EEG synchronisation reveals the impact of group identity and membership duration on social cognitive bias

Figures

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  Fig. 1. The laboratory setup. The participants watched baseball games on a large screen that provided an immersive experience. The screen in this figure is a composite image. Although the lighting is bright in this figure to make the laboratory setting easier to understand, it was dimmed to create a dark environment for video projection during the actual experiment.

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  Fig. 2. Process for calculating EEG synchronization indices.

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  Fig. 3. Subjective ratings after each video. Each box plot illustrates the distribution of subjective ratings, divided by fan groups (x-axis) and the winner of the video (indicated by colours). High scores in the emotional valence, arousal level, and enjoyment score mean “positive”, “excited”, and “enjoyed,” respectively. The score of 4 represents a “neutral” response on each scale. “HT” refers to the Hanshin Tigers, while “OB” represents the Orix Buffaloes, and “DR” indicates a draw. The box plots display the median, the lower (Q1) and upper (Q3) quartiles, and outliers. The box represents the interquartile range (IQR), which contains the middle 50% of the data. The edges of the box indicate Q1 and Q3. The bold line inside the box indicates the median. The whiskers extend from the box to the smallest and largest values within 1.5 times the IQR from the quartiles. Data points outside this range are plotted individually as outliers, indicated by black dots. The enjoyment scores of HT fans after watching the HT victory video and OB fans after watching the OB victory video show little variance, with the Q1, Q3, and median lines overlapping.

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  Fig. 4. ECG results during each video. The bar plots illustrate the HR (left) and LF/HF ratio (right). They are divided by fan groups (x-axis) and the winner of the video (indicated by colours). “HT” refers to the Hanshin Tigers, while “OB” represents the Orix Buffaloes, and “DR” indicates a draw. The error bars show standard errors.

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  Fig. 5. Phase synchrony results. (a) Scatter plots are organised by three electrodes (Fz, Cz, and Pz) and three frequency bands (delta, theta, and alpha). The significant effects are indicated by asterisk (* p < .05) (b) The PLV distribution in the alpha band at Cz and Pz, designed to highlight the differences between the pair categories. The red and blue lines show medians of in-group and out-group.

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  Fig. 6. Power synchrony results. Scatter plots organised by three electrodes (Fz, Cz, and Pz) and three frequency bands (delta, theta, and alpha). The significant effect is indicated by asterisk (* p < .05), pair cat. and fan hist. are abbreviation for pair category and fan history.