Focal Length Affects Depicted Shape and Perception of Facial Images

Static photographs are currently the most often employed stimuli in research on social perception. The method of photograph acquisition might affect the depicted subject’s facial appearance and thus also the impression of such stimuli. An important factor influencing the resulting photograph is focal length, as different focal lengths produce various levels of image distortion. Here we tested whether different focal lengths (50, 85, 105 mm) affect depicted shape and perception of female and male faces. We collected three portrait photographs of 45 (22 females, 23 males) participants under standardized conditions and camera setting varying only in the focal length. Subsequently, the three photographs from each individual were shown on screen in a randomized order using a 3-alternative forced-choice paradigm. The images were judged for attractiveness, dominance, and femininity/masculinity by 369 raters (193 females, 176 males). Facial width-to-height ratio (fWHR) was measured from each photograph and overall facial shape was analysed employing geometric morphometric methods (GMM). Our results showed that photographs taken with 50 mm focal length were rated as significantly less feminine/masculine, attractive, and dominant compared to the images taken with longer focal lengths. Further, shorter focal lengths produced faces with smaller fWHR. Subsequent GMM revealed focal length significantly affected overall facial shape of the photographed subjects. Thus methodology of photograph acquisition, focal length in this case, can significantly affect results of studies using photographic stimuli perhaps due to different levels of perspective distortion that influence shapes and proportions of morphological traits.     

Red is not a proxy signal for female genitalia in humans

Red is a colour that induces physiological and psychological effects in humans, affecting competitive and sporting success, signalling and enhancing male social dominance. The colour is also associated with increased sexual attractiveness, such that women associated with red objects or contexts are regarded as more desirable. It has been proposed that human males have a biological predisposition towards the colour red such that it is 'sexually salient'. This hypothesis argues that women use the colour red to announce impending ovulation and sexual proceptivity, with this functioning as a proxy signal for genital colour, and that men show increased attraction in consequence. In the first test of this hypothesis, we show that contrary to the hypothesis, heterosexual men did not prefer redder female genitalia and, by extension, that red is not a proxy signal for genital colour. We found a relative preference for pinker genital images with redder genitalia rated significantly less sexually attractive. This effect was independent of raters' prior sexual experience and variation in female genital morphology. Our results refute the hypothesis that men's attraction to red is linked to an implied relationship to genital colour and women's signalling of fertility and sexual proceptivity.     

Rapid and socially induced change of a badge of status

This paper reports a new aspect of male signalling in the green swordtail Xiphophorus hellerii. Males are highly ornamented and possess a sword (an extension of the caudal fin), as well as a lateral stripe that has been shown to be a badge of status. Males of one natural population, however, were found to quickly change the colour of their lateral stripe to red when socially dominant over other males and black when subdominant, thereby exploiting the female preference for red stripes while dominant, and avoiding the costs of male aggression while subdominant.     

Second to fourth digit ratio, testosterone and perceived male dominance

Previous studies have shown that male faces with extreme features associated with testosterone are perceived as dominant and masculine. Women have been reported to prefer more masculinized male faces as they may consider testosterone markers to be an 'honest' indication of good health, and such considerations may underlie their aesthetic preferences. However, pronounced testosterone facial markers are also associated with dominance, and several negative personality traits. This suggests that female aesthetic preferences may be an adaptive compromise between positive attributes associated with higher than average testosterone, and negative attributes associated with more extreme masculinization. This current study attempts to clarify the role of hormone markers in female perceptions of dominance, masculinity and attractiveness, in male facial images. Recent evidence suggests that the relative length of the 2nd to 4th finger (2D : 4D ratio) is a pointer to prenatal testosterone levels and may thus serve as a window to the prenatal hormonal environment. We measured 2D : 4D in a sample of male college students and took salivary samples to analyse circulating levels of testosterone. Women rated facial images of these males for dominance, masculinity and attractiveness. Our results show that male 2D : 4D was significantly negatively related to perceived dominance and masculinity but not attractiveness. Circulating testosterone levels were not related to dominance, masculinity or attractiveness. These findings suggest that: (i) high prenatal levels of testosterone serve to 'organize' male facial features to subsequently reflect dominance and masculine characteristics presumably activated during puberty; and (ii) attractiveness is not directly related to testosterone levels. We conclude that facial dominance and masculinity reflect a male's perceived status rather than his physical attraction to women.     

