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The effect on emotions and brain activity by the direct/indirect lighting in the residential environment
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Yu-Bin Shin a,b , Seung-Hyun Woo c , Dong-Hyeon Kim c , Jinseong Kim a,b , Jae-Jin Kim a,d , Jin Young Park a,d,∗ a
Department of Psychiatry and Institute of Behavioral Science in Medicine, Yonsei University College of Medicine, Seoul, South Korea Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, South Korea c Future Device R&D Department, Material & Components R&D Lab., LG Electronics INC., Seoul, South Korea d Department of Psychiatry, Yonsei University, College of Medicine, Gangnam Severance Hospital, Seoul, South Korea b
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h i g h l i g h t s • • • •
We examined the influence of lighting environment on emotion and physiology. A direct/indirect lighting environment produces higher valence and cool ratings. A direct/indirect lighting environment increases the theta frequency band on EEG. An EEG signal can be a biological marker of environmental alteration.
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Article history: Received 1 April 2014 Received in revised form 15 September 2014 Accepted 24 September 2014 Available online xxx
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Keywords: Indirect/direct lighting Emotion Theta activity Spaciousness Cool
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1. Introduction
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This study was performed to explore how direct/indirect lighting affects emotions and brain oscillations compared to the direct lighting when brightness and color temperature are controlled. Twenty-eight subjects (12 females; mean age 22.5) participated. The experimental conditions consisted of two lighting environments: direct/indirect lighting (400 lx downlight, 300 lx uplight) and direct lighting (700 lx downlight). On each trial, a luminance environment was presented for 4 min, followed by participants rated their emotional feelings of the lighting environment. EEG data were recorded during the experiment. Spectral analysis was performed for the range of delta, theta, alpha, beta, and gamma ranges. The participants felt cooler and more pleasant and theta oscillations on the F4, F8, T4, and TP7 electrodes were more enhanced in the direct/indirect lighting environment compared to the direct lighting environment. There was significant correlation between the “cool” rating and the theta power of the F8 electrode. The participants felt more pleasant in the direct/indirect lighting environment, indicating that space with direct/indirect lighting modulated subjective perception. Additionally, our results suggest that theta oscillatory activity can be used as a biological marker that reflects emotional status in different lighting environments. © 2014 Published by Elsevier Ireland Ltd.
Ambient lighting affects human psychophysiology, and interest in the effects of lighting has increased as we spend most of our time surrounded by environments filled with artificial light in which sunlight is often blocked [1,2]. Kruithof, a pioneer in this field of research, reported the psychological effect of light and proposed
∗ Corresponding author at: Department of Psychiatry, Yonsei University, College of Medicine, Gangnam Severance Hospital, 211 Eonju-ro, Gangnam-gu, Seoul 135-720, South Korea. Tel.: +82 2 2019 3341; fax: +82 2 3462 4304. E-mail address: [email protected] (J.Y. Park).
a curve for a comfort zone of the combination of illumination and color temperature [3]. Indoor lighting can influence affective and cognitive processes [4–7], and physiological functions [1]. Indeed, there is ample evidence to support the hypothesis that lighting environment affects human emotion. Despite many studies on lighting environments that have assessed “subjective feelings,” few reports have described the influence of lighting on objective “biological activity” in the brain. In the 1990s, some studies investigated physiological changes induced by different lighting conditions (brightness and color), but these studies are limited by small number of subjects (7–15) that may be due to the difficulty with control of lighting variables with older technology [8–12].
http://dx.doi.org/10.1016/j.neulet.2014.09.046 0304-3940/© 2014 Published by Elsevier Ireland Ltd.
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Fig. 1. Schematic depicting the experimental room showing direct and indirect lighting environment and direct lighting environment, and furniture.
