2.1 Environmental effects on the circadian rhythm for sleep
Hansmann et al. (2007) found that the natural environment had better healing effects than the urban environment. People can feel relaxed and relieve stress by being immersed in natural virtual environments to achieve emotional connection as in the real environment (de Kort et al., 2006). When individuals are stressed, encountering the most unthreatening natural environments will have a stress-reducing or beneficial influence, whereas many urban environments may hamper recuperation (Ulrich et al., 1991). Findings indicate that recovery was faster and more complete when subjects were exposed to natural rather than urban environments. Moreover, findings raised the possibility that responses to nature have a salient parasympathetic nervous system component, but there was no evidence of pronounced parasympathetic involvement in responses to urban settings.
Light plays a primary role in the circadian. Humans are diurnal animals, and the Circadian System drives physiological functions so that activity-related processes happen in the daytime while functions associated with rest occur at night (Dumont & Beaulieu, 2007). A misalignment between the endogenous circadian and the desired sleep schedule is the leading cause of circadian sleep disorders; it may also be involved in certain mood disorders. Since light is the top environmental cue, the circadian system uses it to set its timing to the day-night cycle. Controlled light exposure can treat some mood and sleep disorders in the Circadian System when appropriately handled. The earliest studies on light intensity’s effect on humans suggested that bright light affected sleep and mood disorders in humans. In particular, indoor workers must be exposed to the light change in the context of the 24-hour light-to-dark cycle for a better Circadian System.
A study also concluded that bright light exposure, comparable to the outdoors, was required for the circadian system (Wever, 1989). Therefore, an essential characteristic of the light-to-dark signal is the intensity of the light (Laakso et al., 1991). The circadian effects of light exposure were evaluated in laboratory conditions different from those experienced in the real world. We can find that proper lighting and the natural environment positively affect sleep because they can affect the Circadian System and release stress. Therefore, we will consider the factor of lighting change in the VR scene design in our study.
The research discusses the impact of lighting characteristics on the human circadian system and the design of lighting for various healthcare and medical applications. (Figueiro, 2013). The master clock controls people's circadian rhythms in the suprachiasmatic nucleus (SCN), which has an inherent cycle slightly longer than 24 hours. Light stimuli in bright/dark patterns reaching the retina synchronize the SCN with the 24-hour local time, coordinating and enabling various biological functions to occur at the correct times during the day and night. Without regular light exposure and dark periods, the circadian rhythms of life can become disrupted. Various modern diseases, ranging from sleep disorders to cancer, are associated with disruptions in the circadian rhythms caused by light. However, light is defined based on the human visual rather than the circadian system. Therefore, design in VREs should consider the needs of both the visual and non-visual systems.
2.2 The lighting and colors affect the feelings of experiencing an environment
Color and lighting are essential factors that cause relaxation or stress, providing peace and a pleasant environment for individuals in the home to live together at rest (Babakhani, 2017). Users exposed to different energies of color and standard colors have more prolonged effects on the spirit and have long durability. Color and environmental lighting carry spiritual products, so the load and energy affect users' feelings and decisions. At the same time, physiological investigation proved that colors could create physical and unstable responses such as raising/lowering blood pressure, heartbeat, sweating, respiratory system, and even brain wave patterns.
A good lighting design can regulate human emotions and improve their feelings of comfort in a space. A study explored the effects of four groups of lights (green, blue, red, and yellow) on the participants’ moods and impressions (Xie et al., 2022). The results showed that different light colors significantly affected mood, and red light could arouse emotional changes to calm, irritated, relaxed, nervous, stable, and pleasure. Based on the results, different light colors had a particular relation to the participants’ impressions, which provides another research value for designing the colored light environment for an individual’s affective impressions. However, in studying an individual’s affective images, there is still some uncertainty about how colored lights affect an individual’s moods and impressions toward visual objects.
Color and light are two ambient attributes that can be used to design and modify workspaces. The study by Shahidi et al. (2021) was to investigate the simultaneous effects of warm/cool white light on visual perception and mood in a simulated colored workspace. The participants experienced higher levels of tension, anger, depression, and anxiety and lower levels of visual comfort and calmness in the environment of the red color condition than in the white color of the light. The results showed that the blue wall reduced brightness and increased the attractiveness of the environment compared to a white wall. The preference for cool or warm light depended on the color of the environment. It seemed that combining white and warm or blue colors with cool light had a more favorable effect on visual perception and people's moods in workplaces.
After inducing a sad mood with a short movie, one group of the elderly was immersed in a high positive, arousing (i.e., activating) ambiance and another in a neutral atmosphere (Kuijsters et al., 2015). Similarly, after inducing anxiety with a short movie, one group of the elderly was immersed in a pleasant, low, arousing (i.e., cozy) ambiance and another in a neutral ambiance. The study hypothesized that ambiances with a recognizable, positive affective meaning could effectively mitigate negative moods in the elderly. In this study, they improve the mood of the elderly by exposing them to lighting ambiances with a clear, positive meaning. Sad elderly who were immersed in a high positive arousing (i.e., activating) ambiance were physiologically more aroused than sad elderly who were immersed in a neutral ambiance. The anxious elderly could be effectively calmed with a cozy ambiance.
