We are confronted with groups of objects in our visual environment all the time, whether it is a bouquet of flowers or a crowd of people. So how do we process these groups of objects?
Our brains compute a statistical summary representation. When it comes to human faces - whether we are processing their emotions or physical attractiveness, research shows that we compute the mean level of each set.
This helps explain the so-called Cheerleader Effect, the pop-culture notion that individuals are more attractive when they are in a group.