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Recently, there has been a growing interest in the potential of using highly energy-efficient light-emitting diodes (LEDs). LED technology enables more accurate and precise study of the effects of different wavelengths, and it is also useful in the treatment of seasonal affective disorder [13,14]. Moreover, LED technology allows for the design of standardized and elaborate lightings conditions, such as illuminance and color temperature. We have previously used LED technology to successfully evaluate the effects of lighting on emotion and electroencephalography (EEG) [2,15,16]. Most studies of lighting environments, including our previous work, evaluated luminance and color temperatures based on Kruithof’s study [3]. Besides source light brightness and color temperature, other factors also used to provide high-quality environments. One crucial factor is how to arrange lighting sources. Indirect and direct lighting designs elicit different feelings, and this property is widely exploited in artificial environments. In the fields of architecture and interior design, it is generally accepted that the perception of room size is an important property, as environments that do not provide sufficient space produce feelings of threat and can act as ambient stressors. In addition, increasing population densities have revealed the need for adequate individual space [17]. Therefore, there have been many studies to identify factors that provide the impression of more room within a given volume of space. With respect to artificial lighting, the use of uniform and peripheral lighting was recommended [18]. For overhead central lighting, it was reported that the ratio of direct/indirect lighting modulated spacious perception [19]; the room appeared larger when more light was supplied indirectly. The present study explored the influence of direct/indirect lighting on subjects’ affective and neurophysiological responses in a residential environment. We investigated EEG activity and emotional scores (dimensional affect and subjective feelings) in subjects exposed to different lighting conditions in an ecologically valid living room setting.
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Twenty-eight subjects participated in this study (12 females, mean age 22.5). Written informed consent was obtained after a complete description of the study was provided to the participants. Our study was carried out under the guidelines for the use of human subjects established by the Institutional Review Board (IRB) at Gangnam Severance Hospital, Yonsei University.
2.2. Environmental setting The experiment was conducted in a furnished living room with dimensions of 4.7 m × 4.4 m and a height of 3.1 m. It contained a TV, an entertainment center, sofas, a coffee table, a side table with flowers, wall shelves, and a rug (Fig. 1). Daylight was excluded by shielding the windows. The temperature and relative humidity of the experimental room were 23.3◦ (SD = 0.3◦ ) and 21.3% (SD = 1.0%), respectively. Eight LED lighting panels (600 cm × 600 cm; LG Electronics, Seoul, Republic of Korea) were suspended above the room; four faced up and four faced down (1 panel: 53 W, 4694 lm, 3000 n, 5000 K). A controller (WE7000, Yokogawa, Japan) regulated the illuminance (700 lx) and color temperature (5000 K) of the LEDs. The luminance was measured at table level (0.75 m). 2.3. Design and procedure A counterbalanced within-subject design was employed. The experiment consisted of two different lighting conditions: direct/indirect lighting (400 lx downlight, 300 lx uplight) and direct lighting (700 lx downlight) (Fig. 1). In each trial, following a 4min dark condition (0 lx) to allow subjects to equilibrate to the surroundings, a luminous environment was presented for 4 min. Immediately following luminous environment presentation, the participants were required to complete self-report questionnaires to measure light-induced emotional responses. The same lighting condition was continued while participants completed the questionnaires. The self-report questionnaires included 100-mm pen-andpaper visual analog scales (VAS) and the Self-Assessment Manikin (SAM) [20]. The VAS consisted of a list of three emotion adjectives (cool, refresh, comfortable). The terms “not at all” and “strongly” were written under the left and right ends of the scale, respectively. The SAM was comprised of two nine-point graphical rating scales measuring the valence and arousal dimensions. For the valence dimension, SAM ranged from a happy to unhappy figure. For the arousal dimensions, the SAM figure ranged from excited and aroused to relaxed. Upon arrival, participants were comfortably seated in the experiment room and received instructions. They were only informed about the purpose of the study and were uninformed about the hypothesis. The experimenter instructed participants to focus on and evaluate the overall appearance created by the lighting conditions and stressed that they should maintain the
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Fig. 2. Grand-averaged scalp distributions of theta activity.
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induced emotional states during the presentation of the luminous environment. During the entire experiment, EEG data were recorded continuously from the scalp using a NuAMP amplifier (Nufern, East Granby, CT, USA) and a 10/20 layout 40-channel Quik-cap electrode placement system (Neuroscan Inc., Charlotte, NC, USA) at a sampling rate of 250 Hz. We used the linked mastoid for reference and two bipolar electrodes to measure horizontal and vertical eye movements. The impedance of each electrode was maintained below 10 k. EEG was sampled at 250 Hz (analog band-pass filter 0.1–100 Hz). We used Matlab 7.0.1 (MathWorks, Natick, MA, USA) with the EEGLAB toolbox [21] to preprocess and analyze the data. The data were re-referenced to a common average reference and detrended. Independent component decomposition and visual inspection of data were performed to eliminate artifacts. We used a paired t-tests to investigate differences in subjective feelings and EEG measurements between both environments. We estimated the standard q-value and used it to control the falsediscovery rate (FDR) using the original Benjamini and Hochberg approach to multiple testing [22,23] for EEG measurements. Pearson’s correlation coefficients were used to analyze correlations between EEG measurements and emotional feelings that were found to be significantly different by paired t-tests. Statistical significance was defined as P < 0.05. We did not perform statistical corrections for multiple comparisons of behavioral outcomes or correlations due to the exploratory nature of this study. All statistical comparisons were performed using the Statistical Package for the Social Sciences (SPSS) 18.0 (SPSS Inc., Chicago, IL, USA), and all other computations were performed using Matlab.
