Neural responses of in-group “favoritism” and out-group “discrimination” toward moral behaviors

Journal Pre-proof Neural responses of in-group “favoritism” and out-group “discrimination” toward moral behaviors Wenjian Zhang, Dongmei Mei, Lijun Yin PII:

S0028-3932(20)30046-4

DOI:

https://doi.org/10.1016/j.neuropsychologia.2020.107375

Reference:

NSY 107375

To appear in:

Neuropsychologia

Received Date: 11 August 2019 Revised Date:

2 January 2020

Accepted Date: 2 February 2020

Please cite this article as: Zhang, W., Mei, D., Yin, L., Neural responses of in-group “favoritism” and outgroup “discrimination” toward moral behaviors, Neuropsychologia (2020), doi: https://doi.org/10.1016/ j.neuropsychologia.2020.107375. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

CRediT author statement Wenjian Zhang: Formal Analysis, Investigation, Writing - Original Draft, Writing Review & Editing, Visualization; Dongmei Mei: Formal Analysis, Investigation, Writing - Original Draft, Writing - Review & Editing, Visualization; Lijun Yin: Conceptualization, Methodology, Formal Analysis, Resources, Writing - Original Draft, Writing - Review & Editing, Visualization, Supervision, Project Administration, Funding Acquisition.

Neural responses of in-group “favoritism” and out-group “discrimination” toward moral behaviors Wenjian Zhang1,#, Dongmei Mei2,#, Lijun Yin1,* 1. Guangdong Provincial Key Laboratory of Social Cognitive Neuroscience and Mental Health, and Department of Psychology, Sun Yat-Sen University, Guangzhou 510006, China 2. School of Psychology, Guizhou Normal University, Guiyang 550025, China

#

These authors contributed equally to this study

*Corresponding authors: Lijun Yin, Ph.D., 132 Waihuan Dong Rd., Higher Education Mega Center, Guangzhou 510006, China; E-mail: [email protected].

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Abstract People hate being deceived. However, what would it be if lies come from in-group compared with that from out-group members? In the current Electroencephalography (EEG) study, we recruited thirty-six participants to play a modified estimator and advisor game to investigate the mental and neural processes to lies and truth conveyed by ingroup and out-group members. At the behavioral level, lies are less morally acceptable, arose less positive emotion, and made participants distribute less money to the advisor in a dictator game. Meanwhile, participants liked the in-group university more than the outgroup university and they thought they were more similar to in-group members than to out-group members. However, there were no significant interactions of group type (i.e., in-group and out-group) and message type (i.e., lies and truth) in the aforementioned behavioral assessments. At the neural level, significant interaction effects were found in the parietal N1 and P3 amplitude. More importantly, no significant N1 and P3 amplitude differences between in-group lies and truth were found, while outgroup lies elicited larger P3 amplitude than outgroup truth and out-group truth elicited larger N1 amplitude than outgroup lies. What’s more, P3 amplitude differences between lies vs. truth positively correlated with fairness scores only in the in-group condition but not in the out-group condition. Our study showed that the P3 component was sensitive in capturing subtle differences when participants were processing different types of lies and truth that could not be captured by behavioral measurements. Besides, the fairness trait modulates the ingroup bias related P3 patterns. The current study provides insight into the neurobiological mechanism underlying the mental process of in-group and out-group lies and truth, and

2

suggests individuals’ tendency of general in-group favoritism and out-group discrimination toward moral behaviors. Keywords:

lies,

ERP,

N1,

P3,

in-group

bias

3

1. Introduction Lies are very common in our daily life. In an investigation from Josephson Institute of Ethics, 76% of students reported they lied to their parents about something important and 38% of students said that they would sometimes lie to others to save money (Josephson Institute of Ethics, 2012). Lying refers to a deliberate statement that is made with the communicator’s belief in its falsity, but without providing any clues regarding the falsity. Although lying is a common phenomenon in daily life and people tend to lie for benefits, we still have certain psychological costs or aversion towards lies (Abeler, Becker, & Falk, 2014; Fischbacher & Föllmi-Heusi, 2013; Rosenbaum, Billinger, & Stieglitz, 2014). The mental and neural process regarding lying and truth-telling differ between the two parties on the opposite sides of a lie: decision-makers who decide to lie or not and recipients who get the information. From the perspective of decision-makers, when individuals are facing a situation where they can cheat to gain more money without running the risk of being caught or punished, some still choose to behave honestly (Yin, Hu, Dynowski, Li, & Weber, 2017; Yin, Reuter, & Weber, 2016). People would not lie maximally even when it was financially beneficial to lie (Rosenbaum, et al., 2014). These support the notion that people favor truth-telling and have certain psychological costs towards lying even from the perspectives of liars. From the perspectives of recipients, they often have negative feelings towards lies. Lies are less morally acceptable than truth (Yin & Weber, 2016) and likeability toward liars decreased with increased frequency of deception (Tyler, Feldman, & Reichert, 2006).

