People view brown-eyed faces as more trustworthy than those with blue eyes- unless the blue eyes belong to a man with a broad face, according to a new paper in PLOS ONE. 

The psychologists (and an anthropologists) attempt to answer a big question: What makes us think a person's face looks trustworthy? 

To find out, they asked college students (142 females and 98 males) to rate facial photographs of 40 female and 40 male students and rate them for perceived trustworthiness based on two features: eye color and face shape.  The 80 photos were rated for trustworthiness (dominance/attractiveness) on a ten-point scale where 1 means very trustworthy and 10 very untrustworthy.

A significant number of participants found brown-eyed faces more trustworthy than blue-eyed, whether the faces were male or female. More rounded male faces, with bigger mouths and larger chins, were perceived as more trustworthy than narrow ones, but the shape of a female face did not have much effect on how trustworthy it appeared to the respondents.  

Thin-plate spline visualizations of the way face shape

correlates with eye color (a-f) and trustworthiness (g-i). Citation: Kleisner K, Priplatova L, Frost P, Flegr J (2013) Trustworthy-Looking Face Meets Brown Eyes. PLoS ONE 8(1): e53285. doi:10.1371/journal.pone.0053285

To test which of the two features were more important, the researchers tried a third test, presenting participants with photographs of male faces that were identical except for one difference: eye color.

They found that both eye colors were considered equally trustworthy.

According to the study, "We concluded that although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes."

Citation: Kleisner K, Priplatova L, Frost P, Flegr J (2013) Trustworthy-Looking Face Meets Brown Eyes. PLoS ONE 8(1): e53285. doi:10.1371/journal.pone.0053285