Jason Haberman and David Whitney (2007)
Rapid extraction of mean emotion and gender from sets of faces
Curr Biol 17(17):R751-R753.
We frequently encounter crowds of faces. Here we report that, when presented with a group of faces, observers quickly and automatically extract information about the mean emotion in the group. This occurs even when observers cannot report anything about the individual identities that comprise the group. The results reveal an efficient and powerful mechanism that allows the visual system to extract summary statistics from a broad range of visual stimuli, including faces.
Link to PubMed entry