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Although people usually hate lies, some factors modulate our attitude towards lies. In this research, we will focus on one particular factor: in-group favoritism. This refers to the tendency of favoring members of one’s own group over those in the other groups (Everett, Faber, & Crockett, 2015). Individuals tend to favor and believe in in-group members to a greater extent compared to out-group members (Ben-Ner, McCall, Stephane, & Wang, 2009; Fershtman & Gneezy, 2000). In a previous study about in-group favoritism and out-group discrimination, researchers found stronger punishment of out-group and weaker punishment of in-group versus unaffiliated perpetrators in a costly punishment game, suggesting both in-group favoritism and out-group discrimination drive intergroup bias (Schiller, Baumgartner, & Knoch, 2014). It also has an impact upon recipients’ mental processes towards lies and truth. There are some neurobiological markers, P3 and N1, that would be sensitive to the cognitive process of lies and truth from in-group or out-group members.

1.1 Implicit attitude and P3 By adopting electrocortical measures, the process of implicit stereotyping effects can be captured (Bartholow, Dickter, & Sestir, 2006). The P3 is sensitive to the true evaluative nature of the stimuli instead of individuals’ explicit reports (Amodio, Bartholow, & Ito, 2014). A previous study about racial in-group attention bias showed that significant effects of both target gender and target race emerging in the P3 from the central-parietal midline (Dickter & Bartholow, 2007). Both P3 amplitude and latency have been found sensitive to violations of racial stereotypes during the processing of racial stereotype– incongruent trait words in a sequential priming task (Bartholow, et al., 2006). Sentences that violate conventional stereotypes evoked P3 amplitude but self-reported acceptance 5

ratings did not detect the differences among sentences (Smith, et al., 1990). P3 reflects implicit processing which may not be observable in the behavioral responses (Dickter & Kieffaber, 2013). In addition, P3 is also found to be associated with the lying process. A recently published meta-analysis investigated population effect size for conceptual and methodological a-priori moderators in deception associated event-related potential (ERP) studies (Leue & Beauducel, 2019). The meta-analysis reviewed studies about lying and revealed that parietal P3 amplitude can be used to measure the difference between concealed and truthful knowledge. Therefore, many previous studies supported the point that P3, especially in the parietal zone, is a key component reflecting the implicit attitude and associating with the lying process. Therefore, if we would like to find out whether the implicit attitude might differ among in-group/out-group lies and truth, the P3 component is a sensitive index. If individuals have different attitudes toward lies and truth, significant P3 amplitude differences should be found.

1.2 Emotion and N1 Another important neurobiological marker is N1. Note that being deceiving brings changes in emotion. Earlier studies showed that the discovery of lies brought changes in emotional intensity and reactions (McCornack & Levine, 1990; Yin & Weber, 2016). Individuals would have negative emotions when they discovered deception within a relationship (McCornack & Levine, 1990). Similarly, in a study about the neural responses to the passive reception of lies and truth in an economic game, participants reported more positive emotional reactions toward truth than lies (Yin & Weber, 2016). In addition to that, being deceived modulates the activity in brain regions associated with emotion. The judgment of being the target of deceit and the experience of being deceived 6

arose higher activation in the amygdala and anterior insula (Grezes, Berthoz, & Passingham, 2006). However, to our best knowledge, we haven’t found any EEG studies that have ever investigated the neural response toward lies and truth from the recipients’ point of view. But the N1 component is sensitive to emotional stimuli and thought to reflect early visual processing of emotional content. The principal component analysis showed that the N1 is one of the unique indices for emotional processing (Foti, et al., 2009). Previous studies have found that the N1 amplitude (at the centraoparietal sites) was larger for both pleasant and unpleasant than for neutral stimuli (Carretié, Hinojosa, López-Martín, & Tapia, 2007; Foti, Hajcak, & Dien, 2009; Weinberg & Hajcak, 2010). Increased N1 amplitude for both unpleasant and pleasant pictures was observed compared to the neutral stimuli (Foti, et al., 2009). Therefore, the N1 component may play an important role in reflecting emotional changes which could happen when individuals find out being deceived. However, despite many neuroimaging studies about lying (Christ, Van Essen, Watson, Brubaker, & McDermott, 2009; Farah, Hutchinson, Phelps, & Wagner, 2014; D. Sun, Chan, & Lee, 2012; Yin, et al., 2017; Yin, et al., 2016; Yin & Weber, 2019), little is known about the mental and neural process of lies from the perspective of the recipients (Yin & Weber, 2016), not to mention the modulating effects of different group members (in-group or out-group members). ERPs have some advantages over traditional behavioral measures and the functional magnetic resonance imaging (fMRI) technique. Compared to behavioral measures, it is capable of measuring psychological processes independently from, or in the absence of, any behavioral response (Amodio, et al., 2014). Compared to fMRI, the high temporal resolution of ERP measures of neural activity is 7

suited to the investigation of the dynamic interplay between rapidly unfolding cognitive and affective processes (Amodio, et al., 2014). Considering ERP is capable of measuring psychological processes and P3 and N1 reflect implicit attitudes and emotional processes, our study used this technique to investigate the neural processes of recipients of lies and truth conveyed from in-group and out-group members and explore how lies and truth from different social groups modulate participants’ overt attitude and neural responses. We used a modified advisor and estimator game (Garrett, Lazzaro, Ariely, & Sharot, 2016) where participants played the role of estimator who estimates the amount of money in a glass jar and receives the false or truthful suggestions provided by unknown opponents (the advisor). The advisors were either from the same university as the participants (in-group condition) or from a different one (out-group condition). When participants found out whether or not the ingroup or out-group members lie to them, the implicit process would be involved and reflected in the P3 component. Real-time emotional responses could also be captured in the N1 component. We used different ways to measure participants’ overt attitudes toward different groups, including an embedded dictator game and questionnaires. Moreover, traits of honesty were also collected to investigate the association between honesty traits and neural patterns. With regards to the Electroencephalography (EEG) data, we would like to analyze the stimulus-locked ERPs which reflect cognitive processes when participants found out whether they were lied to. The ERP components, especially N1 and P3, were extracted and analyzed during the time frame when participants realized the truthfulness of the information received. We expected that N1 and P3 could detect the impact of the group type (i.e., in-group or out-group) on neural 8