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The valence ratings for direct/indirect lighting (mean = 6.4, SD = 1.2) were significantly higher (P = 0.005) than those for direct lighting (mean = 5.4, SD = 1.4). However, arousal did not significantly differ between both conditions. The cool scores for direct/indirect lighting (mean = 6.9, SD = 1.6) were significantly higher (P = 0.045) than those for direct lighting (mean = 6.0; SD = 1.9), but the refresh and comfort scores on the VAS were not significantly different between the two conditions (Table 1). A significant difference was observed in the theta frequency band, but there was no significant difference between the two conditions with regard to power in the alpha, beta, and gamma frequency bands. Comparisons of theta bands between the direct/indirect and direct lighting conditions revealed increased theta power spectral values in the right fronto-temporal and left
Table 1 Within-group subjective parameter comparisons. Dependent variable
Refreshing Cool Comfort Arousal Valence *
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1.8 1.6 2.1 1.6 1.2
6.2 6.0 5.1 5.3 5.4
2.0 1.9 2.3 2.0 1.4
t
1.052 2.104* 0.873 0.532 3.074*
P < 0.05, paired t-test.
temporo-parietal regions (F4: P = 0.036 uncorrected, F8: P = 0.035 uncorrected, T4: P = 0.022 uncorrected, TP7: P = 0.039 uncorrected) under the FDR threshold (Fig. 2). To further investigate the relationship between EEG measurements and emotional feeling, we performed correlational analyses. EEG values (F4, F8, T4, TP7) and cool and valence scales that were found to be significantly different with paired t-tests were converted to average scores for the two lighting conditions. Correlational analysis demonstrated that the cool ratings on the VAS scale were positively correlated with theta power spectral value (F8, P = 0.019) (Fig. 3). A scatterplot depicting these results is shown in Fig. 3. There was no correlation between the self-assessment scales and the theta spectra power of other regions.
Fig. 3. Scatterplot showing a positive correlation between cool ratings on the VAS scale and theta power in F8.
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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4. Discussion The aim of this study was to examine the influence of lighting environment, specifically the appearances of the testing environment created by different lighting distributions, on emotion and psychophysiology. The results revealed direct/indirect lighting provided more pleasant and cool feelings than direct lighting. In addition, theta band power in the right fronto-temporal and left temporo-parietal regions increased with direct/indirect lighting. The theta power in the right frontal region showed a positive correlation with the “cool” VAS scores. In affective neuroscience, the dimensional approach is classically used as a standardized method to evaluate affect. Valence indicates the direction of emotional activation (e.g. pleasant or unpleasant) and arousal reflects the intensity of emotional activation [24–26]. As reflected by the valence ratings, the participants felt more pleasant in the direct/indirect lighting environment, which is consistent with previous findings that subjects’ overall preference increased when more indirect lighting was supplied [19] and that subjects preferred a mixed systems of direct and indirect lighting to a direct lighting system [27–30]. There was no significant difference in arousal, which is in accordance with previous findings that arousal was modulated by brightness [31,32] or color temperature [16]. The lighting conditions only differed in the ratio of direct and indirect light – illuminance and color temperature were constant. To date, the dimensional approach has mainly employed picture [24,33], sound [34], music [35,36] and video clips [37,38] in controlled environments. In this study, we successfully used it to evaluate the effects of different lighting environments. The participants felt cooler in the direct/indirect lighting environment than in the direct lighting environment. This result is in line with those of our previous behavioral study [39]. Moreover, as mentioned earlier, a room appears larger when more light was supplied indirectly [19]. A space with direct/indirect lighting elicits cool feelings; that is, different lighting conditions induce different emotional states. Subjects exhibited increased theta band power in the right fronto-temporal and left temporo-parietal regions during the presentation of direct/indirect lighting. Furthermore, we observed a positive correlation between theta power in the right frontal region and cool ratings. These