Based on prior research, we know that different lighting and colors can evoke various sensations and emotions. For instance, dim, cool lighting may induce unease and melancholy, while bright, warm hues might bring comfort and relaxation. The colors and lighting in an environment can impact individuals' psychological and physical aspects. Our study will construct different temporal backgrounds in the VREs setting, featuring sunset, moonlight, and a starry sky through the interplay of lighting and color. We will also explore user-induced emotional experiences in VR with or without a campfire, aiming to facilitate relaxation and sleep assistance for future research and development.
2.3 Emotional responses induced by Virtual Reality
Emotion computing in VR has emerged as a significant area of research, especially with the increasing availability and adoption of immersive VR technologies. While many studies on emotion induction have traditionally relied on non-immersive stimuli, VR offers a unique platform for exploring and manipulating emotional states. One exciting avenue of research in this field involves using immersive VR environments to induce and identify emotional states. For example, researchers have employed the Circumplex model of emotions to design virtual rooms that elicit specific combinations of arousal and valence, allowing for a more comprehensive understanding of emotional responses (Marín-Morales et al., 2018). Various physiological and psychological indicators are used to extract features from signals, enabling the quantification of linear and nonlinear dynamics in the brain and cardiovascular system. In addition to its utility in studying emotions, the development of VR technology has opened up new possibilities for enhancing real-life experiences. The study demonstrates how VR immersion can induce motivation and facilitate emotional adjustment in individuals, particularly in the context of travel and destination preferences (Tussyadiah et al., 2018). The study highlights how practical design in virtual environments can make VR experiences more enjoyable, leading to stronger preferences for specific destinations and an increased intention to visit them. In summary, the intersection of emotion computing and VR technology is a promising area that enriches our understanding of human emotions and offers practical applications in various domains, such as travel and consumer behavior. These advancements signify the growing importance of immersive technologies in shaping our emotional experiences and influencing our decisions.
VREs have become valuable and popular in psychological experiment design due to their low cost and controllability. VR can positively impact human presence, perception, engagement, emotions, and empathy (Pirker & Dengel, 2021). As a result, many studies have begun to design experiments related to psychology through virtual scenarios, especially in understanding how people's emotional expression and adaptation in the real world can be understood through the design of scenes. The research focused on investigating the environmental factors that influence public speaking anxiety (Lo et al., 2022). They designed a parameterized virtual environment for such psychological experiments. The study developed a parameterized VR system that simulates a public speaking environment, exploring how three environmental variables, audience attitude, and environmental lighting brightness, affect the anxiety levels of speakers. The experimental results indicate that the simulated virtual environment can trigger speaker anxiety, and it appears that personal experiences and traits influence the onset of anxiety. In particular, it validated how various environmental factors affect speakers' anxiety responses and acknowledged the presence of individual differences in the influence of the environment.
Freeman et al. (2008) designed a virtual reality experience of the London underground (tube) train and invited nearby residents to participate in the study, which included a questionnaire after the experience. The goal was to demonstrate that individuals in the general population without severe mental illness may also generate unfounded paranoid thoughts during the experience in Virtual Reality. Most participants felt that the characters in the Virtual Reality environment were neutral or even friendly, but a substantial minority reported paranoid concerns. Anxiety, worry, perceptual anomalies, and cognitive inflexibility strongly predicted paranoia. The VREs can induce potential anxiety and fear in the participants, leading to the projection of internal emotional experiences in VR.
The research conducted immersive VR offered a more effective means of transitioning individuals from a stressed state to a relaxed one compared to meditation (Chen & Li, 2022). The sensory information and the VR scenes were controlled and manipulated more easily than the real environment for experiments, making it a highly adaptable tool for experimental purposes. Immersing oneself in a VR environment could heighten positive emotions and induce feelings of joy, which, in turn, facilitated the process of stress alleviation. This research underscores the potential of VR as a valuable resource for promoting relaxation and emotional well-being and suggests its practical applications in stress management and mental health interventions. The ability to harness the controlled environment of VR may provide a novel approach to addressing stress-related concerns.
There have been many studies on the impact of emotion regulation on well-being. Still, in recent years, VR technology has also been included in this type of research. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for system evaluation and analysis, the paper conducted a systematic search and found that many studies have mentioned the use of VR technology to enhance emotion regulation and well-being, confirming that using VR for emotion regulation training can promote users' well-being (JI, PA, & CM, 2020). VR will provide a platform for inducing and measuring emotional responses, creating a highly immersive virtual environment, and allowing participants to feel a sense of presence. VR technology can elicit different emotional experiences by controlling various factors, such as sensory stimulation through sound, visual, and tactile inputs, to modulate the intensity and type of emotions.