Effect of a Virtual Biophilic Residential Environment on the Perception and Responses of Seniors

Abstract

This study investigates the effects of a virtual biophilic residential environment on seniors’ physiological and subjective responses to evaluate its potential to promote healing and recovery. Thirty seniors were exposed to three different scales (units, buildings, complexes) of virtual biophilic residential environments that combined both physical and digital biophilic elements. Physiological responses, including heart rate, heart rate variability, and galvanic skin response, were measured alongside self-reported levels of satisfaction and immersion. The primary objective was to assess the effectiveness of physical and digital design interventions at each residential scale. The findings revealed that the virtual biophilic residential environment reduced physiological stress in seniors, with the most significant impact observed at the unit scale. Digital design interventions further enhance stress relief benefits, indicating that integrating physical and digital elements in biophilic residential environments can positively influence seniors’ stress levels. Additionally, significant correlations were identified between physiological responses and subjective perceptions of immersion and satisfaction. This study is valuable as an initial comparative analysis of the effectiveness of physical and digital approaches in biophilic design. This paper is a preliminary study and is significant in that it systematizes virtual environment research from an age-friendly perspective and expands approaches to biophilic design.

1. Introduction

1.1. Background and Purpose

Rapid urbanization has indigenized residential environments and lifestyles that are separated from nature. Modern people must travel farther to experience quality nature, which requires significant financial and time resources and physical efforts. E. O. Wilson [1] explains the relationship between humans who constantly visit nature and the nature inherent in us through the biophilia hypothesis. Biophilia refers to humans’ instinct to value life. According to the biophilia hypothesis, activating internal biophilia can improve human physiological functioning [2]. Based on this, biophilic design has been promoted in modern built environments to induce positive experiences with nature and activate biophilia. Biophilic design aims to evoke positive interactions with nature within architectural contexts, thereby facilitating improvements in human physiological functions [3]. Kellert, Heerwagen, and Mador [3] identified the benefits of nature relevant to positive human responses to embody the concept of biophilic design. Benefits of nature include improved immune function [4] and enhanced physiological and psychological recovery [5,6], as well as positive impacts on physical health and well-being [7]. Conversely, environments that lack the sense of nature create advantageous conditions for disease spread and socio-psychological deficits [8], particularly affecting vulnerable populations like seniors, who are more susceptible to environmental stress [9]. As seniors age, they prefer to spend more time at home and recover in familiar places [10]. Interaction with nature in the residential environment helps activate seniors’ multisensory experiences and cognitive functions [11], contributing to their overall quality of life (QoL) [12,13]. Nevertheless, urban areas with high housing density, such as apartment complexes, limit seniors’ opportunities to experience nature. Additionally, related studies on the seniors’ experience with nature focused on medical and welfare facilities, resulting in a lack of research addressing everyday places, such as residential spaces.

Previous studies have utilized field investigations, questionnaires, and post-occupancy evaluations to identify natural elements contributing to seniors’ health [14,15,16,17]. Recently, related research has employed virtual environments (VEs) as experimental platforms to assess the quantitative effects of biophilic design. These studies indicate that natural experiences in VEs provide benefits comparable to those in real-world settings [18,19,20]. The authors have established VEs as reliable experimental tools, suggesting the potential for integrating digital methodologies into biophilic practices. However, many research challenges and opportunities remain for biophilic VEs. First, most studies focus on the independent effects of biophilic elements, limiting our understanding of their combined effects. Second, there is a need for more discussion on the impact of biophilic design across different scales. Third, VE simulations have primarily focused on the physical planning of biophilic design. Whether the digital planning of biophilic design can also evoke positive responses is unsolved. Lastly, most VE study participants are healthy young adults, resulting in insufficient data on seniors’ physiological responses and perceptions.

This study focuses on the necessity of and potential for expanding biophilic design for seniors within urban apartment houses. This study aims to apply physical and digital biophilic elements according to residential scales using VEs and analyze the seniors’ physiological and subjective responses. The research addresses three questions: (1) Does exposure to complexly designed virtual biophilic residential environments elicit positive physiological responses in seniors? (2) Do digital design interventions in virtual biophilic residential environments produce positive physiological responses among seniors? (3) Do seniors’ physiological responses to virtual biophilic residential environments correlate with their subjective responses? The focus of the current research is to fill the gap in our understanding of the impact of virtual biophilic settings and approaches on seniors’ health.

