Introduction
According to the World Health Organization (WHO), mental health is a state of psychological well-being that enables individuals to cope with life stress, realize their abilities, and contribute to their communities; and as a fundamental human right, it is determined by various socioeconomic, biological, and environmental factors. Mental health undergoes growth and development through self-understanding and self-acceptance with a positive attitude toward oneself, maintaining a balance between internal needs and external demands, and exhibiting positive psychological characteristics by fulfilling given roles through autonomous decision-making and reality perception (Lee et al., 2022).
Plants and nature are perceived as an inherent home for humans as culture and civilization develop, serving as a fundamental backdrop for human emotions (Lewis, 1996). People living in environments with plants exhibit stronger resistance to stress and stimuli, can experience a deeper sense of meaning in life, and can live in psychological and physical comfort and ease within plants and nature at all times (Ulrich and Parsons, 1992). Research verifying the effects of plants has been conducted in diverse aspects (Kwak, 2004), such as aesthetic effects (Choi et al., 1997), environmental purification effects (Lee, 1993), and psychological therapeutic effects (Kaplan and Kaplan, 1989).
Horticultural therapy, which utilizes these therapeutic functions of plants, has been applied in various fields such as occupational therapy and psychotherapy to promote physical and mental recovery, emotional stability, and rehabilitation (Son et al., 2006), and has recently been employed in care farming. Natural environments lower heart rate (Laumann et al., 2003) and blood pressure (Hartig and Staats, 2003), and enhance psychological well-being (Wells and Evans, 2003), supporting the stress-relieving effects of green natural environments. Moreover, EEG (electroencephalography) measurements were taken to examine the effects of plant color stimuli on brain function, and the results revealed that viewing green plants in indoor environments has positive effects on the improvement of psychophysiological functions, enables comfortable immersion, and improves creativity and external focus of attention (Jang, 2013).
Previous studies using vibraimage have measured psychological functions before and after horticultural therapy in elderly residents of care facilities (Lee, 2019), middle-aged women (Kim, 2024), and adults with developmental disabilities (Park, 2024). However, no research has measured the changes before and after viewing plants using vibraimage. Therefore, this study aimed to quantitatively examine how observing and viewing plants as a medium of horticultural therapy and horticultural activities affects psychological functions by employing vibraimage measurements. Furthermore, by investigating the effects of viewing ornamental flowering plants on psychophysiological functions, the results of this study may contribute to planning horticultural therapy programs to promote psychological functions, creating healing gardens, designing therapeutic environments, and enhancing understanding of the effectiveness of plants and horticultural therapy.
Research Methods
Research design
This study is a pilot experimental study employing a one-group pretest-posttest design to examine changes in psychological functions before and after viewing plants in adults aged 20–64.
Research participants
This study conducted statistical power analysis proposed by Cohen (1988) using G*Power 3.1.9.7. The procedure “A priori: Compute required sample size - given α, power, and effect size” was selected for calculating the minimum sample size, and since previous studies primarily set the effect size at a medium level, this study also adopted a medium effect size (0.5). Following Cohen’s (1988) criteria, the significance level (α err prob) was set at 0.05, and the statistical power (1-β err prob) at 0.8 for final calculation. The total sample size suitable for this experiment was calculated to be 27. Considering a 10% dropout rate, 30 participants were recruited.
This study was conducted after obtaining approval from the Institutional Review Board (IRB) of Dankook University (DKU 2024-10-059-001) to ensure ethical considerations.
The research was carried out at A healing farm located in P city, Gyeonggi-do, which was selected for the ease of recruiting participants, availability of experimental and waiting spaces, and provision of other amenities. Participants were recruited through posters targeting volunteers, club members, and participants in farm-based educational programs who used the healing farm, with the farm owner’s permission. In addition, we directly explained the purpose, intent, and content of this study to encourage participation. After excluding five individuals who either engaged in behaviors that interfered with vibraimage measurement or withdrew from participation, data from a final sample of 25 participants were analyzed.
Research procedure and method
The study was conducted in the following sequence: preparation and relaxation (3 minutes), pre-test vibraimage measurement (1 minute), viewing of plants (2 minutes), and post-test vibraimage measurement (1 minute) (Fig. 1).
