Synchrony enhances ensemble perception of dynamic emotional crowds.

Coordinated group behavior is common for many species, including humans. Perceiving groups is important, too, especially when that group displays emotion. To see a crowd, like a laughing audience or an angry mob, the visual system engages a mechanism known as ensemble coding, which compresses information about the individuals into a summary representation. This ensemble, or "gist", perception is remarkably quick, allowing people to judge the emotion of a large crowd with a mere glance, as if from a snapshot. But emotions are dynamic, and the way group members express their emotions-either in-sync or out-of-sync-may be critical for understanding their collective affect. If groups are defined not just by the proximity of their members, but also by their collective behavior, then ensemble representation should be particularly powerful for extracting emotional information from synchronous groups. On each trial, observers estimated the average emotional expression of a crowd of twelve faces, which included four unique identities. All crowd members displayed the same category of emotional expression (happy, angry, or fearful, on a given trial); each member began at a unique intensity. Across the 1-second presentation, each crowd member oscillated between weak and intense versions of that particular emotion. Critically, the individuals in some crowds changed their expressions synchronously, whereas the individuals in other crowds acted asynchronously. Additional trials contained only a single dynamic face. Observers perceived the emotion of synchronous groups more precisely than asynchronous groups. The benefits of coordinated behavior were so pronounced that synchronous crowds were perceived more precisely than even a single dynamic face. In contrast, asynchronous crowds and single faces were perceived with comparable precision. Our results show that ensemble representation is remarkably sensitive to synchronized group dynamics, and more generally, that collective behavior is critical for understanding and perceiving emotion as it occurs in crowds. Meeting abstract presented at VSS 2015.