1.2. Research Scope and Flow

The contents and flow of this study are summarized as follows. First, the study reviewed the relevant literature to identify the physical and digital elements of biophilic residential design, the scope of application, and the specific needs of seniors. The residential environment covered in this study focuses on urban apartment housing types and is divided into units, buildings, and complexes. This classification helps identify the biophilic design elements that should be emphasized according to each scale. Units consist of individual living spaces; buildings encompass shared areas like lobbies and rooftop gardens; and complexes include interactive spaces with entrances and public facilities for residents. Second, the study systematized the experimental and analytical methods for measuring bio-signals, considering the characteristics of seniors. Third, it measured the physiological stress responses of seniors aged 59 years or older due to VE exposure. Heart rate (HR), heart rate variability (HRV), and galvanic skin response (GSR) were utilized as indicators for assessing short-term stress responses to VE exposure. Finally, a statistical analysis was conducted to compare the differences and changes in the physiological and subjective responses of seniors exposed to virtual biophilic residential environments.

2. Literature Review

2.1. Biophilic Design Experience by Environmental Scale

Kellert [21] delineated three categories from an experiential perspective that are essential for the effective practice of biophilic design. Additionally, he identified 25 sub-attributes associated with these categories, the details of which are illustrated in Figure 1.

Direct experience of nature involves interaction with nature’s characteristics and functions. Early biophilic design focused solely on aspects of nature that were free from human intervention [22]. However, recently, artificial nature that activates ecosystem functions has also been considered a direct experience. This results from pursuing environmentally sustainable development by maximizing nature’s functional benefits [21]. Indirect experiences with nature involve mimicry of nature rather than direct exposure. This includes intentional works such as natural materials and colors that evoke a sense of nature. In addition, this includes exposure to nature through photos and videos; therefore, virtual simulations could be considered to optimize these experiences. Finally, people experience space and place by being exposed to built environments that exhibit the characteristics of the natural context. The experience of space and place draws involuntary attention from humans [23], including spatial properties that arouse human curiosity and interest, such as prospect, refuge, mobility, and wayfinding.

Beatley [24] suggested the Nature Pyramid to experience optimal nature, depending on the environmental scales. The Nature Pyramid is a guideline for discussing the duration and intensities of nature that are essential for human health. At the top level of the Nature Pyramid, the international scale guarantees high immersion and value, but is not easily accessible. Especially for seniors, it is vital to ensure more significant opportunities to experience nature. Therefore, we must discuss efficient ways to experience high-quality biophilic design at the most frequently accessible neighborhood scale. Figure 2 illustrates the biophilic effects based on the framework of the Nature Pyramid and the biophilic design experience.

The experience of biophilic design has a greater effect when delivered through an integrated approach rather than singular attributes [21]. Furthermore, a strategy that integrates both the physical and digital elements of biophilic design has the potential to mitigate the physical limitations inherent in each scale of the Nature Pyramid, thereby enhancing the biophilic experience at the neighborhood scale.

2.2. Residential Environment Planning for the Seniors’ Biophilic Experience

The multifaceted functional decline associated with aging can cause various physiological discomforts and psychosocial problems in seniors [25]. Research shows that biophilic experiences improve recovery and well-being [26] and are linked to residential factors like comfort, value, and accessibility [27]. The benefits of biophilic experiences are also related to residents’ preferences and how they experience nature [28]. In particular, as digital technologies advance and new ways of experiencing nature are explored, biophilic design decisions should consider residents’ needs and capacities for digital and physical experiences.

Lee [29] categorized biophilic residential designs for seniors into physical and digital approaches and proposed 64 planning elements based on the biophilic design experience [21]. Based on these findings, she identified key planning elements by investigating seniors’ preferences. This study identified the top 30% of planning elements from Lee’s [29] preference survey results to understand the seniors’ needs for biophilic residential plans (

Table 1. Seniors’ residential planning preferences based on biophilic design experience.

