Spontaneous attribution of underspecified belief of social partners facilitates processing shared information.

The main question of Theory of Mind research is not only how we represent others' mental states, but also how these representations influence our first-person interaction with our surrounding environment. A novel theory of belief files proposes that we should think about belief tracking as an online, spontaneous, and effortless mechanism giving rise to structured representations, thus easing the use of beliefs in behavior selection. Beliefs are formed by two different sub mechanisms: (1) opening an empty placeholder belief file, for a particular intentional agent, and (2) filling it up with mental content attributed to the agent. This theory opens the possibility of exploiting theory of mind abilities even in situations when we can attribute only underspecified mental contents to others. The goal of the present study was to provide a proof of concept test: whether spontaneous belief tracking starts effortlessly even when we do not know a partner's actual belief content. We created an object detection paradigm, where the visual access of a virtual agent to the object to be detected by the participant was manipulated. The agent getting access to the information for processing always preceded the participant getting access to it, resulting in the need of attributing belief without specified content in it. Our results have shown that participants detected the object with a reduced reaction time when the observed agent had visual access to the object's expected place compared to when the participant watched the same scenario, but the object's location remained occluded for the observed agent and thus was revealed only for the participant. This suggests that the information processing of humans speeds up when another agent has access to a piece of information as well. Thus, we do track agents' potential beliefs without knowing its actual content. This study contributes to our understanding of the effect of spontaneous computation of others' mental states on first-person information processing.