Fairy wrasses perceive and respond to their deep red fluorescent coloration

Fluorescence enables the display of wavelengths that are absent in the natural environment, offering the potential to generate conspicuous colour contrasts. The marine fairy wrasse Cirrhilabrus solorensis displays prominent fluorescence in the deep red range (650–700 nm). This is remarkable because marine fishes are generally assumed to have poor sensitivity in this part of the visual spectrum. Here, we investigated whether C. solorensis males can perceive the fluorescence featured in this species by testing whether the presence or absence of red fluorescence affects male–male interactions under exclusive blue illumination. Given that males respond aggressively towards mirror-image stimuli, we quantified agonistic behaviour against mirrors covered with filters that did or did not absorb long (i.e. red) wavelengths. Males showed significantly fewer agonistic responses when their fluorescent signal was masked, independent of brightness differences. Our results unequivocally show that C. solorensis can see its deep red fluorescent coloration and that this pattern affects male–male interactions. This is the first study to demonstrate that deep red fluorescent body coloration can be perceived and has behavioural significance in a reef fish.     

Male–male aggression is unlikely to stabilize a poison frog polymorphism

Phenotypic polymorphism is common in animals, and the maintenance of multiple phenotypes in a population requires forces that act against homogenizing drift and selection. Male–male competition can contribute to the stability of a polymorphism when males compete primarily with males of the same phenotype. In and around a contact zone between red and blue lineages of the poison frog Oophaga pumilio, we used simulated territorial intrusions to test the nonexclusive predictions that males would direct more aggression towards males of (i) their own phenotype and/or (ii) the phenotype that is most common in their population. Males in the monomorphic red and blue populations that flank the contact zone were more aggressive towards simulated intruders that matched the local coloration. However, males in the two polymorphic populations biased aggression towards neither their own colour nor the colour most common in their population. In sympatry, the rarer colour morph gains no advantage via reduced male–male aggression from territorial males in these O. pumilio populations, and so male aggression seems unlikely to stabilize colour polymorphism on its own. More broadly, these results suggest that the potential for divergent male aggression biases to maintain phenotypic diversity depends on the mechanism(s) that generate the biases and the degree to which these mechanisms persist in sympatry.     

Static and Dynamic Facial Images Cue Similar Attractiveness Judgements

Approaches to the study of human mate preferences commonly involve judgements of facial photographs and assume that these judgements provide a reasonable reflection of how individuals would be perceived in real encounters. However, three recent studies have each reported non‐significant correlations between judgements using photos (static images) and those using videos (dynamic images). These results have led previous authors to conclude that static and dynamic faces are judged according to different evaluative standards and that this may call into question the validity of findings from experiments using static images. However, the extent of the discrepancy in judgements between image formats remains unknown, and may be influenced by different experimental designs. Here, we tested the effects of several experimental design factors on the strength of correlations between image presentation formats. Using both male and female targets, we compared observed static–dynamic judgement correlations when (1) judgements were made by the same or different raters, or (2) by raters of the same‐ or opposite‐sex to the targets, and (3) when dynamic stimuli were collected under different contextual scenarios. For (1) and (2), we also measured correlations when order of presentation of static and dynamic stimuli was alternated. Our results suggest that each design feature has independent effects on the strength of static–dynamic correlations. Correlations were stronger when static and dynamic stimuli were rated by the same raters. They were weakest for judgements of males by females, when based on seeing photos before videos. This interaction with sex is consistent with previous studies, indicating that females are especially responsive to male dynamic cues. However, in contrast to previous findings and in all cases, static–dynamic correlations were strongly and significantly positive, indicating that judgments based on static images provide an accurate representation of someone’s attractiveness during prolonged encounters.     

The relationship between the comb and social behaviour in laying hens

The question of whether attributes of the combs of laying hens have any consistent relationship with dominance behaviour has yet to be answered unequivocally. This study sought to address this by investigating whether a relationship existed between the competitive ability of hens within stable groups and the size or colour of their combs. Pullets (n = 120, Hy-line^® Variety Brown) were allocated randomly to eight groups of 15 hens for 32 weeks. Over this period the length and height of each hen's comb was measured regularly to estimate the total comb area and hens were weighed. In weeks 3-10 the aggressive interactions between hens in each group were observed to calculate a behavioural dominance score (David's score) for each hen. This score was based on the outcome of agonistic interactions with other group members; and accounts for the relative strengths of all opponents. Thus dominance scores reflected the competitive ability of hens from their overall within-group fighting success. The luminance, purity and dominant wavelength of the colour of each hen's comb was measured in week 27 using a telespectroradiometer. Hens with higher dominance scores had larger combs than those with lower dominance scores (gradient of slope = 0.008 ± 0.002, P < 0.001); this relationship was consistent across the experiment. There was no association between body weight and dominance score but there was a significant inverse relationship between dominance score and the dominant wavelength of the comb (gradient of slope = −0.067 ± 0.023, P < 0.01). This indicated that hens with combs perceived by humans as more yellow-red than pure red were generally more successful competitors. Further research is required to ascertain whether or not hens utilise this information on comb size and the underexplored area of comb colour to assess the competitive ability of their opponents.     

