Search advantages for facing social groups reflect optimal interactive group sizes.

Humans are sensitive to the presence of other people as well as their interactions. For example, two individuals are found faster when they face toward (vs. away from) each other. We asked if this perceptual preference for facing social groups might be modulated by group size, being most pronounced for small groups, which are most common in everyday life. In three preregistered experiments, participants searched for facing or non-facing groups, with group size varying from two to eight. Facing groups were found faster than non-facing groups but only for groups up to five people (Experiment 1). This effect replicated when controlling for the number of individuals in the displays (Experiment 2) and was reduced for displays in inverted orientations (Experiment 3). Thus, human perception seems to be well-tuned to detect interactions in small groups, which parallels social preferences in everyday life and bridges across visual perception and social cognition.