responses to lies and truth. Our first hypothesis is that interaction effects of group type and message type in the P3 and N1 amplitudes should be significant in the parietal zone. More specifically, out-group lies would evoke higher parietal N1 and P3 amplitude than out-group truth (out-group discrimination), while N1 and P3 amplitude would not show significant differences between in-group lies and truth (in-group favoritism). The second hypothesis is that honesty traits would differently modulate the extent of in-group favoritism and out-group discrimination reflected by N1 and P3 amplitude change.

2. Methods 2.1. Participants Thirty-six right-handed healthy college students (19 females, mean age ± s.d. = 19.58 ± 1.96 years) from Sun Yat-sen University were recruited in this experiment. All participants had a normal or corrected-to-normal vision and reported no prior history of psychiatric or neurological disorders. Participants all gave written consent before the experiment (two participants who were 17 years old freshmen students gave written informed consent by both their parents and themselves). The experiment was approved by the Ethics Committee of the university. Data from one participant was excluded from EEG data analysis due to insufficient trials (the number of artifact-free epochs was less than 30) (Bengson, Mangun, & Mazaheri, 2012; Karch, et al., 2009; Kober & Neuper, 2011; Marklund, Schwarz, & Lacerda, 2019) in some conditions of interest. Therefore, 35 participants’ data were included in the EEG data analysis (18 females, mean age ± s.d. = 19.57 ± 1.99 years).

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2.2. Task In the EEG experiment, a modified advisor and estimator game (Garrett, et al., 2016) and a dictator game were adopted (Figure 1). There were two types of players in the game: advisor and estimator. Participants were assigned the role of the estimator and participants were told that advisors would be several students from two different universities. If the advisors were from the same university where participants belong to, that would be the in-group condition, otherwise, it would be the out-group condition. Participants were told that the advisors would first see pictures of a coin jar with high resolution. The advisors then provided information to the estimator about the amount of money in the jar in order to provide information for the estimator to estimate the amount. There were five possible amounts of money contained in the jar: 10, 15, 20, 25 and 30 yuan. Five scale lines were marked in the jar so that the advisors could clearly estimate the amount of money. After viewing the picture, the advisor would choose one proposed value (20 in the example in Figure 1) from 5 possible options to send to the estimator. The message could be either truthful or false (in-group lies or truth if the advisors are ingroup members; otherwise would be out-group lies or truth). After the advisor made a decision, a certain range of the chosen amount (±1; in the example in Figure 1, the options would be: 19, 20 and 21) would be generated for the estimator. As the estimator, participants could only see the scrambled version of the picture and the message sent by the advisor, so that participants could not judge the amount of money based on the picture they saw. Importantly, they had to choose the estimated value from the limited options restricted by the advisor. In this way, in the situation where the advisor lied to the estimator, the estimator could not do anything about it and he/she would definitely lose

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money. Then the estimator’s neural responses would not be influenced by his/her own decisions of believing the message or not. After participants submitted the estimated amount, they would see the actual amount and find out if advisors lied to them. They would also find out the payoffs for both players at the same time. The condition would be an in-group lie condition if the message did not match with the actual amount in the ingroup session. The condition would be an out-group truth condition if the message matched with the actual amount in the out-group session. The interaction of group type (in-group or out-group) and message type (lies or truth) would reflect the modulation effect of the group type on the neural responses toward lies and truth. All the information was presented at once. If the difference between the actual value and estimated value was less than 10%, participants could gain an extra 20 yuan and advisors would lose 20 yuan. Otherwise, participants would lose 20 yuan and the advisor could gain 20 yuan. That is, if the advisor lied to the estimator, the advisor would gain money and the estimator would lose money. To test if participants’ decisions in the dictator game would be affected by the experience of being treated honestly or dishonestly, after participants found out the type of the message they played a dictator game where they split an endowment (30 yuan) between themselves and the corresponding advisor.

2.3. Experimental design The current study adopted a two by two within-subject design with two factors of message type (lies or truth) and group type of advisors (in-group or out-group members). The experimental task contained two sessions: in-group session and out-group session. The orders of the two sessions were counterbalanced. Each session contained 160 trials,

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including 80 trials of the lies condition and 80 trials of the truth condition. The lies and truth trials were presented randomly within each session. Each trial started with a fixation that lasted for a random interval of 500-1000ms. Then participants would see a scrambled picture of a jar with coins, a university badge that indicates the advisor’s group and the advice sent by the advisor. Participants should choose an estimated amount from three possible options within 3000ms. Then, after a blank screen that lasts for 500-1000ms, participants would see the actual amounts and the proposed value from the advisor of this trial for 2000ms. After a 500-1000ms blank screen, participants allocated 30 yuan between themselves and the corresponding advisor within 5000ms.

