In an influential paper, Kosfeld et al. (2005) showed that intranasal administration of oxytocin (OT) increases the transfers made by investors in the trust game-suggesting that OT increases trust in strangers. Subsequent studies investigating the role of OT in the trust game found inconclusive effects on the trusting behaviour of investors but these studies deviated from the Kosfeld et al. study in an important way-they did not implement minimal social contact (MSC) between the investors and the trustees in the trust game. Here, we performed a large double-blind and placebo-controlled replication study of the effects of OT on trusting behaviour that yields a power of more than 95% and implements an MSC condition as well as a no-social-contact (NoC) condition. We find no effect of OT on trusting behaviour in the MSC condition. Exploratory post hoc analyses suggest that OT may increase trust in individuals with a low disposition to trust in the NoC condition, but this finding requires confirmation in future research.

(1) Background: Why and when images of watching eyes encourage prosocial behavior is still subject to discussion, and two recent meta-analyses show no effect of watching eyes on generosity. This study aims to discern the effect of watching eyes of different valence on two separate aspects of prosocial behavior, and additionally investigates whether individuals' social value orientation moderates the effect of eyes. (2) Methods: Individuals take on the role of either a first or second mover in an incentivized, anonymous sequential prisoner's dilemma (n = 247), a two-person game which separates the need to form expectations about the other player (first mover cooperation, trust) from the motive of greed (second mover cooperation, reciprocity). During decision-making, a picture of either kind eyes, unkind eyes, or a control picture is presented above each decision matrix. (3) Results: The results indicate that unkind eyes, and not kind eyes, significantly boost first mover cooperation. In contrast, neither type of eye cues increase second mover cooperation. Social value orientation does not moderate these effects. (4) Conclusions: Thus, the data suggest that the valence of eye cues matters, and we propose that unkind eyes urge first movers to live up to the interaction partner's expectations.

Accumulating evidence corroborates that power asymmetries influence how people respond to violations of the equality norm. We investigate with functional magnetic resonance imaging how preferences for advantageous (receiving more than other) and disadvantageous (receiving less than other) inequality are affected by having social power and whether or not this differs according to an individual’s social value orientation. Forty participants were primed with either a leader- or a teammate role (control) before conducting a task in the scanner during which they rated 36 monetary distributions which varied in degree of inequality. Behavioral data indicate that taking on a leader role generally increases aversion to disadvantageous inequality (DA-IE), but that it decreases aversion to larger advantageous inequality, especially for proself individuals. Consistently, the blood oxygen level–dependent (BOLD) data reveal that, as advantageous inequality mounts and the temptation to have more than others increases, leaders show reduced neural activation in regions associated with perspective taking and cognitive control (precuneus and frontal eye field). Proself leaders in particular show reduced activity in the left and right dorsolateral prefrontal cortex, which could be interpreted as a weaker restrain of self-interest when processing advantageous inequality. We found no evidence for an effect of power on processing DA-IE.

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