The reward value of infant facial cuteness tracks within-subject changes in women's salivary testosterone

Selective attention towards infants in nulliparous women across the menstrual cycle

Research in women showed that testosterone is associated with decreased selective attention towards infant stimuli, which can be compensated for by oxytocin administration. In theory, caregiving behavior is thought to be mediated by oxytocin. Oxytocin binds to dopaminergic neurons and thus supposedly motivates aspects of caregiving through its influence on dopaminergic transmission. Most previous studies on caregiving behaviors were thereby performed in women under hormonal contraception to avoid hormonal fluctuations. However, recent studies repeatedly demonstrated decisive influences of the hormonal changes across the female menstrual cycle on dopamine-mediated behaviors, suggesting that estradiol acts as dopamine agonist in the follicular phase and progesterone as dopamine antagonist in the luteal phase. In the present study, we investigated selective attention towards infants as one central aspect of caregiving behavior over the natural menstrual cycle and in relation to interindividual differences of estradiol and progesterone. As expected, we found that women with higher estradiol in the follicular phase also showed higher selective attention towards infant faces among adult distractors, whereas the correlation disappeared in the luteal phase. In contrast, progesterone did not correlate with selective attention towards infants. The present findings collectively support the assumption that estradiol may act as dopamine agonist in the follicular phase, thereby supposedly promoting an important aspect of caretaking behavior.

Testosterone's role in modulating human behaviors relevant to mating and parenting

Testosterone (T) is linked to human mating and parenting. Here, we comprehensively reviewed evidence on whether, in men and women, (1) basal T levels are related to mating and parenting behaviors, (2) T responds to reproduction-relevant cues, (3) acute changes in T map onto subsequent mating and parenting behaviors, and (4) single-dose exogenous T administration causally affects mating and parenting behaviors. We examined whether the available evidence supports trade-off interpretations of T's adaptive function whereby high T levels correspond to greater mating/reproductive effort and competition and low T levels to greater parenting effort and nurturance. We found mixed support for trade-off hypotheses, suggesting that T's function in modulating human mating and parenting might be more nuanced and highly dependent on context and individual trait differences. Results were largely similar for men and women, although studies with women were scarcer than those with men for most behaviors we reviewed.

Face inversion effect on perceived cuteness of infant faces

Research has demonstrated that attractiveness evaluations of adult faces were less accurate when faces were inverted than upright. It remains unknown, however, whether a similar effect applies to perceived cuteness of infants, which is assumed to be based on elemental facial features called the "baby schema." In this research, we studied the face inversion effect on perceived cuteness of infant faces in a rating task and a two-alternative forced-choice (2AFC) task. We also examined beauty as a control dimension. Although the rating task revealed no inversion effect, the 2AFC task showed poorer discrimination performance with inverted faces than with upright faces in both evaluations. These results indicate that infant cuteness and beauty dimensions are correlated well with each other, and their perception not only relies on elemental features that are not strongly affected by inversion but is also affected by holistic facial configurations when a detailed comparison is required.

Putting Effort into Emotion Regulation: Manipulating Desirability and Motivational Strength

Although people often want to regulate their emotions, they are sometimes reluctant to invest the necessary effort in doing so. We propose that people could be motivated to invest effort in emotion regulation, by rendering the target emotional state more desirable. Rendering an emotion goal more desirable can motivate people to invest effort in emotion regulation, ultimately facilitating successful emotion regulation. In three studies (N = 452), we show that both inside and outside the lab, rendering calmness more desirable, boosted the motivational strength to increase calmness, increasing the effort people invested to increase calmness, and ultimately made people calmer. This investigation points to the importance of motivational strength as a potential means to promote effort and success in emotion regulation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42761-022-00155-0.

