EEG frequency tagging reveals the integration of dissimilar observed actions.

Extensive research has demonstrated that visual and motor cortices can simultaneously represent multiple observed actions. This ability undoubtedly constitutes a crucial ingredient for the understanding of complex visual scenes involving different agents. However, it is still unclear how these distinct representations are integrated into coherent and meaningful percepts. In line with studies of perceptual binding, we hypothesized that similar movements would be more easily integrated. To test this hypothesis, we developed an EEG frequency tagging experiment in which two hand movements were displayed simultaneously at two different presentation rates. Crucially, the degree of similarity between the two movements varied along two dimensions, namely action identity (i.e., same or different performed movement), and agent identity (i.e., one agent performing a bimanual movement, or two agents moving each one hand). Contrary to our predictions, we found a larger intermodulation oscillatory component, indexing the integrated processing of the two individual movements, when they were less similar. We propose that integration-by-dissimilarity might serve as a top-down process to solve conflict caused by incongruent movements, thus contributing to the global understanding of distinct moving individuals in a complex social scene.