非表示:
キーワード:
-
要旨:
Introduction:
Color-tinted lenses are employed, even in the professional context, to mediate the detrimental effects of environmental lighting and enhance perceived contrast. Besides this, there is some evidence to suggest that they can influence how we respond to emotional events. Given their prevalent use, we investigate whether their use can have an influence on how the brain appraises the valence of emotional events. Previous related work has focused on color (Jalil et al., 2012) and less on tinted lenses.
Color can exert a strong influence on our physiology. For example, blue light has an essential function in chronobiology as a pacemaker of the circadian rhythm (Berson et al. 2002). Green light exacerbates migraine headache significantly less than white, blue, amber or red lights (Noseda et al., 2016). Colors can also influence the emotional processing of affective stimuli. For instance, red is associated with excitement (Wexner et al., 1954) and can increase arousal i.e., greater Electroencephalography (EEG) alpha wave recovery (Ali, 1972).
Here, we investigate the effect of tinted lenses on a brain’s response to emotional events. Emotions can be classified into two categories: affective valence (pleasure-displeasure axis) and arousal (arousal-sleepiness axis), (Russell, 1980); these categories showed a clear relation to physiological responses (Lang et al., 1993). According to that, stimuli are usually separated into non-emotional (neutral) stimuli with low arousal and emotional (pleasant, unpleasant) stimuli with high arousal e.g. Keil et al. (2002). Here, we used stimuli from the International Affective Picture System (IAPS) with normalized ratings for valence and arousal level (Lang et al., 2008) and we focused on a particular EEG component, the late positive potential (LPP), a slow change with a positive shift which can begin around 200-300ms (Cuthbert et al., 2000) or later around 500ms (Sobolewski et al., 2011). Previous work has shown that control group had higher LPP than meditators for unpleasant IAPS stimuli (Sobolewski et al., 2011).
Methods:
In this work, we investigate if the emotional processing of images from the IAPS is affected when experienced through tinted lenses. Pictures were presented at a ViewPixx 3D LCD-Display, with adapted luminance to each tinted lens resulting in 2.40±0.07cd/m² measured by a spectrometer. 31 participants were enrolled in this study. The objective refractive errors (mean spherical refractive error: OD −2.80±2.37D, OS -2.55±2.28D) were corrected to normal vision using trial lenses measured with an open field autorefractor.
The experiment presented IAPS images (valence: 32 neutrals, 32 pleasant, 32 unpleasant) for a duration of 3s after 500ms fixation and followed by a 6s inter-trial-interval. Participants wore tinted lenses (tint: none, blue, red, yellow, green). During image presentation, we measured EEG. To record the EEG, 63 active electrodes were attached with electrode gel on the scalp at the head via the international 10-20 system. The contact to the skin was ensured by gelling the electrodes to ensure low impedance (<20kOhm). BrainVision Recorder Professional (V. 1.20.0701) recorded the EEG-data with a sampling rate of 1000Hz, a sampling interval of 1000µS, a low cut-off of 10s, a high cut-off at 1000Hz and a resolution of 0.1µV. Further, the recorded data was down sampled to 250Hz. In offline processing, the data was high-pass filtered at 0.1Hz, line noise was removed using Matlab CleanLine function by Tim Mullen, and Artifact Subspace Reconstruction (ASR) was used to reject bad channels and correct EEG data. The activity of removed channels was interpolated, followed by an Adaptive Mixture Independent Component Analysis (AMICA) and a single equivalent current dipoles estimation for removing the biological artifacts. Data was then back-projected to the sensor space.
Results:
In the EEG, we observed an event-related potential (ERP) component that differentiated for the factors of valence (Fig. 1) and tint (Fig. 2), which was similar to the LPP (500-1500ms), at Cz. An ANOVA of the mean voltage potential returned significant main effects for valence (Cz: F(2,60)=13.7, p<0.001) and tint (Cz: F(4,120)=3.4, p<0.05). Post-hoc test for valence showed a significant elevation for pleasant (p<0.001) and unpleasant (p<0.05) pictures compared to neutral pictures. Interestingly, LPP with pleasant pictures was significantly increased compared to unpleasant pictures (p<0.05).
Post-hoc tests reveal a significant difference between red tinted lens and no filter condition (p<0.001) as well as between red and yellow tinted lenses (p<0.05). Additionally, the difference between green and none tinted lens revealed to be significant (p<0.05). All valence conditions with red tinted lenses showed the highest LPP values (Fig. 3), whereas green tinted lens reached a similar level in the pleasant condition compared to red.
Discussion:
Results suggest that our participants reacted to emotional pictures with an increased LPP, especially pleasant pictures. Red tinted lenses elevated the LPP during emotional picture presentation. This enhanced perception might come from visual attention, which is captured by emotionally arousing pictures (Miskovic et al., 2015). To avoid effects from luminance, luminance was controlled for each tint condition. Previous studies have shown that higher valence image presentation is associated with higher LPP e.g. Cuthbert et al. (2000). The red tint showed a higher LPP, even for neutral stimuli. This might therefore, indicate a stronger emotional response of the perceived stimulus. Findings from color psychology studies support this red enhancing effect. Furthermore, green tinted lenses increased LPP as well, but mainly in pleasant picture condition, which supports the idea that green is associated with positive mood (Akers et al., 2012). In conclusion, we could show the first time, that red tinted lenses, increase physiological parameters as the LPP, which is elevated when affective pictures are presented. Possible implications could be to keep arousal level high during tiring work with red tinted lenses.
