CENTENNIAL HONORS COLLEGE Western Illinois University Undergraduate Research Day 2015 Poster Presentation Can you trust a stranger? Choices during the Prisoner’s Dilemma and Snowdrift Dilemma Ariel Wilson Faculty Mentor: Sandra McFadden Psychology Knowledge about the neural basis of choices made during social dilemma tasks is limited. Previous research has focused on two choices, cooperation and defection, made during a social dilemma task called the Prisoner’s Dilemma (PD). EEG activity recorded from the prefrontal cortex showed different patterns of activation for the two choices, with greater beta (12-24 Hz) and gamma (>25 Hz) activity during defection choices. The present study extended previous research by using an additional social dilemma task, called the Snowdrift Dilemma, and a different method of recording EEG activity called hyperscanning. Undergraduate students played the two games in pairs, while EEG was recorded. EEG data for cooperation and defection choices were analyzed separately. Participants’ reactions were also analyzed based on outcomes. We expected more cooperative choices in Snowdrift versus PD, and greater alpha (8-12 Hz) activity and lower beta activity during cooperative choices versus defection. Results showed greater alpha activity and lower beta activity for cooperative choices, as predicted. Pairs who cooperated the most frequently had the highest levels of alpha activation. The EEG results indicate that fewer cognitive resources are required for cooperation than for defection. In future studies it will be interesting to compare different groups (e.g., people with and without depression or ADHD) to explore differences in social interactions.