Biophilic Design Experience	Biophilic Residential Planning
Direct experience of nature	Physical	Water spaces and decor Openings and spatial structures facilitating natural ventilation Openings with views of natural elements Indoor garden or plant decor Light well or courtyard
	Digital	Immersive media on the dynamic properties of water Automatic window opening and ventilation based on indoor air quality
Indirect experience of nature	Physical	Natural materials and color scheme Air vents and circulation systems Artificial natural lighting and warm lighting Indirect and diffuse lighting
	Digital	Virtual 3D natural elements and objects Automatic air purification and temperature/humidity control based on resident status Biogas energy generation and bioprocessing of waste
Experience of space and place	Physical	Visually opened small resting areas Community garden and edible landscaping Ecosystem-friendly pathways Seating or spaces providing a sense of protection
	Digital	Project mapping utilizing spatial characteristics Controllable transparent switching glass window

).

Seniors prefer design elements related to water, particularly favoring various approaches to its dynamic qualities. They also prefer direct interaction with plants and favor materials and colors that evoke nature. Additionally, they appreciate digital services that can be automatically controlled based on the surrounding setting and digital devices (e.g., displays and projections) that support visual stimulation of nature. Previous studies have expanded the framework of biophilic design for seniors, and more empirical research is needed to develop these findings into effective practices.

2.3. Virtual Environment and the Physiological Response

Many studies use VEs to encourage the immersion and interaction of subjects. Related studies have examined the health benefits of biophilic designs through human responses to stress. These studies frequently employ self-report questionnaires or in-depth interviews to complement physiological measures [19]. This study reviewed the application and limitations of VEs through prior research, including physiological response measurements. Findings are presented in

Table 2. Studies on the application of VEs to measure responses to experiences with nature.

Parameters	Applications	Limitations/Opportunities
Subjects and Sample size	Many studies conduct experiments on healthy, young intellectuals [30,31] The minimum sample size is 26 [32], and the average number of subjects is small, around 50 [33,34]	Little research on populations with physical or cognitive disabilities Need for biophilic VE research on individuals with diverse demographic characteristics and backgrounds
VE setting	Emphasize forests and urban parks and include comparisons with modern cities or real-world settings [35,36] Focus on direct experiences in medical facilities or workspaces [19]	Research on biophilic architecture and indoor environments is lacking Different methods and scales for biophilic design should be considered
Exposure time	The appropriate exposure time for virtual biophilic environments is 1–5 min [19,37,38] A “washing-out” process prevents carryover between variables [35]	Extended VE exposure increases the severity of cybersickness Lack of diverse experimental samples to generalize effective exposure times
Physiological measuring	Compare autonomic nervous system responses to baseline or include stress tasks [18,19] Clinical studies have shown cortisol level variations especially correlating with electrocardiogram (e.g., HRV) [39,40] and electrodermal activity (e.g., GSR) [41,42]	VEs’ limited viewing angle and low-quality rendering can lead to discomfort by disconnecting users from the real [32] Instantaneous self-reports are used to annotate the collected stress data levels and provide individuals’ perception of stress [43]
VE devices and sensors	Using panoramic images or 360° videos [18] Integrating biometric sensors with eye-tracking enhances measurement reliability [19]	HMD use is associated with higher cybersickness [44] and may interfere with bio-signal sensors [33] Crucial to investigate devices, notably three-dimensional or curved displays, which may offer potential solutions to alleviate cybersickness [45,46]
Experimental environment	It is crucial to maintain IEQ under consistent conditions throughout the entire experiment [19,47]	There are limitations in generalizing the correlation between neurophysiological responses and external environmental conditions An integrated control and management system is required to reduce the influence of the external environment

Notes: VE = virtual environments; HRV= heart rate variability; GSR = Galvanic skin response; HMDs = head-mounted displays; IEQ = Indoor environmental quality.

.

Most experimental research using VEs is based on dichotomies [48], such as ‘nature or green versus building or city’, and limited research compares and analyzes the impact of various design elements in combination. In prior studies, the recommended exposure time to VEs is proposed to be 1–5 min to induce stress and recovery effects [37]. A recent study [19] has reported that the first 4 min of exposure significantly affected recovery from acute stress. Participants adapt and immerse themselves more easily in VEs that they have experienced or are likely to encounter [49], which depends on providing a level of sensory stimulation similar to reality. In studies for seniors, immersive devices should be used cautiously as they may interfere with wearable sensors for physiological measurements [33], and individual adverse effects must be considered. Previous studies have emphasized that cybersickness and psychological rejection, which can occur when using head-mounted displays (HMDs), are factors that mediate emotional and physiological responses, especially in senior participants [32]. Further empirical studies are required to elucidate the correlation between seniors’ psychological and physiological responses to VEs.

