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Physical strength and gender identification from dance movements
Personality and Individual Differences 76 (2015) 13–17
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Physical strength and gender identification from dance movements Carla Hufschmidt a, Bettina Weege a, Susanne Röder b, Katarzyna Pisanski c, Nick Neave d, Bernhard Fink a,⇑ a
Institute of Psychology and Courant Research Center Evolution of Social Behavior, University of Göttingen, Kellnerweg 6, D-37077 Göttingen, Germany Department of General Psychology and Methodology, University of Bamberg, Markusplatz 3, D-96047 Bamberg, Germany c Department of Communication Studies, Center for Behavior, Evolution and Culture, University of California, Los Angeles, CA 90095 United States d Department of Psychology, Northumbria University, Newcastle upon Tyne NE1 8ST, United Kingdom b
a r t i c l e
i n f o
Article history: Received 5 November 2014 Received in revised form 20 November 2014 Accepted 21 November 2014
Keywords: Dance Gender identification Physical strength Handgrip Men Women
a b s t r a c t Here we show that gender identification of male (but not female) heterosexual, right-handed dancers correlates with physical strength (measured via handgrip strength) after controlling for the effect of body-mass-index on strength. Using optical motion capture technology, we collected the dance movements of men and women for subsequent animations of uniform shape- and texture-standardized virtual characters (avatars). Short video clips (15 s) of these movements were presented to male and female adults and children, who were asked to identify the gender of the avatar. Gender identification performance was significantly higher than chance for both adults and children. Among adults (but not among children) the avatars of male dancers who were physically stronger were perceived as males significantly more often than were the avatars of male dancers who were physically weaker. There was no relationship between strength and gender identification for female dancers. We conclude that physical strength affects gender identification from human dance movements at least for male dancers, and that prepubertal children might not be sensitive to strength cues in dance movements. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Gender constitutes a key facet of an individual’s personal and social identity as it influences virtually all aspects of social communication and social life (Deaux & Major, 1987; Money & Ehrhardt, 1972; West & Zimmerman, 1987). The expression of gender, and our ability to differentiate the gender of others, is often influenced by various physical traits and characteristics. Research suggests that observers can use sexually dimorphic physical features such as body height, weight, muscularity, body hair, facial morphology, and voice pitch, to accurately differentiate adult men and women (Neave, 2008; Puts, 2010). Gender identification has been demonstrated in infants aged 10 months old (Levy & Haaf, 1994) showing that the cognitive abilities required for categorizing social information, such as gender, are present early in life. Studies using dynamic point-light walkers have demonstrated that adult observers can also accurately judge gender from gait (i.e., an individual’s walk) in the absence of all other physical or behavioural cues to gender (Barclay, Cutting, & Kozlowski, 1978; Kozlowski & Cutting, 1977, 1978; Mather & Murdoch, 1994; Sumi, 2000; Troje, 2002). The ability to identify the gender of a
⇑ Corresponding author. Tel.: +49 551 39 9344; fax: +49 551 39 7299. E-mail address: bernhard.fi[email protected] (B. Fink). http://dx.doi.org/10.1016/j.paid.2014.11.045 0191-8869/Ó 2014 Elsevier Ltd. All rights reserved.
person based simply on motion cues implies characteristic differences in the way that men and women move their bodies (Pollick, Kay, Heim, & Stringer, 2005; Pollick, Paterson, Bruderlin, & Sanford, 2001). Cutting, Proffitt, and Kozlowski (1978), for example, reported that men swing their shoulders from side to side more than do women while walking, whereas women swing their hips from side to side more than do men. Indeed, when asked to make judgements of the gender of an animated walker, observers focus primarily on the shoulders and hips (Saunders, Williamson, & Troje, 2010). Other studies suggest that the motion of the legs provides important sex-relevant information (Todd, 1983; Yamasaki, Saki, & Torii, 1991). Thus, gait appears to communicate cues to gender that adult observers are sensitive to. It is not clear what factors contribute to differences in the way that men and women move, and whether observers utilize these same factors to assess gender. Recent work suggests that sexually dimorphic traits affect body movement in a way that may provide observers with socially relevant, sex-specific information. Sexually dimorphic characteristics develop under the influence of sex steroid hormones, most notably testosterone, and provide the basis for many subsequent observations of sex-specific behaviours in adulthood (Neave, 2008). In perceptual studies of body movement, physical strength appears to be a key sexually dimorphic characteristic affecting social perception. Men are on average twice as strong as are women (Miller, MacDougall, Tarnopolsky, & Sale,
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1993). Strength has been linked to the perceived quality and attractiveness of men’s dance movements (McCarty, Hönekopp, Neave, Caplan, & Fink, 2013). Men’s dance movements also affect other’s perceptions of their sensation seeking behaviour (Hugill, Fink, Neave, Besson, & Bunse, 2011), which correlates positively with men’s physical strength (Fink, Hamdaoui, Wenig, & Neave, 2010). Because men’s dance movements appear to indicate strength, a highly sexually dimorphic trait, it follows that physical strength may mediate observer’s ability to differentiate men from women through their body movements. Compared to gait, dance is a much more complex human body movement and one that is cross-culturally universal (Hanna, 1987; Kaeppler, 1978; Kurath, 1960). Dance is typically characterized by various gender-specific movements (Hanna, 1987, 2010) and appears to play an important role in courtship behaviour (for reviews, see Fink, Weege, Neave, Ried, & do Lago, 