2.4. Procedure Three days before the EEG experiment, participants completed questionnaires (see 2.5. Questionnaires) and provided demographic information online. Right before the EEG experiment, all participants read the instruction and completed a questionnaire to ensure that they fully understood the task. Next, participants completed a practice session with 5 trials to get familiar with the experiment. After the EEG experiment, participants filled out several questionnaires (see 2.5. Questionnaires). One trial was randomly selected from both the in-group session and the out-group session. We paid participants based on the outcomes in these two trials. Participants were debriefed and paid accordingly.

2.5. Questionnaires To investigate whether there are interactions between personality traits of participants and neural responses toward in-group and out-group lies and truth, participants filled out

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a 60-item version of the HEXACO Personality Inventory-Revised personality inventory (Ashton & Lee, 2009). To check on participants’ subjective judgments towards different experimental factors, before the experiment, they were also asked to rate on how much they like their own university (in-group condition) and three other universities (out-group condition; “how much do you like the university X”, from 1 = not at all to 9 = very much, X stands for one of three listed universities) and how similar they are with the students from their university (in-group condition) and the other universities (out-group condition; “how similar you think you are with the students from the university X”, from 1 = not at all to 9 = very much). Although we were interested in participants’ attitudes to the ingroup university and out-group university, two more local universities were included in the ratings in order to reduce the possible effect of demand characteristics. After the experiment, participants rated on the degree of being deceived in the in-group and out-group condition (“to what extent do you think you were deceived when the message you received were different from the actual amount”, from 1 = not at all to 9 = very much). They were also asked to rate on the liking and similarity scales again. In addition, they provided moral acceptance ratings toward in-group lies and out-group lies (e.g., in-group condition: “when you received the message sent by the advisor from your university and the message was different from the actual amount of money in the jar, to what extent do you think that is morally acceptable”, from 1 = not at all to 9 = very much) and the emotional states (e.g., in-group lies condition: “when you received the message sent by the advisor from your university and the message was different from the actual amount of money in the jar, how do you feel”, from 1 = totally negative to 9 = totally positive). 13

With regard to the HEXACO questionnaire, we were especially interested in the Honesty-Humility subscale. The Cronbdach's Alpha was 0.79 in the college sample (Ashton & Lee, 2009) and was 0.56 in the current study. Four domains were included in the Honesty-Humility scale (from 1 = strongly disagree to 5 = strongly agree): sincerity, fairness, greed, and modesty. The sincerity subscale has three items (Cronbach’s alpha = 0.61), the fairness subscale has three items (Cronbach’s alpha = 0.60), the greedavoidance subscale has two items (Cronbach’s alpha = 0.24), and the modesty subscale has two items (Cronbach’s alpha = 0.58). Specifically, the fairness scale assesses a tendency to avoid fraud and corruption. Individuals with low scorers are willing to gain by cheating or stealing, whereas people with high scorers are unwilling to take advantage of other individuals or of society at large.

2.6. Electroencephalogram recording and data processing Presentation 21.0 software (Neurobehavioral Systems, https://www.neurobs.com/) was used to present stimuli and collect behavioral data. During the task, participants sat comfortably in an electrically shielded room, with a distance of 90cm from a 23-inch color computer screen. Participants were seated in a dimly lit, electrically shielded, sound-attenuation chamber. The electroencephalogram (EEG) was recorded from 64 scalp sites with Ag/AgCI electrodes mounted in an elastic cap (NeuroScan, Inc., Herndon, VA, USA) according to the international 10/20 system. Participants were grounded with a forehead electrode. All EEG channels were referenced to the left mastoid and were rereferenced off-line to the average of the left and right mastoids. Electrooculograms (EOG) were recorded bipolarly, all electrodes, both horizontally from electrodes at the outer canthi of the eyes and vertically from a pair of electrode impedances were kept below 5 14

kΩ. The EEG and EOG were sampled at an A/D rate of 500 Hz/channel and a band-pass of 0.01-100 Hz. EEG

data

were

preprocessed

and

analyzed

using

EEGLAB

(https://sccn.ucsd.edu/eeglab/). The segmented EEG data was stimulus-locked to the onsets of showing the outcome of the game when participants found out whether the opponents lied to them. There are four types of epochs, lies from in-group members, truth from in-group members, lies from out-group members, and truth from out-group members. For each participant, ocular artifacts were corrected by independent component analysis (ICA). EEG data were rereferenced to the common average. The signal passed through a 0.5-30 Hz band-pass filter (Cui, et al., 2017). Segmented EEG data were stimulus-locked to the onset of the feedback phase. The ERP epochs were trimmed (from 0ms to 1000ms) and the pre-stimulus baseline (-100ms to 0ms) were corrected. Epochs with amplitude values exceeding ±70µV at any electrode were excluded from the average. After removing artifacts, ERPs were averaged within four conditions. Data would be excluded from subsequent analysis if the remaining trials in any of the four conditions were less than 30 (means and standard deviations of the numbers of artifact-free epochs in the condition of the in-group lie: 64.00 ± 9.89; in-group truth: 62.91 ± 9.70; out-group lies: 62.37 ±12.29; and out-group truth: 62.43 ± 11.79). Electrode clusters were chosen along the midline for analysis: the frontal zone (AP3, AF4, F1, F2, and FZ), the central zone (FCz, FC1, FC2, and Cz), the parietal zone (Pz, PO3, POz, and PO4), and the occipital zone (O1, Oz, and O2). The electrodes clustered for analysis were referred to previous studies (Chen, et al., 2014; Fields & Kuperberg, 2015; Hu, Wu, & Fu, 2011; Molinaro, Conrad, Barber, & Carreiras, 2010; S.-Y. Sun, Mai, Liu, 15

Liu, & Luo, 2011; Yang, Perfetti, & Schmalhofer, 2007). The ERPs were stimulus-locked (when participants could find out they were lied to or not) and two components (i.e., N1, and P3) are of our interests. The time windows for each component were: N1, 120-170ms and P3, 350-450ms. The amplitude (peak to baseline) was defined as the mean amplitude of the electrode zone of the time windows of each component.

