How Good Are You at Reading Human Expressions? (Quiz)

It's clear we gauge how other people are feeling based on their facial expressions. But how exactly do our faces convey these feelings, and how do people on the receiving end detect them? A new study suggests it's all in the eyes.

Scientists Daniel H. Lee, a research associate at University of Colorado Boulder and Adam K. Anderson, associate professor at Cornell University, did two experiments. In the first, they created images of six facial expressions using popular photo databases. For the most part, participants were able to correctly pair expressions with their corresponding emotions. In the second experiment, the researchers tried to trick participants by creating faces with conflicting eye-emotions and mouth-emotions (say, an angry mouth paired with excited eyes). Despite the two being at odds, most participants determined the emotions based on the eyes alone.

According to the researchers, this is a story of co-evolution: Lee points out that when we open our eyes wide, we increase our visual sensitivity, while narrowing them increases attention to detail. "These optical functions that evolved for the expresser were then socially co-evolved for receivers such that wider eyes are perceived to convey mental states of sensitivity and narrower eyes are perceived to convey discrimination, suspicion, or scrutiny."

From an evolutionary standpoint, it's useful to read emotions via the eyes, because they convey information about what the other person is seeing. "The eyes tell your friends where to look for potential threats, and our expressions can enhance that information," Lee says. For example, when people widen their eyes, the contrast between the pupil and the whites of their eyes nudge those around them to look in the same direction.

Test your own emotion recognition using the below quiz, which was developed by Simon Baron-Cohen, director of the University of Cambridge's Autism Research Center. Baron-Cohen (yes, cousin of actor Sacha Baron-Cohen) was seeking to evaluate people on the autism spectrum, but also gave the test to people without a diagnosis. On average the latter group scored 26/37; see how well you do.