findings are consistent with previous studies reporting that theta band activity is associated with affective processing. Theta oscillatory activity is relevant with orientation, attention, memory, associative information and affective processing, and increased with greater task demands [40]. Several studies have reported theta synchronization activity is related with valence during presentation of emotional pictures [33,40,41], pleasant musical excerpts [36] and blissful positive states during meditation [42]. Therefore, theta band activity seems to reflect emotions in various statuses, and in our study, only theta power was different according to lighting environments. Our observation of regional brain activation pattern differences is consistent with those described by previous studies. Much of the existing literature reported frontal EEG asymmetry in the valence dimension. Davidson and Fox suggested valencedependent bilateral activity in the prefrontal cortex, that is, positive and negative emotion activated left- and right-sided frontal activation, respectively [43,44]. However, we did not find differences in these regions. This could be due to several reasons. First, previous studies used emotional pictures, music, or video clips for stimuli to induce emotion, whereas we employed ambient stimuli to elicit emotional responses. Accordingly, lighting induced different emotional states, but the regional differences were less robust than those achieved with other types of stimuli. Second,
the obtained results indicate that direct/indirect lighting elicits more pleasant emotion relative to direct lighting. That is, bilateral activation may require a considerable difference in behavioral ratings. Note that drowsiness is an important issue for interpreting the results because the drowsy-alert level induces changes in EEG (e.g., a decrease or disappearance of alpha and/or an increase in theta during a drowsy period). In this study, we assessed valence and arousal to evaluate emotions, and arousal may reflect the drowsiness-alertness continuum [45,46]. As shown in Table 1, the arousal was not different between both conditions. Furthermore, we also asked participants to rate items to estimate the extent of drowsiness after the experiment. This result is not shown because the questions were designed to assess experimental validity and were not part of the study’s objectives. Drowsy state was self-rated on a 100-mm VAS. The terms “strongly drowsy” and “strongly alert” were written under the left and right ends of the scale, respectively. The results show the mean drowsy rating during the entire experiment was 5.6 (SD = 1.9), indicating that it was unlikely to affect the results. 5. Limitations The present study has several limitations. First, subjective feelings toward the environment can be altered depending on the amount of sunshine, lighting hardware, length of suspended lighting, interior decoration, and other variables. Second, we did not employ multiple comparisons due to the explorative nature of this study, thus there was the possibility of detecting an effect that was not “true” (i.e., type 1 error). Third, although the experimenter only informed about the overall purpose of the study, participants may have assumed the hypothesis. It may have influenced the result, but it could not be evaluated. Fourth, although the sample size was sufficient to investigate EEG activity, it is still a small number for the generalization of results. 6. Conclusions The present study demonstrated ambient light in an environment can significantly influence brain cortical activity, and EEG signals can serve as a biological marker of environmental alterations. In contrast with previous studies that have been concentrated on controlling the external stimuli such as picture, sound, music and film-clips, this study focused on lighting variables at environmental level, and elucidated the effect of the lighting on neurophysiology. Further research into how other lighting variables, such as brightness, color, lighting arrangement, and the ratio of upward and downward light, affect psychophysiology are required to make recommendations to optimize different lighting environments. Authors contributions Y.B.S. carried out the experiment, conducted the data analysis, and wrote the manuscript. S.H.W., D.H.K., J.S.K., and J.J.K. participated in designing the research study, constructed the experimental room, and interpreted the results. J.Y.P. had full access to all of the data in the study, takes responsibility for the integrity of the data, designed the study and wrote the manuscript. Conflict of interest The authors declare they have no competing interests.
