Participants will complete an experimental task assessing their social perception of male and female faces manipulated to resemble themselves and their co-participant. Specifically, it will be tested whether participants judge self-resembling male or female faces as either more trustworthy or more attractive than a set of control faces (as in, e.g., DeBruine et al., 2011). ### Stimulus creation Stimuli will be created using the same method as DeBruine et al. (2011), and is described in detail here. #### Composite faces In order to create self-resembling faces, we will first create composite faces which will be used to transform face stimuli. We will make twelve separate composite faces. Male and female composites will be created separately, and composites will be grouped according to six age groups: 18-25, 26-35, 36-45, 46-55, 56-65 and 66-75. Each composite face will average the shape and colour information of 10 individual faces of the respective categories. See DeBruine et al. (2008) for details on the averaging process. #### Self-resembling faces For each participant, we will create one self-resembling male face and one self-resembling female face. These will be done by first calculating the shape and colour differences between the participant's image taken in week 1 and the same-sex age-matched composite face mentioned above. Fifty percent of these differences will then be applied to both the male and female age-matched composite faces. Essentially, this results in a same-sex and an other-sex composite face that have been transformed to resemble the participant. This method has been previously shown to create subtle resemblance, with the experimental manipulation remaining undetected by participants (e.g., DeBruine, 2005). Additional faces will also be made to resemble the participant's co-participant. Here, the differences will be calculated between the co-participant's face and the composite that matches the co-participant's age and sex, but these differences will then be applied to the composite faces that age- and sex-match the participant doing the rating. #### Foil faces For each composite face described above, 10 foil faces will be created. These will be created using the same method of transforming faces as described above, but using faces of 10 separate individuals who are not known to any of the participants. These separate individuals will match the respective composite's sex and age group. ### Procedure Participants will be asked to rate 4 sets of faces in separate blocks, each set containing 20 trials. The 4 blocks are: 1) attractiveness judgements of male faces, 2) attractiveness judgements of female faces, 3) trustworthiness judgements of male faces, and 4) trustworthiness judgements of female faces. For each trial, participants will be asked to make a two-alternative forced-choice decisions between each of the 10 foil faces, and either a) the participant's self-resembling face, or b) the participant's co-participant's self-resembing face. The instructions presented will either be: 1) 'Which face is more trustworthy?', or 2) ‘Which face is more attractive?'. The order of the four blocks (male attractiveness, male trustworthiness, female attractiveness and female trustworthiness) will be randomized. For each block, the order of presentation of face pairs will be randomized, and the side of presentation of faces will be randomized for each trial. ### Yoked participants For each main participant, a sex- and age-matched yoke participant will be recruited. These yoke participants will complete the task with the same sets of faces as the respective main participant. This will allow us to ensure any self-resembling preference is specific to the participant, and not because any participant's face is preferred by everyone. ---- ### References DeBruine, L.M. (2005). Trustworthy but not lust-worthy: context-specific effects of facial resemblance. *Proceedings of the Royal Society B, 272*, 919-922. doi:10.1098/rspb.2004.3003 DeBruine, L. M., Jones, B. C., Little, A. C. & Perrett, D. I. (2008). Social Perception of Facial Resemblance in Humans. *Archives of Sexual Behavior, 37*(1), 64-77. doi:10.1007/s10508-007-9266-0 DeBruine, L.M., Jones, B.C., Watkins, C.D., Roberts, S.C., Little, A.C., Smith, F.G. & Quist, M.C. (2011). Opposite-sex siblings decrease attraction, but not prosocial attributions to self-resembling opposite-sex faces. *Proceedings of the National Academy of Sciences, 108*(28), 11710-11714.