2014). Indeed, unlike gait, the main purpose of dance is not locomotion but rather to express oneself or to impress a counterpart. Thus, dance movements may express salient cues that facilitate gender identification more readily than do other types of body movement, including gait. A large body of research has examined the ontogeny and development of gender expression and gender identification. This work suggests that behavioural gender differentiation develops at a young age – often the ability is present in infants and toddlers – but becomes increasingly pronounced and stereotyped with age and social experience (see, e.g., Bussey & Bandura, 1999; Martin, Ruble, & Szkrybalo, 2002; Yee & Brown, 1994). Past work has shown that infants as young as 4–7 years old show gendertypicality in their body movements and gait (König, Schölmerich, & Troje, 2008), and that children as young as 5 years old can accurately assess emotion from body and dance movements (Boone & Cunningham, 1998). However, no study has examined the ability of young children to accurately identify gender from body movements, including dance. In the present study, we tested whether the ability of male and female adults (aged 18–29 years) and children (aged 6–10 years) to accurately identify gender from dance movements was facilitated by the physical strength of the dancers after controlling for differences in the dancers’ body size. Male and female dancers were presented in the form of gender-neutral avatars in video clips, created using motion capture technology. We predicted that both adults and children would correctly discriminate the gender of dancers. However, because sexual dimorphism in strength develops around the time of puberty (after age 11) under the influence of testosterone (Seger & Thorstensson, 2000), and appears to play a key role in indicating mate quality (Hugill et al., 2011), any facilitating effect of strength on gender perception from dance may be more pronounced among adults than children. Thus, we predicted that adults would rely more heavily on sexually dimorphic strength cues to gauge the gender of male and female dancers than would children.
2. Methods 2.1. Stimuli We recruited 167 participants (81 men, 86 women; aged 18– 42 years; mainly graduate and undergraduate students of Northumbria University, U.K.) as part of a large-scale study on body movement, in which participants also reported sexual orientation and handedness. Height (cm) and weight (kg) measurements were collected to calculate body-mass-index (BMI; mass/height (m)2) – a known correlate of handgrip strength (Chandrasekaran, Ghosh, Prasad, Krishnan, & Chandrasharma, 2010). Handgrip strength
(kgf) was measured using a hand dynamometer (Takei Kiki Kogyo, Japan). Participants were asked to perform a maximum force trial with each hand (‘‘Squeeze as hard as you can’’). Strength measurements were collected twice for each participant and the means of two recordings were calculated. Dance movements were recorded using a 12-camera optical motion-capture system (Vicon, Oxford) running Vicon Nexus software. None of the participants were professional dancers and none reported physical injuries or current health problems that could have affected their movements. Thirty nine 14 mm retro-reflective markers were attached to each participant in accordance with the Vicon Plug-In-Gait marker set to capture all major body structures. Following calibration, participants danced for 30 s to a popular song, of which only the core drumbeat was presented to eliminate possible music likeability effects. No specific instruction was given on how they should dance. These motion-capture data were applied to a featureless, gender-neutral humanoid character (avatar), using Autodesk MotionBuilder (Autodesk, Inc., San Rafael, CA, USA) and finally rendered in the form of 773 632 pixel video clips (see Fig. 1). Fifteen-second sequences were extracted from the middle of each dance video for the subsequent gender identification task. For one man and six women, no dance movement video could be produced due to incomplete motion capture data. Thus the final set of stimuli used for presentation in subsequent rating studies included dance movement videos of 80 male and 80 female participants. 2.2. Rating studies Our sample of adult raters comprised 49 men and 51 women, aged 18–29 years (M = 22.80, SD = 2.76), mainly heterosexual by self-report (94%), who were recruited predominantly from the student population at the University of Göttingen (Germany). Each participant viewed a random selection of 40 clips out of the total set of dance movement videos. Following each clip, the participant was prompted to indicate whether the dancer was male or female by clicking a button below the video. Clips were presented in a serial, randomised order, centred on a 15.4’’ laptop screen (1440 900 pixels resolution) using Medialab 2012 (Empirisoft Inc., New York) presentation software. The core audio track played during dance recording was not presented to raters. Our sample of child raters comprised 43 boys and 42 girls between the ages of 6 and 10 years (M = 8.19, SD = 1.16) recruited from an elementary school in Lower Austria (Austria). Permission for testing was obtained from legal guardians and the methodology was approved by the ethical committee of the University of Göttingen. The experimental setup was the same as for adult participants, but children viewed 10 videos out of the entire set, owing to time constraints with children’s availability and concentration capacity. 2.3. Statistical analysis For the statistical analysis, we calculated the number of trials on which the gender of each dancer was correctly identified. Children’s gender identification performance data were not available for two dancers due to the randomization procedure. We focused on right handgrip strength, which was found to correlate highly positively with left handgrip strength in our sample (r = .94, p < .001). Moreover, we considered only those dancers for analysis who claimed to be exclusively heterosexual and right-handed, rendering the final sample size as N = 135 dancers (69 males, 66 females; M = 21.33, SD = 4.12). Significance tests for group comparisons in gender identification performance were two-tailed and correlations of gender identification performance and handgrip strength were one-tailed with an alpha set to 0.05.
