Journal of Experimental Psychology: Human Perception and Performance 2008, Vol. 34, No. 4, 884 – 893 Copyright 2008 by the American Psychological Association 0096-1523/08/$12.00 DOI: 10.1037/0096-1523.34.4.884 Are Attractive Men’s Faces Masculine or Feminine? The Importance of Type of Facial Stimuli Jennifer L. Rennels P. Matthew Bronstad and Judith H. Langlois University of Nevada, Las Vegas The University of Texas at Austin The authors investigated whether differences in facial stimuli could explain the inconsistencies in the facial attractiveness literature regarding whether adults prefer more masculine- or more feminine-looking male faces. Their results demonstrated that use of a female average to dimorphically transform a male facial average produced stimuli that did not accurately reflect the relationship between masculinity and attractiveness. In contrast, use of averages of masculine males and averages of feminine males produced stimuli that did accurately reflect the relationship between masculinity and attractiveness. Their findings suggest that masculinity contributes more to male facial attractiveness than does femininity, but future research should investigate how various combinations of facial cues contribute to male facial attractiveness. Keywords: facial attractiveness, masculinity, femininity, face perception, averaged faces O’Toole et al., 1998; Penton-Voak et al., 2001; Scheib, Gangestad, & Thornhill, 1999), but other studies found that adults perceive feminine male faces as attractive (Dunkle & Francis, 1990; Little, Burt, Penton-Voak, & Perrett, 2001; Little & Hancock, 2002; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes, Hickford, & Jeffery, 2000). Our interest lies in exploring why these inconsistencies occur, so that we can better understand the contribution of masculinity and/or femininity to male facial attractiveness. A considerable amount of research has been conducted to define what makes a face attractive. Most researchers agree that averageness, symmetry, and sexually dimorphic cues (masculine and feminine facial characteristics) all contribute to attractiveness (e.g., Fink & Penton-Voak, 2002; Grammer & Thornhill, 1994; Little, Penton-Voak, Burt, & Perrett, 2002; Rhodes, 2006; Thornhill & Gangestad, 1993). It is interesting to note that there is greater agreement among researchers about female than male facial attractiveness (e.g., Thornhill & Gangestad, 1999; Townsend & Wasserman, 1997; Wiederman & Dubois, 1998), particularly in regard to the contribution of sexually dimorphic cues. Researchers agree that femininity, rather than masculinity, contributes to female facial attractiveness (e.g., Fink & Penton-Voak, 2002; Grammer & Thornhill, 1994; Little et al., 2002; Rhodes, 2006; Thornhill & Gangestad, 1993), and these cues are desired regardless of the short- or long-term nature of the relationship (e.g., Buss & Barnes, 1986; Buss & Schmitt, 1993). In contrast, researchers disagree about how masculinity and femininity cues contribute to male facial attractiveness (Fink & Penton-Voak, 2002), and the desired cues appear dependent on the short- or long-term nature of the relationship and the phase of a woman’s ovulatory cycle (e.g., Johnston, Hagel, Franklin, Fink, & Grammer, 2001). Specifically, several studies found that adults perceive masculine male faces as attractive (Brown, Cash, & Noles, 1986; Cunningham, Barbee, & Pike, 1990; Dunkle & Francis, 1996; Grammer & Thornhill, 1994; Johnston et al., 2001; Beauty Is Good It is important to determine what makes a male face attractive because cues that differentiate high and low attractive individuals elicit discrepant judgments and treatments from perceivers that favor high attractive individuals, a phenomenon known as the “beauty is good” stereotype (Dion, Berscheid, & Walster, 1972). For example, perceivers judge attractive male and female adults as more occupationally and interpersonally competent, better adjusted, and more socially appealing than their less attractive counterparts. In regard to differential treatment, attractive adults receive more attention, cooperation, and help and tend to have more positive interactions than less attractive peers (Langlois et al., 2000). The responses evoked by an individual’s appearance may serve to either create a self-fulfilling prophecy (Snyder, Tanke, & Berscheid, 1977) or reinforce traits already characteristic of that individual (Scarr & McCartney, 1983) because there are behavioral differences seen in high and low attractive males and females as well: Attractive adults date more, are more extraverted, are higher in self-confidence and self-esteem, and enjoy more occupational success and higher wages (Langlois et al., 2000). These differences are large enough to be observed during actual social interactions and occur regardless of the perceiver or target’s gender and their familiarity with one another (Langlois et al., 2000). So, it is clearly important to understand what makes some faces more attractive than others and subsequently causes attractive individuals to evoke positive responses from others. Jennifer L. Rennels, Department of Psychology, University of Nevada, Las Vegas; P. Matthew Bronstad and Judith H. Langlois, Department of Psychology, The University of Texas at Austin. P. Matthew Bronstad is now at Schepens Eye Research Institute, Boston, Massachusetts. Correspondence concerning this article should be addressed to Jennifer L. Rennels, Department of Psychology, University of Nevada, Las Vegas, 4505 Maryland Parkway, Box 455030, Las Vegas, NV 89154-5030. E-mail: [email protected] 884 MALE FACIAL ATTRACTIVENESS Theories of Attractiveness and the Stimuli Used to Test the Theory Over the past 2 decades, various theories of attractiveness have been developed and empirically tested. In testing these theories, researchers have devised innovative ways of digitally manipulating facial stimuli to support or refute the various theories. The manipulations