Adaptation aftereffects reveal representations for encoding of contingent social actions

Significance Why is it so easy for humans to interact with each other? In social interactions, humans coordinate their actions with each other nonverbally. For example, dance partners need to relate their actions to each other to coordinate their movements. The underlying neurocognitive mechanisms supporting this ability are surprisingly poorly understood. We show that human brain processes are sensitive to pairs of matching actions that make up a social interaction. These findings provide insights into the perceptual architecture that helps humans to relate actions to each other. This capability is essential for social interactions, and its understanding will aid future development of therapies to treat social cognitive disorders.
A hallmark of human social behavior is the effortless ability to relate one’s own actions to that of the interaction partner, e.g., when stretching out one’s arms to catch a tripping child. What are the behavioral properties of the neural substrates that support this indispensable human skill? Here we examined the processes underlying the ability to relate actions to each other, namely the recognition of spatiotemporal contingencies between actions (e.g., a “giving” that is followed by a “taking”). We used a behavioral adaptation paradigm to examine the response properties of perceptual mechanisms at a behavioral level. In contrast to the common view that action-sensitive units are primarily selective for one action (i.e., primary action, e.g., ‘throwing”), we demonstrate that these processes also exhibit sensitivity to a matching contingent action (e.g., “catching”). Control experiments demonstrate that the sensitivity of action recognition processes to contingent actions cannot be explained by lower-level visual features or amodal semantic adaptation. Moreover, we show that action recognition processes are sensitive only to contingent actions, but not to noncontingent actions, demonstrating their selective sensitivity to contingent actions. Our findings show the selective coding mechanism for action contingencies by action-sensitive processes and demonstrate how the representations of individual actions in social interactions can be linked in a unified representation.