Perceived Sexual Orientation Based on Vocal and Facial Stimuli Is Linked to Self-Rated Sexual Orientation in Czech Men

Previous research has shown that lay people can accurately assess male sexual orientation based on limited information, such as face, voice, or behavioral display. Gender-atypical traits are thought to serve as cues to sexual orientation. We investigated the presumed mechanisms of sexual orientation attribution using a standardized set of facial and vocal stimuli of Czech men. Both types of stimuli were rated for sexual orientation and masculinity-femininity by non-student heterosexual women and homosexual men. Our data showed that by evaluating vocal stimuli both women and homosexual men can judge sexual orientation of the target men in agreement with their self-reported sexual orientation. Nevertheless, only homosexual men accurately attributed sexual orientation of the two groups from facial images. Interestingly, facial images of homosexual targets were rated as more masculine than heterosexual targets. This indicates that attributions of sexual orientation are affected by stereotyped association between femininity and male homosexuality; however, reliance on such cues can lead to frequent misjudgments as was the case with the female raters. Although our study is based on a community sample recruited in a non-English speaking country, the results are generally consistent with the previous research and thus corroborate the validity of sexual orientation attributions.     

The Dartmouth Database of Children’s Faces: Acquisition and Validation of a New Face Stimulus Set

Facial identity and expression play critical roles in our social lives. Faces are therefore frequently used as stimuli in a variety of areas of scientific research. Although several extensive and well-controlled databases of adult faces exist, few databases include children’s faces. Here we present the Dartmouth Database of Children’s Faces, a set of photographs of 40 male and 40 female Caucasian children between 6 and 16 years-of-age. Models posed eight facial expressions and were photographed from five camera angles under two lighting conditions. Models wore black hats and black gowns to minimize extra-facial variables. To validate the images, independent raters identified facial expressions, rated their intensity, and provided an age estimate for each model. The Dartmouth Database of Children’s Faces is freely available for research purposes and can be downloaded by contacting the corresponding author by email.     

布氏田鼠雄性的优势地位

在实验条件下对雄性成年布氏田鼠（Microtus brandti）相遇后的优势地位及生理指标的研究结果表明：布氏田鼠雄性之间存在严格的等级关系;优势雄鼠生理指标中睾丸重量和血清睾酮激素含量高于从属雄鼠,而血清中皮质醇激素的含量低于从属雄鼠。优势雄鼠的探究、攻击和修饰等行为频次显著高于从属雄鼠,而从属雄鼠在跳跃频次上多于优势雄鼠。随着观察时间的延长,不论优势个体还是从属个体,其探究频次都呈现明显的下降趋势,其他行为的频次则没有显著差异。相关性检验说明,除攻击行为可以作为判断区分雄鼠等级的依据之外,修饰行为也可以作为判断的依据。     

Familiarity affects the assessment of female facial signals of fertility by free-ranging male rhesus macaques

Animals signal their reproductive status in a range of sensory modalities. Highly social animals, such as primates, have access not only to such signals, but also to prior experience of other group members. Whether this experience affects how animals interpret reproductive signals is unknown. Here, we explore whether familiarity with a specific female affects a male's ability to assess that female's reproductive signals. We used a preferential looking procedure to assess signal discrimination in free-ranging rhesus macaques, a species in which female facial luminance covaries with reproductive status. We collected images of female faces throughout the reproductive cycle, and using faecal hormone analysis to determine ovulation, categorized images as coming from a female's pre-fertile, ovulating, or post-fertile period. We printed colour-calibrated stimuli of these faces, reproducing stimuli perceptually the same in colour and luminance to the original appearance of females. These images were presented to males who were either unfamiliar or familiar with stimuli females. Overall, males distinguished ovulatory from pre-ovulatory faces. However, a significant proportion of males did so only among males familiar with stimuli females. These experiments demonstrate that familiarity may increase a receiver's ability to use a social partner's signals to discern their reproductive status.     