Hormonal and behavioral responses to an infant simulator in women with and without children

We investigated the impact of maternal status on hormonal reactivity and behavioral responses to an infant simulator in 117 women (54 primiparous, 63 nulliparous). The amount of affectionate touch and motherese were analyzed as behavioral measures of caregiving. Saliva was collected before and 10 min after interaction with the infant simulator to analyze oxytocin, testosterone, cortisol, and estradiol levels. Nulliparous women also provided information about their fertility motivation. Linear mixed models indicated that greater use of affectionate touch was associated with lower overall testosterone levels. Cortisol decreased in response to the interaction in both groups. In the primiparous group, the amount of affectionate touch associated inversely with cortisol levels, whereas in the nulliparous group such association was not found. Oxytocin or estradiol reactivity to the simulator did not differ between the groups, nor were these hormones associated with behavior. Higher fertility motivation in nulliparous women was related to more motherese, and lower testosterone levels. Our results indicate that the simulator elicits hormonal reactivity both in mothers and nonmothers, but the patterns of associations between caregiving behavior and hormonal levels may be partially different. These results encourage using the infant simulator to explore hormonal processes related to the transition to parenthood.

Testing the role of testosterone versus estrogens in mediating reproductive transitions in female rhesus macaques

In male vertebrates, testosterone is generally known to coordinate reproductive trade-offs, in part by promoting the transition to the next reproduction at the expense of current parental care. The role of testosterone in reproductive transitions has been little tested in female vertebrates, especially in mammals. The present study sought to fill this gap, by first undertaking an experimental study, in which we identified DHT, androstenediol, and in particular etiocholanolone, as fecal androgen metabolites which reflect serum testosterone concentration in female rhesus macaques (Macaca mulatta). Using concentrations of fecal etiocholanolone as proxy for circulating testosterone, we then conducted a field study on 46 free-ranging rhesus macaques of Cayo Santiago, Puerto Rico, to test if testosterone mediates the trade-off between reproductive transition (a higher chance of reproducing in the next year) and current reproduction (providing more care to current offspring). While the evidence for testosterone was weak, the testing of fecal immunoreactive estrogen metabolites suggested a potential role of estrogen in reproductive trade-offs. We found large individual differences in fecal etiocholanolone concentrations during the early postpartum period that were unexplained even after accounting for sociodemographic factors such as age and dominance rank. Further investigation is needed to understand this variation. Our study suggests that the actions of testosterone in females may not have evolved to fulfil the same role in primate reproductive transitions as it does in males, and we encourage more studies to consider the function of testosterone in reproductive behaviors and life history transitions in females of mammalian taxa.

Creation and Validation of the Japanese Cute Infant Face (JCIF) Dataset

Research interest in cuteness perception and its effects on subsequent behavior and physiological responses has recently been increasing. The purpose of the present study was to produce a dataset of Japanese infant faces that are free of portrait rights and can be used for cuteness research. A total of 80 original facial images of 6-month-old infants were collected from their parents. The cuteness level of each picture was rated on a 7-point scale by 200 Japanese people (100 men and 100 women in their 20s–60s). Prototypical high- and low-cuteness faces were created by averaging the top 10 and bottom 10 faces according to the mean cuteness ratings. Then, 50 composite faces were made by mixing two faces randomly chosen from the 60 unused middle-cuteness faces. The normative cuteness ratings of these composite faces were obtained from 229 Japanese men and women in their 20s–60s. The shape of each composite face was transformed to be cuter (+50%) or less cute (–50%) along a continuum between the high- and low-cuteness prototypical faces. A two-alternative forced-choice task (N = 587) confirmed that cuteness discrimination was better than the chance level for all 50 face pairs. Moreover, the results showed that young men had poorer sensitivity to cuteness differences in infant faces than older men and women of any age. This Japanese Cute Infant Face (JCIF, “jay-sif”) dataset, including composite face images and normative rating scores, is publicly available online.

Mothers are more sensitive to infant cues after breastfeeding compared to bottle-feeding with human milk

The belief that breastfeeding promotes maternal bonding is widely held by both the public and professional health organizations. Yet to our knowledge, all research examining the link between breastfeeding and maternal behavior in humans has been correlational, limiting our ability to draw causal conclusions. In many mammals, the hormone prolactin, which is central to milk production, rises in response to each breastfeeding session and promotes maternal sensitivity, yet there is a dearth of research in human mothers. To fill these research gaps, we randomly assigned 28 breastfeeding mothers to either breastfeed in the lab or feed their infants previously expressed breastmilk in a bottle before participating in a video-recorded free play session with their infant. Plasma prolactin was measured 40 min after the start of the feeding session and video observations were coded for maternal sensitivity. We found that women randomly assigned to breastfeed were more sensitive to infant cues than women randomly assigned to bottle-feed. Prolactin levels did not differ between feeding groups, although prolactin was positively correlated with maternal sensitivity. Our results suggest that feeding milk directly from the breast (compared to bottle-feeding) increases maternal sensitivity towards infants, at least in the short term.