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Fig. 1. Snapshots of the creation process of a virtual dance character. The initial stick figure with captured markers (left), application of the motion data to the actor (middle) and the final avatar for presentation (right).
3. Results Gender identification performance in both adults and children was significantly better than expected by chance (0.5) (adults: M = .78, SD = .19, t134 = 17.01, p < .001; children: M = .68, SD = .25, t132 = 8.59, p < .001) with adults performing significantly better than children in this task (t132 = 5.00, p < .001). We found no significant effect of the rater’s sex on gender identification performance among adult raters (F1,133 = .26, p = .61). However, there was a significant effect of the dancer’s sex (F1,133 = 4.48, p < .05) with gender identification of male dancers (82%) higher than that of female dancers (75%) (see Table 1). In addition, there was a significant interaction effect of the raters’ and the dancers’ sex on gender identification performance (F1,133 = 5.00, p < .05). Males performed slightly better than females in identifying males by their dance movements (84% vs. 80%, respectively) and females performed slightly better than males in identifying females by their dance movements (76% vs. 74%, respectively). Among children, there were no significant effects of the raters’ sex (F1,114 = 1.53, p = .22) and no significant interaction between the raters’ and the dancers’ sex on gender identification performance (F1,114 = .84, p = .36). Table 1 reports descriptive statistics of physical measurements of male and female dancers. There were significant sex differences for height, weight, BMI, and handgrip strength, wherein men were physically larger and stronger than were women. We ran partial
correlations to test the influence of handgrip strength on gender identification performance from dance movements while controlling for body-mass-index. Considering adult’s gender identification performance (both males and females together), handgrip strength was significantly positively correlated with gender identification performance (rp = .20, p < .05). Running these correlations separately for male and female dancers, there was a significant positive correlation between handgrip strength and gender identification performance in male but not in female dancers (male dancers: rp = .22, p < .05; female dancers: rp = .07, p = .29). A more detailed inspection of these relationships conducted separately for male and female raters revealed significant relationships between handgrip strength and gender identification of male (but not female) dancers among both male and female raters (male dancers, male raters rp = .21, p < .05; male dancers, female raters: rp = .22, p < .05; female dancers, male raters rp = .06, p = .32; female dancers, female raters: rp = .09, p = .23). Testing these relationships in children revealed no significant relationships throughout.
4. Discussion The results of this study show that adults and children easily accomplish gender identification from dance movements. Our findings also suggest that adults are sensitive to physical strength
Table 1 Descriptive statistics (means and standard deviations) of anthropometric measurements and gender identification of male and female dancers. Males
Height Weight BMI Handgrip strength Gender identification by adults Gender identification by children
Females
M
SD
M
SD
176.24 77.03 24.76 38.24 0.82 0.68
6.48 13.43 3.94 8.93 0.15 0.24
164.30 62.86 23.23 25.05 0.75 0.69
6.23 11.50 3.67 6.26 0.23 0.25
t
p
11.03 6.66 2.35 9.90 2.16 0.06
.001 .001 .020 .001 .033 .951
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cues when assessing the gender of a dancer. However, it might be that such sensitivity is not (yet) present in pre-pubertal, schoolaged children. Previous research has demonstrated that the cognitive processes underlying gender identification are present in young infants (Levy & Haaf, 1994), and these processes become more advanced with age (Bussey & Bandura, 1999; Martin et al., 2002; Yee & Brown, 1994). In adults, successful gender identification is accomplished via the assessment of a variety of sexually dimorphic traits. Men are on average, for example, taller and heavier, have more facial and bodily hair and speak with lower fundamental frequencies than do women. Men and women use these sex-specific morphological characteristics (more feminine structures in women and more masculine structures in men) to discriminate the gender of another person (Neave, 2008; Puts, 2010). Additionally, it has been suggested that this ability in recognizing sexually dimorphic traits is important not only for gender identification but also for choosing a sexual mate (Enquist, Ghirlanda, Lundqvist, & Wachtmeister, 2002), as secondary sexual characteristics in both sexes have been found to be highly relevant for attractiveness judgements of potential mates (for review see Barber, 1995). Sexually dimorphic facial and bodily characteristics as well as sexual attraction to these traits in the context of mate choice develop during puberty under the influence of sex steroids, primarily oestrogen and testosterone, and can indicate sexual maturity, reproductive potential and health (Johnston & Franklin, 1993; Thornhill & Gangestad, 1996; Thornhill & Møller, 1997). When viewing dynamic stimuli, it is also apparent that certain movement cues can accurately signify the gender of the person who is moving. Even when dynamic stimuli are presented with limited visual information (e.g., individuals are seen only as a collection of moving lights) correct gender identification is significantly above chance, with observers seemingly basing their correct judgements on differences in shoulder and hip movements displayed by males