Do I trust you when you smile? Effects of sex and emotional expression on facial trustworthiness appraisal

Abstract

Background: Trust is a prerequisite for successful social relations. People tend to form a first impression of people's trustworthiness based on their facial appearance. The sex of the judging person and its congruency with the sex of the judged people influence these appraisals. Moreover, trustworthiness and happiness share some facial features, which has led to studies investigating the interplay between both social judgments. Studies revealed high correlation in judging happiness and trustworthiness across different facial identities. However, studies are missing that investigate whether this relationship exists on a within-subject level and whether in-group biases such as the congruency between the sex of the judging and judged individual influence this relationship. In the present study, we addressed these questions.

Methods: Data were collected in an online-survey in two separate samples (N = 30, German sample, N = 107 Dutch sample). Subjects assessed the intensity of happiness and trustworthiness expressed in neutral and calm facial expression of the same characters (50% males, 50% females). Statistical analyses comprised rm-Anova designs based on rating scores and estimates of within-subject associations between both judgments.

Results: Our findings replicate high correlations between happiness and trustworthiness ratings across facial identities based on average scores across participants. However, the strength of this association was strongly dependent on the methodological approach and inter-subject variability was high. Our data revealed an in-group advantage for trustworthiness in women. Moreover, the faces' sex and emotional expressions differentially influenced the within-subject correlation between both judgments in men and women.

Conclusion: Our findings replicate previous studies on the association between happiness and trustworthiness judgments. We extend our understanding of the link between both social judgments by uncovering that within-subject variability is high and influenced by sex and the availability and appraisal of positive emotional facial cues.

Fig 1. Mean and standard error for happiness and trustworthiness ratings of neutral and calm facial expressions a) sample 1, b) sample 2, c) separated for the sex of the participants and the facial stimuli (pooled for sample 1 and sample 2).

Please note: Fig 1a and 1b: *** indicates p < .001 for the main effects of ‘emotion’ and ‘task’, xxx indicates p < .001 for the interaction effect; Fig 1c: *** indicates p < .001 for the interaction effects of ‘sex-stim’ * ‘emotion’, xxx indicates significant differences between pairwise comparisons with p < .001 for the interaction effect ‘sex * sex-stim * task’.

Fig 2. Correlation between mean happiness and trustworthiness ratings for neutral and calm faces.

a) For different facial stimuli based on rating scores averaged across participants separately for each stimulus (pooled for sample 1 and sample 2). b) For different participants based on rating scores averaged across characters. c) Distributions of within-subject correlation coefficients between happiness and trustworthiness judgments.

Fig 3. Mean and standard error for Fisher’s z-scores estimating the within-subject relationship between happiness and trustworthiness judgments in neutral and calm female and male facial expressions separated for male and female participants please note: *** indicates p < .001 for the interaction effects of ‘sex * sex-stim’, xxx indicates significant pairwise comparisons with p < .001 for the interaction effect ‘sex-stim * emotion’.