The neighborhood of interaction in human crowds is neither metric nor topological, but visual

Abstract

Global patterns of collective motion in bird flocks, fish schools, and human crowds are thought to emerge from local interactions within a neighborhood of interaction, the zone in which an individual is influenced by their neighbors. Both topological and metric neighborhoods have been reported in birds, but this question has not been addressed in humans. With a topological neighborhood, an individual is influenced by a fixed number of nearest neighbors, regardless of their physical distance; whereas with a metric neighborhood, an individual is influenced by all neighbors within a fixed radius. We test these hypotheses experimentally with participants walking in real and virtual crowds, by manipulating the crowds density. Our results rule out a strictly topological neighborhood, are approximated by a metric neighborhood, but are best explained by a visual neighborhood with aspects of both. This finding has practical implications for modeling crowd behavior and understanding crowd disasters.