and females (Barclay et al., 1978; Cutting et al., 1978; Kozlowski & Cutting, 1977; Mather & Murdoch, 1994; Pollick et al., 2005; Saunders et al., 2010; Troje, 2002). Research is now beginning to show that the sexually dimorphic characteristic of physical strength also influences social perceptions when viewing dynamic stimuli. Handgrip strength, as a measure for physical strength, is a sexually dimorphic characteristic often used as an easily obtainable indirect measure of health (Gallup, O’Brien, White, & Wilson, 2010). Usually, men have greater handgrip strength than do women throughout their life span when controlling for weight and/or body mass index (BMI) (Peterson, Petrick, Connor, & Conklin, 1989). This sex difference in strength is caused by higher levels of testosterone (Page et al., 2005), greater muscle mass (Kallman, Plato, & Tobin, 1990) and greater height and weight in boys and men (Kamarul, Ahmad, & Loh, 2006). Male dancers who are stronger are perceived as better dancers (McCarty et al., 2013) thus demonstrating that movement can serve to provide honest information about the physical qualities of the dancer. Such information should be particularly useful for adults seeking to make mate-choice decisions about a prospective mate, and it is perhaps not surprising that our adult raters were making accurate gender-identity decisions partly on the basis of the strength of the dancer. Male physical strength can be an accurate indicator of the formidability of the male (and hence his potential social status), and can enhance his survival and ability to acquire and defend resources (Lassek & Gaulin, 2009; Puts, 2010). It is important for males to be able to discern the physical qualities of another male in relation to potential intrasexual competition (Puts, 2010). In addition, females show a preference for males who are physically stronger and athletic because forming a partnership with healthy dominant males will enhance their reproductive success (Buss & Schmitt, 1993). It is thus perhaps not
surprising that we found that both adult males and females were able to accurately determine the strength and gender of a male dancer. The lack of a relationship in the child observers is also to be expected; while accurate gender determination in itself is useful in many social contexts, the association between gender identification and physical strength is of little use until the individual reaches puberty and begins to engage in mate-choice decisions. Skrzipek (1981) investigated gender-specific preference for sextypical facial and body silhouettes in a sample of 6607 children and adults, showing that pre-pubertal children (up to the age of 9 years) tend to prefer same-sex faces and bodies compared to the preferences of adults for opposite-sex stimuli. It was concluded that adults rely heavily on sex-typical physical characteristics (such as an oval vs. square facial outline), and that this preference develops around early puberty. It would be interesting to investigate at what point children come to associate strength and gender; we assume that this will begin to emerge during adolescence and develop more strongly as puberty accelerates, peaking when the individual enters the mating market for the first time. Although the results of the present study suggest that pre-pubertal children do not share the sensitivity for strength cues in dance movements with adults, these findings should be regarded as preliminary. Compared to the sample of adult assessors of gender identity, the sample of children was relatively small. Considering that each child only saw 10 videos, the number of single ratings per video for calculating the means potentially lacked power. Thus, a replication of the result in children is clearly needed. Future studies on the development of opposite-sex preferences should also extend to non-visual cues. Saxton, Caryl, and Roberts (2006) reported that women judge men with more attractive faces higher on vocal attractiveness – a result that was obtained with adults and adolescents, but not with children. Thus it is likely that concordant judgements of attractiveness cues, including the sensitivity to sex-specific movement patterns, reflect hormone-mediated developmental change of preferences toward opposite-sex individuals that generalize to sex-typical information, which people derive when mate quality assessment becomes relevant. In summary, we have demonstrated that the physical strength of a male dancer provides information to enable adults to determine their gender with greater accuracy. While children can determine the gender of a dancer at a level above chance, they are not as accurate as adults, perhaps because they do not perceive cues to physical strength. Acknowledgements We thank Irene Fink and the staff of the elementary school in Biedermannsdorf (Austria) for their assistance with data collection. Preparation of this study was funded by the German Research Foundation (DFG), grant numbers FI1450/4-1 and FI 1450/7-1 awarded to B.F. References Barber, N. (1995). The evolutionary psychology of physical attractiveness: Sexual selection and human morphology. Ethology and Sociobiology, 16, 395–424. Barclay, C., Cutting, J., & Kozlowski, L. (1978). Temporal and spatial factors in gait perception that influence gender recognition. Perception and Psychophysics, 23, 145–152. Boone, R. T., & Cunningham, J. G. (1998). Children’s decoding of emotion in expressive body movement: The development of cue attunement. Developmental Psychology, 34, 1007–1016. Buss, D. M., & Schmitt, D. P. (1993). Sexual strategies theory: An evolutionary perspective on human mating. Psychological Review, 100, 204–232. Bussey, K., & Bandura, A. (1999). Social cognitive theory of gender development and differentiation. Psychological Review, 106, 676–713.