allowed researchers to carefully control stimulus variation. An unintentional outcome, however, was that certain manipulations produced results different from unaltered faces. By unaltered, we mean images of real or natural faces—images of faces that have not been manipulated by digital or other means. Averageness One theory that has received a great deal of attention and empirical support is that “averaged” faces are attractive (Langlois & Roggman, 1990). Adults rate faces whose configuration is close to the population average as attractive, and infants look longer at these faces than at faces adults rate as low attractive (e.g., Jones & Hill, 1993; Little & Hancock, 2002; Rhodes & Tremewan, 1996; Rubenstein, Kalakanis, & Langlois, 1999). Preferences for averageness may signal a preference for health or may be a by-product of the information-processing system in that people prefer the central tendency (prototype) of a category (Langlois & Roggman, 1990; Rhodes, 2006). Stimuli used in studies investigating the effects of averageness on attractiveness preferences were unaltered facial images, mathematically averaged facial images, and/or images altered to be more or less average (i.e., anticaricatures and caricatures). Averaged facial images are created by digitizing two images and computing the mean pixel values of the corresponding facial features on the two images to produce an average of the two images. Adults typically rate averaged faces comprised of at least 16 faces as attractive (e.g., Langlois & Roggman, 1990). Individual faces can be altered to be more or less average (anticaricatured or caricatured) by digitally warping the image toward or away from an averaged face (Rhodes & Tremewan, 1996). A metaanalysis found that the effect size of averageness on attractiveness is large and positive, although it is larger for digitally averaged and anticaricatured– caricatured images than for unaltered facial images (Rhodes, 2006). The discrepancy in effect size suggests that the type of facial stimuli used is an important consideration in facial attractiveness research. Symmetry Some researchers have suggested that it is the symmetry of average faces, rather than averageness, that makes the face attractive because symmetry advertises the quality of a potential mate (e.g., Alley & Cunningham, 1991; Grammer & Thornhill, 1994). Direct tests of this hypothesis, however, dispel this notion and support the idea that averageness is necessary and sufficient for a face to be attractive (e.g., Baudouin & Tiberghien, 2004; Langlois, Roggman, & Musselman, 1994; Rhodes, Sumich, & Byatt, 1999). Although facial symmetry is positively correlated with attractiveness (e.g., Grammer & Thornhill, 1994; Jones et al., 2004; PentonVoak et al., 2001; Perrett et al., 1999; Scheib et al., 1999), it contributes to facial attractiveness independent of averageness, and 885 the importance of averageness does not disappear even when symmetry is held constant (Rhodes et al., 1999). Stimuli used in studies investigating the effects of symmetry on attractiveness preferences were unaltered facial images and images altered to be more symmetrical in one of the following ways: by creating chimeras by splitting faces at the midline and copying and flipping the right (or left) side of the face onto the other side (e.g., Langlois et al., 1994) or by blending a facial image with its mirror image by averaging the two images together (e.g., Rhodes et al., 1999). Whereas the former technique tends to exaggerate abnormalities in the face, the latter technique confounds averaging with making the face more symmetrical. In line with these technical concerns, Rhodes’s (2006) meta-analysis demonstrates that when chimeras are used, the effect size of symmetry on attractiveness is large and negative; when blending is used, however, the effect size is moderate and positive; and when unaltered facial images are used, the effect size is small and positive. Once again, type of facial stimuli used appears important. Masculinity–Femininity Cues Other researchers have focused on how facial masculinity and femininity contribute to facial attractiveness more than, or in addition to, averageness (e.g., Grammer & Thornhill, 1994; Johnston et al., 2001; Perrett et al., 1998; Rhodes et al., 2000; Scheib et al., 1999). Masculinity cues in male faces and femininity cues in female faces should make it easier to identify their gender, an important factor in mating and attractiveness decisions (e.g., Enquist, Ghirlanda, Lundqvist, & Wachtmeister, 2002). This proposed positive correlation between male–female facial attractiveness and masculinity–femininity seems intuitive, but a number of studies have suggested the correlation between male facial attractiveness and masculinity is negative (Dunkle & Francis, 1990; Little et al., 2001; Little & Hancock, 2002; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). Given the importance of type of facial stimuli on the results of attractiveness studies, we compared the stimuli used in studies assessing preferences for masculinity and femininity in male faces to examine potential reasons for the discrepancies in results. Most studies finding preferences for masculine-looking male faces used unaltered faces (Brown et al., 1986; Cunningham et al., 1990; Dunkle & Francis, 1996; Grammer & Thornhill, 1994; O’Toole et al., 1998; Penton-Voak et al., 2001; Scheib et al., 1999), although there were some exceptions (e.g., Johnston et al., 2001). In contrast, most studies finding preferences for feminine-looking male faces used averaged faces that were dimorphically transformed to look more masculine or more feminine (Little et al. 2001; Little & Hancock, 2002; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). Dimorphically transformed faces are created by digitally increasing or decreasing the appearance differences between an averaged male and averaged female face (Little et al., 2001; Little & Hancock, 