Original Study: A Review of the Benefits of Nature Experiences: More Than Meets the Eye. Conducted by the International Journal of Environmental Research and Public Health)
This research article provides a comprehensive review of the multi-sensory pathways through which nature benefits are delivered to humans. It explores the evidence surrounding the effects of nature on human health and well-being, considering the sensory and non-sensory avenues involved. The review encompasses five sections, covering visual experiences, auditory stimuli, olfactory sensations, taste perceptions, tactile interactions, as well as non-sensory pathways such as phytoncides, negative air ions, and the influence of microorganisms. The article highlights the need to expand research beyond the visual sense and emphasizes the potential synergistic interactions among the various sensory modalities. The findings underscore the importance of understanding the interdependence of our senses in experiencing the full range of nature benefits.
This paper is a narrative review that aims to provide a reference for further reading rather than a systematic review of the evidence. The authors did not attempt a systematic search or synthesis but instead used various search terms related to senses and nature benefits to include relevant literature. The review includes different study designs and research on both humans and animals. The definition of nature used in the paper is broad and includes landscapes, microorganisms, pets, and nature simulations. Health is defined as freedom from illness or injury, and wellbeing is described as a state of comfort, health, and happiness, encompassing various domains such as mental, social, physical, and spiritual wellbeing. The paper does not differentiate between passive reception and active searching of senses but focuses more on passive sensing due to the larger body of literature in that area. The distinction between sensing and perception is not consistently made in the literature but could be an area for future research.
The Visual Elements of Nature
This section highlights the repeated demonstrations of the range of benefits that viewing nature provides for human health and well-being. These benefits include reduced anxiety, stress, shorter hospital stays, lower heart rate, and increased directed attention. However, the specific elements of a nature view that contribute to these benefits remain unclear, hindering the design of natural therapy interventions and urban green spaces.
Many studies only make a broad distinction between "urban" and "nature" without delving into the specific visual elements responsible for the benefits. It is uncertain whether a combination of elements or individual elements alone are responsible for conferring benefits. The colors of nature, such as blues and greens, are associated with low arousal, low anxiety, and preference, while the gray colors of urban scenes can evoke aggression and dominance. Other visual cues, including the absence of straight lines, the shape of vegetation, visual variety, and fractals, may also contribute to the restorative effects of nature environments.
Although the visual aspect plays a role in driving benefits, it is not the sole mechanism, as evidence suggests that moderately realistic computer animations do not elicit the same cognitive and affective responses as real environments. Further research is needed to unravel the specific visual elements that contribute to the health and well-being benefits of nature experiences.
The Therapeutic Power of Nature Sounds
This section highlights the significance of hearing and its association with the restorative benefits of nature sounds. Hearing is the perception of acoustic waves that provide valuable information about the environment. Natural sounds, such as wind, water, and animals, are considered complex and informative, offering cues related to species, season, and temporality. The richness of information content in nature sounds contributes to the restorative nature of natural landscapes.
Research consistently demonstrates that nature sounds are preferred over anthropogenic sounds, such as traffic or industrial noise. Rural soundscapes and botanical gardens are favored over urban park soundscapes, which are preferred over urban soundscapes. These preferences imply that nature sounds may have restorative properties.
Therapeutically, nature sounds have been used to alleviate stress, enhance perceived restoration, and aid in attention recovery. Birdsong, in particular, has been found to increase stress recovery, and the sound of water has been cited as a reason for visiting natural environments due to its relaxing effects. Combining nature sounds with visual stimuli, such as images of cities or 3D environments, enhances perceived pleasure, realism, and preference. The presence of nature sounds can improve the perceived realism, naturalness, solitude, and freedom of simulated environments. Furthermore, nature sounds have been found to decrease perceived crowding, increase interpersonal encounter tolerance, and enhance overall soundscape pleasantness and eventfulness.