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Acknowledgments
We are thankful to Yeon-ju Hong for making the illustrations used in this paper, and Hyemin Park and Jeeye Choi for their assis319 tance with data acquisition. This work was supported by a 2012 320 research grant from LG Electronics and the Basic Science Research 321 Program through the National Research Foundation of Korea (NRF), 322 Q2 funded by the Ministry of Science, ICT, and Future Planning (Grant 323 Number 2013R1A1A1013207 to J.Y.P.). 324 318
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Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet
The effect on emotions and brain activity by the direct/indirect lighting in the residential environment
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Yu-Bin Shin a,b , Seung-Hyun Woo c , Dong-Hyeon Kim c , Jinseong Kim a,b , Jae-Jin Kim a,d , Jin Young Park a,d,∗ a
Department of Psychiatry and Institute of Behavioral Science in Medicine, Yonsei University College of Medicine, Seoul, South Korea Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, South Korea c Future Device R&D Department, Material & Components R&D Lab., LG Electronics INC., Seoul, South Korea d Department of Psychiatry, Yonsei University, College of Medicine, Gangnam Severance Hospital, Seoul, South Korea b
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We examined the influence of lighting environment on emotion and physiology. A direct/indirect lighting environment produces higher valence and cool ratings. A direct/indirect lighting environment increases the theta frequency band on EEG. An EEG signal can be a biological marker of environmental alteration.
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Article history: Received 1 April 2014 Received in revised form 15 September 2014 Accepted 24 September 2014 Available online xxx
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Keywords: Indirect/direct lighting Emotion Theta activity Spaciousness Cool
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1. Introduction
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This study was performed to explore how direct/indirect lighting affects emotions and brain oscillations compared to the direct lighting when brightness and color temperature are controlled. Twenty-eight subjects (12 females; mean age 22.5) participated. The experimental conditions consisted of two lighting environments: direct/indirect lighting (400 lx downlight, 300 lx uplight) and direct lighting (700 lx downlight). On each trial, a luminance environment was presented for 4 min, followed by participants rated their emotional feelings of the lighting environment. EEG data were recorded during the experiment. Spectral analysis was performed for the range of delta, theta, alpha, beta, and gamma ranges. The participants felt cooler and more pleasant and theta oscillations on the F4, F8, T4, and TP7 electrodes were more enhanced in the direct/indirect lighting environment compared to the direct lighting environment. There was significant correlation between the “cool” rating and the theta power of the F8 electrode. The participants felt more pleasant in the direct/indirect lighting environment, indicating that space with direct/indirect lighting modulated subjective perception. Additionally, our results suggest that theta oscillatory activity can be used as a biological marker that reflects emotional status in different lighting environments. © 2014 Published by Elsevier Ireland Ltd.
Ambient lighting affects human psychophysiology, and interest in the effects of lighting has increased as we spend most of our time surrounded by environments filled with artificial light in which sunlight is often blocked [1,2]. Kruithof, a pioneer in this field of research, reported the psychological effect of light and proposed
∗ Corresponding author at: Department of Psychiatry, Yonsei University, College of Medicine, Gangnam Severance Hospital, 211 Eonju-ro, Gangnam-gu, Seoul 135-720, South Korea. Tel.: +82 2 2019 3341; fax: +82 2 3462 4304. E-mail address: [email protected] (J.Y. Park).
a curve for a comfort zone of the combination of illumination and color temperature [3]. Indoor lighting can influence affective and cognitive processes [4–7], and physiological functions [1]. Indeed, there is ample evidence to support the hypothesis that lighting environment affects human emotion. Despite many studies on lighting environments that have assessed “subjective feelings,” few reports have described the influence of lighting on objective “biological activity” in the brain. In the 1990s, some studies investigated physiological changes induced by different lighting conditions (brightness and color), but these studies are limited by small number of subjects (7–15) that may be due to the difficulty with control of lighting variables with older technology [8–12].
http://dx.doi.org/10.1016/j.neulet.2014.09.046 0304-3940/© 2014 Published by Elsevier Ireland Ltd.
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Fig. 1. Schematic depicting the experimental room showing direct and indirect lighting environment and direct lighting environment, and furniture.
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Recently, there has been a growing interest in the potential of using highly energy-efficient light-emitting diodes (LEDs). LED technology enables more accurate and precise study of the effects of different wavelengths, and it is also useful in the treatment of seasonal affective disorder [13,14]. Moreover, LED technology allows for the design of standardized and elaborate lightings conditions, such as illuminance and color temperature. We have previously used LED technology to successfully evaluate the effects of lighting on emotion and electroencephalography (EEG) [2,15,16]. Most studies of lighting environments, including our previous work, evaluated luminance and color temperatures based on Kruithof’s study [3]. Besides source light brightness and color temperature, other factors also used to provide high-quality environments. One crucial factor is how to arrange lighting sources. Indirect and direct lighting designs elicit different feelings, and this property is widely exploited in artificial environments. In the fields of architecture and interior design, it is generally accepted that the perception of room size is an important property, as environments that do not provide sufficient space produce feelings of threat and can act as ambient stressors. In addition, increasing population densities have revealed the need for adequate individual space [17]. Therefore, there have been many studies to identify factors that provide the impression of more room within a given volume of space. With respect to artificial lighting, the use of uniform and peripheral lighting was recommended [18]. For overhead central lighting, it was reported that the ratio of direct/indirect lighting modulated spacious perception [19]; the room appeared larger when more light was supplied indirectly. The present study explored the influence of direct/indirect lighting on subjects’ affective and neurophysiological responses in a residential environment. We investigated EEG activity and emotional scores (dimensional affect and subjective feelings) in subjects exposed to different lighting conditions in an ecologically valid living room setting.
