Analysis of human electroencephalogram features in different indoor environments
Introduction
People spend most of their lives indoors and the comfort of the indoor environment plays an important role in ensuring human health and work efficiency [1,2]. In addition, energy consumption and life cycle costs of buildings are directly or indirectly affected by the behavior of the occupants, which may be triggered by the perception of uncomfortable indoor environments. To effectively design and operate buildings, it is important to understand how occupants perceive the indoor environment.
Several scholars have studied the comfort of indoor environments and explored the influence of the thermal, acoustic, and light environment, air quality, indoor background, and composite environmental factors on human comfort [[3], [4], [5], [6]]. Subjective evaluation is the most commonly used method for indoor environmental evaluation. While subjective indicators are important tools for understanding perceived experience, the subjectivity of human consciousness makes it difficult to compare, quantify, and justify this impact [7]. In recent years, research methods have shifted from the subjective evaluation to the combination of subjective and objective parameters. An increasing number of convergent teams are being formed between the disciplines of Humanities, Arts, and Social Sciences and Science, Technology, Engineering, and Medicine to bring interdisciplinary industry expertise to this field of research [8].
An electroencephalogram (EEG) is a physiological parameter and reflects the overall electrophysiological activity of the brain measured on the surface of the cerebral cortex or scalp [9]. Different external stimuli produce different EEG signals at different locations on the cerebral cortex. Stimuli in the external environment such as sound, light, and heat will elicit auditory, visual, and thermal sensations in the human body, respectively. External environmental stimuli are first received by the sensory organs. The stimulus energy is then converted into electrical signals which are transmitted as nerve impulses to the sensory center through nerve fibers to elicit corresponding sensations. The human brain integrates information from different sensory pathways to form an overall cognition, that is, multisensory integration [10]. The nervous system plays a role in regulating the physiological processes of various organs of the body. EEG parameters are of great significance to the normal activities in human life and at the same time represent a personal unified physiological response to external factors. Furthermore, an EEG can measure both conscious and subconscious responses without the need to interrupt and bias the subject, offering a higher degree of objectivity. Therefore, the analysis of EEG features is an effective way of studying physiological and psychological states [11].
Due to development of science and technology, EEG signals are not only used in clinical diagnosis but also in pattern recognition, psychology, and other fields. With regard to ergonomics, EEG technology has been widely used to evaluate human comfort, such as clothing comfort [12,13], comfort of wearing diapers [14] and waist belts [15], and physiological responses when using sanitary napkins [16]. The brain has well-recognized patterns of activity for various emotional responses [[17], [18], [19]]. EEG was applied to environmental evaluation, like natural environment research [20,21], garden landscape design [22], and virtual environments [23,24]. Concerning the indoor environment of buildings, the characteristics of human brain electrical signals under different light environments were explored [[25], [26], [27], [28]]. Some studies explored the effect of temperature on occupants via EEG. Yao et al. studied the effect of thermal conditions on subjects’ static status using a bipolar EEG while they are lying down with their eyes closed [29]. Choi et al. studied the effect of temperature on attention ability based on electroencephalogram measurements [30]. Wang et al. investigated the effect of indoor thermal environment on occupants' mental workload and task performance using EEG [31]. Human stress levels in two combined environments were evaluated via EEG [32]. However, no studies have reported the relationship between total comfort and EEG signals in a complex environment. Indoor environment experiments generally only evaluate a single environmental variable, focusing solely on heat, sound, air quality, or lighting. However, the real world is a combined environment that operates in a complex manner, making it necessary to study the effects of multiple variables in an indoor combined environment.
Therefore, this study focuses on exploring the features of human EEG signals under different total comforts, incorporating EEG responses to reduce the subjectivity and ambiguity that are unavoidable in human responses. With the increasing number of portable EEG devices entering the market and the development of brain-computer interface technology, this research method and results can be extended to architectural intelligent control systems.
Section snippets
Methods
In the part of the methods, we introduced the participants, experimental settings, experimental contents, experimental procedure, data processing and statistics.
Results
Both subjective and physiological measurements results in different environments were analyzed and compared.
Discussion
In this study, we explored the changes in subjective feelings in a complex environment, including thermal, acoustic, visual, and total comfort. Pearson correlation analysis results show that thermal, acoustic, visual, and total comfort are significantly correlated. This result is consistent with the conclusions of Refs. [[35], [50]]. In stimulations of the environment such as sound, heat, and light, individuals will experience acoustic, thermal, and visual sensations. External environmental
Limitations and further research
There are some limitations to this study. Although the changes in total EEG energy and the ratio of the theta frequency band in comfortable and uncomfortable environments were significant, and even fewer subjects were analyzed in other studies [30,[61], [62], [63], [64]], it is still necessary to expand the sample size and consider the subjects' health status, age group, and cultural background.
This study aimed to explore a method of basic research for the assessment of a more realistic
Conclusions
Climate chamber tests were conducted to explore the possibility of using neurological responses and associated subjective states to overcome the limitations of subjective evaluations. The present study found that thermal, acoustic, visual, and total comforts are significantly correlated. The indoor environment can significantly influence brain cortical activity and the EEG signal can serve as a biological marker of environmental alterations. Compared with an uncomfortable environment, the total
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This study has been financially supported by the National Natural Science Foundation of China (No. 51778305). The author would like to thank the engineers of Beijing Fistar Technology Co., LTD for their guidance and help.
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