The role of pigment based plumage traits in resolving conflicts

The role of melanin ‘badges of status’, in male–male competition has been well‐studied, in contrast, carotenoid based plumage has largely been examined in the context of female mate choice. Recent work has shown that carotenoid signals can also function in male–male competition, although the functions of the two types of signals is currently unclear. Here, we examine the relationships between colouration, dominance and aggression in the crimson finch Neochmia phaeton, a species where males have both conspicuous red carotenoid plumage and a black melanin patch. We examined the importance of carotenoid and melanin based signals in three contexts: 1) among free‐living birds interacting at a feeding station: we found that neither colour signal influenced the outcome of interactions; 2) in staged dyadic contest in captivity: we found that coloration from carotenoid pigments was positively related to the probability of winning a contest, while the size of the melanin plumage patch was not related to winning; and 3) in staged dyadic contests where male plumage colour had been masked: we found that the number of interactions required to determine dominance increased. While the underlying natural plumage colour was still important in these contests, birds with more intense carotenoid colouration were now more likely to lose. These results confirm carotenoid‐based signalling in male–male contests. However this signal is used in conjunction with other factors such as self‐assessment and body condition. Contrary to traditional expectations, the black melanin patch was not found to be important in this context.     

Dominance is not always an honest signal of male quality,but females may be able to detect the dishonesty

Females prefer dominant males as mating partners in numerous species. Male dominance rank is considered as an honest signal of male quality, because only healthy males in good condition are thought to be able to win fights with other males. Here, we tested whether activation of the immune system influences the success of males in male–male competition and mating in the field cricket, Gryllus integer. We activated the immune system of males with a nylon monofilament (to mimic a parasitoid larva), and arranged fights between male pairs to assess male dominance and associated mating success. Activation of the immune system with nylon monofilament substantially enhanced the fighting success of males during male–male competition but had no effect on mating success. However, sham-manipulation (a wound only) did not have any effect on fighting success although females mated more often with dominant males. Our study suggests that when male crickets meet an apparent survival threat they may behave more dominantly, probably owing to terminal investment. Male success during male–male competition is not always an honest signal of males’ quality, but females may be able to detect this dishonesty.     

Inter- and intraspecific competition between the fox species Alopex lagopus and Vulpes vulpes: an evaluation trial under penned conditions

This study compared competition capacity and dominance relations between arctic foxes (Alopex lagopus) and red foxes (Vulpes vulpes). Experiments were carried out in semi-natural earthen floor enclosures using farm-bred colour types of both species (blue fox and silver fox) as subjects. Results of the dominance scoring and open field behaviour after weaning in August-September showed that blue foxes dominated over silver foxes. Thereafter, the situation gradually became reversed and silver foxes were dominant during the breeding and whelping seasons. Housing both species together from weaning produced more curious animals as compared to when these species were placed in common quarters after the autumn equinox. In the case of blue foxes, the male dominated highly over all females. In silver foxes, the difference in dominance between the sexes was, however, less pronounced. The most dominant individuals in the study groups were typically among the heaviest. Breedings and whelpings succeeded better in silver than in blue foxes. However, none of litters born survived more than one week. The present results support the conclusion that when both fox species are housed together, Vulpus vulpus tends to dominate over Alopex lagopus. Received: 22 March 1996/Accepted: 30 June 1996     

Be Happy Not Sad for Your Youth: The Effect of Emotional Expression on Age Perception

Perceived age is a psychosocial factor that can influence both with whom and how we choose to interact socially. Though intuition tells us that a smile makes us look younger, surprisingly little empirical evidence exists to explain how age-irrelevant emotional expressions bias the subjective decision threshold for age. We examined the role that emotional expression plays in the process of judging one’s age from a face. College-aged participants were asked to sort the emotional and neutral expressions of male facial stimuli that had been morphed across eight age levels into categories of either “young” or “old.” Our results indicated that faces at the lower age levels were more likely to be categorized as old when they showed a sad facial expression compared to neutral expressions. Mirroring that, happy faces were more often judged as young at higher age levels than neutral faces. Our findings suggest that emotion interacts with age perception such that happy expression increases the threshold for an old decision, while sad expression decreases the threshold for an old decision in a young adult sample.     