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2. Methods
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2.1. Participants
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Twenty-eight subjects participated in this study (12 females, mean age 22.5). Written informed consent was obtained after a complete description of the study was provided to the participants. Our study was carried out under the guidelines for the use of human subjects established by the Institutional Review Board (IRB) at Gangnam Severance Hospital, Yonsei University.
2.2. Environmental setting The experiment was conducted in a furnished living room with dimensions of 4.7 m × 4.4 m and a height of 3.1 m. It contained a TV, an entertainment center, sofas, a coffee table, a side table with flowers, wall shelves, and a rug (Fig. 1). Daylight was excluded by shielding the windows. The temperature and relative humidity of the experimental room were 23.3◦ (SD = 0.3◦ ) and 21.3% (SD = 1.0%), respectively. Eight LED lighting panels (600 cm × 600 cm; LG Electronics, Seoul, Republic of Korea) were suspended above the room; four faced up and four faced down (1 panel: 53 W, 4694 lm, 3000 n, 5000 K). A controller (WE7000, Yokogawa, Japan) regulated the illuminance (700 lx) and color temperature (5000 K) of the LEDs. The luminance was measured at table level (0.75 m). 2.3. Design and procedure A counterbalanced within-subject design was employed. The experiment consisted of two different lighting conditions: direct/indirect lighting (400 lx downlight, 300 lx uplight) and direct lighting (700 lx downlight) (Fig. 1). In each trial, following a 4min dark condition (0 lx) to allow subjects to equilibrate to the surroundings, a luminous environment was presented for 4 min. Immediately following luminous environment presentation, the participants were required to complete self-report questionnaires to measure light-induced emotional responses. The same lighting condition was continued while participants completed the questionnaires. The self-report questionnaires included 100-mm pen-andpaper visual analog scales (VAS) and the Self-Assessment Manikin (SAM) [20]. The VAS consisted of a list of three emotion adjectives (cool, refresh, comfortable). The terms “not at all” and “strongly” were written under the left and right ends of the scale, respectively. The SAM was comprised of two nine-point graphical rating scales measuring the valence and arousal dimensions. For the valence dimension, SAM ranged from a happy to unhappy figure. For the arousal dimensions, the SAM figure ranged from excited and aroused to relaxed. Upon arrival, participants were comfortably seated in the experiment room and received instructions. They were only informed about the purpose of the study and were uninformed about the hypothesis. The experimenter instructed participants to focus on and evaluate the overall appearance created by the lighting conditions and stressed that they should maintain the
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Fig. 2. Grand-averaged scalp distributions of theta activity.
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induced emotional states during the presentation of the luminous environment. During the entire experiment, EEG data were recorded continuously from the scalp using a NuAMP amplifier (Nufern, East Granby, CT, USA) and a 10/20 layout 40-channel Quik-cap electrode placement system (Neuroscan Inc., Charlotte, NC, USA) at a sampling rate of 250 Hz. We used the linked mastoid for reference and two bipolar electrodes to measure horizontal and vertical eye movements. The impedance of each electrode was maintained below 10 k. EEG was sampled at 250 Hz (analog band-pass filter 0.1–100 Hz). We used Matlab 7.0.1 (MathWorks, Natick, MA, USA) with the EEGLAB toolbox [21] to preprocess and analyze the data. The data were re-referenced to a common average reference and detrended. Independent component decomposition and visual inspection of data were performed to eliminate artifacts. We used a paired t-tests to investigate differences in subjective feelings and EEG measurements between both environments. We estimated the standard q-value and used it to control the falsediscovery rate (FDR) using the original Benjamini and Hochberg approach to multiple testing [22,23] for EEG measurements. Pearson’s correlation coefficients were used to analyze correlations between EEG measurements and emotional feelings that were found to be significantly different by paired t-tests. Statistical significance was defined as P < 0.05. We did not perform statistical corrections for multiple comparisons of behavioral outcomes or correlations due to the exploratory nature of this study. All statistical comparisons were performed using the Statistical Package for the Social Sciences (SPSS) 18.0 (SPSS Inc., Chicago, IL, USA), and all other computations were performed using Matlab.