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Physical strength and gender identification from dance movements Carla Hufschmidt a, Bettina Weege a, Susanne Röder b, Katarzyna Pisanski c, Nick Neave d, Bernhard Fink a,⇑ a
Institute of Psychology and Courant Research Center Evolution of Social Behavior, University of Göttingen, Kellnerweg 6, D-37077 Göttingen, Germany Department of General Psychology and Methodology, University of Bamberg, Markusplatz 3, D-96047 Bamberg, Germany c Department of Communication Studies, Center for Behavior, Evolution and Culture, University of California, Los Angeles, CA 90095 United States d Department of Psychology, Northumbria University, Newcastle upon Tyne NE1 8ST, United Kingdom b
a r t i c l e
i n f o
Article history: Received 5 November 2014 Received in revised form 20 November 2014 Accepted 21 November 2014
Keywords: Dance Gender identification Physical strength Handgrip Men Women
a b s t r a c t Here we show that gender identification of male (but not female) heterosexual, right-handed dancers correlates with physical strength (measured via handgrip strength) after controlling for the effect of body-mass-index on strength. Using optical motion capture technology, we collected the dance movements of men and women for subsequent animations of uniform shape- and texture-standardized virtual characters (avatars). Short video clips (15 s) of these movements were presented to male and female adults and children, who were asked to identify the gender of the avatar. Gender identification performance was significantly higher than chance for both adults and children. Among adults (but not among children) the avatars of male dancers who were physically stronger were perceived as males significantly more often than were the avatars of male dancers who were physically weaker. There was no relationship between strength and gender identification for female dancers. We conclude that physical strength affects gender identification from human dance movements at least for male dancers, and that prepubertal children might not be sensitive to strength cues in dance movements. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Gender constitutes a key facet of an individual’s personal and social identity as it influences virtually all aspects of social communication and social life (Deaux & Major, 1987; Money & Ehrhardt, 1972; West & Zimmerman, 1987). The expression of gender, and our ability to differentiate the gender of others, is often influenced by various physical traits and characteristics. Research suggests that observers can use sexually dimorphic physical features such as body height, weight, muscularity, body hair, facial morphology, and voice pitch, to accurately differentiate adult men and women (Neave, 2008; Puts, 2010). Gender identification has been demonstrated in infants aged 10 months old (Levy & Haaf, 1994) showing that the cognitive abilities required for categorizing social information, such as gender, are present early in life. Studies using dynamic point-light walkers have demonstrated that adult observers can also accurately judge gender from gait (i.e., an individual’s walk) in the absence of all other physical or behavioural cues to gender (Barclay, Cutting, & Kozlowski, 1978; Kozlowski & Cutting, 1977, 1978; Mather & Murdoch, 1994; Sumi, 2000; Troje, 2002). The ability to identify the gender of a
⇑ Corresponding author. Tel.: +49 551 39 9344; fax: +49 551 39 7299. E-mail address: bernhard.fi[email protected] (B. Fink). http://dx.doi.org/10.1016/j.paid.2014.11.045 0191-8869/Ó 2014 Elsevier Ltd. All rights reserved.
person based simply on motion cues implies characteristic differences in the way that men and women move their bodies (Pollick, Kay, Heim, & Stringer, 2005; Pollick, Paterson, Bruderlin, & Sanford, 2001). Cutting, Proffitt, and Kozlowski (1978), for example, reported that men swing their shoulders from side to side more than do women while walking, whereas women swing their hips from side to side more than do men. Indeed, when asked to make judgements of the gender of an animated walker, observers focus primarily on the shoulders and hips (Saunders, Williamson, & Troje, 2010). Other studies suggest that the motion of the legs provides important sex-relevant information (Todd, 1983; Yamasaki, Saki, & Torii, 1991). Thus, gait appears to communicate cues to gender that adult observers are sensitive to. It is not clear what factors contribute to differences in the way that men and women move, and whether observers utilize these same factors to assess gender. Recent work suggests that sexually dimorphic traits affect body movement in a way that may provide observers with socially relevant, sex-specific information. Sexually dimorphic characteristics develop under the influence of sex steroid hormones, most notably testosterone, and provide the basis for many subsequent observations of sex-specific behaviours in adulthood (Neave, 2008). In perceptual studies of body movement, physical strength appears to be a key sexually dimorphic characteristic affecting social perception. Men are on average twice as strong as are women (Miller, MacDougall, Tarnopolsky, & Sale,
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1993). Strength has been linked to the perceived quality and attractiveness of men’s dance movements (McCarty, Hönekopp, Neave, Caplan, & Fink, 2013). Men’s dance movements also affect other’s perceptions of their sensation seeking behaviour (Hugill, Fink, Neave, Besson, & Bunse, 2011), which correlates positively with men’s physical strength (Fink, Hamdaoui, Wenig, & Neave, 2010). Because men’s dance movements appear to indicate strength, a highly sexually dimorphic trait, it follows that physical strength may mediate observer’s ability to differentiate men from women through their body movements. Compared to gait, dance is a much more complex human body movement and one that is cross-culturally universal (Hanna, 1987; Kaeppler, 1978; Kurath, 1960). Dance is typically characterized by various gender-specific movements (Hanna, 1987, 2010) and appears to play an important role in courtship behaviour (for reviews, see Fink, Weege, Neave, Ried, & do Lago, 2014). Indeed, unlike gait, the main purpose of dance is not locomotion but rather to express