Male-male competition and speciation: aggression bias towards differently coloured rivals varies between stages of speciation in a Lake Victoria cichlid species complex

Sympatric speciation driven by sexual selection by female mate choice on a male trait is a much debated topic. The process is problematic because of the lack of negative frequency-dependent selection that can facilitate the invasion of a novel colour phenotype and stabilize trait polymorphism. It has recently been proposed that male-male competition for mating territories can generate frequency-dependent selection on male colouration. Rare male cichlid fish would enjoy a fitness advantage if territorial defenders bias aggression towards male cichlid fish of their own colour. We used blue (ancestral type) and red phenotypes of the Lake Victoria cichlid species complex Pundamilia. We tested the aggression bias of wild-caught territorial blue male cichlid fish from five separate populations for blue vs. red rival male cichlid fish using simulated intruder choice tests. The different populations vary in the frequency of red male cichlid fish, and in the degree of reproductive isolation between red and blue, reflecting different stages of speciation. Blue male cichlid fish from a population that lack red phenotypes biased aggression towards blue stimulus male cichlid fish. The same was found in two populations where blue and red are reproductively isolated sister species. This aggression bias may facilitate the invasion of a novel colour phenotype and species coexistence. Blue male cichlid fish from two populations where red and blue are hybridizing incipient species biased aggression towards red stimulus male cichlid fish. Thus, after a successful invasion of red, aggression bias alone is not likely to generate frequency dependence required to stabilize the coexistence of phenotypes. The findings show that aggression bias varies between stages of speciation, but is not enough to stabilize the process of speciation.     

Male voice pitch mediates the relationship between objective and perceived formidability

Acoustic signals function in intrasexual mating competition in a wide variety of species, including humans. The low voice pitch of human males has been proposed to represent an honest signal of formidability. Although voice pitch in men affects perceptions of size and dominance, it is relatively weakly associated with objective measures of formidability such as body size and strength. As a result, some authors have argued that low male voice pitch is not a valid signal of formidability but is deceptive and salient only because it hijacks a tendency to perceive lower frequency sounds as emanating from larger sources. In this paper, we consider theoretical and empirical issues associated with this perceptual exploitation hypothesis and ask whether male voice pitch transmits information about formidability. We utilize mediation models to investigate whether male voice pitch is an honest signal of formidability in data collected from university students in the U.S. (n = 231 male speakers, 565 male raters) and Canada (n = 74 male speakers, 108 female raters, 65 male raters). In both data sets, male voice pitch mediated the relationship between objective (measured by height) and perceived formidability. Collectively, these results indicate that men’s voice pitch transmits information about formidability from signaler to receiver.     

Effects of partner conception risk phase on male perception of dominance in faces

Several studies have suggested that women may prefer to engage in extra-pair copulations with males who appear dominant and to do so near ovulation. While there is some evidence that males are more jealous of dominant rivals and more proprietary when their partners are near ovulation, there is none that suggests the existence of counterstrategic perceptual shifts that mirror those seen in women. We provide such evidence here. Composites of male faces that were either high or low in rated dominance were presented to male participants who provided ratings of dominance. A three-way interaction between stimulus-face dominance, partner conception risk phase, and partner oral contraceptive use was found; men whose partners did not use an oral contraceptive and were in the high conception risk phase of their cycle displayed increased dominance ratings of high-dominance male faces. We conclude that males have evolved counterstrategies to deal with female infidelity that include an overattribution of dominance to those rivals most likely to present a threat at times when that threat is greatest. This overattribution is likely to lead to increases in jealousy and mate-retention behaviors.     

Effects of emotional expression of an irrelevant face image on recognition of visual stimuli

Psychophysiological experiments were performed on 34 healthy subjects. We analyzed the accuracy and latency of motor response in recognizing two types of complex visual stimuli, animals and objects, which were presented immediately after a brief presentation of face images with different emotional expressions: anger, fear, happiness, and a neutral expression. We revealed the dependence of response latency on emotional expression of the masked face. The response latency was lower when the test stimuli were preceded by angry or fearful faces compared to happy or neutral faces. These effects depended on the type of stimulus and were more expressive when recognizing objects compared to animals. We found that the effects of emotional faces were related to personal features of the subjects that they exhibited in the emotional and communicative blocks of Cattell’s test and were more expressive in more sensitive, anxious, and pessimistic introverts. The mechanisms of the effects of unconsciously perceived emotional information on human visual behavior are discussed.