The positive effects of nature sounds on health and well-being highlight the importance of sound in influencing our perceptions and appraisals of different environments. The absence of human-made sounds, allowing for the perception of nature sounds, is often regarded as highly pleasurable. These findings emphasize the therapeutic power of nature sounds and their potential to contribute to improved health and well-being.
The Power of Touch
This section highlights the often overlooked importance of the tactile sense in humans and its significant impact on various aspects of human life. Touch, being the first sense to develop in utero, plays a crucial role in creating bonds, strengthening relationships, and reducing stress. It is essential for love, social bonding, and overall well-being.
Nature experiences provide opportunities for tactile stimulation, particularly through animal interactions. Contact with animals has been found to yield positive benefits, including reduced blood pressure, increased relaxation and comfort, improved social responses, and enhanced well-being, especially for individuals who are asocial or autistic. Pets, in particular, have been shown to increase pain tolerance, decrease loneliness, aid in stress recovery, and reduce the need for medical care. Tactile comfort provided by animals may contribute to these benefits, alongside factors like companionship and increased physical activity.
Furthermore, there is literature exploring the haptic benefits of interacting with nature directly. Forest schools, for example, encourage children to engage in hands-on experiences with nature, leading to improvements in confidence, social skills, language development, concentration, physical abilities, and knowledge. Motor skills, specifically, have been found to improve more significantly through play in forest settings compared to traditional playgrounds.
By recognizing the tactile aspect of nature experiences and animal interactions, we gain a deeper understanding of the multifaceted benefits they provide to human health and well-being. The power of touch in fostering connections, promoting learning, and enhancing overall quality of life should not be underestimated.
Touching animals, such as dogs, has been found to have beneficial cardiovascular effects, resulting in lower blood pressure and heart rate. The act of petting a dog reduces stress, decreases cortisol levels, and contributes to anxiety reduction. Remarkably, these benefits are observed regardless of an individual's attitude towards animals, highlighting the universal impact of touch on well-being.
Similar findings extend beyond dogs to other animals. Brief periods of petting rabbits and turtles have shown to lower anxiety scores in stressful situations, while petting a soft toy did not produce the same effects. Touching living things, irrespective of one's attitude towards them, induces positive feelings and reduces stress, pain, and anxiety.
Long-term benefits of touch are evident as well. Pet owners, compared to non-pet owners, exhibit lower blood pressure, heart rates, and triglyceride levels. Studies have shown that pet owners have higher one-year survival rates among heart disease patients. While these findings are correlational and factors other than touch may contribute to these effects, they underscore the potential significance of touch in promoting better health outcomes, particularly for individuals at higher risk.
Human-animal interactions trigger the release of oxytocin, a hormone associated with decreased social stress and various physiological and psychological benefits. Stroking animals increases oxytocin production and leads to increased social interaction, reduced stress, lowered pain thresholds, anti-inflammatory effects, decreased anxiety, and improved digestive function. Oxytocin may play a crucial role in the nature benefits derived from touch.
Animal-assisted interventions have been utilized in psychiatric settings to reduce fear, anxiety, and depression. Companion animal therapy with outpatient psychiatric children has shown promising results. Touching animals has been found to decrease cardiovascular activity in hypertensive patients. Additionally, college students petting live dogs have exhibited an increase in IgA, an indicator of enhanced immune system function, suggesting that petting animals may also have immune-boosting effects.
Interestingly, there is a significant research gap in investigating the health and well-being effects of non-animal aspects of nature through touch. Exploring the tactile experiences of walking on grass, feeling water, or the sensation of wind could provide valuable insights into additional benefits beyond visual and auditory aspects of nature. Further research is needed to investigate the potential blood pressure effects of activities like lying in grass and understand the sensual and touch-related components that contribute to the pleasure experienced by gardeners when in physical contact with soil.