2002; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). Henceforth, we refer to male faces created via this procedure as dimorphically female-transformed (with the “female” referring to the gender of face used to make the transformation) or we specifically refer them to as masculinized or feminized faces. Rhodes’s (2006) meta-analysis confirmed that the effect size for the relationship between masculinity and attractiveness is moder- 886 RENNELS, BRONSTAD, AND LANGLOIS ate and negative when dimorphically female-transformed faces are used, whereas the relationship between masculinity and attractiveness is moderate and positive when unaltered faces are used. Rhodes (2006) concluded that “reported preferences for feminized male faces appear to be an artifact of using sex continua that do not adequately capture sexual dimorphism” (p. 211). She also expressed concerns about the extent to which averaged male faces appropriately capture masculine traits. No empirical research, however, has directly investigated these concerns. Our goals were to (a) understand whether dimorphic female-transformations appropriately represented male facial masculinity–femininity and (b) determine whether averaged male faces could be used to examine how sexually dimorphic cues affect male facial attractiveness. There are reasons why using dimorphically female-transformed faces may be problematic for concluding that feminine-looking males are more attractive than masculine-looking males. First, the masculinization and feminization procedures do different things to the transformed faces. The feminization procedure warps an averaged male face toward an averaged female face, whereas the masculinization procedure warps an averaged male face away from an averaged female face. It is possible these differences in techniques of moving toward or away from a female averaged face contributed to the averageness (anticaricaturing) or distortion (caricaturing) of the resulting face, respectively. There may be some debate as to whether moving the average of one gender toward the average of the other gender increases facial averageness, but it seems more likely to result in increased attractiveness than moving a face away from an average, which typically makes faces less average. Moreover, although dimorphic female-transformations clearly alter the original averaged face to look more masculine or more feminine, it is unclear whether or not this technique has external validity. For example, if the neural representations of men’s and women’s faces are separated to some degree, as Little, DeBruine, and Jones (2005) argue, then transforming a male face with a female average is not consistent with how faces are psychologically represented. Thus, it may be problematic to use feminized or masculinized male faces created via this technique to test the effects of sexual dimorphism on attractiveness. Mathematically averaged and symmetrically blended faces (which require averaging to create) produce effects similar in direction to effects of unaltered images when researchers test how averageness and symmetry contribute to facial attractiveness (Rhodes, 2006). These similarities suggest averaged faces may appropriately represent characteristics of unaltered facial images. Although use of averaged faces may inflate effect sizes (Rhodes, 2006), use of averaged faces may prove valuable for testing the direction of the relationship between sexual dimorphism and attractiveness. In two studies, we investigated how different image manipulations affect preferences for male facial stimuli. Specifically, we assessed adults’ attractiveness preferences for dimorphically female-transformed male facial images that were similar to images used in previous studies (e.g., Perrett et al., 1998; Rhodes et al., 2000) and compared those results with adult preferences for averages of masculine and feminine male faces using both a forcedchoice (Experiment 1) and a nonforced-choice method (Experiment 2). We used both methods because most studies finding preferences for feminine-looking male faces have used dimorphically female-transformed facial images and a forced-choice pro- cedure (Little et al., 2001; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000), whereas most studies finding preferences for masculine-looking male faces used unaltered images and nonforced-choice methods (Brown et al., 1986; Cunningham et al., 1990; Dunkle & Francis, 1996; Grammer & Thornhill, 1994; O’Toole et al., 1998; Penton-Voak et al., 2001; Scheib et al., 1999). Experiment 1 The purpose of Experiment 1 was to compare attractiveness judgments of dimorphically female-transformed male facial images with attractiveness judgments of averages of masculine and feminine male facial images. To replicate previous research findings, we included a masculinized, feminized, or averaged male face within the pairs for the dimorphically female-transformed condition—we created these stimuli using a technique similar to that of previous researchers (e.g., Perrett et al., 1998; Rhodes et al., 2000). The averaged-biased condition included a masculine-biased averaged face created from high masculine male faces, a nonbiased averaged face created from nonextreme high and low masculine male faces, or a feminine-biased averaged face created from low masculine male faces within the pairs—these types of stimuli have not been previously used in studies assessing the effects of sexual dimorphism on attractiveness. We used a forced-choice method for Experiment 1 so that we could directly compare our results with the results of previous studies—studies that used dimorphically female-transformed male faces also tended to use a forced-choice method (e.g., Little et al., 2001; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). Stimulus Faces (General Information) For both studies, we created facial stimuli via computer graphic techniques using a subset of the facial images described here. The facial images came from a database containing