oneself or to impress a counterpart. Thus, dance movements may express salient cues that facilitate gender identification more readily than do other types of body movement, including gait. A large body of research has examined the ontogeny and development of gender expression and gender identification. This work suggests that behavioural gender differentiation develops at a young age – often the ability is present in infants and toddlers – but becomes increasingly pronounced and stereotyped with age and social experience (see, e.g., Bussey & Bandura, 1999; Martin, Ruble, & Szkrybalo, 2002; Yee & Brown, 1994). Past work has shown that infants as young as 4–7 years old show gendertypicality in their body movements and gait (König, Schölmerich, & Troje, 2008), and that children as young as 5 years old can accurately assess emotion from body and dance movements (Boone & Cunningham, 1998). However, no study has examined the ability of young children to accurately identify gender from body movements, including dance. In the present study, we tested whether the ability of male and female adults (aged 18–29 years) and children (aged 6–10 years) to accurately identify gender from dance movements was facilitated by the physical strength of the dancers after controlling for differences in the dancers’ body size. Male and female dancers were presented in the form of gender-neutral avatars in video clips, created using motion capture technology. We predicted that both adults and children would correctly discriminate the gender of dancers. However, because sexual dimorphism in strength develops around the time of puberty (after age 11) under the influence of testosterone (Seger & Thorstensson, 2000), and appears to play a key role in indicating mate quality (Hugill et al., 2011), any facilitating effect of strength on gender perception from dance may be more pronounced among adults than children. Thus, we predicted that adults would rely more heavily on sexually dimorphic strength cues to gauge the gender of male and female dancers than would children.
2. Methods 2.1. Stimuli We recruited 167 participants (81 men, 86 women; aged 18– 42 years; mainly graduate and undergraduate students of Northumbria University, U.K.) as part of a large-scale study on body movement, in which participants also reported sexual orientation and handedness. Height (cm) and weight (kg) measurements were collected to calculate body-mass-index (BMI; mass/height (m)2) – a known correlate of handgrip strength (Chandrasekaran, Ghosh, Prasad, Krishnan, & Chandrasharma, 2010). Handgrip strength
(kgf) was measured using a hand dynamometer (Takei Kiki Kogyo, Japan). Participants were asked to perform a maximum force trial with each hand (‘‘Squeeze as hard as you can’’). Strength measurements were collected twice for each participant and the means of two recordings were calculated. Dance movements were recorded using a 12-camera optical motion-capture system (Vicon, Oxford) running Vicon Nexus software. None of the participants were professional dancers and none reported physical injuries or current health problems that could have affected their movements. Thirty nine 14 mm retro-reflective markers were attached to each participant in accordance with the Vicon Plug-In-Gait marker set to capture all major body structures. Following calibration, participants danced for 30 s to a popular song, of which only the core drumbeat was presented to eliminate possible music likeability effects. No specific instruction was given on how they should dance. These motion-capture data were applied to a featureless, gender-neutral humanoid character (avatar), using Autodesk MotionBuilder (Autodesk, Inc., San Rafael, CA, USA) and finally rendered in the form of 773 632 pixel video clips (see Fig. 1). Fifteen-second sequences were extracted from the middle of each dance video for the subsequent gender identification task. For one man and six women, no dance movement video could be produced due to incomplete motion capture data. Thus the final set of stimuli used for presentation in subsequent rating studies included dance movement videos of 80 male and 80 female participants. 2.2. Rating studies Our sample of adult raters comprised 49 men and 51 women, aged 18–29 years (M = 22.80, SD = 2.76), mainly heterosexual by self-report (94%), who were recruited predominantly from the student population at the University of Göttingen (Germany). Each participant viewed a random selection of 40 clips out of the total set of dance movement videos. Following each clip, the participant was prompted to indicate whether the dancer was male or female by clicking a button below the video. Clips were presented in a serial, randomised order, centred on a 15.4’’ laptop screen (1440 900 pixels resolution) using Medialab 2012 (Empirisoft Inc., New York) presentation software. The core audio track played during dance recording was not presented to raters. Our sample of child raters comprised 43 boys and 42 girls between the ages of 6 and 10 years (M = 8.19, SD = 1.16) recruited from an elementary school in Lower Austria (Austria). Permission for testing was obtained from legal guardians and the methodology was approved by the ethical committee of the University of Göttingen. The experimental setup was the same as for adult participants, but children viewed 10 videos out of the entire set, owing to time constraints with children’s availability and concentration capacity. 2.3. Statistical analysis For the statistical analysis, we calculated the number of trials on which the gender of each dancer was correctly identified. Children’s gender identification performance data were not available for two dancers due to the randomization procedure. We focused on right handgrip strength, which was found to correlate highly positively with left handgrip strength in our sample (r = .94, p < .001). Moreover, we considered only those dancers for analysis who claimed to be exclusively heterosexual and right-handed, rendering the final sample size as N = 135 dancers (69 males, 66 females; M = 21.33, SD = 4.12). Significance tests for group comparisons in gender identification performance were two-tailed and correlations of gender identification performance and handgrip strength were one-tailed with an alpha set to 0.05.
