Changes in the physiological and emotional states of workers depending on plant decoration and document writing activities were examined using electroencephalographic (EEG), electrocardiogram (ECG), and semantic differential (SD) methods. Subjects were selected among workers who were suitable for general brain research, using offline notice boards in the National Institute of Horticultural and Herbal Science. They were selected among those who were right-handed, had no mental disease, visual impairment and brain disease, and did not take medicines (Lee et al., 2009; Son et al., 1998, 1999). A total of 31 participants (14 males and 17 females) aged 26.5 (±3.5) years on average were selected, and they were sufficiently informed of the purpose, measurement items and methods of this study. They participated in this research after signing a voluntary participation consent form. They were instructed not to drink alcohol from two days before this experiment, and sny beverage that stimulates the brain such as coffee, green tea, caffeine drinks from two hours before this experiment.

Electroencephalographic (EEG), electrocardiogram (ECG), and semantic differential (SD) analysis were conducted in a research room in the National Institute of Horticultural and Herbal Science between 10am and 4pm (Fig. 2). A desk was placed in the light gray room (length 3.5 m, width 3.0 m, height 2.6 m), and the intensity of illumination at the desk height was 400±10 lux on average (UT383 Mini Light Meters, Japan). The temperature and humidity in the room were 25±0.5°C and 70±10% respectively (TR-72Ui, T&D CORP., Japan). Light from outside was blocked to prevent its impact on the psychology of subjects, and the fluorescent light on the ceiling was turned on.

Subjects performed two types of activities for 10 minutes respectively: decorating a glass container (diameter 30 cm) with plants, and writing a document. Changes before and after the two activities were measured. For the plant decoration activity, three indoor foliage plants (Anthurium andraeanum, Davallia mariesii, Trachelospermun asiaticum), one 30 cm-diameter glass container, fresh moss, two little rabbit ornaments and volcanic stones were used to create a plant decoration. For the document writing activity, subjects were instructed to type a given text. Before and after each activity, their EEG and ECG were measured two times, in total 4 times (Kim, 1998; Jang et al., 2014), and SD analysis was conducted after each activity only (Fig. 1, 2). To compare the two activities, the document writing activity was set as the control group. An EEG and ECG device (BIOS-S24, BioBrain Inc., Daejeon, Korea) was placed 30 cm behind subjects. Once a subject entered the EEG experimental room, he or she was informed of the overall process of the experiment, and signed a research consent form. While 12 electrodes were attached on the head, subjects were allowed to get used to the internal environment. Cup electrodes were attached to 8 channels for the frontal lobes (F), the temporal lobes (T), the parietal lobes (P), and the occipital lobes (O), and 1 reference electrode and 1 ground electrode behind the two ears respectively, 1 disposable ECG electrode below the left chest, and 1 disposable ECG electrode above the right chest (Fig. 1-3). Cup electrodes are a disc-type electrode coated with gold, and they were attached after cleaning dirts off the skin surface to minimize their contact resistance with the skin using a EEG conductive paste (Elefix z-401ce, 2016, Nihon Kohden, Japan). They wore earplugs in order to prevent them from being exposed to noise from outside. Before measuring, they were instructed to close their eyes for the first 3 minutes to take a rest, and while they were taking a rest, materials for the first activity were placed on a desk (length 120, width 45, height 70 cm). The two activities were randomly peformed without any order between the two activities. To ensure subjects do not see the materials of the second activity in advance, the materials were prepared in a separate room next to the EEG experimental room, and one activity was performed at a time. The EEG of the subjects was measured before and after each activity for 2 minutes and 10 seconds, and the SD questionnaire survey, for 2 minutes. After answering the questionnaire, subjects were instructed to close their eyes for 2 minutes again to take a rest. The same process was performed for the other activity. The materials for the second activity were promptly placed on the table for the two minutes when the subjects closed their eyes to take a rest. It took a total of 60 minutes to conduct the entire process for each subject (Fig. 1, 2).

Semantic differential (SD) is a method widely used to assess landscapes of which relationships with emotional adjectives or factors that are obtained through factor analysis are difficult to quantify due to the subjective preference of individuals (Kim, 2012; Park, 2010). SD analysis in this study was conducted using 3 pairs of emotional adjectives that were used to assess landscapes in earlier studies and associated with plants as shown in Table 6 (Im, 2009). A 7-point likert scale (from 1 (strongly disagree) to 7 (strongly agree)) and a SD method suggested by an American psychologist, Osgood et al. (1957) and widely used to assess emotions or landscapes, were used for the questionnaire survey in this study (Kim, 2012; Park, 2010).

Statistical analysis in this study was performed using IBM SPSS ver. 20.0, and to verify the reliability of the measurement tool, Cronbach’s α was calculated. The results of EEG and ECG were statistically analyzed using relative power ratio, and emotional adjectives for SD, using the paired sample t-test; and the preference of activities, using the paired sample t-test and frequency analysis.