3. Materials and Methods

3.1. Participants

This study was approved by the Institutional Review Board of Keimyung University. All participants provided written informed consent before participating. Recruitment occurred from April to May 2024 at eight senior welfare centers in Daegu, South Korea. Participants were recruited using posters, notices, and emails.

Eligibility criteria included: (1) Koreans in the Daegu area, (2) adults over 55 capable of independent living, and (3) individuals living in an apartment for over a year. Homogeneous convenience samples obtained through such conditioning exhibit narrower yet clearer generalizability [50]. Thirty seniors aged 59 to 80 (mean age 70.30 ± 6.56) participated, with 66.7% over 65 and 53.3% female (see

Table A1. Characteristics of the participants.

Variable		F(n) or Mean	% or SD
Age	Middle-aged (59–64years)	10	33.3
	Seniors (>65 years)	20	66.7
Sex	Male	14	46.7
	Female	16	53.3
Total		30	100.0

). Participants were advised against excessive exercise, caffeine, alcohol, or smoking within 12 h [19,51]. During the experimental period of approximately three weeks, participants visited the same site at a set time (10:00–13:00).

3.2. Study Design

This empirical study extends beyond literature reviews, building on previous experimental designs [18,19,20,52,53,54] that used a similar methodology. By referencing the results of previous studies that have proven to be valid, we focused on controlling confounding factors according to experimental conditions and procedures, such as physical environment, etc., and reducing potential bias in the results. Consequently, we randomly assigned the visit and exposure orders through a randomized cross-over design and utilized repeated measures data from the same individual. Repeated measures data can help control potential time-invariant factors, such as sociodemographic characteristics. This study utilized a 3D simulation video for VE exposure and provided stimuli through a curved monitor. This is based on the following reasons. First, to minimize negative responses and potential carryover effects caused by the subject wearing HMD. The results of previous studies reflect that seniors have a high potential risk of cybersickness [55,56], and have a high preference for large displays and curved monitors [57,58,59]. Furthermore, related studies [45,46] have demonstrated that while 3D desktop displays or curved displays enhance the sense of presence, they do not directly influence cybersickness. Second, to reduce the time to adapt to the experimental environment and variables and the degradation of biophilic VE quality. Immersive displays can provide intense immersion and realism, but older adults need sufficient time to adapt to unfamiliar devices. Related studies [60,61] did not find significant differences between device types in the effects of nature exposure through HMD (360° video), TV, and PC displays. Moreover, VEs utilizing 360° videos and real-time rendering may experience image quality and movement lag degradation, depending on the output device or software used. To prevent this, this study provided high-definition (1920 × 1080) videos as stimuli and confirmed through preliminary tests that there were no related problems depending on the device or application software used.

3.3. VE Simulation

Virtual biophilic residential environments include differentiated strategies across three scales: units, buildings, and complexes. We selected six planning elements based on Table 1. The selection criteria are as follows: (1) reflecting the seniors’ needs [29]; (2) applying the three biophilic experiences, including physical and digital planning elements; and (3) giving priority to planning elements that can be applied to all three residential scales. The selection and simulations of planning elements were reviewed and refined through a process involving three experts in biophilic design research. Figure 3 shows the detailed settings for VEs.

The biophilic residential environment was modeled in SketchUp Pro 2021, and VEs were created as 3D videos using Enscape 3.1. Considering the participants’ housing type, each residential environment was designed to have a familiar structure [35]. The exposure time for each residential scale was set at 4 min, which has been reported to have the most significant effect on stress recovery in biophilic VEs [19,37,38]. The VE videos consist of physical and digital intervention sections. Each planning element was applied complexly according to the residential scales.

3.4. Outcome Measures

This study measured seniors’ autonomic nervous system responses using HR, HRV, and GSR signals, validated in prior research [51,62,63,64]. HR data are the most used indicators of the acute stress response. HRV is a powerful indicator of the overall control of the autonomic nervous system activity, reflecting the ability of the heart to react to or adapt to unexpected stimuli quickly. This study utilized the Standard Deviation of Normal to Normal (SDNN) intervals for HRV analysis. GSR indicates changes in skin conductivity due to emotional and mental stimuli [65], and is used to evaluate emotional levels on the valence dimension (e.g., positive and negative).

