Joint actions often require agents to track others’ actions while planning and executing physically incongruent actions of their own. Previous research has indicated that this can lead to visuomotor interference effects when it occurs outside of joint action. How is this avoided or overcome in joint actions? We hypothesized that when joint action partners represent their actions as interrelated components of a plan to bring about a joint action goal, each partner’s movements need not be represented in relation to distinct, incongruent proximal goals. Instead they can be represented in relation to a single proximal goal – especially if the movements are, or appear to be, mechanically linked to a more distal joint action goal. To test this, we implemented a paradigm in which participants produced finger movements that were either congruent or incongruent with those of a virtual partner, and either with or without a joint action goal (the joint flipping of a switch, which turned on two light bulbs). Our findings provide partial support for the hypothesis that visuomotor interference effects may be reduced when two physically incongruent actions can be represented as mechanically interdependent contributions to a joint action goal.

In order to sustain cooperation, it is important that we have a sense that the distribution of efforts is fair. But how proficient are we at comparing our effort relative to that of others? Does the perception of our effort differ in individual and joint action contexts? To address these questions, we asked participants to squeeze a hand dynamometer at varying degrees of force to meet three target levels alone and with a partner. The results do not reveal a significant difference in the perception of effort between the two conditions. However, participants’ estimation of their effort skewed towards half when they made partial contribution to the target and this effect was more pronounced in the joint action. Taken together, the findings suggest that participants might have applied heuristics when perceiving their effort and in addition, expected fairness in the effortcontribution in a joint action context.

People who strongly endorse conspiracy theories typically exhibit biases in domain-general reasoning. We describe an overfitting hypothesis, according to which (a) such theories overfit conspiracy-related data at the expense of wider generalisability, and (b) reasoning biases reflect, at least in part, the need to reduce the resulting dissonance between the conspiracy theory and wider data. This hypothesis implies that reasoning biases should be more closely associated with belief in implausible conspiracy theories (e.g., the moon landing was faked) than with more plausible ones (e.g., the Russian Federation orchestrated the attack on Sergei Skripal). In two pre-registered studies, we found that endorsement of implausible conspiracy theories, but not plausible ones, was associated with reduced information sampling in an information-foraging task and with less reflective reasoning. Thus, the relationship between belief in conspiracy theories and reasoning is not homogeneous, and reasoning is not linked specifically to the “conspiracy” aspect of conspiracy theories. Instead, it may reflect an adaptive response to the tension between implausible theories and other beliefs and data.

People who strongly endorse conspiracy theories typically exhibit biases in domain-general reasoning. Previous studies, however, have mostly focused on less plausible conspiracy theories (e.g., the moon landing was faked), rather than more plausible ones (e.g., the Russian Federation orchestrated the attack on Sergei Skripal). Here we examine whether reasoning biases are associated with belief in all conspiracy theories or only with belief in less plausible conspiracy theories. In two pre-registered studies, we found that endorsement of implausible conspiracy theories, but not plausible ones, was associated with reduced information sampling in an information-foraging task and with less reflective reasoning. Thus, the relationship between belief in conspiracy theories and reasoning is not homogeneous, and reasoning is not linked specifically to the “conspiracy” in conspiracy theories, but to other factors (e.g., motivations towards sense making) that feature in many types of implausible belief (e.g., paranormal beliefs, delusions).