Laboratory preparation
The experiment was conducted in a customer lounge at the healing farm used as the laboratory, which was measured 2.3 m in width, 2.5 m in length, and 2.5 m in height, with white walls and no windows. The average illuminance in the laboratory was 700 lux, the temperature was maintained at 23°C, and the humidity at 27%. A table measuring 100 cm in width, 70 cm in length, and 60cm in height and a chair with a backrest were prepared. Twenty plants were placed together in a tray measuring 50cm in width × 40 cm in length × 8cm in height, grouped to resemble a single plant cluster. To allow participants to observe the plants on the table, the grouped tray was placed on a box measuring 60 cm in width × 45 cm in length × 20 cm in height, with the back of the tray elevated by approximately 10cm for a slanted display. The vibraimage device was installed in front of the grouped plants. To prevent participants from seeing the plants prior to the experiment, a movable white partition (90 cm in width × 60 cm in length) was used as a divider. On the table, positioned 80 cm in front of the participants, the vibraimage, partition, and plants were arranged in sequence (Fig. 2).
Selection of plants
Based on previous research reporting that green color induces a more comfortable and stable state than other color stimuli, enhancing cerebral activity, and that bright yellow stimuli positively influence the experience of pleasure (Jang, 2013), we selected Kalanchoes blossfeldiana cv. featuring both yellow flowers and green leaves (height 20–25 cm, diameter 10 cm, 20 pots), and placed 20 plants in a tray and grouped them together to appear as a single plant cluster.
Prior preparation of participants
Prior to the experiment, we requested the selected participants not to consume alcohol the day before, to avoid caffeinated or energy drinks within one hour prior to the experiment, and to refrain from intense exercise before the experiment. This was because the intake of caffeine, stimulants, or alcohol could affect vibraimage measurements.
Vibraimage measurements
After entering the laboratory, participants were instructed to face the wall (a white partition) and relax, followed by a pre-test vibraimage measurement. Then, the participants were exposed to the plants and asked to view them for 2 minutes. After viewing the plants, a post-test vibraimage measurement was conducted.
At the beginning of each step, verbal cues were given in a soft voice: “You may begin,” “Please look at the plants,” and “You may stop.”
Research instrument
In this study, psychophysiological functions were measured using Vibraimage 8 PRO (ELYSIS Co., Ltd.). The vibraimage technology is a non-contact system that analyzes emotional and psychological states based on video data capturing micro-vibrations of a person using a digital webcam ( Fig. 3 ). These micro-vibrations of the human body are associated with psychophysiological conditions and reflect emotional and psychological states. The mental functional state measured by the Vibra system is divided into three domains: positive, negative, and physiological. To assess mental functional state, 10 variables are measured: aggression, stress, tension, suspicion, balance, charm, energy, self-regulation, inhibition, and neuroticism (Fig. 4).
Data analysis
Data were analyzed using SPSS Statistics 23.0. The general characteristics of participants were analyzed using percentages and means (Table 1). Changes in psychophysiological functions were analyzed using paired samples t-tests and the Wilcoxon signed-rank test. The Shapiro-Wilk test was conducted to assess the normality of the variables. As a result, 9 out of 13 variables satisfied normality assumptions (p > .05), while 4 variables (balance, inhibition, neuroticism, physiological) did not (p < .05). Accordingly, paired samples t-tests were performed for variables meeting the normality assumption, and Wilcoxon signed-rank tests were conducted for variables that did not (Table 2).
Results
General characteristics of participants
The mean age of participants was 57.32 years, and by age group, 60% (15 participants) were in their 60s, 28% (7 participants) in their 50s, and 4% (1 participant each) in their 40s, 30s, and 20s. 92% were female (23 participants) and 8% (2 participants) were male, and 60% (15 participants) were employed.
Psychophysiological functions
Changes in psychophysiological functions measured using vibraimage before and after viewing ornamental flowering plants are presented in Table 2.
First, aggression decreased from a mean of 49.97±8.38 before the experiment to a mean of 47.93±7.64 after, showing a decrease of 2.04 points with a statistically significant difference (t = 2.647, p = .014).
