Social anxiety and perception of (un)trustworthiness in smiling faces

• Socially anxious individuals especially mistrust smiling faces with non-happy eyes.
• Reductions of trustworthiness occur for neutral and for negatively valenced eyes.
• Small changes in the eye expression affect anxious more than non-anxious individuals.
• The effect of non-happy eyes in socially anxious individuals is not emotion-specific.
• Social anxiety does not bias trustworthiness evaluation of prototypical happy faces.

In social environments the smile can be driven by different motives and convey different emotions. This makes a smiling face ambiguous and amenable to alternative interpretations. We investigated how social anxiety is related to trustworthiness evaluation of morphed dynamic smiling faces depending on changes in the eye expression. Socially anxious and non-anxious participants judged the un/trustworthiness of people with different smiles. Social anxiety was related to reduced trustworthiness of (a) faces with a neutral mouth unfolding to a smile when the eyes were neutral at the beginning or end of the dynamic sequence, and (b) faces with a smiling mouth when happy eyes slightly changed towards neutrality, surprise, fear, sadness, disgust, or anger. In contrast, social anxiety was not related to trustworthiness judgments for non-ambiguous expressions unfolding from neutral (eyes and mouth) to happy (eyes and mouth) or from happy to neutral. Socially anxious individuals are characterized by an interpretation bias towards mistrusting any ambiguous smile due to the presence of non-happy eyes.