We used a noninvasive biomonitoring sensor, the Shimmer3 GSR+Unit, to measure bio-signals. It was attached to the index and middle fingers of the subject’s right hand and collected HR (bpm), HRV (ms), and GSR (μSiemens) signals through two electrodes. The sensor was connected to the iMotions Biomedical Research Platform v.8.0 software, allowing data acquisition and real-time analysis. Additionally, participants self-reported subjective satisfaction and immersion levels. Subjective immersion is sensory attention to the exposure environment and could be influenced by the degree to which external stimuli from the environment are substituted by technology [66]. Therefore, participants were asked to report on the degree of realism of the presented stimuli. They evaluated the realism of the stimuli using a 5-point Likert scale from 1 (lowest) to 5 (highest) (see Supplemental Materials).

3.5. Experimental Procedure

Biophilic VEs were presented to the participants through a high-resolution (3440 × 1440) ultra-wide curved monitor (LG, Seoul, Republic of Korea). External factors like noise and lighting were minimized, and consistent conditions (air quality, temperature, and humidity) were maintained throughout the experiment. Indoor Environmental Quality (IEQ) is a pivotal determinant that can impact the results of seniors’ physiological responses. This was monitored in real-time using an integrated IEQ sensor (LG, Seoul, Republic of Korea), with criteria based on the WHO’s Indoor Air Quality Guidelines [67] and prior studies [31,68] using similar physiological indicators. The measured IEQ data and related criteria from the experiment are outlined in

Table A2. Indoor environmental quality measurement data and appropriate range.

Variable	Appropriate Range	Mean ± SD
PM2.5 (μg/m3)	≤100	0.3 ± 0.5
CO2 (ppm)	≤1000	712 ± 97
Temperature (°C)	22.3~26.5	23.4 ± 1.1
Relative Humidity (%)	32~48	36.4 ± 8.3

.

Figure 4 shows the experimental environment and measurement equipment. The participants were informed about the biophilic design experience and VE stimulation before the experiment, and the sensor (Shimmer Wearable Sensor Technology, Dublin, Ireland) was worn only after obtaining their consent. Before watching the VE video, the participants rested with their eyes closed for baseline measurements, and their HR, HRV, and GSR were continuously measured until the end of the experiment. Participants were exposed to different scales of the biophilic residential environment in a random order, and a 5 min break (black screen) was provided to minimize interference between measurement signals when the VE stimuli were switched. After VE exposure, the sensor device was removed, and a questionnaire was administered to gather the participants’ general information and their subjective perceptions of the virtual experience. Seniors quickly become exhausted from lengthy hours of experiments and intricate procedures, which may have harmful physiological repercussions. Accordingly, the complete exam was planned to last no more than one hour to maintain and protect their physiological condition, while reducing or eliminating any physiological stress to those senior test participants. The sequence of the experimental procedure is shown in Figure 5.

3.6. Statistical Analysis

All collected data were analyzed using the IBM SPSS statistics release 27. The statistical processing and analysis methods of this study are as follows. First, the change in the score of physiological measurement values at baseline was used as an outcome variable (e.g., ΔHR) to adjust for potential gaps between participants’ physiological data. This is recommended as one way to control for covariates in repeated measures data in pre- and post-tests [69]. Second, a one-way repeated measures ANOVA was performed to test the difference in changes in physiological responses among the three residential scales. Third, paired t-tests were conducted to compare the physical and digital intervention sections, verifying whether significant differences existed in physiological responses. Finally, Spearman’s rank-order correlation was performed to test the relationship between self-reported perception levels and physiological responses and to identify more important variables in future studies. All analyses were considered statistically significant using a minimum alpha level of 0.05 within a 95% confidence interval.

4. Results

4.1. Descriptive Statistics

Table 3. Description of all study variables.