Air Ions: Mood and Health Benefits
This section explores the concept of air ions and their potential impact on physiological and mood benefits, particularly in natural environments. Air ions are charged particles that form through the detachment and attachment of electrons from gas molecules, influenced by various energy sources such as radiation, cosmic rays, solar waves, waterfalls, thunder, radiant energy, and UV light. Natural places like forests and waterfalls are rich in air ions, and they have been proposed as a potential mechanism for the positive effects of nature on well-being.
Built environments, on the other hand, often suffer from ion depletion, with indoor air containing significantly fewer ions compared to the outdoors. As urban populations spend the majority of their time indoors, this reduced contact with nature's abundance of air ions may be an overlooked pathway that contributes to reduced mood and health. Outdoor rural air typically has a higher concentration of air ions than outdoor urban air due to the tendency for small air ions to cluster around pollutants and dissipate.
The presence of vegetation significantly influences air ion abundance, with forests having higher concentrations compared to open grassy parks. Plants not only produce air ions directly but also draw up radon from groundwater, which serves as an additional source of ions. Mountainous areas exhibit the highest levels of air ions, while rural and coastal sites have moderate amounts, and urban sites have the lowest levels.
Although air ions have been believed to exert biological influences for a long time, experimental results have been contradictory due to flawed methodologies and inadequate assessments. Nevertheless, there is evidence suggesting that negative air ions have various effects. They can kill bacteria, promote plant and insect growth, and induce physiological and behavioral changes in humans and animals. Some individuals, particularly about one-third of the population, are sensitive to air ions and may experience symptoms of depression, lassitude, migraine, nausea, insomnia, and respiratory problems in response to shifts in ion concentration.
Negative air ions have shown positive effects on thermal comfort, alertness, and well-being. They can reduce stuffiness, nausea, dizziness, and headaches in office workers. Negative ions also decrease serotonin concentration, which may contribute to a serotonin irritation syndrome that manifests as the aforementioned symptoms. On the other hand, negative ions improve mood, decrease anxiety, enhance performance, and increase natural killer cell activity. They have been utilized in the treatment of seasonal affective disorder and have shown benefits in improving depression and anxiety symptoms.
Animals, such as rats, also demonstrate improved learning, performance, and reduced fear in the presence of negative air ions. Indoor ion depletion has been correlated with depression and somnolence, while increased levels of negative air ions stabilize mood, increase vigor and friendliness, improve alertness and concentration, and decrease tension. Higher levels of air ions have even been associated with longevity in a Chinese city known for its long-lived residents.
Overall, air ions, especially negative ions, appear to be a potentially significant contributor to the benefits derived from nature. Further research is needed to fully understand their mechanisms and harness their potential for improving mood and health.
In this conclusion, the authors emphasize the need to broaden research on the benefits of nature beyond the visual sense. While visual benefits have been extensively studied, there are other pathways through which nature provides advantages, including sound, smell, taste, touch, phytoncides, negative air ions, and microbes. The idea that feeling connected to nature can provide psychological benefits is briefly mentioned as an alternative pathway worth exploring further.
The authors highlight the evidence supporting the positive effects of viewing nature, listening to natural sounds, experiencing pleasant smells, consuming natural diets, interacting with animals, exposure to phytoncides, negative air ions, and the interplay between gut and brain microbiota. They suggest that these sensory and non-sensory pathways may work together synergistically, additively, or sub-additively to deliver nature's benefits.
The limitations of the review are acknowledged, including its narrative nature and the need for future studies to adopt a more systematic approach. The authors suggest focusing on specific health or well-being outcomes in more narrowly defined studies. They also mention that correlational or preference studies were used in cases where experimental research was lacking to explore potential sensory pathways for nature benefits.
It is emphasized that humans have evolved as multi-sensory organisms, and our health and well-being likely depend on multiple sensory channels. To fully understand the interdependence of nature and our well-being, research needs to encompass the full range of our senses and explore how nature benefits are delivered through these sensory pathways.
A Review of the Benefits of Nature Experiences: More Than Meets the Eye (International Journal of Environmental Research and Public Health)