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Fig. 1. Snapshots of the creation process of a virtual dance character. The initial stick figure with captured markers (left), application of the motion data to the actor (middle) and the final avatar for presentation (right).
3. Results Gender identification performance in both adults and children was significantly better than expected by chance (0.5) (adults: M = .78, SD = .19, t134 = 17.01, p < .001; children: M = .68, SD = .25, t132 = 8.59, p < .001) with adults performing significantly better than children in this task (t132 = 5.00, p < .001). We found no significant effect of the rater’s sex on gender identification performance among adult raters (F1,133 = .26, p = .61). However, there was a significant effect of the dancer’s sex (F1,133 = 4.48, p < .05) with gender identification of male dancers (82%) higher than that of female dancers (75%) (see Table 1). In addition, there was a significant interaction effect of the raters’ and the dancers’ sex on gender identification performance (F1,133 = 5.00, p < .05). Males performed slightly better than females in identifying males by their dance movements (84% vs. 80%, respectively) and females performed slightly better than males in identifying females by their dance movements (76% vs. 74%, respectively). Among children, there were no significant effects of the raters’ sex (F1,114 = 1.53, p = .22) and no significant interaction between the raters’ and the dancers’ sex on gender identification performance (F1,114 = .84, p = .36). Table 1 reports descriptive statistics of physical measurements of male and female dancers. There were significant sex differences for height, weight, BMI, and handgrip strength, wherein men were physically larger and stronger than were women. We ran partial
correlations to test the influence of handgrip strength on gender identification performance from dance movements while controlling for body-mass-index. Considering adult’s gender identification performance (both males and females together), handgrip strength was significantly positively correlated with gender identification performance (rp = .20, p < .05). Running these correlations separately for male and female dancers, there was a significant positive correlation between handgrip strength and gender identification performance in male but not in female dancers (male dancers: rp = .22, p < .05; female dancers: rp = .07, p = .29). A more detailed inspection of these relationships conducted separately for male and female raters revealed significant relationships between handgrip strength and gender identification of male (but not female) dancers among both male and female raters (male dancers, male raters rp = .21, p < .05; male dancers, female raters: rp = .22, p < .05; female dancers, male raters rp = .06, p = .32; female dancers, female raters: rp = .09, p = .23). Testing these relationships in children revealed no significant relationships throughout.
4. Discussion The results of this study show that adults and children easily accomplish gender identification from dance movements. Our findings also suggest that adults are sensitive to physical strength
Table 1 Descriptive statistics (means and standard deviations) of anthropometric measurements and gender identification of male and female dancers. Males
Height Weight BMI Handgrip strength Gender identification by adults Gender identification by children
Females
M
SD
M
SD
176.24 77.03 24.76 38.24 0.82 0.68
6.48 13.43 3.94 8.93 0.15 0.24
164.30 62.86 23.23 25.05 0.75 0.69
6.23 11.50 3.67 6.26 0.23 0.25
t
p
11.03 6.66 2.35 9.90 2.16 0.06
.001 .001 .020 .001 .033 .951
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cues when assessing the gender of a dancer. However, it might be that such sensitivity is not (yet) present in pre-pubertal, schoolaged children. Previous research has demonstrated that the cognitive processes underlying gender identification are present in young infants (Levy & Haaf, 1994), and these processes become more advanced with age (Bussey & Bandura, 1999; Martin et al., 2002; Yee & Brown, 1994). In adults, successful gender identification is accomplished via the assessment of a variety of sexually dimorphic traits. Men are on average, for example, taller and heavier, have more facial and bodily hair and speak with lower fundamental frequencies than do women. Men and women use these sex-specific morphological characteristics (more feminine structures in women and more masculine structures in men) to discriminate the gender of another person (Neave, 2008; Puts, 2010). Additionally, it has been suggested that this ability in recognizing sexually dimorphic traits is important not only for gender identification but also for choosing a sexual mate (Enquist, Ghirlanda, Lundqvist, & Wachtmeister, 2002), as secondary sexual characteristics in both sexes have been found to be highly relevant for attractiveness judgements of potential mates (for review see Barber, 1995). Sexually dimorphic facial and bodily characteristics as well as sexual attraction to these traits in the context of mate choice develop during puberty under the influence of sex steroids, primarily oestrogen and testosterone, and can indicate sexual maturity, reproductive potential and health (Johnston & Franklin, 1993; Thornhill & Gangestad, 1996; Thornhill & Møller, 1997). When viewing dynamic stimuli, it is also apparent that certain movement cues can accurately signify the gender of the person who is moving. Even when dynamic stimuli are presented with limited visual information (e.g., individuals are seen only as a collection of moving lights) correct gender identification is significantly above chance, with observers seemingly basing their correct judgements on differences in shoulder and hip movements displayed by males and females (Barclay et al., 