2.7. Statistical analysis The mean amplitude of each ERP component (N1 and P3) were submitted in 2 (group type: in-group and out-group) × 2 (message type: lies and truth) × 4 (position: frontal, central, parietal and occipital zones) within-subject repeated measurements ANOVA. The mean amplitudes of each ERP component (N1 and P3) in four regions (frontal, central, parietal and occipital) were submitted in 2 (group type: in-group and out-group) × 2 (message type: lies and truth) within-subject repeated measurements ANOVA. To check out the electrode location effect for the N1 and P3 amplitudes in the parietal zone, we performed a 2 (group type: in-group and out-group) × 2 (message type: lies and truth) × 4 (electrode location: Pz, PO3, PO4, and POz) repeated measurement ANOVA (associated results please see Supplementary Material). Pearson correlations were applied to test the relation between scores of subscales and amplitude of components of interest. Differences were considered statistically significant at p < 0.05; post-hoc comparisons were Bonferroni-corrected at p < 0.05.

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3. Results 3.1. Behavioral results 3.1.1. The group effects (in-group vs. out-group) Before the experiment, participants were asked to give liking and similarity ratings. By applying paired sample t-tests, participants’ liking ratings toward their own university (mean ± s.d. = 7.56 ± 1.48) were significantly higher than that toward the out-group university (mean ± s.d. = 5.58 ± 1.56; t(35) = 6.12, p < 0.001, 95% CI [1.32, 2.63]), indicating that they did like the in-group university more than the out-group. Participants also thought they were more similar with students from their own university (mean ± s.d. = 6.94 ± 1.80) than that from the out-group university (mean ± s.d. = 4.86 ± 1.99; t(35) = 5.56, p <0.001, 95% CI [1.32, 2.84]). After the experiment, participants rated how much they like two universities. We applied a 2 (measurement time: before and after experiment) × 2 (group type: in-group and outgroup university) repeated measures ANOVA on liking and similarity ratings. We found that significant main effects of measurement time and group type. Participants’ liking ratings collected after the EEG experiment (mean ± s.d. = 6.97 ± 1.52) were significantly higher than that collected before the EEG experiment (mean ± s.d. = 6.57 ± 1.81; F(1, 35) = 7.74, p = 0.009, η2 = 0.181). Their liking ratings toward their own university (mean ± s.d. = 7.74 ± 1.30) were significantly higher than that toward the out-group university (mean ± s.d. = 5.81 ± 1.44; F(1, 35) = 47.40, p < 0.001, η2 = 0.575). No significant interaction was found (F(1, 35) = 0.14, p = 0.715, η2 = 0.004). As for similarity, participants thought that they were more similar to students from their own university

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(mean ± s.d. = 7.03 ± 1.62) than that from another university (mean ± s.d. = 4.88 ± 1.85; F(1, 35) = 39.21, p < 0.001, η2 = 0.528), while similarity ratings collected before the experiment (mean ± s.d. = 5.90 ± 2.16) did not differ from that collected after the experiment (mean ± s.d. = 6.00 ± 1.93; F(1, 35) = 0.29, p = 0.595, η2 = 0.008) and no significant interaction was found (F(1, 35) = 0.58, p = 0.454, η2 = 0.016).

3.1.2. The effects of message type (lies vs. truth) With regard to reaction time in the dictator game, we applied 2 (messages type: lies and truth) × 2 (group type: in-group and out-group members) repeated measures ANOVA. A main effect of message type (F(1, 35) = 30.38, p < 0.001, η2 = 0.465) was found, indicating that participants’ response time in the dictator game was shorter when they were treated dishonestly (mean ± s.d. = 1131.75 ± 374.24 ms) than that when they were treated honestly (mean ± s.d. = 1270.51 ± 445.52ms). No significant interaction (F(1, 35) = 0.58, p = 0.453, η2 = 0.016) and main effect of group type (F(1, 35) = 0.89, p = 0.351, η2 = 0.025) were found. Regarding the money left for the advisors in the dictator game, a main effect of message type (F(1, 35) = 28.17, p < 0.001, η2 = 0.446) was found. Participants allocated less money to the advisors when the advisors lied to them (mean ± s.d. = 1.06 ± 2.18) than when the advisors sent truthful messages (mean ± s.d. = 8.84 ± 9.19). However, no significant interaction effect (F(1, 35) = 0.01, p = 0.936, η2 < 0.001) and the main effect of group ( F(1, 35) = 0.45, p = 0.507, η2 = 0.013) were found. To check if message type and group type would modulate participants’ emotion or moral judgment, after the experiment we asked participants to answer several related questions.

