarkable increase in coldness (−1.41 ± 0.28) and closedness (−1.18 ± 0.31), generally showing negative responses.

As a result of POMS data analysis on landscape, middle floor views with high closedness showed remarkably high negative mood states such as tension-anxiety (T-A; 4.71 ± 0.97), hostility (A-H; 2.63 ± 0.69), and confusion (C; 5.46 ± 0.90) (Fig. 3). On the other hand, these negative emotions were remarkably low in low floor views (T-A, 2.33 ± 0.71; A-H, 0.92 ± 0.40; C, 3.50 ± 0.75), while vigor (V, 7.04 ± 1.00) increased significantly. In high floor views showing the sky, vigor (V, 5.58 ± 0.98) was also higher than middle floor views. This result implies that apartment landscape may constantly affect the psychological state of residents, and it partially supports the fact that children living on middle floors exposed to this closed and stuffy landscape are showing a relatively high disease incidence (Choi and Kang, 2001). Indoor green space in apartments reduces spatial closedness felt by residents and has a positive effect on changes in their emotions and mood states (Hung and Chang, 2021), and thus it can be used as a means to solve health problems caused by the environment.

As a result of analyzing HRV data when looking at the views, it was found that the physiological responses of participants varied depending on the landscape. HF, which is the indicator of parasympathetic nervous system activity, showed higher means in low floors (2,294.96 ± 169.79; Fig. 4) compared to middle floors (1,553.45 ± 84.66; p < .01) and high floors (1,523.02 ± 70.49; p <.01), showing a statistically significant difference. LF/HF, which is the indicator of the sympathetic nervous system increased in tension, showed significantly lower means in low floors (1.30 ± 0.07; p <.01) and middle floors (1.34 ± 0.06; p < .01) compared to high floors (1.83 ± 0.09; Fig. 5). The results of analyzing systolic blood pressure (low floors, 112.05 ± 2.90; high floors, 116.67 ± 3.12; p < .01; Fig. 6) and pulse rate(low floors, 70.05 ± 2.02; high floors, 71.18 ± 2.05; p < .05; Fig. 7) also showed significantly lower means in low floor than high floor views. This indicates that residents have lowest physiological stress, by which they are unconsciously affected, on low floor views where they can see the landscape, which is because green space resolves psychological tension and reduces physiological stress (Herzog et al., 1997; Roe et al., 2013; Shin and Shin, 2020). A preference survey on apartment views also proved that people preferred low-rise apartments with a higher ratio of natural landscapes than mid-rise apartments (Moon et al., 2006), and this result clearly shows the psychological response that explains the difference in landscape preference. The interesting thing is that high floor views tended to inhibit parasympathetic nervous system activity and accelerate sympathetic nervous system activity, which indicates that high floor views may unconsciously have a negative impact on psychological health. A study on high-rise settings also showed similar results as this study (Kim and Ha, 1996). Views from high floors induce fear and anxiety and simulate the sympathetic nervous system, thereby increasing blood pressure. With the growing concerns of health due to the increase in high-rise residential environment (Kang and Choi, 2008), this study proves that landscape or views may be a direct factor that affects resident health.