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3. Results
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The valence ratings for direct/indirect lighting (mean = 6.4, SD = 1.2) were significantly higher (P = 0.005) than those for direct lighting (mean = 5.4, SD = 1.4). However, arousal did not significantly differ between both conditions. The cool scores for direct/indirect lighting (mean = 6.9, SD = 1.6) were significantly higher (P = 0.045) than those for direct lighting (mean = 6.0; SD = 1.9), but the refresh and comfort scores on the VAS were not significantly different between the two conditions (Table 1). A significant difference was observed in the theta frequency band, but there was no significant difference between the two conditions with regard to power in the alpha, beta, and gamma frequency bands. Comparisons of theta bands between the direct/indirect and direct lighting conditions revealed increased theta power spectral values in the right fronto-temporal and left
Table 1 Within-group subjective parameter comparisons. Dependent variable
Refreshing Cool Comfort Arousal Valence *
Direct/indirect
Direct
Mean
SD
Mean
SD
6.6 6.9 5.6 5.5 6.4
1.8 1.6 2.1 1.6 1.2
6.2 6.0 5.1 5.3 5.4
2.0 1.9 2.3 2.0 1.4
t
1.052 2.104* 0.873 0.532 3.074*
P < 0.05, paired t-test.
temporo-parietal regions (F4: P = 0.036 uncorrected, F8: P = 0.035 uncorrected, T4: P = 0.022 uncorrected, TP7: P = 0.039 uncorrected) under the FDR threshold (Fig. 2). To further investigate the relationship between EEG measurements and emotional feeling, we performed correlational analyses. EEG values (F4, F8, T4, TP7) and cool and valence scales that were found to be significantly different with paired t-tests were converted to average scores for the two lighting conditions. Correlational analysis demonstrated that the cool ratings on the VAS scale were positively correlated with theta power spectral value (F8, P = 0.019) (Fig. 3). A scatterplot depicting these results is shown in Fig. 3. There was no correlation between the self-assessment scales and the theta spectra power of other regions.
Fig. 3. Scatterplot showing a positive correlation between cool ratings on the VAS scale and theta power in F8.
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4. Discussion The aim of this study was to examine the influence of lighting environment, specifically the appearances of the testing environment created by different lighting distributions, on emotion and psychophysiology. The results revealed direct/indirect lighting provided more pleasant and cool feelings than direct lighting. In addition, theta band power in the right fronto-temporal and left temporo-parietal regions increased with direct/indirect lighting. The theta power in the right frontal region showed a positive correlation with the “cool” VAS scores. In affective neuroscience, the dimensional approach is classically used as a standardized method to evaluate affect. Valence indicates the direction of emotional activation (e.g. pleasant or unpleasant) and arousal reflects the intensity of emotional activation [24–26]. As reflected by the valence ratings, the participants felt more pleasant in the direct/indirect lighting environment, which is consistent with previous findings that subjects’ overall preference increased when more indirect lighting was supplied [19] and that subjects preferred a mixed systems of direct and indirect lighting to a direct lighting system [27–30]. There was no significant difference in arousal, which is in accordance with previous findings that arousal was modulated by brightness [31,32] or color temperature [16]. The lighting conditions only differed in the ratio of direct and indirect light – illuminance and color temperature were constant. To date, the dimensional approach has mainly employed picture [24,33], sound [34], music [35,36] and video clips [37,38] in controlled environments. In this study, we successfully used it to evaluate the effects of different lighting environments. The participants felt cooler in the direct/indirect lighting environment than in the direct lighting environment. This result is in line with those of our previous behavioral study [39]. Moreover, as mentioned earlier, a room appears larger when more light was supplied indirectly [19]. A space with direct/indirect lighting elicits cool feelings; that is, different lighting conditions induce different emotional states. Subjects exhibited increased theta band power in the right fronto-temporal and left temporo-parietal regions during the presentation of direct/indirect lighting. Furthermore, we observed a positive correlation between theta power in the right frontal region and cool ratings. These findings are consistent with previous studies reporting that theta band activity is associated with affective processing. Theta oscillatory activity is relevant with orientation, attention, memory, associative information and affective processing, and increased with greater task demands [40]. Several studies have reported theta synchronization activity is related with valence during presentation