a large sample of male and female college students posed with neutral facial expressions and whose clothing was masked with a white sheet. The faces in the database were rated at different times by different groups of adults using a standardized procedure: At least 40 adults, with relatively equal amounts of male and female judges, rated the faces for attractiveness using a 1 (very unattractive) to 5 (very attractive) Likert scale with high interrater agreement (␣s ⫽ .90 or greater). From the database, we randomly selected 150 male and 150 female faces with the constraint that faces from low, medium, and high levels of attractiveness were equally represented within each gender (50 faces from each attractiveness level) so as to represent a wide range in facial attractiveness. Mean attractiveness ratings ranged from 1.03 to 4.06 (M ⫽ 2.39, SD ⫽ 0.82) for the male faces and from 1.33 to 4.19 (M ⫽ 2.53, SD ⫽ 0.72) for the female faces. Different groups of adults rated the faces on masculinity–femininity using a 1 (very feminine) to 5 (very masculine) Likert scale. Interrater agreement was highly reliable (␣ ⫽ .97 for the male faces and .98 for the female faces). Ratings ranged from 1.80 to 4.65 (M ⫽ 3.53, SD ⫽ 0.52) for the male faces and from 1.25 to 4.12 (M ⫽ 2.49, SD ⫽ 0.61) for the female faces. Like previous studies that used unaltered faces, we found that the correlation between masculinity and attractiveness ratings for the male faces was positive and significant (r ⫽ .36, p ⬍ .001). MALE FACIAL ATTRACTIVENESS We standardized all facial images to be the same size, have the same background, and be of similar brightness and contrast using Adobe Photoshop (Version 6.0, Macintosh). Henceforth, we refer to these faces as the set of male facial images and the set of female facial images. Method Participants. A sample of 77 undergraduate students (34 male) participated in the dimorphically female-transformed condition: 53% Caucasian, 22% Asian American/Pacific Islander, 21% Hispanic, 3% African American, and 1% did not indicate race or ethnicity. An additional participant’s data were collected but deleted due to a data-recording error. Another independent sample of 143 undergraduate students (54 male) participated in the averagedbiased condition: 47% Caucasian, 17% Hispanic or Spanish origin, 15% Asian American/Pacific Islander, 10% mixed race, 8% African American, and 3% indicated other or did not indicate race or ethnicity. We had more participants for the averaged-biased condition because the dimorphically female-transformed condition was a replication of previously reported research (e.g., Perrett et al., 1998; Rhodes et al., 2000), whereas the averaged-biased condition was a new study. Participants received credit for partial fulfillment of their research requirements for an introductory psychology class. Facial stimuli. For the dimorphically female-transformed condition, the stimuli consisted of three male facial images created via Morph 2.5 (1992–1994) software. As in previous studies, we created images of an averaged male face, a masculinized version of the averaged male face, and a feminized version of the averaged male face (e.g., Perrett et al., 1998; Rhodes et al., 2000). We created the averaged male face by morphing together 32 digitized images of individual male faces randomly selected from the set of male facial images. Using keypoints placed around the facial structure and features of one image, we mapped these same keypoints onto the corresponding locations of another facial image so that the mathematical (pixel) values of the points on the two images could be averaged to create a 2-face composite. We then averaged the 2-face composite with another 2-face composite to create a 4-face composite. The process continued until the composite comprised 32 faces because adults rate 32-face composites as attractive, and there is little to be gained from adding more faces to the composite (Langlois & Roggman, 1990). 887 To masculinize the averaged male face, we then created an averaged female face by morphing together 32 digitized images of randomly selected female faces from the set of female facial images. We created the masculinized version of the averaged male face by warping the averaged male face 50% away from the averaged female face, exaggerating the appearance differences between the averaged male and female faces. To create the feminized version of the averaged male face, we warped the averaged male face 50% toward the averaged female face, reducing the appearance differences between the averaged male and female faces (see Perrett et al., 1998 and Rhodes et al., 2000 for details). Figure 1 shows the masculinized, averaged, and feminized male facial images. For the averaged-biased condition, the stimuli consisted of three averaged faces created via Morph 2.5 software: A feminine-biased averaged male; a nonbiased averaged male; and a masculinebiased averaged male. We created each of these averages from 32 individual faces using the same procedure as described in the dimorphically female-transformed condition for creating the averaged face: The feminine-biased averaged male face consisted of the 32 male faces rated lowest in masculinity from the set of male facial images, and the masculine-biased averaged male face consisted of the 32 male faces rated highest in masculinity from the set of male facial images, with 1 exception. There was 1 highly masculine male face from the top 32 masculine male faces that could not be averaged with the other male faces; the location of his features differed drastically from the other males due to his extremely large forehead, creating a blurry image. Thus, the face rated 33rd in masculinity was included in the masculine-biased average. To create the nonbiased averaged face, we wanted to avoid using extremely masculine or extremely feminine faces. Plus, we wanted to ensure that the nonbiased averaged male had a facial masculinity as close as possible