Outcomes		Biophilic Residential Environments (Exposure)				Baseline (Mean ± SD)
		Unit (Mean ± SD)	Building (Mean ± SD)	Complex (Mean ± SD)	Total (Mean ± SD)
Physiological response	HR (bpm)	66.35 ± 9.12	69.47 ± 8.99	67.23 ± 10.50	67.68 ± 9.65	69.19 ± 6.53
	GSR (μSiemens)	0.467 ± 0.17	0.506 ± 0.17	0.497 ± 0.19	0.489 ± 0.176	0.589 ± 0.244
	HRV (ms)	68.06 ± 14.98	63.51 ± 15.63	64.88 ± 14.80	65.15 ± 15.28	62.26 ± 11.83
Self-reported perception (Likert 5)	Satisfaction	4.13 ± 1.01	3.87 ± 1.25	3.90 ± 0.99	3.97 ± 1.10	-
	Immersion	4.10 ± 1.03	3.70 ± 0.99	3.83 ± 1.12	3.88 ± 1.13

Notes: SD = standard deviation; - = no data. The most positive results were bolded.

presents the physiological and self-reported outcomes by residential scale and baseline. When stress is alleviated, HR and GSR decrease, whereas HRV increases. The results showed that compared to baseline, when exposed to a biophilic residential environment, HR (−1.51 bpm) and GSR (−0.1 μS) decreased, and the HRV (2.89 ms) increased. The average subjective satisfaction of the participants was 3.97 ± 1.10, and the immersion was 3.88 ± 1.13. As a consistent finding, participants’ physiological recovery levels and subjective perceptions were all observed to be most positive on the unit scale.

4.2. Physiological Response by Residential Scales

Figure 6 shows the physiological measurement values change scores for each residential scale from baseline. Participants showed mostly positive physiological responses in the biophilic residential environment, especially the lowest HR (−2.84 bpm) and GSR (−0.12 μS) and longer HRV (+5.81 ms) intervals on the residential unit scale, indicating higher recovery compared to other residential scales. Although these patterns were similar for the other two scales, we observed inconsistent results for changes in HR on the building scale. HR (+0.28 bpm) showed a slight increase in the building scale compared to the baseline, and GSR and HRV exhibited relatively low recovery levels. However, there was directional consistency in that the changes in HR, HRV, and GSR all showed high levels of physiological recovery in the order of the unit–building–complex scales.

A repeated measures ANOVA was performed in

Table 4. Repeated measures ANOVA on the changes in physiological responses according to residential scales.

Variable	SS	df	F	p	η2
Δ HR (bpm)	174.108	2	1.584	0.214	0.052
Δ GSR (μSiemens)	382.690	2	0.970	0.378	0.032
Δ HRV (ms)	1.564	2	0.651	0.525	0.022

Notes: Δ (Delta) = changes in physiological measures from baseline. The significance level for the p-value is 0.05.

to test the differences in physiological responses according to the residential scale. As a result of Mauchly’s sphericity test, the significance probability of all models was close to 1 (p-value > 0.7), which was judged to be a suitable level for analysis. The model results showed no significant difference in changes in HR, GSR, and HRV for the residential scales, indicating that virtual exposure between the three biophilic residential scales had similar effects on the physiological responses of the senior.

4.3. Physiological Response by Physical Versus Digital Intervention

Figure 7 shows the results of the paired t-test. Participants showed greater decreases in HR and GSR levels and longer HRV intervals in the digital intervention section. These results showed statistically significant differences in all physiological responses, except for the changes in GSR at the building scale. Both sections showed positive physiological changes compared to baseline, although some physical sections showed increased HR and decreased HRV compared to baseline. These responses in the physical section were significant and more pronounced at the building scale, with differences of 2.68 ± 4.72 bpm and 7.17 ± 5.15 ms in HR and HRV, respectively, compared to the digital intervention section. Therefore, the results indicated that digital design interventions had a greater effect on reducing physiological stress in seniors than just physical design, across all scales of biophilic residential environments.

4.4. Correlation Between Physiological Response and Subjective Perception

Spearman’s rank correlation analysis confirmed a strong correlation (p < 0.000) between HR and GSR responses and subjective perception (Figure 8 and Figure 9). Although the correlation coefficients were negative, the decrease in HR and GSR reflects emotional relief, thus interpreted as a positive relationship. Self-reported satisfaction significantly correlated with GSR and HRV. The strong correlation between satisfaction and GSR suggests a direct link between participants’ decreased GSR and increased subjective satisfaction. These correlations with GSR were also observed across the different scales (see

Table A3. Result of Spearman’s rank-order correlation analysis.