To examine changes in the psychophysiological conditions of workers after doing activities using plants, plant the plant decoration and document writing activities were performed for 10 minutes respectively. The EEG and ECG of subjects were measured before and after performing the activities, and differences between them were compared (Table 1-3, Fig. 1-3). It was found that the relative slow alpha power spectrum (RSA), an indicator of stability and relaxation, after performing the plant decoration activity was statistically significantly high, compared to the document writing activity, in the frontal lobes (T3, T4) that control the comprehensive functions of the brain including the ability of thinking; in the parietal lobes (P3, P4) that plays an important role in visual and spatial processing; and in the occipital lobe in the left hemisphere (O1) (p<.05). In addition, the ratio of alpha to high beta (RAHB) was statistically significantly high in the parietal lobes (P3, P4), which indicates that the level of stability and relaxation increased in the state of almost no stress or tension. These results show that the level of RSA and RAHB after performing the document writing activity was statistically significantly high, compared to the plant decoration activity, in the frontal lobes, the parietal lobes, and occipital lobes. The results are attributable to the fact that the activity of the frontal lobes that provide high-level recognition, emotions and mental functions; the parietal lobes that control visual organs; and the occipital lobes increased. The results coincide with those of Kim et al. (2002) and Son et al. (1998, 1999) that the visual elements of plants indoors increased the ratio of alpha, having positive effects on the activity of brain functions and psychophysiological conditions. However, the RFA that control visual functions after performing the document writing activity was statistically significantly high, compared to the plant decoration activity, in the parietal lobe (P3) in the left hemisphere, which indicates that the level of immersion while writing a document was higher than decorating plants. The relative high beta power spectrum (RHB) after performing the document writing activity was relatively higher overall than the plant decoration activity, although it was not statistically significant. These results can be interpreted that the document writing activity shows a higher level of concentration than the plant decoration activity, actively absorbs information about things, and improves concentration significantly, but that it also increases the activity of the brain as well as tension and anxiety. Yoon (2001) pointed out that even the act of watching green plants indoors reduced visual fatigue, changed brainwaves, and thus increased concentration, and Lee and Son (1999) also found that the act of watching green plants soothed the mind, released tension, and activated the functions of the brain, thus giving comfortable and happy feelings to humans. These results support those of this study that the plant decoration activity was more effective for stability and relaxation than the document writing activity.

Changes in the brainwaves of subjects after performing the plant decoration and document writing activities were examined through brain maps. The ratio of SMR to theta (RST), the ratio of mid beta to theta (RMT), the ratio of (SMR~Mid Beta) to theta (RSMT), and SEF50 (spectral edge frequency 50%), an indicator of brain activity were not statistically significant, but indicators for stability and relaxation, including RST, RSMT and SEF50, after performing the plant decoration activity were relatively higher than the document writing activity. The level of RMT, an indicator of concentration accompanied by tension, tended to decrease more after performing the plant decoration activity than the document writing activity. In particular, the level of RMT is in general clearly higher in the right hemisphere that controls emotional responses, than in the left hemisphere that controls rational responses (Kim and Chang, 2001; Kimura, 1973), and thus tends to be accompanied by tension from an emotional aspect, rather than from a logical and rational aspect. The results of Chang and Chen (2005) that the level of tension and vigilance of workers was high when there was no natural landscape or plant to be seen through windows in their office support those of this study that the level of tension was lower but the level of stability and relaxation was higher after performing the plant decoration activity than the document writing activity. Therefore, it seems that plant decoration activities using indoor plants are helpful to stabilize emotions particularly in an environment that requires a high level of concentration in a stable and relaxed condition such as an excessive use of devices like computers.

Changes in the autonomic nervous system depending on the plant decoration and document writing activities were analyzed, and there was almost no difference, as well as no statistically significant difference in the heart rate between the two activities (Fig. 4). However, the level of HF (high frequency) (Fig. 5), an indicator of the activity of the parasympathetic nervous system, was higher, and the level of LF (low frequency) (Fig. 6), an indicator of the activity of the sympathetic nervous system, was lower after performing the plant decoration activity than the document writing activity, which coincided with the results of the EEG. In addition, Lee et al. (2011) reported that the activity of the sympathetic nervous system decreased statistically significantly after performing horticultural activities which were found to be effective in stabilizing physiological conditions. The results were similar to those of this study that the level of the activity of the sympathetic nervous system was low, and that the level of the activity of the parasympathetic nervous system was high.

The preference of subjects and the preference ratio between the plant decoration and document writing activities were analyzed (Table 4-5), and the mean preference level of the plant decoration activity (4.00/5) was statistically significantly higher than that of the document writing activity (2.58/5). In addition, the preference ratio of the plant decoration activity was high in the range of answers from “normal” to “highly preferred,” while that of the document writing activity was high in the range of answers from “never preferred” to “normal.” Out of the entire subjects, 81% answered that they preferred the plant decoration activity, and 52% answered that they did not prefer the document writing activity.

Changes in emotions depending on the plant decoration and document writing activities were examined using semantic differential (SD) analysis (Table 6), and the level of “pleasant,” “natural” and “calm” was statistically significantly higher after performing the plant decoration activity than the document writing activity (p<.000). The emotional quotient of the plant decoration activity was 1.13 in “pleasant,” 1.65 in “natural,” and 1.06 in “calm,” and that of the document writing activity, -0.23, -1.06, and 0.03 respectively. Some earlier studies (Kwak, 2004; Lee, 2006; Ulrich, 1981) reported that contacting plants in an artificial indoor space had both environmental and emotional effects such as psychological stability, calmness, reduced visual stress, etc., and Lee et al. (2011) also found that horticultural activities were more effective for psychological pleasantness, relaxation and stability than tasks requiring the use of computers. These results support those of this study that subjects felt more natural and calm when performing the plant decoration activity than the document writing activity.