From an environmental aesthetics point of view, aesthetic gratification results in a positive emotional response. The preference for landscapes is understood as providing a strong incentive for human activity from an evolutionary perspective. The first reactions to the environment—emotional reactions—are essential to human survival and function [1
This study explores the effects of perception of landscapes in daytime and nighttime scenery as a restorative quality. As an intriguing medium for peoples’ perceptions of a landscape, the aspects of environmental composition play an important role [5
]. According to Partin et al. [9
], integrated landscape assessments address the interdependent values that hold a direct relationship between co-analysis and other factors. The capacity of human cognition and thought is based on a process that is consistent with a particular environment, rather than a neutral or universal-purpose process. In other words, it has the characteristic of coordinating with the environmental influence in information processing by functioning efficiently in the material world [10
Restorative and recovery characteristics of viewing landscapes can reduce a person’s psychological and physical stress and restore their health to its original state [11
]. Landscapes with these characteristics can lead to recreational experiences, which recharge depleted concentration levels and lead to the reflection of an individual’s inner world [12
]. The restorative and recovery characteristics are known to be inherent mainly in natural scenery. The argument that natural landscapes contain more restorative and recovery qualities than artificial landscapes can be understood in two dimensions: evolutionary and cultural perspectives [15
]. From an evolutionary point of view, this is related to the fact that human information processing has evolved to suit natural environments, as long-term human evolution has mainly taken place in natural landscapes. Thus, while the information found in urban environments puts a strain on human information processing, natural environments relieve these burdens. From a cultural point of view, human civilization has all always relied on the destruction of nature, even though it began on the basis of its abundance. Thus, in any civilized society, the preciousness of nature is established through cultural awareness, and this cultural learning appears as a natural preference to the value of nature’s restorative and recovery characteristics. Both of the above aspects suggest that the restorative and recovery qualities inherent in natural scenery have a positive effect on human health, regardless of peoples’ personal or sociocultural differences. According to research studies to date, the restorative and recovery effects of natural scenery are experienced by various social and cultural groups, indicating that these characteristics have a universal and fundamental effect on the human experience of landscapes [3
The question arises here of whether the effect found above is due to the restorative and recovery characteristics of landscapes in general or specific to the type of landscape (natural or artificial). This is not clear because most of the research to date has compared natural and artificial landscapes. In order to clarify this, Van den Berg et al. [23
] controlled the effect of the type of landscape (natural or artificial landscape) and investigated the effect of the restorative and recovery characteristics of the landscape, and found that the greater the restorative and recovery characteristics of the landscape, the higher the preference for the landscape. These findings specifically demonstrate that restorative and recovery characteristics of landscapes create a positive landscape experience, regardless of the type of landscape or the sociocultural differences of human beings. Despite these implications, no study has been conducted to verify the effect of the restorative and recovery characteristics of landscapes at nighttime. If the restorative and recovery characteristics of landscapes are verified as measurement tools that can identify the characteristics of nighttime scenery, it is possible to understand the nighttime scenery from a multi-level point of view, and to come up with a variety of ways to develop design guidelines for nighttime landscapes.
Landscape preference and restorative quality evaluation methods can be divided into non-verbal and verbal evaluation methods. The non-verbal evaluation method analyzes external expressions of emotions, such as facial expressions, voices, and gestures, or measures physiological reactions using scientific experimental equipment. A verbal evaluation method is a method of describing one’s emotional state using self-reporting questionnaires or adjectives [24
]. Environmental psychology researchers have consistently focused on the restorative potential of natural environments rather than urban environments and have often used verbal evaluation methods, such as video and photographic experiments that employ subjective measures in the laboratory [25
]. There are several research studies on restorative and recovery effects of landscapes using both non-verbal and verbal evaluation methods. Ulrich [18
] measured psychological and physiological changes to images of nature (green vegetation), water and nature, and urban environments. This study used psychological measurement tools, such as the “Semantic Scale” [26
], which consists of 36 items grouped into four factors—dominance, wakefulness, attention or interest, and stability—and the “Zuckerman Inventory of Personal Reaction” [27
] which groups emotions into five factors—fear and arousal, positive affect, anger or aggression, attentiveness, and sadness. Physiological measurement tools were used, such as alpha waves of electroencephalography (EEG), which is most sensitive to psychological changes, electrocardiographs (EKG), and blood pressure (BVP). In this experiment, Ulrich showed that the two scenes containing nature produced a positive psychological change compared to the urban scenery, and that the alpha wave also increased in the order of urban scenery, nature scenery, and lastly water scenery with nature. Similarly, Chan measured psychological and physiological changes using photographs of native landscapes that could potentially restore attention based on four factors of the attention restoration theory (ART) from a Kaplan et al. [12
]. The perceived restorative scale (PRS), developed in Hartig et al. [28
], was used as a psychological measurement tool, and EKG, EEG, and BVP were used as physiological measurement tools. Most of these studies adopted EEG measurement as a non-verbal evaluation method.
