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  • The current research was approved by the University of Birmingham Committee for Ethical Review. All participants were asked to sign their written informed consent prior to participation. A total of 60 participants (50 female), with a mean age of 19 (range = 18-23, SD = 1.0) were recruited from the University of Birmingham, UK. Participants received course credit in return for their participation. The Levenson Self-Report Psychopathy Scale (LSRP) [27] was completed by all participants as part of a battery of questionnaire based measures. The LSRP, designed for the measurement of psychopathic personality traits in non-institutionalized populations, consists of a 16 item primary subscale and a 10 item secondary subscale. While the primary subscale taps the selfish and uncaring characteristics associated with Factor 1 of the PCL-R, the secondary subscale measures behavioral and lifestyle factors associated with Factor 2, including boredom and impulsivity. Adequate internal validity of the LSRP has been demonstrated in a sample of 487 undergraduate psychology students, with a Cronbach’s alpha of .82 for the primary subscale and .63 for the secondary subscale, which was considered adequate for a ten item scale [27]. We used two separate tasks to assess the intergroup bias in relation to primary and secondary psychopathic traits: a computerized dictator game, a computerized ultimatum game. All tasks were prepared using E-Prime 2.0 stimulus presentation software. Participants always completed the dictator game prior to the ultimatum game. This order was enforced as proposed amounts during dictator game trials are typically dictated by generosity. However, ultimatum game trials require more careful thought as offers may either be accepted or rejected. Thus, we wished to avoid a scenario in which participants continued to make carefully judged proposals on the dictator game as a result of having first completed the ultimatum game. The Dictator Game and Ultimatum Game: Prior to the first dictator game trial, participants received on-screen instructions that they were to split an amount of £10 between themselves and an on-screen player. The minimum amount a participant could allocate was £1, with a maximum allocation of £9. In order to maximize personal gains, participants may be expected to propose only a minimal amount to the on-screen player. However, higher proposals may represent attempts to appear generous. Following completion of all dictator game trials, participants were presented with additional instructions for ultimatum game proposals. Participants were again instructed to split an amount of £10 between themselves and the on-screen player. However, participants were informed that their offers could subsequently be accepted or rejected by the respective on-screen players. If an offer was rejected, participants were instructed that both they and the on-screen player would receive nothing. A total of 38 Caucasian faces (10 female) were selected from the PUT face database [32] for use in the dictator game and ultimatum game. Each face was paired with a forename and allocated to either the in-group or the out-group using a same or other university manipulation. This was achieved through presentation of either same (University of Birmingham) or other (University of Manchester) university logos, including corporately formatted names and crests, alongside each face and forename (see Figure 1; please note that the photograph used in the figure is not the original image used in the study, but a similar image used for illustrative purposes only. The subject of the photograph has given written informed consent, as outlined in the PLOS consent form, to publication of their photograph). Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0069565.g001 Overview of the dictator game and the ultimatum game.For each of 38 trials participants view a central fixation cross for 500ms. This is followed by a 500ms presentation of a false forename and University logo which primes the same (University of Birmingham) or other (University of Manchester) University affiliation. University logos are then joined by a picture of the person to whom participants believe they are to make an offer. Once participants make an offer the next trial begins. Note: experimental trials included corporately formatted logos and text, not displayed above. Participants were informed that the current research was a collaborative investigation with the University of Manchester, assessing the impact of differing personality factors on economical decision making. Both the information sheet and consent forms included the name and official crests of both the University of Birmingham and the University of Manchester. Each task consisted of 38 trials. For each trial, participants were presented with a central fixation cross for 500ms. The fixation period was followed by a 500ms presentation of a university logo indicating same (University of Birmingham) or other (University of Manchester) university affiliation, alongside a false forename. University affiliation primes were subsequently joined by the image of a face to whom participants were to make a proposed split while acting as the proposer in the dictator game and the ultimatum game. The trial was terminated when participants indicated the proposed amount to be allocated to the on-screen player.
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