People view brown-eyed faces as more trustworthy than those with blue eyes, except if the blue eyes belong to a broad-faced man, according to research published January 9 in the open access journal PLOS ONE by Karel Kleisner and colleagues from Charles University in the Czech Republic.

The study's results attempt to answer a larger question: What makes us think a person's face looks trustworthy? The authors asked study participants to rate male and female faces for trustworthiness based on two features: eye color and face shape. 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 shapecorrelates with eye color (af) and trustworthiness (gi).

(Photo Credit: 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. Here, 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."

Source: Public Library of Science