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Participants had less positive emotion if they were treated dishonestly (mean ± s.d. = 4.56 ± 1.69) than that when they were treated honestly (mean ± s.d. = 7.31 ± 1.49; F(1, 35) = 80.58, p < 0.001, η2 = 0.697). The interaction effect (F(1, 35) = 0.07, p = 0.797, η2 = 0.002) and the main effect of group type (F(1, 35) = 0.19, p = 0.670, η2 = 0.005) were not significant. With regards to moral judgment, there was no significant difference between the extent to which participants felt being deceived in the in-group session (mean ± s.d. = 6.28 ± 2.24) and out-group session (mean ± s.d. = 6.36 ± 1.94; t(35) = -0.36, p = 0.723, 95% CI [-0.56, 0.39]). Participants’ ratings upon the moral acceptance toward the lying behaviors showed no significant difference between the in-group (mean ± s.d. = 6.56 ± 1.66) and out-group lies (mean ± s.d. = 6.50 ± 1.65), t(35) = 0.26, p = 0.793, 95% CI [0.37, 0.48]).

3.2. ERP results 3.2.1. Interaction effects of group type and message type N1 (120-170ms) To check out the position effect, we first performed a 2 (group type: in-group and outgroup) × 2 (message type: lies and truth) × 4 (position: frontal, central, parietal and occipital zones) repeated measurement ANOVA on N1 amplitude. This revealed a significant main effect of position (F(3, 32) = 8.52, p < 0.001, η2 = 0.444). The main effect of group type (F(1, 34) = 0.03, p = 0.872, η2 = 0.001), the main effect of message type (F(1, 34) = 0.39, p = 0.537, η2 = 0.011), the two-way interaction of group type and position (F(3, 32) = 1.84, p = 0.161, η2 = 0.147), the two-way interaction of message type and position, (F(3, 32) = 0.27, p = 0.847, η2 = 0.025) and the three-way interaction (F(3, 19

32) = 1.73, p = 0.180, η2 = 0.140) were not significant. Importantly, a significant interaction of group type and message type was also found (F(1, 34) = 4.69, p = 0.037, η2 = 0.121). In the parietal zone, we performed a 2 (group type: in-group and out-group) x 2 (message type: lies and truth) repeated measurement ANOVA with N1 amplitude in the parietal zone as dependent variables. The main effect of group (F(1, 34) = 1.40, p = 0.711, η2 = 0.004) and the main effect of message type (F(1, 34) = 0.82, p = 0.371, η2 = 0.024) were not significant. We hypothesized that interaction of group type and message type should be found in the parietal N1 amplitude. Aligned to our hypothesis, the interaction between group type and message type was significant (F(1, 34) = 4.89, p = 0.034, η2 = 0.126; Figure 2 and 3). The post-hoc analyses revealed that there was significant difference between lies (mean ± s.d. = -0.88 ± 2.61) and truth (mean ± s.d. = -1.41 ± 2.10) from the out-group members (p = 0.048, η2 = 0.110). However, out-group truth, rather than outgroup lies, elicited larger N1 amplitude. No significant difference was found between lies (mean ± s.d. = -1.34 ± 2.02) and truth (mean ± s.d. = -1.11 ± 2.04) in the in-group condition (p = 0.279, η2 = 0.034). No significant main effects and interactions were found on the N1 component in the central, frontal and occipital zones (ps > 0.06; SFigure 1).

P3 (350-450ms) To check out the position effect, we first performed a 2 (group type: in-group and outgroup) × 2 (message type: lies and truth) × 4 (position: frontal, central, parietal and occipital zones) repeated measurement ANOVA with P3 amplitude as dependent variable. This revealed significant main effects for both position (F(3, 32) = 24.29, p < 0.001, η2 =

20

0.695) and message type (F(1, 34) = 5.64, p = 0.023, η2 = 0.142). The main effect of group type (F(1, 34) = 0.01, p = 0.922, η2 < 0.001), the interaction of group type and position (F(3, 32) = 0.58, p = 0.632, η2 = 0.052), the interaction of message type and position, (F(3, 32) = 1.34, p = 0.279, η2 = 0.111) and the three-way interaction (F(3, 32) = 1.68, p = 0.191, η2 = 0.136) were not significant. Importantly, a significant interaction effect of group type and message type was found (F(1, 34) = 4.11, p = 0.051, η2 = 0.108). In the parietal zone, we performed a 2 (group type: in-group and out-group) x 2 (message type: lies and truth) repeated measurement ANOVA with P3 amplitude in the parietal zone as dependent variables. The main effect of group type was not significant (F(1, 34) = 0.05, p = 0.825, η2 = 0.001), but the main effect of message type (F(1, 34) = 6.66, p = 0.014, η2 = 0.164) and the interaction effect (F(1, 34) = 5.12, p = 0.030, η2 = 0.131) were significant (Figure 2 and 3). Consistent with our prediction, post-hoc analyses showed that the parietal P3 amplitude in the out-group lies (mean ± s.d. = 2.32 ± 2.95) was significantly higher than that in the out-group truth (mean ± s.d. = 1.54 ± 2.56; p < 0.001, η2 = 0.307). Besides, the parietal P3 amplitude did not differ between in-group lies and truth (lies: mean ± s.d. = 2.01 ± 2.55; truth: mean ± s.d. = 1.97 ± 2.42; p = 0.863, η2 = 0.001). No significant main effects and interactions were found on the P3 component in the central and frontal zones (ps > 0.06; SFigure 1). In the occipital zone, a significant main effect of message type (F(1, 34) = 6.23, p = 0.018, η2 = 0.155) was found on the P3 (350-450ms). Lies (mean ± s.d. = 2.69 ± 0.35) elicited larger P3 than truth (mean ± s.d. = 2.37 ± 0.32). The main effect of group (F(1, 34) = 0.16, p = 0.695, η2 = 0.005) and the interaction effect (F(1, 34) = 2.77, p = 0.105, η2 = 0.075) were not significant.