Preliminary data on increased reactivity towards children in distress after testosterone administration in women: A matter of protection?

Emotional reactivity to others' distress is a vital prerequisite for a caring response. Testosterone, in contrast, is mostly associated with protection of personal dominance and decreased responsiveness to others' needs. However, experimental work also indicates that rising testosterone levels in response to infant distress can potentially facilitate protection. We assessed the impact of testosterone administration on participants' emotional reactivity to infants in distress, measuring their facial responses on the corrugator supercilii forehead muscle ('frowning') and the zygomaticus major ('smiling') as an index of emotional responses towards children. Moreover, we probed whether the effect of testosterone is moderated by participants' self-reported nurturance and protective tendencies. Our preliminary results showed that testosterone not only increased emotional reactivity to empathy eliciting images of children, but that this increase was strongest in participants with strong protective tendencies. Our administration study is the first to link testosterone to infant protection.

White matter integrity moderates the relation between experienced childhood maltreatment and fathers' behavioral response to infant crying

The ability to provide appropriate responses to infant distress is vital to paternal care, but may be affected by fathers' experiences of childhood maltreatment. Detrimental effects of childhood maltreatment have been found in the adult brain's white matter fibers, accompanied with impaired emotional and cognitive functioning. In the current study (N = 121), we examined new and expectant fathers' childhood maltreatment experiences (i.e. emotional and physical abuse and neglect), current behavioral responses (i.e. handgrip force) to infant cry sounds, and white matter integrity using diffusion tensor imaging. First, more exposure to childhood maltreatment was associated with more use of excessive handgrip force in response to infant crying by fathers. Second, the association between experienced childhood maltreatment and white matter integrity was not significant in whole-brain analyses. Lastly, we found that the association between maltreatment exposure and excessive handgrip force during infant crying was absent in fathers with high tract integrity in the bilateral uncinate fasciculus. These findings possibly point to insufficient behavioral inhibition or emotional dysregulation in fathers who experienced childhood maltreatment, but buffering for this effect in those with larger integrity in brain fibers connecting the amygdala and prefrontal cortex.

Consumer self-reported and testosterone responses to advertising of luxury goods in social context

Despite the growing demand for luxury goods, there is limited understanding about how consumers respond to luxury-goods advertising and how viewing advertising in different social contexts affects these responses. This study investigates the link between luxury goods advertising and expected utility from a biological perspective by looking at males’ hormonal responses to advertising of luxury versus non-luxury branded goods. Using traditional and consumer neuroscience methods, we collected salivary testosterone data pre- and post-ad viewing. Self-reported scores on social and quality value of the brands were compared to salivary testosterone levels from participants placed in different social conditions (Alone versus Together with another person). The results show that higher post-viewing testosterone levels were associated with higher scores on quality, but not on social value and only for branded goods viewed in the Together condition, compared to the Alone condition. These results suggest that changes in testosterone levels reflect a rewarding experience or activate social competitiveness when male consumers appraise the quality but not the social value of the advertised luxury goods and that social context modulates this effect.

Not all "caregivers" are created equal: Liking, caring and facial expression responses to the baby schema as a function of parenthood and testosterone

The baby schema elicits care from potential caregivers. However, much of the research on the baby schema is based on self-report only. To address this issue, we explored the effects of baby schema and child age on facial expressions (EMG) and eye-blink startle, in addition to self-reported liking and caring for 43 men and 48 women (39 parents). Further, basal testosterone was assessed. All groups responded with liking and caring to high baby schema, but only women also responded with more positive facial expressions. Caring and smiling towards infants compared to first graders depended on parenthood and testosterone levels. Basal testosterone levels were negatively associated with overall responsiveness to children in women and fathers, but positively in non-fathers. Whereas the baby schema overall lead to positive affect and caring, the scope of these responses and the processes underlying them depended on gender, parenthood and hormonal status.

