Adolescents’ preferences for sexual dimorphism are influenced by relative exposure to male and female faces

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Abstract

Exposure to a particular population of faces can increase ratings of the normality and attractiveness of similar-looking faces. Such exposure can also refine the perceived boundaries of that face population, such that other faces are more readily perceived as dissimilar. We predicted that relatively less exposure to opposite-sex faces, as experienced by children at single-sex compared with mixed-sex schools, would decrease ratings of the attractiveness of sexual dimorphism in opposite-sex faces (that is, boys at single-sex schools would show a decreased preference for feminised faces, and girls at single-sex schools would show a decreased preference for masculinised faces). Consistent with this prediction, girls at single-sex compared with mixed-sex schools demonstrated significantly stronger preferences for facial femininity in both male and female faces. Boys at single-sex compared with mixed-sex schools demonstrated marginally stronger preferences for facial masculinity in male faces, but did not differ in their ratings of female faces. These effects were attenuated among some single-sex school pupils by the presence of adolescent opposite-sex siblings. These data add to the evidence that long-term exposure to a particular face population can influence judgements of other faces, and contribute to our understanding of the factors leading to individual differences in face preferences.

Introduction

It is a long-standing tenet of psychology that increased familiarity of a stimulus enhances ratings of its attractiveness (Bornstein, 1989, Zajonc, 1968). The attractiveness of familiar faces may contribute to the findings that individuals prefer faces of genetically-similar individuals (DeBruine, 2004, Roberts et al., 2005); that marriage partners tend to resemble each other (Bereczkei et al., 2002, Bereczkei et al., 2004, Spuhler, 1968, Zajonc et al., 1987); that an individual’s opposite-sex parent and partner demonstrate similarities in facial appearance (Bereczkei et al., 2008, Bereczkei et al., 2002, Bereczkei et al., 2004) and also in hair and eye colour (Little, Penton-Voak, Burt, & Perrett, 2003); and that increased parental age corresponds positively with higher ratings of age cues in judgements of facial attractiveness (Perrett et al., 2002). In the same way, children with greater experience of same-age peers show stronger preferences for faces similar to their peers, where similarity is manipulated by adjusting the height of the internal features of the face (Cooper, Geldart, Mondloch, & Maurer, 2006). Children also rate faces whose internal features are placed lower in the face than normal as more attractive than do adults, possibly because of their increased experience with viewing foreshortened faces from their lower perspective (Cooper et al., 2006).

Over shorter time periods, judgements of visual attractiveness can also be manipulated experimentally. Visual adaptation to faces manipulated to adjust the spacing of the facial features can lead to subsequent, similar faces being judged as more normal and attractive (Cooper and Maurer, 2008, DeBruine et al., 2007, Jones et al., 2008, Little et al., 2005, Rhodes et al., 2003, Rhodes et al., 2004). Similarly, visual adaptation to images of masculinised faces increases the rated attractiveness of new masculinised faces viewed subsequently, so long as the sex of the adapting face is congruent with the sex of the rated face (Buckingham et al., 2006, Little et al., 2005; see also Bestelmeyer et al. (2008) for further evidence of sex-contingent face aftereffects).

Visual adaptation leads to shifts in perceptions of visual category boundaries. Webster, Kaping, Mizokami, and Duhamel (2004) showed that laboratory-based visual adaptation to faces of a particular sex, ethnicity or emotional expression affects the viewer’s perceptual boundaries, such that subsequently-viewed test faces are more likely to be judged to be of a dissimilar sex, ethnicity or emotional expression (see also Bestelmeyer, Jones, Debruine, Little, & Welling, in press). Webster et al. (2004) also demonstrated similar adaptation effects as a result of extended visual experience in the real world. Asian visitors to the United States, who made judgements about the ethnic boundary of faces on an Asian–Caucasian continuum, were more likely to judge a face to be Asian if they had had more recent experience with Caucasian faces. The degree to which faces were more likely to be classified as Asian increased in line with the amount of time the judge had spent in the US and the quantity of the judge’s interactions with Caucasian individuals. In other words, exposure to a population of faces appears to increase the visual salience of the differences of a contrasting population of faces.

We set out to investigate whether similar effects could arise in relation to judgements of the attractiveness of facial sexual dimorphism, contingent upon real-world differences in exposure to male and female faces. In our study, over 240 adolescents at single-sex and mixed-sex schools underwent forced-choice preference tests to determine preferences for sexual dimorphism in male and female faces. Adolescents also provided details of other children living within the home, to investigate home-based visual experience with opposite-sex faces. Following Webster et al. (2004), we predicted that exposure to feminine faces should increase the salience of facial masculinity, and vice versa. Thus, compared with children at mixed-sex schools, girls at single-sex schools, who are exposed to proportionally larger numbers of female faces, might perceive faces as more masculine, whereas boys at single-sex schools might perceive faces as more feminine, compared with children at mixed-sex schools. If all else is equal, this would lead to a greater apparent preference for feminised faces by girls at single-sex schools, and a greater apparent preference for masculinised faces by boys at single-sex schools.

It was unclear whether we should expect differences in face judgements in relation to both male and female faces, or only in relation to the faces commonly experienced. On the one hand, in laboratory testing sessions, visual adaptation effects can be instilled independently in male and female faces (Bestelmeyer et al., 2008, Little et al., 2005). Further, studies of contemporary partners have found similarity between an individual’s partner and opposite-sex parent, and not, or to a greater extent than, that individual’s same-sex parent (Bereczkei et al., 2008, Little et al., 2003), suggesting that changes in attractiveness judgements that are contingent upon differences in experience can be greater within sex. On the other hand, under some circumstances, adaptation effects generalise across face categories such as male and female faces (Webster et al., 2004) or adult and child faces (Cooper et al., 2006).

Section snippets

Stimuli

Digital photographs of 60 Caucasian children were separated evenly among the categories male and female, and younger (11–13 years) or older (13–15 years). The facial features (eyes, nose, etc.) of the digital images were marked out with 179 points using dedicated software (Tiddeman, Burt, & Perrett, 2001). The positions of these points were used to calculate the shape difference between the average face shape of the 15 older girls and the average face shape of the 15 older boys. Twelve

Effects of school type

Mixed model analysis (within-subjects factor: sex of target face [same- or opposite-sex to rater]; between-subjects factors: school type, sex and age group of judge; covariate: age in months) was carried out on the proportion of times each child chose the face whose manipulation matched their own gender (i.e. the proportion of times that the girls chose the feminine face as more attractive, and the proportion of times that the boys chose the masculine face as more attractive; in single-sex

Discussion

Pupils aged 11–16 from single-sex and mixed-sex schools made forced-choice preference judgements between feminised and masculinised versions of age-matched faces. All children tended to prefer feminised faces, but children at single-sex schools were significantly more likely to select the face manipulated to resemble their own gender than were children at mixed-sex schools. That is, overall, preference for facial femininity by girls, and preference for facial masculinity by boys, was

Acknowledgments

The data analysed here are also used in, and the methods section abridged from Saxton et al. (in press). The authors thank Andrew Boardman, Kristina Gilbertson, Gideon Gluckman, Shelly Kemp, Robert Kennedy, Jenny Saxton, Thom Scott-Phillips, Sue Toole (help with data collection), the Perception Lab, University of St. Andrews (useful comments and discussion), and the staff and pupils from George Heriot’s School, and other anonymous schools and social groups who provided participants. A.C.L. is

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