of emotional pictures [33,40,41], pleasant musical excerpts [36] and blissful positive states during meditation [42]. Therefore, theta band activity seems to reflect emotions in various statuses, and in our study, only theta power was different according to lighting environments. Our observation of regional brain activation pattern differences is consistent with those described by previous studies. Much of the existing literature reported frontal EEG asymmetry in the valence dimension. Davidson and Fox suggested valencedependent bilateral activity in the prefrontal cortex, that is, positive and negative emotion activated left- and right-sided frontal activation, respectively [43,44]. However, we did not find differences in these regions. This could be due to several reasons. First, previous studies used emotional pictures, music, or video clips for stimuli to induce emotion, whereas we employed ambient stimuli to elicit emotional responses. Accordingly, lighting induced different emotional states, but the regional differences were less robust than those achieved with other types of stimuli. Second,
the obtained results indicate that direct/indirect lighting elicits more pleasant emotion relative to direct lighting. That is, bilateral activation may require a considerable difference in behavioral ratings. Note that drowsiness is an important issue for interpreting the results because the drowsy-alert level induces changes in EEG (e.g., a decrease or disappearance of alpha and/or an increase in theta during a drowsy period). In this study, we assessed valence and arousal to evaluate emotions, and arousal may reflect the drowsiness-alertness continuum [45,46]. As shown in Table 1, the arousal was not different between both conditions. Furthermore, we also asked participants to rate items to estimate the extent of drowsiness after the experiment. This result is not shown because the questions were designed to assess experimental validity and were not part of the study’s objectives. Drowsy state was self-rated on a 100-mm VAS. The terms “strongly drowsy” and “strongly alert” were written under the left and right ends of the scale, respectively. The results show the mean drowsy rating during the entire experiment was 5.6 (SD = 1.9), indicating that it was unlikely to affect the results. 5. Limitations The present study has several limitations. First, subjective feelings toward the environment can be altered depending on the amount of sunshine, lighting hardware, length of suspended lighting, interior decoration, and other variables. Second, we did not employ multiple comparisons due to the explorative nature of this study, thus there was the possibility of detecting an effect that was not “true” (i.e., type 1 error). Third, although the experimenter only informed about the overall purpose of the study, participants may have assumed the hypothesis. It may have influenced the result, but it could not be evaluated. Fourth, although the sample size was sufficient to investigate EEG activity, it is still a small number for the generalization of results. 6. Conclusions The present study demonstrated ambient light in an environment can significantly influence brain cortical activity, and EEG signals can serve as a biological marker of environmental alterations. In contrast with previous studies that have been concentrated on controlling the external stimuli such as picture, sound, music and film-clips, this study focused on lighting variables at environmental level, and elucidated the effect of the lighting on neurophysiology. Further research into how other lighting variables, such as brightness, color, lighting arrangement, and the ratio of upward and downward light, affect psychophysiology are required to make recommendations to optimize different lighting environments. Authors contributions Y.B.S. carried out the experiment, conducted the data analysis, and wrote the manuscript. S.H.W., D.H.K., J.S.K., and J.J.K. participated in designing the research study, constructed the experimental room, and interpreted the results. J.Y.P. had full access to all of the data in the study, takes responsibility for the integrity of the data, designed the study and wrote the manuscript. Conflict of interest The authors declare they have no competing interests.
Please cite this article in press as: Y.-B. Shin, et al., The effect on emotions and brain activity by the direct/indirect lighting in the residential environment, Neurosci. Lett. (2014), http://dx.doi.org/10.1016/j.neulet.2014.09.046
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Acknowledgments
We are thankful to Yeon-ju Hong for making the illustrations used in this paper, and Hyemin Park and Jeeye Choi for their assis319 tance with data acquisition. This work was supported by a 2012 320 research grant from LG Electronics and the Basic Science Research 321 Program through the National Research Foundation of Korea (NRF), 322 Q2 funded by the Ministry of Science, ICT, and Future Planning (Grant 323 Number 2013R1A1A1013207 to J.Y.P.). 324 318
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