Traditional work on bystander intervention in violent emergencies has found that the larger the group, the less the chance that any individual will intervene. Here, we tested the impact on helping behavior of the affiliation of the bystanders with respect to the participants. We recruited 40 male supporters of the U.K. Arsenal football club for a two-factor between groups study with 10 participants per group. Each participant spoke with a virtual human Arsenal supporter (V), the scenario displayed in a virtual reality system. During this conversation, another virtual character (P), not an Arsenal fan, verbally abused V for being an Arsenal fan leading eventually to physical pushing. There was a group of three virtual bystanders who were all either Arsenal supporters indicated by their shirts, or football fans wearing unbranded shirts. These bystanders either encouraged the participant to intervene or dissuaded him. We recorded the number of times that participants intervened to help V during the aggression. We found that participants were more likely to intervene when the bystanders were out-group with respect to the participant. By comparing levels of intervention with a “baseline” study (identical except for the presence of bystanders), we conclude that the presence of in-group bystanders decreases helping. We argue therefore that, other things being equal, diffusion of responsibility is more likely to be overcome when participant and victim share group membership, but bystanders do not. Our findings help to develop understanding of how diffusion of responsibility works by combining elements of both the bystander effect and the social identity approach to bystander behavior.

暴力紧急情况下旁观者干预的传统研究发现，群体越大，任何个人进行干预的机会就越小。在这里，我们测试了旁观者对参与者的从属关系对帮助行为的影响。我们招募了 40 名英国阿森纳足球俱乐部的男性支持者进行两因素组间研究，每组 10 名参与者。每个参与者都与虚拟的阿森纳支持者 (V) 进行了交谈，该场景显示在虚拟现实系统中。在这次谈话中，另一个虚拟角色（P），不是阿森纳球迷，口头辱骂 V 是阿森纳球迷，最终导致身体推搡。有一组三个虚拟的旁观者，他们要么是球衣上标明的阿森纳支持者，要么是穿着无品牌球衣的足球迷。这些旁观者要么鼓励参与者进行干预，要么劝阻他。我们记录了参与者在攻击期间干预以帮助 V 的次数。我们发现，当旁观者相对于参与者而言是外群体时，参与者更有可能进行干预。通过将干预水平与“基线”研究（除了旁观者的存在之外相同）进行比较，我们得出结论，群体内旁观者的存在减少了帮助。因此，我们认为，在其他条件相同的情况下，当参与者和受害者共享团体成员身份时，更有可能克服责任分散，而旁观者则不然。我们的发现有助于通过结合旁观者效应和旁观者行为的社会认同方法的元素来理解责任的分散如何运作。