Second, energy decreased from a mean of 30.22 ± 7.85 before the experiment to a mean of 29.09±8.12 after, showing a decrease of 1.13 points with a statistically significant difference (t=2.604, p =.016).
Third, inhibition decreased from a mean of 31.40 ± 23.50 before the experiment to a mean of 29.54±22.07 after, showing a decrease of 1.86 points with a statistically significant difference (z=−2.662, p =.008).
Fourth, no statistically significant differences were observed for changes in stress, tension, suspicion, balance, charm, self-regulation, neuroticism, and in the positive, negative, and physiological emotions.
Discussion
This study was conducted to how viewing ornamental flowering plants changes the psychophysiological functions of adults. First, aggression decreased with statistical significance after viewing ornamental flowering plants (t = 2.647, p = .014). Aggression refers to hostile, injurious, or destructive behavior or outlook and often the expression of pent-up rage (Merriam-Webster Dictionary, n.d.). In research literature, aggression is often translated as anger, rage, or aggressive behavior; and in the context of this study, aggression refers to a sensitive response to external stimuli, a tendency to become easily excited, and the expression of aggressive behaviors in response to aggressive remarks or stimuli. Although direct comparison is difficult as there are no previous studies reporting changes before and after viewing ornamental flowering plants, the findings of this study are consistent with prior research. For example, Jung (2020) reported a reduction in aggression measured by vibraimage in high school students after participating in interpersonal care horticultural activities that involved working with plants rather than simply viewing them, and Park (2024) found a statistically significant decrease in aggression as a result of measuring mental health using vibraimage in adults with developmental disabilities after participating in a gardening program. These results are also in line with studies that measured aggression using survey-based instruments rather than vibraimage, reporting that horticultural activity programs reduced aggression in problem children (Joo, 2008) and elementary school students (Jung and Lee, 2009). On the other hand, Lee (2019), who assessed the effects of a horticultural activity program on older adults in care facilities using vibraimage, reported no significant change in aggression; and Kim (2024), who assessed the effects of a horticultural activity program on middle-aged women, found that aggression significantly increased over time, showing results different from this study. Office workers who observed roses showed a significant increase in parasympathetic activity as measured by heart rate variability (HRV) (Ikei et al., 2014). This aligns with the present study’s findings, as a reduction in aggression indicates a decreased sensitivity to external stimuli and a lower tendency to become easily excited.
Second, energy decreased with statistical significance after viewing ornamental flowering plants (t = 2.604, p = .016). Energy is a fundamental entity of nature that is transferred between parts of a system in the production of physical change within the system and usually regarded as the capacity for doing work ( Merriam-Webster Dictionary, n.d.). In the context of this study, energy refers to the ability to act or engage in activities, as well as positive mental strength. Higher energy values indicate faster achievement of work outcomes and greater drive, whereas lower energy values reflect reduced persistence and diminished power of execution. Energy helps transform a lethargic emotional state, lifting the mood and enabling engagement in daily activities. The observed decrease in energy values in this study is likely due to reduced physical movement during plant viewing in the laboratory, and the emotions typically expressed as excitability were calmed simply by appreciating the natural qualities of the plants, providing psychological stability (Seo and Lee, 2004). Although direct comparison is difficult as there are no previous studies reporting changes before and after viewing plants, the findings of this study are consistent with prior research. For example, one study examined brainwave changes, a measure of brain function, induced by visual stimulation from green plants and found that it was effective in promoting physiological and psychological relaxation in adults (Jung and Park, 2021). Another study used near-infrared spectroscopy (NIRS) to continuously measure oxyhemoglobin (oxy-Hb) concentration in the prefrontal cortex along with subjective evaluations via self-report questionnaires, and reported that visual stimulation from observing foliage plants led to physiological relaxation, with positive physiological responses appearing almost immediately (Park et al., 2016). On the other hand, Lee (2019) who studied older adults reported no significant differences in energy, while Kim (2024) who examined middle-aged women found that energy significantly increased over time, highlighting a difference from the present study.
