When we see someone’s face, our brains quickly decide if we can trust them, usually in less time than it takes to blink. However, new research from Chicago Booth suggests that these snap judgments might not be as accurate as we think, for two main reasons.

Firstly, our judgments can be influenced by stereotypes that have been around for a long time, even if they’re not true. Secondly, a simple smile can lead us in the wrong direction.

Snap judgments

Quick trust assessments likely evolved to help us quickly figure out if someone is a threat. Knowing how these judgments work is important because being seen as trustworthy can affect things like getting elected, getting a loan, or receiving a lenient sentence.

The study investigated how these trust stereotypes develop. Participants were shown computer-generated faces with varying levels of perceived trustworthiness, paired with amounts of money that characters had supposedly shared in a trust game. Participants had to guess the percentage of money each character shared. Over time, judgments of trustworthiness focused on simple positive facial features, regardless of the initial trustworthiness assigned to each face.

One significant factor influencing trust stereotypes is attractiveness, known as the “halo effect.” In another set of experiments, researchers removed attractiveness from the equation. Even when faces were made less attractive, those who seemed happier and more approachable were still seen as trustworthy. This pattern held true when both humans and computers were involved in the experiments, showing a shared perception that happier and friendlier faces are more trustworthy.

“The ?ndings clearly show that emotional expressive behavior is an important cue for perceived trustworthiness,” the researchers conclude. Thus stereotypes and a smile can lead you to judge someone trustworthy, even when the person isn’t.