Synchrony and Physiological Arousal Increase Cohesion and Cooperation in Large Naturalistic Groups

Abstract

Separate research streams have identified synchrony and arousal as two factors that might contribute to the effects of human rituals on social cohesion and cooperation. But no research has manipulated these variables in the field to investigate their causal - and potentially interactive - effects on prosocial behaviour. Across four experimental sessions involving large samples of strangers, we manipulated the synchronous and physiologically arousing affordances of a group marching task within a sports stadium. We observed participants' subsequent movement, grouping, and cooperation via a camera hidden in the stadium's roof. Synchrony and arousal both showed main effects, predicting larger groups, tighter clustering, and more cooperative behaviour in a free-rider dilemma. Synchrony and arousal also interacted on measures of clustering and cooperation such that synchrony only encouraged closer clustering-and encouraged greater cooperation-when paired with physiological arousal. The research helps us understand why synchrony and arousal often co-occur in rituals around the world. It also represents the first use of real-time spatial tracking as a precise and naturalistic method of simulating collective rituals.

Figure 1

Experimental marching task (synchrony condition) as seen from the hidden camera (left panel) and as reconstructed by our tracking software (right panel). Coloured lines in the right panel correspond to participants’ movements over the tracking period.

Figure 2

Group formation (top panels) and dispersal (bottom panels). The left-hand panels depict participants at the beginning of the tasks. The right-hand panels depict participants at the conclusion of the tasks.

Figure 3

Group size (far left), interpersonal proximity during dispersal (middle) and speed during the cooperation task (far right) as a function of the arousal and synchrony conditions.