title: Perceived facial similarity: rethinking its use in conceptualising romantic couples
Creators: name: Cassar, Rachel
Publisher: name: University of Glasgow
Year: 2022

description: 'Like attracts like’, yet robust hypothesis testing for facial similarity in romantic couples remains lacking. Two main explanations govern research on similarity in couples: (i) an adaptive hypothesis which predicts that similarity is a kinship cue for which preferences guide individuals to choose a mate with an optimal amount of relatedness, and (ii) a by-product hypothesis which predicts that similarity is a consequence of a familiarity effect where repeated exposure to familiar objects enhances their appeal in general. Previous studies on homogamy tend to adopt study designs that make assumptions about the proximate mechanisms driving homogamy, resulting in confounded variables of interest and overzealous support for an explanation without ruling out other possibilities. The aim of this thesis was to study how people respond to facial similarity in different contexts and to assess whether explanations for homogamy hold when tested under different study designs. Study 1 explored how perceptions of similarity relate to couple judgments and sibling judgments on a set of facial images of couples. A binomial mixed effects model was used to assess whether perceived similarity predicts couple and sibling judgments and whether this effect differed between the two contexts. The findings from this study revealed that perceived similarity strongly predicted sibling judgments but did not predict couple judgments, suggesting a distinction in the way similarity is used to inform assessments of consanguine and affine relationships. Study 2 replicates Study 1 while incorporating random foil pairs to additionally test how accurately people judge couples, as well as whether sibling judgments distinguish between actual couples and foil pairs. The results from this study are in agreement with Study 1 in that similarity was a better predictor of sibling judgments than couple judgments, although the latter effect was weaker than the former. Furthermore, actual couples were more likely than foils to be judged as both couples and siblings, indicating that the visual information used to make couple judgements is likely to have some overlap with the visual information used to make sibling judgements. Study 3 examined secondary data on attributions of attractiveness and trustworthiness in two-alternative forced choice tasks on self-resembling and partner-resembling transforms paired with non-resembling controls. Analysis with a mixed effects model revealed conflicting results as well as issues with the original study design. A self or partner-resembling bias was found on both attributions of attractiveness and trustworthiness and, contrary to expectations, this bias was stronger in the attractiveness condition. Additionally, partner-resembling faces were chosen more frequently when they were in the opposite-sex category and self-resembling faces were chosen more often when they were in the same-sex category. These findings could indicate that the self- and/or partner-resembling bias is driven by a familiarity effect, however, this could also be an artefact of the study design and thus further research is required to address this matter before making any such conclusion.