Regarding EEG usability as a landscape measurement tool, with the development of mobile EEG devices, research on architectural spaces or outdoor environments has started to be actively carried out. Previous studies using EEG in the field of space planning provided implications for architectural and outdoor environmental planning, focusing on environmental settings, specific building elements, and areas of user interest in the architectural field. These are classified into three trends: (1) measurement of user influence on specific elements of indoor environments [29
]; (2) tools for determining specific architectural elements [30
]; and (3) analysis of visual attention with the user’s areas of interest [32
]. Many EEG studies on aspects of environments have shown the generally beneficial effects of green spaces or specific colors and environments in producing preference or restorative effects from natural landscapes. However, there have been no sufficient research studies involving a comparative analysis of daytime and nighttime scenery. Accordingly, this study used EEG to evaluate daytime and nighttime scenery related to the perceived restorative qualities and various environmental settings. Not only were the differences between daytime and nighttime scenery explored, but also the landscape types of each image were compared to verify the usability of EEG in landscape evaluation.
The purpose of this study is to investigate the effects of daytime and nighttime scenery on the psychological and physiological changes to the human body, focusing on restorative and recovery effects. To do this, we use a visual stimulus with a sensory perception ability of 87% of human senses. As a non-verbal evaluation method, we attempt to use EEG technology, which is directly related to peoples’ perceptions of an environment. Through this study, we intend to build fundamental data on what kind of invisible emotional benefits regarding restorative and recovery effects can be given to humans through psychological and physiological changes that occur when viewing daytime and nighttime images under the same conditions.
1.2. Landscape Preference and Landscape Restorative and Recovery Potential
Landscape preference, beyond aesthetic meanings, has a positive effect on physiological and psychological recovery and mental health [33
]. Based on the commonality of landscape preferences, natural landscapes have been shown to be very high in aesthetic satisfaction and refilling effects [35
]. In particular, Ulrich [11
] showed that a nature-like environment with high visibility was related to positive emotions. Moreover, preferences related to behavior were explained by environmental psychologists, and attitude changes to landscape preference and behavioral induction were examined using socio-psychological theory [36
]. That is, the study of landscape-to-human interaction can predict how the landscape is perceived and the relationship between intended behavior and experience in the specific landscape [37
]. Ivarsson and Hagerhall [38
] posited that the restorative effects of the landscape, which include recovery potential, are affected by preferences. Thus, landscape preference is adjusted by an internal assessment of potential restorative or recovery effects.
The theoretical background for the restorative and recovery characteristics of a landscape is the attention restoration theory (ART) [12
] and the psychophysiological stress recovery theory (PSRT) [39
]. PSRT describes stress release in various aspects, such as psychology and menstruation, whereas ART refers to the restorative and recovery effects of the landscape based on information processing and cognitive functions [38
]. According to ART, the attention required in daily life is intentional and requires a lot of energy, resulting in a depletion of concentration that has a negative effect on human perception, emotions, and behavior, which can be restored by viewing a landscape or an activity with restorative and recovery characteristics. It can also be considered as an environment in which you can participate in activities without any specific intention. This implies that the restorative and recovery effects have positive relationships with staying in a preferred environment. Hence, the restorative and recovery qualities of landscapes can be measured with subjective indicators, such as aesthetics, attractiveness, and peacefulness [12
]. A previous study [12
] demonstrates that these qualities are subdivided into four elements: (1) “being away”; (2) “extent”; (3) “fascination”; and (3) “compatibility”. The higher the perceived intensity of these four factors, the greater the recreational and restorative effects induced by the landscape.
“Being away” refers to physical or mental distance from daily life that requires intentional concentrations and efforts. These feelings arise when new and unfamiliar landscapes are experienced. However, if the sense of responsibility and duty is not present, the feeling of being elsewhere does not occur. An escape from daily life is a prerequisite. “Fascination” is the most important element of the four factors as it causes involuntary attention of the landscape experience. Since involuntary attention does not require any mental energy, rest has an effect of recharging attention. “Extent” is related to the spatial margin of the landscape- the harmony with elements inside and outside the landscape. Overall, “extent” consists of scope and connectedness. Scope encompasses the perception of the spatial margin of experience and the person’s experience through movement. Connectedness refers to the perception that the elements of landscape are in coherence with each other and are connected without being heterogeneous to the environment. “Compatibility” entails the activities and functions of individuals that are predicted within the landscape. It is the perception of how the conditions, such as the characteristics and needs of the landscape, correspond with the purpose and intention of the experiencer. The general consensus on ART research demonstrates the effects of restorative and recovery of landscape in two dimensions: (1) a specific dimension, including psychology, physiology, and cognition; (2) a comprehensive dimension, focusing on landscape preferences. Existing research that examines the restorative characteristics and comprehensive landscape preferences reveals a positive relationship between restorative and recovery effects with preferences [4
In contrast to ART, typical environments with a lot of recovery environmental factors are considered as natural environments in PSRT [12
]. Several studies have shown that in environments where natural elements predominate over artificial elements, the recovery quality tends to be more prevalent [35
]. Therefore, it is possible to draw more attention to natural environments than urban environments [23
]. The achievement of attention recovery through recovery environments facilitate psychological benefits, such as stress relief and emotional enhancement [45
Existing research on landscape preference and restorative potential have focused on confirming whether natural scenery has a higher preference rather than built-environment scenery [42
]. Unlike previous studies that focused on the positive effects of the natural environment, this study identifies perceived restorative and recovery potentials between daytime and nighttime sceneries.