The ability to interpret and predict other people's actions is highly evolved in humans and is believed to play a central role in their cognitive behavior. However, there is no direct evidence that this ability confers a tangible benefit to sensory processing. Our quantitative behavioral experiments show that visual discrimination of a human agent is influenced by the presence of a second agent. This effect depended on whether the two agents interacted (by fighting or dancing) in a meaningful synchronized fashion that allowed the actions of one agent to serve as predictors for the expected actions of the other agent, even though synchronization was irrelevant to the visual discrimination task. Our results demonstrate that action understanding has a pervasive impact on the human ability to extract visual information from the actions of other humans, providing quantitative evidence of its significance for sensory performance.
