The participants were asked to guess the percentage of the money that each character had shared. In a learning phase, each guess was followed by a display of the amount that the researchers had attached to that face. After that, the subjects guessed the percentages without receiving any feedback. Those values then informed the learning phase for a second generation of participants, and so forth. After multiple rounds, the researchers find, judgments of trustworthiness converged around simple positive assessments of facial characteristics, regardless of the initial level of trustworthiness assigned to each face. Even if the first participants learned that a certain happy, attractive character had shared less than they had expected, participants over time nevertheless indicated that they trusted the character to share. This shows that “participants held a strong bias,” the researchers write.
A key element to the stereotypes underlying trustworthiness is attractiveness, known for a century to scientists as the “halo effect.” Todorov worked with another group of researchers to demonstrate that in the absence of the halo effect, faces that seem happier or more approachable also appear trustworthy.
This team ran three experiments on what makes a face seem trustworthy if attractiveness is removed from the equation. They used the same system as the first team for generating artificial faces but tweaked the “trustworthy” faces to make them less attractive—and didn’t alter them to make them smile or frown. Then they showed the faces to dozens of online participants.
Faces seen as happier and more approachable rated as more trustworthy even if they weren’t deemed attractive, they find. When the researchers carried out the same experiments using machine learning in place of human participants, the computers and the humans concurred: faces that seemed happier and more approachable were perceived as more trustworthy.
“The findings clearly show that emotional expressive behavior is an important cue for perceived trustworthiness,” the researchers write. Thus stereotypes and a smile can lead you to judge someone trustworthy, even when the person isn’t.