1978; Cutting et al., 1978; Kozlowski & Cutting, 1977; Mather & Murdoch, 1994; Pollick et al., 2005; Saunders et al., 2010; Troje, 2002). Research is now beginning to show that the sexually dimorphic characteristic of physical strength also influences social perceptions when viewing dynamic stimuli. Handgrip strength, as a measure for physical strength, is a sexually dimorphic characteristic often used as an easily obtainable indirect measure of health (Gallup, O’Brien, White, & Wilson, 2010). Usually, men have greater handgrip strength than do women throughout their life span when controlling for weight and/or body mass index (BMI) (Peterson, Petrick, Connor, & Conklin, 1989). This sex difference in strength is caused by higher levels of testosterone (Page et al., 2005), greater muscle mass (Kallman, Plato, & Tobin, 1990) and greater height and weight in boys and men (Kamarul, Ahmad, & Loh, 2006). Male dancers who are stronger are perceived as better dancers (McCarty et al., 2013) thus demonstrating that movement can serve to provide honest information about the physical qualities of the dancer. Such information should be particularly useful for adults seeking to make mate-choice decisions about a prospective mate, and it is perhaps not surprising that our adult raters were making accurate gender-identity decisions partly on the basis of the strength of the dancer. Male physical strength can be an accurate indicator of the formidability of the male (and hence his potential social status), and can enhance his survival and ability to acquire and defend resources (Lassek & Gaulin, 2009; Puts, 2010). It is important for males to be able to discern the physical qualities of another male in relation to potential intrasexual competition (Puts, 2010). In addition, females show a preference for males who are physically stronger and athletic because forming a partnership with healthy dominant males will enhance their reproductive success (Buss & Schmitt, 1993). It is thus perhaps not
surprising that we found that both adult males and females were able to accurately determine the strength and gender of a male dancer. The lack of a relationship in the child observers is also to be expected; while accurate gender determination in itself is useful in many social contexts, the association between gender identification and physical strength is of little use until the individual reaches puberty and begins to engage in mate-choice decisions. Skrzipek (1981) investigated gender-specific preference for sextypical facial and body silhouettes in a sample of 6607 children and adults, showing that pre-pubertal children (up to the age of 9 years) tend to prefer same-sex faces and bodies compared to the preferences of adults for opposite-sex stimuli. It was concluded that adults rely heavily on sex-typical physical characteristics (such as an oval vs. square facial outline), and that this preference develops around early puberty. It would be interesting to investigate at what point children come to associate strength and gender; we assume that this will begin to emerge during adolescence and develop more strongly as puberty accelerates, peaking when the individual enters the mating market for the first time. Although the results of the present study suggest that pre-pubertal children do not share the sensitivity for strength cues in dance movements with adults, these findings should be regarded as preliminary. Compared to the sample of adult assessors of gender identity, the sample of children was relatively small. Considering that each child only saw 10 videos, the number of single ratings per video for calculating the means potentially lacked power. Thus, a replication of the result in children is clearly needed. Future studies on the development of opposite-sex preferences should also extend to non-visual cues. Saxton, Caryl, and Roberts (2006) reported that women judge men with more attractive faces higher on vocal attractiveness – a result that was obtained with adults and adolescents, but not with children. Thus it is likely that concordant judgements of attractiveness cues, including the sensitivity to sex-specific movement patterns, reflect hormone-mediated developmental change of preferences toward opposite-sex individuals that generalize to sex-typical information, which people derive when mate quality assessment becomes relevant. In summary, we have demonstrated that the physical strength of a male dancer provides information to enable adults to determine their gender with greater accuracy. While children can determine the gender of a dancer at a level above chance, they are not as accurate as adults, perhaps because they do not perceive cues to physical strength. Acknowledgements We thank Irene Fink and the staff of the elementary school in Biedermannsdorf (Austria) for their assistance with data collection. Preparation of this study was funded by the German Research Foundation (DFG), grant numbers FI1450/4-1 and FI 1450/7-1 awarded to B.F. References Barber, N. (1995). The evolutionary psychology of physical attractiveness: Sexual selection and human morphology. Ethology and Sociobiology, 16, 395–424. Barclay, C., Cutting, J., & Kozlowski, L. (1978). Temporal and spatial factors in gait perception that influence gender recognition. Perception and Psychophysics, 23, 145–152. Boone, R. T., & Cunningham, J. G. (1998). Children’s decoding of emotion in expressive body movement: The development of cue attunement. Developmental Psychology, 34, 1007–1016. Buss, D. M., & Schmitt, D. P. (1993). Sexual strategies theory: An evolutionary perspective on human mating. Psychological Review, 100, 204–232. Bussey, K., & Bandura, A. (1999). Social cognitive theory of gender development and differentiation. Psychological Review, 106, 676–713.
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