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3.2.2. The components’ amplitude and honesty traits To investigate if N1 and P3 are modulated by traits associated with honesty, we did correlation analysis on scores of four subscales of the Honesty-Humility scale and amplitude differences between lies and truth in the in-group (in-group lies vs. truth) and out-group conditions (out-group lies vs. truth). The parietal P3 amplitude in the contrast of in-group lies vs. truth positively correlated with fairness score (r = 0.35, p = 0.040; Figure 4), while P3 amplitude in the contrast of out-group lies vs. truth did not correlate with individuals’ fairness scores (r = -0.22, p = 0.211; Figure 4). No significant results were found between P3 components in the contrasts of in-group/out-group lies vs. truth and scores in the other 3 subscales (ps > 0.21; Supplementary Material). Unexpectedly, no significant results were found between N1 components in the contrasts of ingroup/out-group lies vs. truth and scores in all 4 subscales (ps > 0.06; Supplementary Material).

4. Discussion In this study, we investigated the mental and neural processes associated with lies and truth conveyed by in-group and out-group members. The first hypothesis was that lies would evoke higher parietal N1 and P3 amplitude in the out-group condition rather than the in-group condition. As a result, we did find significant interactions in the parietal zone. More specifically, no significant differences in both N1 and P3 were found between lies and truth in the in-group condition. For the P3 component, consistent with our hypotheses, the out-group lies evoked higher P3 amplitude than the out-group truth. However, as for N1, out-group truth evoked a higher amplitude than the out-group lies.

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In our experiment, overt attitudes were measured via different ways, including the dictator game embedded in the experiment right after participants knew about the falsity and questionnaires asking about similarity, likeability, degree of being deceived, moral acceptability and emotion. At the behavioral level, the effects of message type were found in the moral acceptance, emotion, reaction time and money distributed to the advisor in the dictator game. Lies were less morally acceptable, evoked less positive emotions, required longer reaction time to make decisions in the dictator game and made participants distribute less money to the advisor. The effects of group type were found in the liking ratings and similarity. Participants liked their own university compared to some other universities and they thought they were more similar to students from the in-group university. The results of group type effect showed that participants did favor the ingroup rather than the out-group. Among these measurements, there are key items that show the modulation effects of group type on participants’ attitudes toward lies and truth, including moral acceptance, emotion, and decisions in the dictator game. However, we did not observe any significant interaction effects. There are several ways that could be used to explain the results. First, the same trial numbers of four conditions might weaken the interaction effect. Note that the frequency of lies influences the attitude of people toward liars. With the increased frequency of deception, likeability toward the liars decreased (Tyler, et al., 2006). However, in our experiment, the frequencies of in-group and out-group lies were the same. It is also possible that the differences between in-group and out-group conditions would be larger if participants were deceived more often in the experiment. Secondly, the effect of message type seems to be stronger than the effect of group type and it might 23

make the modulation effect of group type hard to capture using behavioral measurements. In a previous study about neural responses toward beneficial and harmful lies and truth, the effects of message types could be captured both at the behavioral and neural levels (Yin & Weber, 2016). However, this might not be the case when it comes to explicit responses towards lies and truth from in-group and out-group members. Some people would like to cover their stereotypes in their explicit reports. Finally, the collected items might not reflect their actual feelings during the experiment. Most of the items we collected were with high face validity. The overt attitude of in-group bias might be suppressed or ament by participants. They might have the tendency to cover or adjust their explicit ratings. Besides, it is also possible that participants adjusted their attitude after the experiment even though they felt differently during the task. Independently of the response generation processes, ERP is capable of indexing cognitive operations, capturing the implicit attitude and detecting in-group bias (Bartholow, et al., 2006; Schiller, et al., 2014). Therefore, ERP is better at capturing subtle differences when participants were processing different types of lies and truth. Although no significant interaction effects were found in the behavioral results, the ERP results indicate that the neural process of lies and truth was modulated by group types. Our results showed significant interactions of group type and message type in the N1 and P3 in the parietal zone. Both N1 and P3 components distinguished the out-group lies and truth whereas no significant differences were found between in-group lies and truth. With regard to P3, a larger P3 was elicited by out-group lies. Importantly, no significant differences were observed in the P3 between in-group lies and truth. An oddball study using event-related fMRI and intracerebral ERP recordings suggests that P3 potential 24