Third, inhibition decreased with statistical significance after viewing ornamental flowering plants (t = 3.011, p = .006). Inhibition is an inner impediment to free activity, expression, or functioning, as well as the act of inhibiting and the state of being inhibited (Merriam-Webster Dictionary, n.d.). In this study, inhibition refers to mental processes that impose limitations on other psychological functions such as behavior, cognition, perception, or emotion. Extremely low inhibition may be associated with antisocial phenomena or symptoms of mental disorders. Inhibition increases when one conceals their minds and lies. Excessively high inhibition can result in extremely unstable emotional state and, consequently, physiological problems in feeling and expressing certain emotions (Vibrasystem, 2018b). In the experimental group, inhibition values decreased with statistical significance after viewing the plants, which can be interpreted as participants moving toward a more relaxed and stable emotional state by viewing the plants. This finding is consistent with Lee (2019), who reported a decrease in inhibition following horticultural activity programs for older adults. A reduction in inhibition suggests that individuals can express themselves more comfortably, experiencing less restraint from suppressed perceptions or emotions. This aligns with previous research showing that visual stimulation using flowers in horticultural activities decreased sympathetic nervous system activity, as measured by HRV, and participants reported feelings of comfort and naturalness (Igarashi et al., 2015).
Fourth, no statistically significant results were observed in stress, tension, suspicion, balance, charm, self-regulation, neuroticism, or in the positive, negative, and physiological domains after viewing ornamental flowering plants. Although direct comparison is difficult since Park (2024) examined adults with developmental disabilities, the results aligned with the findings of the present study as there were no significant changes in stress, tension, suspicion, or neuroticism measured using vibraimage. While tension increased by 1.84 points, this change was not statistically significant. This differs from Jang (2013), who reported that the presence of plants enhanced attention, allowing participants to actively process information about objects and achieve a high level of concentration, while the active brain activity was also accompanied by tension and anxiety. The somewhat unfamiliar, windowless experimental space in this study may have slightly increased the tension in participants, which should be examined further in future replication studies. Neuroticism decreased by 2.71 points, but this change was not statistically significant. Although direct comparison is difficult because Lee (2019) studied older adults residing in care facilities rather than adults, the study measuring the effects of a horticultural activity program on psychological functions using vibraimage similarly found no significant changes in stress, balance, charm, or self-regulation, aligning with the findings of the present study. Furthermore, Lee (2019) reported significant increases in tension, suspicion, and the negative domain, decreases in neuroticism and the physiological domain, and maintenance of scores in the positive domain in the experimental group compared to the control group. In contrast, no such changes were observed in the present study. Although this study involved adults, Kim (2024) presented the effects of horticultural activity programs only for middle-aged women, reporting that balance significantly increased over time, while stress and neuroticism significantly decreased in the subdomains of psychological functions measured by vibraimage. However, the present study found no significant changes in balance, self-regulation, stress, or neuroticism, indicating a difference from Kim’s (2024) study. This discrepancy may be due to the inclusion of male adults in the present study, suggesting the need for future research to examine potential gender differences in balance, self-regulation, stress, and neuroticism.
Conclusion
The results of this study revealed that viewing ornamental flowering plants led to a statistically significant decrease in aggression, energy, and inhibition. Observing and viewing plants for two minutes reduced aggression, prevented sensitive response to external stimuli, induced psychological stability and physiological relaxation, lowered energy to create a stable state, and reduced inhibition to feel more comfortable and express emotions freely. This study demonstrates that viewing ornamental flowering plants can benefit mental health and confirms the utility of using flowering plants as a medium in horticultural activities. Moreover, visual stimulation from viewing plants serves as a meaningful preliminary activity in horticultural therapy that stimulates the senses. The findings will provide foundational data for planning horticultural therapy programs aimed at enhancing psychological functions and for promoting understanding of plant and horticultural therapy.
The following suggestions can be made based on these findings.
This study has limitations in that it focused only on adults and utilized ornamental flowering plants. Future research is suggested to measure changes in psychophysiological functions across a wider range of age groups. Furthermore, we suggest conducting studies using a variety of plants such as foliage plants in addition to ornamental flowering plants to assess psychological functions and also exploring potential differences according to gender.
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