Physiological Response		Self-Reported Satisfaction			Self-Reported Immersion
		Unit	Building	Complex	Unit	Building	Complex
HR	Unit	−0.113	0.167	−0.126	−0.897 ***	0.072	−0.018
	Building	0.026	0.148	0.053	−0.104	−0.931 ***	0.122
	Complex	−0.063	−0.072	−0.321	0.007	0.311	−0.925 ***
HRV	Unit	−0.109	−0.068	−0.309	−0.072	0.096	0.157
	Building	0.220	0.511 **	0.064	0.076	0.084	0.109
	Complex	0.089	0.217	0.076	0.038	0.228	−0.133
GSR	Unit	−0.900 ***	−0.594 **	−0.431 **	0.083	−0.251	−0.046
	Building	−0.630 ***	−0.874 ***	−0.460 **	0.251	−0.020	−0.174
	Complex	−0.604 ***	−0.422 **	−0.890 ***	−0.122	−0.061	−0.227

Notes: ** p < 0.01; *** p < 0.000.

), possibly due to the overall positive outcomes of participants’ satisfaction and GSR. Additionally, HRV showed a correlation (p < 0.05) with subjective satisfaction, but it was only observed at the building scale. Subjective immersion uniquely correlated with HR changes, which indicates a close relationship between the participants’ increase in HR and the decrease in perceived immersion. Therefore, considering the significant results, the overall correlation coefficient of GSR (r_s ≤ −0.874) and HR (r_s ≤ −0.897) is high levels, indicating a significant association between the seniors’ subjective perceptions and physiological responses in the virtual biophilic residential environment.

5. Discussion

5.1. Benefits of the Virtual Biophilic Residential Environment

Participants showed reduced stress levels in the virtual biophilic residential environment compared to the baseline, which is consistent with previous studies [18,19]. While not statistically significant, the positive physiological changes in the participants differ among the three types of residential scales. Exposure to the unit scale resulted in a lower HR and GSR than the other scales, and the HRV interval increased significantly. This may relate to findings that show that seniors view their home spaces as healing places [10].

Furthermore, these positive findings may support the stress recovery theory [5] that biophilic environments can reduce acute stress. As an exception, we observed a slight increase in seniors’ HR at the building scale. This may reflect differences in physiological responses to physical and digital design interventions. Nevertheless, no significant differences were observed across the three residential scales.

5.2. Effects of Physical and Digital Designs

This study showed that digital design interventions in biophilic residential environments induced lower HR and GSR and longer HRV responses. Since this study was based on a physiological baseline, these findings may enhance recovery from acute stress. However, at the building scale, seniors’ GSR was more stable in the physical section than in digital interventions. Given that GSR is known to react sensitively to negative emotions such as tension or fear [65], this result may be attributed to the sense of place inherent in the scale. The building scale was simulated based on a rooftop garden, which may have provided participants with greater visual stimulation due to its elevated location and open surroundings. Consequently, the exceptional responses observed at the building scale were not statistically significant. Nevertheless, given that the rooftop garden encompasses key attributes of biophilic experiences, such as ‘prospect and refuge’ and ‘landscapes’, this study suggests that further research is needed to determine suitable height and openness for seniors.

Several studies underscore the significance of complex and digital approaches to biophilic design [21,24,29,57,70]. Beatley [24] emphasizes the unique experiences of nature we rarely see around us. The VE in this study complexly simulates planning elements favored by seniors, featuring captivating natural elements and dynamic water properties. Therefore, our findings support the theoretical hypothesis that the effectiveness of biophilic design correlates with the complexity and diversity of biophilic attributes [11]. This study also extends existing biophilic design approaches for seniors. Digitalized biophilic design provides immersion and flexible accessibility to nature, creating a more positive experience based on individual needs. The participants in this study are active urban seniors engaged in welfare and leisure activities. Accordingly, this study presents the possibility of digital design from the perspective of customization of biophilic experience for active aging.

