Gaze patterns and brain activations in humans and marmosets in the Frith-Happé theory-of-mind animation task

Theory of Mind (ToM) refers to the ability to ascribe mental states to other individuals. This process is so strong that it extends even to the attribution of mental states to animations depicting interacting simple geometric shapes, such as in the Frith-Happé animations in which two triangles move either purposelessly (Random condition), or as if one triangle is reacting to the other triangle’s mental state (ToM condition). Currently, there is no evidence that nonhuman primates attribute mental states to moving abstract shapes. Here we investigated whether highly social marmosets (Callithrix jacchus) process ToM and Random Frith-Happé animations differently. Our results show that marmosets and humans (1) follow more closely one of the triangles during the observation of ToM compared to Random animations, and (2) activate large and comparable brain networks when viewing ToM compared to Random animations. These findings indicate that marmosets, like humans, process ToM animations differently from Random animations.