to the midpoint of the masculine-biased and feminine-biased averaged faces. Therefore, we could not use the averaged face included in the dimorphically female-transformed condition. Instead, we used the 16 faces in the higher half of the 32 faces rated low in masculinity and the 16 faces in the lower half of the 32 faces rated high in masculinity to create the nonbiased averaged face. Having the nonbiased average and the averaged face located approximately midway between the masculine-biased and feminine-biased facial images and the masculinized and feminized facial images, respectively, allowed us to Figure 1. The masculinized, averaged, and feminized versions of the digitally transformed male faces used in Experiments 1 and 2 (dimorphically female-transformed condition). RENNELS, BRONSTAD, AND LANGLOIS 888 more easily compare the two conditions. See Figure 2 for pictures of the masculine-biased, nonbiased, and feminine-biased averaged male facial images. Procedure. Participants chose which face was more attractive within one of the following pairs in the dimorphically femaletransformed condition: (a) the masculinized male face paired with the averaged male face (n ⫽ 25), (b) the masculinized male face paired with the feminized male face (n ⫽ 26), or (c) the averaged male face paired with the feminized male face (n ⫽ 26). Participants rated which face was more attractive within one of the following pairs in the averaged-biased condition: (a) the masculine-biased averaged male face paired with the nonbiased averaged male face (n ⫽ 48), (b) the masculine-biased averaged male face paired with the feminine-biased averaged male face (n ⫽ 48), or (c) the nonbiased averaged male face paired with the feminine-biased averaged male face (n ⫽ 47). Across participants, we altered the sides on which participants saw the paired faces so as to avoid any side bias. In line with research using unaltered male faces that have found preferences for masculinity, we predicted that participants would prefer the more masculine than feminine averaged faces in the averaged-biased condition. This prediction was confirmed: Participants chose the more masculine of the two faces as being more attractive, 2(1, N ⫽ 143) ⫽ 18.19, p ⬍ .001. Table 1 shows participants’ choice of face according to condition and type of face pair and demonstrates the direction of effects in each condition held regardless of the particular face pair. When masculine-biased or feminine-biased averaged male faces were used as stimuli, adults preferred more masculine male faces. Dimorphically female-transformed masculinized and feminized averages, however, produced the opposite results. Because the findings for the masculine-biased and feminine-biased averages are in agreement with studies using unaltered male faces, we suggest that facial averages retain masculinity cues representative of the population of faces from which they were configured. Thus, masculine-biased and feminine-biased facial averages may serve as useful stimuli for testing effects of sexual dimorphism. Results and Discussion To determine how the type of face seen in the two conditions affected participants’ choice of the most attractive face, we conducted a multinomial logistic regression analysis. Our dependent variable was choice of face, coded as the more masculine or more feminine of the two faces within the pair. For example, if participants in the dimorphically female-transformed condition chose the averaged face rather than the masculinized face in Pair 1, we coded their choice as feminine because it was the more feminine of the two faces. The independent variables were condition and gender of participant. As predicted, we found a significant main effect for condition, 2(1, N ⫽ 220) ⫽ 20.32, p ⬍ .001. To better understand the direction of the condition effect, we conducted chi-square analyses for choice of face in each condition across each type of pair. Because the faces in the dimorphically female-transformed condition were modeled after faces created in previous studies, we predicted that we would replicate previous findings—participants would prefer the more feminine than more masculine versions of the faces (e.g., Perrett et al., 1998; Rhodes et al., 2000). This prediction was confirmed: Participants chose the more feminine of the two faces as being more attractive, 2(1, N ⫽ 77) ⫽ 5.73, p ⫽ .009. Experiment 2 Most studies using dimorphically female-transformed faces have also used a forced-choice procedure like the one we used in Experiment 1 (Little et al., 2001; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). To overcome the general confounding of using forced-choice procedures with dimorphically female-transformed faces, we reran the study using a nonforcedchoice measure. We expected the nonforced choice procedure to better represent participants’ preferences. For example, participants may find the faces from which to choose to be equally attractive or equally unattractive, but the forced-choice method does not permit this response. The literature is replete with evidence of problems with the reliability of forced-choice methods used in assessments of personality, achievement motivation, personnel decisions, knowledge, and vocational choices (Grosse & Wright, 1985; Jackson, Neill, & Bevan, 1973; Nederhof, 1985; Ray, 1980, 1982; Travers, 1951). The problems of reliability result from forcing individuals to make decisions that were not necessarily accurate characterizations of the person being rated (i.e., overestimating or underestimating the quality of the individual being rated; Travers, 1951). This problem can be extended to Figure 2. The masculine-biased, nonbiased, and feminine-biased averaged male faces used in Experiments 1 and 2 (average-biased condition). MALE FACIAL ATTRACTIVENESS 889 Table 1 Percentage of Participants in Each Condition Choosing the More Masculine or More Feminine Face for Each Type of Pair in Experiment 1 Dimorphically female-transformed