The Mere Reminder of Others: A Cognitive Modelling Approach to the Implicit Bystander Effect

The bystander effect suggests that people are less likely to assist in an emergency when others are present. Traditional theoretical accounts attribute this effect to top-down reflective processes, such as the diffusion of responsibility. However, recent research has proposed a two-system approach, suggesting that an individual's initial response to an emergency is personal distress and avoidance, which is further amplified by the presence of bystanders. In this study, we embed the two-system approach into an evidence accumulation model and argue that a higher distress and avoidance response causes slower evidence accumulation. We conducted a reaction time experiment where participants got exposed to faces or control stimuli and had to judge if a scene was dangerous. Our results confirm our hypothesis: Individuals exposed to faces had slower evidence accumulation for dangerous decisions. These findings contribute to a mechanistic understanding of how the anticipated bystander presence can influence early reflexive reactions to emergencies.