came from the parietal lobe (Brázdil, et al., 2005). Most previous ERP studies about deception aim to investigate liars’ cognitive and neural processes of lying behaviors or decisions. In studies with a within-subject design of deception tasks, larger concealed versus non-concealed parietal P3 was found in participants who were the decision-makers (Leue & Beauducel, 2019). Studies have found that P3 is sensitive to critical items (probe) in a concealed information test compared to irrelevant stimuli (Ambach, Bursch, Stark, & Vaitl, 2010; Rosenfeld, Hu, Labkovsky, Meixner, & Winograd, 2013). The neural response towards lies and truth might differ between liars and recipients. For liars, higher cognitive resources might be required when telling a lie. But for recipients, the differences observed in the P3 amplitude between lies and truth reflect differences in implicit attitude. The P3 amplitude is associated with the process of allocating cognitive and neural resources which is sensitive to implicit social categorization decisions (Ito & Urland, 2003). Out-group lies evoked larger P3 amplitude and no significant differences were found between in-group lies and truth. We speculate that the differences between lies and truth might be eliminated by the in-group factor, showing a special type of ingroup “favoritism”, while the differences between lies and truth could be clearly distinguished in the out-group condition, showing out-group “discrimination” toward moral transgression. Although the N1 component showed significant interaction, contrary to our expectation, a larger N1 amplitude was evoked by out-group truth instead of outgroup lies. Findings from previous studies suggest that increased N1 amplitude might be associated with the process of emotional stimuli regardless of valence (Carretié, et al., 2007; Foti, et al., 2009; Weinberg & Hajcak, 2010). It might be the case that out-group truth is not treated as neutral and default state as we used to believe.

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Our second hypothesis was that honesty traits would differently modulate the extent of in-group favoritism and out-group discrimination, and such moderating effect would reflect by N1 and P3 amplitude change. To investigate individual differences and check if honesty traits are associated with neural responses towards lies versus truth from in-group and out-group members, we extracted P3 amplitude from the contrasts of lies versus truth in both the in-group condition and out-group condition and ran correlation analyses on four subscales from the Honesty/Humility domain of HEXACO. We only found that the in-group parietal P3 amplitude in the contrast of in-group lies vs. truth positively correlated with fairness score, while no such correlation was observed in the out-group condition. Although at the group level, P3 amplitude differences in the in-group condition were not significant, individuals with high scores of fairness who are supposed to be unwilling to gain by immoral acts show larger differences between two conditions and had less in-group “favoritism” with regards to in-group members’ moral violating behaviors. The results suggest that the in-group “favoritism” exists in those individuals who do not care that much about selfish moral violations, supported by the decreasing differences between lies and truth. Besides, a similar effect was not found in the outgroup condition despite that at the group level, participants’ neural responses toward lies were significantly different from that toward truth. It might suggest a more general outgroup “discrimination” in the moral domain.

4.1. Limitations Although it is highly possible that the observed neural responses may reflect participants’ actual attitudes, we did not measure their actual or implicit attitudes. The mental process behind the observed neural patterns, especially the P3 component, might due to the 26

implicit attitude. For example, a study found that white targets elicited larger P3 in black participants and black targets elicited larger P3 in white participants (Dickter & Bartholow, 2007). It would be better if we could try to find a way to measure their true feelings or emotional responses in real-time. We could then correlate the real-time responses with the neural responses to further confirm our speculations. In conclusion, we found that participants processed lies and truth differently in the ingroup and out-group conditions. The interaction effect of the group type and message type in the N1 and P3 components suggests that out-group lies might arise an early attention bias, be affectively different from out-group truth. It further suggests that participants’ tendency of fairness modulated in-group favoritism and general out-group discrimination in response to moral violations. The current study provides insights into the neurobiological mechanism underlying the mental process of in-group and out-group lies and truth.

Acknowledgments This work was supported by the National Natural Science Foundation of China (NSFC; 31800960) and the Fundamental Research Funds for the Central Universities (18wkpy59) to Lijun Yin.

Financial Disclosure All

authors

declare

no

conflicts

of

interest.

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Lengends Figure 1. The schema of the task. Participants would first play the modified advisor and estimator game and then finish a dictator game. In the advisor and estimator game, participants played the role of the estimator. They would first see the scrambled picture of a coin jar and received messages sent by advisors who were either from participants’ university (in-group condition) or from another university (out-group condition). The university badges were showed to the participants to indicate the identities of advisors. Participants selected their estimated value from three restricted options. Afterward, three sentences about the result of the current trial were presented at once. They would know if the message sent by the advisor is true or not and the payoffs for both players. If the messages were from the in-group advisors, then the conditions are in-group lies or truth, otherwise would be out-group lies or truth. Next, they completed a dictator game by entering the money amount sent to the corresponding advisor (30 yuan in total). Figure 2. (a) Time-courses of the N1 and P3 components in the parietal zone (including POz, Pz, PO3, and PO4). (b) Time-courses of the P3 component at POz, Pz, PO3, and PO4. A significant interaction of message type and group type was found. The mean amplitude of P3 was significantly higher in out-group lies condition than out-group truth condition whereas the difference between lies and truth in the in-group condition was not significant. Figure 3. 2D-maps for N1 (left panel) and P3 (right panel) components under each condition (in-group lies, in-group truth, out-group lies, and out-group truth) in the parietal zone.

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Figure 4. The correlations between fairness and P3 amplitude differences in the contrast of lies versus truth. Significant positive correlation was found between fairness and P3 amplitude differences in the contrast of in-group lies versus truth (blue; r = 0.35, p = 0.040). The correlation between fairness and P3 amplitude differences in the contrast of out-group lies versus truth (red; r = -0.22, p = 0.211).

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Highlights

N1 and P3 significantly differed between the out-group lies and truth

No significant N1 and P3 differences between in-group lies and truth

P3 differences between in-group lies and truth correlated with fairness trait