face pairs Average-biased face pairs Choice Masculinizedaveraged Masculinizedfeminized Averagedfeminized Masculinebiased-nonbiased Masculine-biasedfeminine-biased Nonbiasedfeminine-biased Masculine Feminine 36 64 38 62 35 65 71 29 73 27 60 40 Note. Significant results are indicated in bold. studies of attractiveness in that researchers may conclude that the most commonly chosen face is more attractive than it actually is. Examining whether the preferences participants exhibited in Experiment 1 maintain or change when a nonforced-choice procedure is used helps us to determine whether the robustness of the results depends on method of preference assessment. Method Participants. A new sample of 77 undergraduate students (40 female) participated in the dimorphically female-transformed condition: 65% Caucasian, 17% Asian American/Pacific Islander, 9% Hispanic, 5% African American, and 4% indicated other. An additional participant’s data were collected but deleted because of a data-recording error. Another independent sample of 144 undergraduate students (96 female, 1 unknown) participated in the averaged-biased condition: 42% Caucasian, 23% Hispanic or Spanish origin, 14% Asian American/Pacific Islander, 11% mixed race, 8% African American, and 3% indicated other or did not indicate race or ethnicity. An additional participant failed to complete the data form. Sample size differences for the two conditions mirrored sample size differences for the two conditions in Experiment 1. Participants received credit for partial fulfillment of their research requirements for an introductory psychology class. Facial stimuli. Stimulus faces were the same images used in Experiment 1 (see Figures 1 and 2). Procedure. The procedure was similar to Experiment 1 except that participants could choose one face as more attractive than the other or choose both faces as equally attractive. This nonforcedchoice procedure enabled us to more easily compare results with Experiment 1 than would a rating measure, which is a common measure in studies using unaltered facial images (e.g., O’Toole et al., 1998; Penton-Voak et al., 2001; Scheib et al., 1999). Results and Discussion Because participants had three potential responses for each pair of stimuli in this study, as opposed to two potential responses in Experiment 1, there was no statistical analysis that we could use to directly compare the results of the two studies. We did, however, execute a multinomial logistic regression analysis similar to the one in Experiment 1 and compared how responses differed when participants had the choice of stating both faces were equally attractive or were forced to choose a single face. Choice of face was the dependent variable (i.e., choosing the more masculine or more feminine face as more attractive or both faces as equally attractive), and condition and participant gender were the independent variables. Once again, we found that participants responded differently depending on whether they participated in the dimorphically female-transformed or averaged-biased condition, 2(2, N ⫽ 221) ⫽ 27.60, p ⬍ .001. To determine the direction of effects in each of the two conditions, we executed chi-square analyses for choice of face across each type of comparison. In the dimorphically female-transformed condition, participants were again more likely to choose the more feminine face as being more attractive, 2(2, N ⫽ 77) ⫽ 11.64, p ⫽ .002; this finding, however, differed depending upon the type of comparison. Within both the feminized and masculinized face pair and the averaged and masculinized face pair, participants chose the more feminine face as more attractive. Within the feminized and averaged face pair, however, participants showed no significant difference in choice (see Table 2). Table 2 Percentage of Participants in Each Condition Choosing the More Masculine or More Feminine Face or Both Faces as Equally Attractive for Each Type of Pair in Experiment 2 Dimorphically female-transformed face pairs Average-biased face pair Choice Masculinizedaveraged Masculinizedfeminized Averagedfeminized Masculine-biasednonbiased Masculine-biasedfeminine-biased Nonbiased-femininebiased Masculine Feminine Both 20 60 20 19 58 23 19 35 46 59 14 27 64 19 17 33 31 35 Note. Significant results are indicated in bold. RENNELS, BRONSTAD, AND LANGLOIS 890 In the averaged-biased condition, participants were more likely to choose the more masculine face as being more attractive, 2(2, N ⫽ 144) ⫽ 23.29, p ⬍ .001. This finding, however, differed depending upon the type of comparison. Within both the masculine-biased and nonbiased averaged face pair and the masculine-biased and feminine-biased averaged face pair, participants chose the more masculine face as more attractive. Within the nonbiased and feminine-biased averaged face pair, however, participants showed no significant choice (see Table 2). The results in the forced-choice and nonforced-choice versions of the study are similar, but the differences within the averaged and feminized pairs and the nonbiased and feminine-biased averaged pairs in the two different types of procedures are informative (cf. Table 1 with Table 2). Note that when either the masculinized or masculine-biased averaged face is not included in the comparison and participants have the opportunity to rate both faces as equally attractive, they perform differently (they show no clear choice) than when the masculinized or masculine-biased averaged face is included in the comparison (they are more likely to demonstrate little preference for the masculinized male face and a strong preference for the masculine-biased averaged face). The differences in responding signify that there are important appearance differences between the masculinized and the masculine-biased averaged male faces. General Discussion The results of male facial attractiveness studies are inconsistent: Some have found that adults prefer more masculine-looking male faces, whereas