Abstract
Transferring resources among kin and non-kin is ubiquitous in all human societies. A common form of resource transfer is achieved by the act of giving, during which a resource is passed on between two agents: an actor who gives and a recipient. Both linguistic expressions and infant’s studies implied that the giving act is represented as an instance of a social interaction, even in the absence of other cues of social engagement. It is not yet known whether adult observers would also interpret a skeletal act of giving as a social interaction. To assess how the participants interpreted the events, we exploited the fact that the mu rhythm (also known as the sensorimotor alpha rhythm, 8–13 Hz) of the electroencephalogram (EEG) can reflect action understanding. In two experiments we found that specific features of animated events modulated alpha-band neural activity over the right centro-parietal cortex of observers. In particular, contingent interaction among agents, which converted a following action into a chasing action, enhanced the attenuation of alpha band oscillations, and so did the reversal of the direction of a resource transfer action, which converted a taking action to a giving action. Importantly, such an effect was not observable when these action interpretations were disrupted by spatial separation of the agents, which disallowed perceiving their contingent interaction as chasing, or by replacing the target of a resource transfer with an inanimate recipient, which excluded the possibility of perceiving the transfer as an instance of giving. The comparison between chasing and following suggested that the attenuation of alpha oscillations can be used to assess the perceived level of social interaction. Hence, we demonstrated that observed giving actions are perceived as social interactions, irrespective of the contribution of the recipient.
Acknowledgement: National Natural Science Foundation of China (Grant no. 31600871) Advanced Investigator Grant of the European Research Council (#742231, PARTNERS)