5.3. Physiological Response and Satisfaction and Immersion

We found that changes in seniors’ HR, GSR, and HRV in a virtual biophilic residential environment may reflect their subjective perceptions. The results showed significant correlations between HR and subjective immersion and between GSR and HRV and subjective satisfaction. These results are particularly striking in HR and GSR recovery and are significantly consistent across the three residential scales. Our findings are significant given that previous VE studies comparing subjective immersion and physiological responses are limited and lack prior data focused on seniors. We recommend using HR as an evaluation indicator for seniors’ immersion in VEs and suggest future comparisons with various VE approaches.

6. Conclusions

6.1. Intellectual Contributions and Innovations

This study applied a composite biophilic design, breaking away from the dichotomous design of previous VE research. In particular, the biophilic design effects suggested in previous studies were applied to the residential environment, and the physiological short-term impact on seniors was presented. This is valuable because it strengthens existing theoretical evidence and suggests a biophilic design approach that contributes to senior health. Moreover, this study addresses the intersection of technology and urban design by examining how digitalized biophilic elements can be extended into virtual residential environments for seniors. Discourse on digitalized biophilic design for seniors has been limited due to concerns about their digital capabilities and a lack of empirical evidence. However, since integrating digital technologies is essential to improving the biophilic experience of seniors in dense urban built environments, biophilic design should be evaluated both in the early design phase and after occupancy. This study demonstrates the physiological capacity of seniors in VEs that integrate digitalized biophilic design, providing a significant initial step towards expanding seniors’ biophilic experiences.

6.2. Implications

The virtual biophilic residential environment proposed in this study can enhance seniors’ physiological function, subjective satisfaction, and immersion. This implies the potential benefits of biophilic design in creating a healthy residential environment. This study highlights the combination of biophilic design attributes, suggesting that integrating digital elements into physical designs might be a better biophilic approach for seniors. In particular, composing and simulating effective biophilic elements for residents’ needs can further enrich their experience. Our findings offer insights into the age-friendly housing industry and can provide fresh motivation for biophilic design-related technologies. Furthermore, the physiological indicators correlated with subjective perceptions may help clarify the mechanisms of biophilic design effects in future research.

6.3. Limitations and Opportunities

This study has several limitations and potential opportunities. First, we focused on residential scales and biophilic design approaches rather than equivalent comparison conditions in a VE. This limits our ability to analyze differences in a typical residential or actual environment. However, dichotomous study designs may involve participants’ subjective judgments (e.g., favorable vs. negative) regarding the controlled environment [19], potentially affecting their physiological responses and leading to biased outcomes. Second, this study involved a combination of implementable biophilic designs for different residential scales; therefore, it is limited in its ability to analyze the effects of a single biophilic element. Consequently, subtle factors, such as the residential scale or digital media content, may influence participants’ responses. We acknowledge the practical limitations of applying biophilic design consistently across purposes and scales and aim to minimize these gaps. Lastly, the sample size of 30 based on convenience sampling in this study may limit the generalizability of the results. We are one of the few studies simulating VEs in digitalized biophilic designs and various residential scales. Accordingly, we lacked prior information to understand the variability of seniors’ physiological responses to these VEs. For example, while this study identified effective exposure times and wash-out periods based on similar experimental research conducted with healthy young adults, it remains unclear whether these exposure durations are suitable for seniors. Nonetheless, our findings can be used to estimate the short-term impacts of digitalized biophilic design and subsequent stress recovery in future studies of apartment houses for seniors.

6.4. Future Research Directions

Future research should identify specific factors, such as cultural and regional backgrounds or connectivity with nature, that may influence seniors’ physiological responses to biophilic design. It is important to analyze standard benchmark datasets to obtain formal sample sizes and refine comparison groups. The reference dataset should include age-specific samples, environmental stress stimuli, and multimodal stress indexes to estimate the effects of biophilic design in various built environments, and there is a need to build a reliable dataset. In addition, considering the results of this study, it is necessary to systematically organize biophilic design elements based on digital media and conduct independent analyses of the physiological and emotional impacts of these elements, to explore ways to replace or enhance the biophilic effects provided in real settings. This requires the support of technological resources that can effectively simulate multisensory stimuli, including visual, auditory, tactile, and olfactory stimuli. In particular, interdisciplinary research integrating environmental psychology, human-computer interaction, and gerontechnology is needed to understand the effect of biophilic design based on digital media in age-friendly spaces. Furthermore, biophilic design research using VEs should expand to include more building types, such as hospitals and nursing homes, for individuals who primarily experience nature indoors.