Contact with nature has been proposed as a solution to achieve physiological relaxation and stress recovery, and a number of scientific verification outcomes have been shown. Compared with studies of the other senses, studies investigating the visual effects of nature have been at the forefront of this research field. A variety of physiological indicators adopted for use in indoor experiments have shown the benefits of viewing nature. In this systematic review, we examined current peer-reviewed articles regarding the physiological effects of visual stimulation from elements or representations of nature in an indoor setting. The articles were analyzed for their stimulation method, physiological measures applied, groups of participants, and outcomes. Thirty-seven articles presenting evidence of the physiological effects of viewing nature were selected. The majority of the studies that used display stimuli, such as photos, 3D images, virtual reality, and videos of natural landscapes, confirmed that viewing natural scenery led to more relaxed body responses than viewing the control. Studies that used real nature stimuli reported that visual contact with flowers, green plants, and wooden materials had positive effects on cerebral and autonomic nervous activities compared with the control. Accumulation of scientific evidence of the physiological relaxation associated with viewing elements of nature would be useful for preventive medicine, specifically nature therapy.

Exposure to natural sounds is known to induce feelings of relaxation; however, only few studies have provided scientific evidence on its physiological effects. This study examined prefrontal cortex and autonomic nervous activities in response to forest sound. A total of 29 female university students (mean age 22.3 ± 2.1 years) were exposed to high-resolution sounds of a forest or city for 60 s, using headphones. Oxyhemoglobin (oxy-Hb) concentrations in the prefrontal cortex were determined by near-infrared spectroscopy. Heart rate, the high-frequency component of heart rate variability (which reflects parasympathetic nervous activity), and the ratio of low-frequency to high-frequency (LF/HF) components (which reflects sympathetic nervous activity) were measured. Subjective evaluation was performed using the modified semantic differential method and profiles of mood states. Exposure to the forest sound resulted in the following significant differences compared with exposure to city sound: decreased oxy-Hb concentrations in the right prefrontal cortex; decreased ln(LF/HF); decreased heart rate; improved feelings described as “comfortable,’’ “relaxed,” and “natural”; and improved mood states. The findings of this study demonstrated that forest-derived auditory stimulation induced physiological and psychological relaxation effects.

To better understand how fragrance may enhance human health, this study examined psychophysiological responses to Japanese plum blossom fragrance. Although previous studies used essential oils or fragrance components, the present study measured the effects of floral scent naturally diffused by the plant itself to simulate the way we generally experience natural scent in everyday life. Subjects were Japanese males (n = 26), and the data collected included cerebral and autonomic nervous system activities, semantic differential (SD) scale, and profile of mood states (POMS). Exposure to the fragrance significantly activated the sympathetic nervous system and the cerebral areas related to movement, speech, and memory. SD scale and POMS results showed the fragrance evoked cheerful, exciting, and active images and changed mood states by enhancing vigor while suppressing feelings of depression. These findings indicate that contact with a floral scent such as plum blossom fragrance can improve mood states and may foster the brain functions of memory, speech, and movement, potentially leading to improvements in emotional health, depression, and memory disorders.

The number of people addicted to gambling has increased worldwide. They often suffer from debilitating medical conditions associated with stress or depression. This study examined the physiological and psychological reactions of gambling disorder (GD) patients while listening to high-definition forest or city sounds using headphones. In total, 12 Japanese male GD patients were exposed to high-definition forest or city sound waves for 1 min via headphones. Near-infrared spectroscopy of the prefrontal cortex was used to examine oxyhemoglobin (oxy-Hb) concentrations. Heart rate and heart rate variability are indicators of autonomic nervous function. We performed subjective evaluation via the modified version of the semantic differential (SD) method with the profiles of the mood states (POMS). Experiencing forest sounds led to substantial differences as opposed to listening to city sounds: (1) oxy-Hb levels of the bilateral prefrontal cortices were lower (2) the modified SD method resulted in increased comfortable and relaxed feelings, (3) the negative POMS subscale scores were significantly lower, indicating that negative emotions diminished markedly when patients listened to forest sounds. This is the first study to show that sounds of forest relaxed individuals physiologically and psychologically to minimize GD.

Growing interest in the relaxation effect of nature has elicited demands for scientific verification of the various natural elements. This study investigated the physiological and psychological responses of 27 females in their 20 s to viewing a waterfall and urban images (control) presented via a large, high-resolution display for 90 s. High-frequency [HF] for parasympathetic nervous activity and the ratio of low-frequency (LF)/[LF + HF] for sympathetic nervous activity by heart rate variability and heart rate were recorded. Simultaneous changes in oxyhemoglobin concentration in the prefrontal cortex were recorded by near-infrared time-resolved spectroscopy. The modified semantic differential method and Profile of Mood States Second Edition were used to assess the psychological effects on the participants after viewing each image. The results showed that viewing the waterfall image, compared with viewing the urban image, (1) increased sympathetic nervous activity; (2) provided comfortable, relaxed, and natural impressions; (3) improved mood states. In conclusion, visual contact with a waterfall image physiologically activated sympathetic nervous activity and psychologically evoked positive moods and feelings.

Empirically, viewing nature landscapes, including mountains, can promote relaxation. This study aimed to examine the physiological and psychological effects of visual stimulation using an autumn foliage mountain landscape image on autonomic nervous and brain activities. We included 27 female university students who viewed mountain and city (control) landscape images displayed on a large, high-resolution display for 90 seconds. As an indicator of autonomic nervous activity, heart rate variability (high frequency [HF], reflecting parasympathetic nervous activity, and low frequency/high frequency [LF/HF], reflecting sympathetic nervous activity) and heart rate were recorded. Simultaneously, as an indicator of brain activity, oxyhemoglobin concentrations in the prefrontal cortex were assessed using near-infrared time-resolved spectroscopy. Viewing the mountain landscape image significantly increased HF, indicating increased parasympathetic nervous activity. Furthermore, the visual stimulation using the mountain image induced comfortable, relaxed, and natural feelings, as well as improved mood states. In conclusion, viewing an autumn foliage mountain landscape image via large display induced physiological and psychological relaxation in women in their 20s.