Holzleitner IJ, O'Shea KJ, Fasolt V, Jones BC & DeBruine LM (2018). Which 3D shape cues drive perceptions of facial similarity? in ..

Objective: Previous studies have used rated similarity of faces as a means to investigate kin recognition as well as homogamy in romantic partners. Little is known, however, about which facial cues drive perceptions of similarity. Here, we use a data-driven approach to investigate whether perceived facial similarity is linked to similarity in 3D face morphology, and which facial dimensions are most important in eliciting perceptions of similarity. Methods: We took three-dimensional images of 139 heterosexual couples aged 19-72. Paired images of each couple were presented to 26 raters (13 male, 13 female), who were blind to the nature of the pictures and asked to rate how similar each face pair looked. 3D face models were subjected to a principal component analysis of shape, and two sets of similarity measures were derived: closeness in 3D face space, as well as distance on individual face dimensions (shape PCs). The same set of measures was also derived for locally circumscribed regions, i.e. eye, nose and mouth regions. Results: Mixed-effect models showed that faces were perceived as more similar the closer they were in face space. In particular, similarity in face width vs height (PC2) was a strong predictor of perceived similarity. Looking at individual facial regions, similarity in eye (size) and nose (width/height) but not mouth regions predicted perceptions of similarity. Conclusions: When asked to judge the similarity of opposite-sex faces, raters mainly relied on similarity in facial dimensions that explained substantial parts of general variance in face shape (higher-order shape PCs). In a next step, we will test whether these features can also be used to predict kinship.

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