others have found that adults prefer more femininelooking male faces (cf. Brown et al., 1986; Cunningham et al., 1990; Dunkle & Francis, 1996; Grammer & Thornhill, 1994; Johnston et al., 2001; O’Toole et al., 1998; Penton-Voak et al., 2001; Scheib et al., 1999, with Dunkle & Francis, 1990; Little et al., 2001; Little & Hancock, 2002; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). These differences in findings have inspired several researchers to provide theoretical explanations for the discrepancies (e.g., Johnston et al., 2001; Little et al., 2002; Penton-Voak et al., 1999; Perrett et al., 1998). In an effort to understand what makes a male face attractive, we examined whether methodology (i.e., stimulus differences) could account for these inconsistencies. The results from our studies strongly suggest that using female facial averages to dimorphically transform male facial images creates faces that do not accurately reflect the relationship between attractiveness and masculinity– femininity. Differences in Stimuli Cause Differences in Results In Experiment 1, using a forced-choice procedure, adults chose the more feminine of the transformed faces as more attractive in the dimorphically female-transformed condition, preferring the feminized to masculinized male faces. These results sharply contrasted with those obtained in the average-biased condition, wherein adults chose the more masculine of the averaged faces as more attractive, preferring the average of masculine men’s faces to the average of feminine men’s faces. We obtained similar results in Experiment 2 using a nonforced-choice procedure, with some exceptions. Specifically, the results from the nonforced-choice procedure suggested that participants found the masculinized male face less attractive than the alternatives and the masculine-biased averaged male face more attractive than the alternatives. When those faces were not included in the pairs, there appeared to be no strong preferences. The results from the masculine-biased and feminine-biased male facial averages in the average-biased condition were consistent with studies that used unaltered facial images (i.e., masculinity was positively and significantly associated with male facial attractiveness) and were inconsistent with studies that used dimorphically female-transformed facial images. Whereas the association between masculinity and attractiveness obtained with averaged faces is congruent with the correlation between attractiveness and masculinity of unaltered faces, the association between masculinity and attractiveness obtained with dimorphically femaletransformed faces is not. We suggest that averages of a particular sample of faces may be useful for testing effects of sexual dimorphism on facial attractiveness because averages retain information about the masculinity–femininity of the face sample. The results from the dimorphically female-transformed faces in Experiment 2 suggest participants did not find the masculinized male attractive, and subsequently defaulted to preferring the feminized male. To better understand why we found this result, refer to the masculinized male in Figure 1. Recall that this face was created by warping a male facial average away from a female facial average, which caused caricaturing of masculine (or nonfeminine) facial characteristics. Caricaturing an averaged male face away from an averaged female face greatly affects face width—the masculinized male face in Figure 1 is stretched wide and is reminiscent of athletes who have used steroids. The distortion from the stretching likely contributed to little preference for the masculinized male face in Experiments 1 and 2. Moreover, some researchers have suggested that the neural representations of men’s and women’s faces are separated to some degree (Little et al., 2005), so transforming a male facial average with a female facial average may not be consistent with how faces are psychologically represented. We therefore caution against using othergender images to make facial transformations, at least for studies examining facial attractiveness and masculinity–femininity. Dimorphically female-transformed male faces represent the relationship between attractiveness and masculinity–femininity differently from how it is represented in unaltered male and averaged faces, suggesting that dimorphically female-transformed male faces are not ecologically valid. These findings point toward problems with studies that used such images to conclude that feminine-looking males are attractive (Little et al., 2001; Little & Hancock, 2002; Penton-Voak et al., 2003; Perrett et al., 1998; Rhodes et al., 2000). We therefore have caveats about using dimorphically female-transformed masculinized and feminized male facial stimuli for testing hypotheses about male facial attractiveness, and we recommend using masculine- or feminine-biased averages instead. Implications for Male Facial Attractiveness Masculinity significantly contributes to male facial attractiveness. Studies using unaltered male faces find a positive relationship between masculinity and attractiveness (Brown et al., 1986; Cunningham et al., 1990; Dunkle & Francis, 1996; Grammer & MALE FACIAL ATTRACTIVENESS Thornhill, 1994; O’Toole et al., 1998; Penton-Voak et al., 2001; Scheib et al., 1999). The correlation between the attractiveness and masculinity ratings from our set of 150 male facial images was significant and positive. In addition, adults rated a masculinebiased averaged male face as more attractive than nonbiased or feminine-biased averaged males. Thus, a summary representation of masculine males is considered more attractive than a summary representation of males in general. Although there should be no disputing the importance of masculinity, it is clear that because of the moderate correlation between masculinity and attractiveness, masculinity in and of itself does not make a male face attractive. Participants’ lack of preference for the