Abstract

This thesis describes three behavioral and one fMRI study in which the underlying psychological and neural mechanisms of stay/leave decision making in both a nonsocial and social context were investigated and compared. In Study 1A and 1B participants played a social or nonsocial version of a novel economic game in which participants were dependent on a social partner or nonsocial resource to increase their monetary outcomes. Both actual and expected reward probability of social partners and nonsocial resources positively affected the time participants decided to stay with a specific social partner or nonsocial resource. The effect of expected reward probability on staying times was much more pronounced in the nonsocial context. In Study 2, Reinforcement Learning models were fitted to participant's choices in a social and nonsocial version of the 4-armed bandit task in which prior beliefs about partners or resources were manipulated. The effects of Study 1B were replicated. Furthermore, it was found that participants weight expectancy-consistent and inconsistent new observations differentially when learning about both social partners and nonsocial resources. Participants had generally higher learning rates in the social than nonsocial context but this was not the case when prior beliefs were not induced. In Study 3, participants played a social and nonsocial version of the 4-armed bandit task while undergoing fMRI. Increased activation in caudate nucleus was associated with stay decisions in a social rather than nonsocial context; and the dorsal anterior cingulate cortex showed differential activation as a function of stay and leave decisions and this pattern was reversed in the nonsocial and social context. Interpretation of these results are discussed in light of a fundamental need to belong that motivates people to stay with social partners specifically and resist against breaking social connections.