For decades, the study of adult friendship has been swamped by a tsunami of research on romantic relationships. Even in journals dedicated to the study of all personal and social relationships (and not just romantic ones), studies of romantic relationships have overwhelmed everything else. It was as if scholars believed that friendship was just for kids.

That’s still largely true, but little by little, friendship is getting its due. In the New York Times, science reporter Natalie Angier described the results of some new research:

Scientists have found that the brains of close friends respond in remarkably similar ways as they view a series of short videos: the same ebbs and swells of attention and distraction, the same peaking of reward processing here, boredom alerts there.

The neural response patterns evoked by the videos — on subjects as diverse as the dangers of college football, the behavior of water in outer space, and Liam Neeson trying his hand at improv comedy — proved so congruent among friends, compared to patterns seen among people who were not friends, that the researchers could predict the strength of two people’s social bond based on their brain scans alone.

The new findings are intriguing for lots of reasons. One is that they suggest a psychology of friendship that goes deeper than the usual similarities between friends that have long been documented. For example, friends are often similar in age, education, wealth (or lack thereof), race, and attractiveness, and they tend to share political attitudes and social attitudes.

Many years ago, in my first year as a new professor, I had the great experience of getting to work with a very smart undergraduate, Dorothea (Dot) Brauer. Dot thought that pairs of friends might see their social worlds in similar ways, whereas pairs of strangers would not.

To test her idea, we teamed up to do a simple study. We recruited 20 women – 10 pairs of friends – and showed them 20 photos that had been validated as a test of nonverbal sensitivity (the still version of the PONS test). Each photo shows either the face or the body (neck down) of a person in various everyday life situations involving emotions, such as expressing gratitude, threatening someone, or asking for forgiveness. Test takers view each photo one at a time and indicate their interpretation by choosing from two different answers.

In the study Dot and I did, the women recorded their interpretations of the photos completely independently. They did not get to talk to each other or communicate in any way.

We compared the interpretations of the pairs of friends, and the interpretations of pairs of people who participated in the study but were not friends.

The results were clear. The friends interpreted the facial expressions of emotions very similarly – much more so than the pairs of women who were not friends. (They were not similar to each other in their interpretations of the photos that only showed the body.)

We asked the friends how long they had been friends. We also asked them to tell us whether they had discussed a number of different topics with each other. The topics ranged from superficial to intimate.

The more enduring the friendship, the more similar the friends were in their reading of the facial expressions. Also, friends who discussed more of the intimate topics with each other agreed more on what the facial expressions meant. Discussing casual topics didn’t matter – friends who talked to each other about a lot of superficial things were no more similar in their reading of the facial clues.

I was really proud of Dot for thinking up that intriguing idea and getting beautiful results when we tested it. But it was just a small study, so I always thought it was worth replicating.

It took 15 years to get around to it, but thanks to two grad students who went on to become professors, Matthew Ansfield and Kathy Bell, we tested the idea once again. We started out by recruiting 12 women and 10 men who watched a series of pleasant and unpleasant and unusual slides. We videotaped their facial expressions as they did so. Then, the 22 participants nominated a close friend of the same sex to take part in the second half of the study.

The 22 original participants and the 22 friends watched videos of the facial expressions of people from the first part of the study. Everyone watched facial expressions of their friend, and of strangers of the same sex. They indicated each time which kind of slide they thought the person was watching (pleasant or unpleasant or unusual). Each person watched the videos in a room with no one else present, so they could not be influenced by anyone else.

The results for the women were just the same as they were in the first study that Dot Brauer and I did. Pairs of women who were friends with each other were far more similar to each other in how they interpreted the facial expressions than pairs of women who were not friends. In fact, the pairs of female friends read the facial expressions very similarly regardless of whether they were interpreting the faces of people watching pleasant slides or unpleasant slides or unusual ones, and regardless of whether the facial expressions they were observing were those of their friends or those of strangers.

In both studies, female friends who look at facial expressions of emotions see the same thing – even when they are observing those expressions in separate rooms, without ever getting to consult with each other.

As for the pairs of men who were friends, there was only one wisp of similarity in their reading of facial expressions. They agreed only when they were watching strangers reacting to unpleasant slides.

(The people in the two studies were undergraduates and were almost certainly all single. But the studies were not specifically about single people. I still hadn’t turned my attention to that yet. To read about friendship in the lives of people who are single, check out this set of articles.)

Photo by Marion Doss