Their study is evidence people's visual biases change when surrounded by members of their own group, creating a perception of "safety in numbers," they said.
"Having one's group or posse around actually changes the perceived seriousness of the threat," psychology Professor Joseph Cesario said. "In that situation, they don't see the threat quite so closely because they have their people around to support them in responding to the threat."
The research was inspired by an earlier MSU study of wild hyenas in Kenya where scientists played recordings of hyenas from other parts of Africa and found the Kenya hyenas were more likely to approach the source of the sound when they were in groups and more likely to flee when they were alone.
In two studies of more than 300 participants, Cesario and colleague Carlos Navarrete found people who are alone judge threats as much closer than when they are in a group.
It's an evolutionary adaptation found in many social species, they said.
"This is about evolutionarily significant threats, such as members of a different group coming to steal resources or attack you," Cesario said. "The cost of not responding soon enough to a threat like that could be death or serious injury. So seeing that threat as closer allows you to respond with enough time to spare.
"What our work shows is that having your group or coalition around you makes that kind of early responding less necessary."