dimorphically female-transformed, masculinized male in Experiments 1 and 2 suggests that extremes in masculinity are not attractive. This finding replicates previous research that found adults seem to prefer a male face with both mature and babyish features (Cunningham et al., 1990). Such findings suggest that different combinations of cues may define male facial attractiveness. For example, because of the established importance of masculinity cues for male facial attractiveness, a greater amount of masculine than feminine features may make averageness and symmetry cues secondary to the masculinity cues. In contrast, an extreme amount of masculine or feminine features may make the presence of averageness and symmetry cues necessary (primary) for the male face to be considered attractive. Researchers have hinted at the importance of these different combinations of cues (e.g., Fink & Penton-Voak, 2002), but little research has specifically manipulated different weightings of averageness, symmetry, and masculinity–femininity cues to determine their combined role in contributing to male facial attractiveness. Others have proposed, in terms of stimulus control theory, that preferences for averageness and sexual dimorphism are solutions to the problem of finding a mate of the appropriate species and sex (Enquist et al., 2002), but again the ideal combination of these cues has not been assessed. Testing such ideas could require digital manipulations of facial images. Before using digitally manipulated facial images to test a particular hypothesis regarding male facial attractiveness, we highly encourage face perception researchers to first test the ecological validity of their facial stimuli. Implications for Face Perception Research Given the concerns about the ecological validity of dimorphically female-transformed faces, our findings have implications for other studies that have used these images (e.g., Penton-Voak, Jacobson, & Trivers, 2004; Penton-Voak & Perrett, 2000; PentonVoak et al., 1999). For example, researchers have used such faces to make conclusions about how female preferences for certain types of male faces shift during the ovulatory cycle (Little et al., 2002; Penton-Voak & Perrett, 2000; Penton-Voak et al., 1999). If women’s preferences do shift during their ovulatory period, it is now unclear what the direction of this shift is. Until studies assessing how ovulatory phase affects female’s preferences for male faces are replicated with unaltered facial images, the field is ill-equipped to make strong conclusions about the nature of these shifts. Researchers have also used dimorphically female-transformed faces to make claims about the relationship between self and others’ ratings of attractiveness (Penton-Voak et al., 2003) and to 891 explore cross-cultural differences in female preferences for males (Penton-Voak et al., 2004). In addition, researchers have used variations of the dimorphic transformation techniques to create “juvenilized” faces by warping an averaged adult male or averaged adult female face toward an averaged child male or averaged child female face, respectively (Hanae, Gyoba, Kamachi, Mukaida, & Akamatsu, 2004; Ishi & Gyoba, 2001). Because of the caveats associated with using such transformations for creating stimulus faces, the results from these studies should be interpreted with caution until the findings are replicated with unaltered facial images. Note that we are not claiming it is never appropriate to use transformed faces as stimulus materials in research. If the goal is to gain a better understanding of perceptual processes (e.g., categorical perception), then using transformed facial images may be appropriate (e.g., Beale & Keil, 1995). If the goal, however, is to model natural facial variation, then researchers should ensure the ecological validity of their faces before generalizing conclusions to actual faces. Indeed, Johnston et al. (2001) used a different procedure for manipulating the masculinity–femininity of male faces than the procedure we examined in our studies. They found results more congruent with those using unaltered real faces, so it would be beneficial to further examine the ecological validity of facial stimuli created via this technique. Limitations Because our sample was restricted in age and race, we do not claim that these results will necessarily generalize beyond the population sampled. The sample of faces we used, however, were very typical of samples used in the published literature (see Rhodes, 2006, review), which enabled us to compare our results with those of other published studies. Plus, strong cross-cultural agreement about who is and is not attractive (Langlois et al., 2000) suggests that our findings may be generalizable to other face populations. Moreover, factors other than stimulus faces may impact the results of male facial attractiveness studies. Understanding male facial attractiveness requires an investigation of how stimulus faces, rater characteristics, context, and the question being asked (e.g., attractiveness preferences in general vs. mating preferences) interact with one another to affect preferences. Conclusions By exploring the problems associated with certain stimuli used in male facial attractiveness studies, we hope to have resolved the debate about whether masculine or feminine male faces are more attractive. Our results clearly point in favor of masculinity contributing more than femininity to attractiveness in men. 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Received April 26, 2006 Revision received July 2, 2007 Accepted December 13, 2007 䡲 E-Mail Notification of Your Latest Issue Online! Would you like to know when the next issue of your favorite APA journal will be available online? This service is now available to you. Sign up at http://notify.apa.org/ and you will be notified by e-mail when issues of interest to you become available!
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