The baby schema effect in adolescence and its difference from that in adulthood

The baby schema effect induced by particular features of baby faces acts as an innate releasing mechanism that evokes positive emotions and instinctual behavioral responses. Our prior research in adults has revealed that this effect initially found in infancy extends into child faces. Adolescence is an important period involving development in various aspects of cognition, including face perception. Here, we investigated whether the extended baby schema effect we previously found in adult observers develops earlier-in adolescence-and how different it appears in adolescents as compared with in adults. In the current study, 76 adolescents and 77 adults were asked to judge the likeability of 148 neutral faces of infants and children (0.08-6.5 years of age) on 7-point scales. Results showed that both adolescents and adults perceived the faces of both infants and children younger than 4.6 years as more likeable relative to those of older children, indicating that the baby schema effect previously found in adulthood also occurs in adolescence. However, adolescents rated lower than adults toward the infant and child faces across all face ages, suggesting that this effect might be under development in adolescence. Overall, our findings provide new evidence for the development of face perception in adolescence and demonstrate age-related changes in innate releasing mechanisms in our protective and caretaking responses toward infants and children.

What a cute baby! Preliminary evidence from a fMRI study for the association between mothers' neural responses to infant faces and activation of the parental care system

Infant facial characteristics, i.e., baby schema, are thought to automatically elicit parenting behavior and affective orientation toward infants. Only a few studies, conducted in non-parents, have directly examined the neural underpinnings of this baby schema effect by manipulating distinctiveness of baby schema in infant faces. This study aims to further our understanding of the intuitive nature of parenting, by studying the baby schema effect in mothers of young children (at least one child aged between 2 and 6 years old). Functional magnetic resonance imaging (fMRI) was used to examine mothers' (N = 23) neural responses to unfamiliar infant faces varying in distinctiveness of baby schema. Also, it was studied how this neural activation to infant faces was associated with maternal nurturance. Results revealed that infant faces elicited widespread activation in bilateral visual cortices, the hippocampus, sensory-motor areas, parietal and frontal cortices, and the insula, which was not modulated by the distinctiveness of baby schema in the infant faces. Furthermore, higher self-reported maternal nurturance was related to increased neural responses to infant faces in the putamen and amygdala, brain regions known to be associated with reward and salience processing. These findings could suggest that in our small sample of mothers some of the core networks involved in reward and salience processing might be less sensitive to variation in distinctiveness of baby schema. Also, unfamiliar infant faces seem to be rewarding only for mothers who report high nurturance. These findings should be considered preliminary, because they need to be replicated in studies with larger samples.

Mechanisms for the Cognitive Processing of Attractiveness in Adult and Infant Faces: From the Evolutionary Perspective

Research on the cognitive processing of facial attractiveness has mainly focused on adult faces. Recent studies have revealed that the cognitive processing of facial attractiveness in infant faces is not the same as that in adult faces. Therefore, it is necessary to summarize the evidence on the processing of facial attractiveness in each kind of face and compare their underlying mechanisms. In this paper, we first reviewed studies on the cognitive processing of facial attractiveness in adult faces, including attentional and mnemonic processing, and then discussed the underlying mechanisms. Afterward, studies on facial attractiveness in infant faces were reviewed, and the underlying mechanisms were also discussed. Direct comparisons between the two kinds of cognitive processing were subsequently made. The results showed that the mechanisms for the processing of attractiveness in adult faces and infant faces are mainly motivated by the perspectives of mate selection and raising offspring, respectively, in evolutionary psychology. Finally, directions for future research are proposed.

Exploring the neural basis for paternal protection: an investigation of the neural response to infants in danger

Perceiving potential threat to an infant and responding to it is crucial for offspring survival and parent–child bonding. Using a combination of functional magnetic resonance imaging and multi-informant reports, this longitudinal study explores the neural basis for paternal responses to threat to infants pre-natally (N = 21) and early post-natally (n = 17). Participants viewed videos showing an infant in danger and matched control videos, while instructed to imagine that the infant was their own or someone else’s. Effects were found for infant-threatening vs neutral situations in the amygdala (region-of-interest analyses) and in clusters spanning cortical and subcortical areas (whole-brain analyses). An interaction effect revealed increased activation for own (vs unknown) infants in threatening (vs neutral) situations in bilateral motor areas, possibly indicating preparation for action. Post-natal activation patterns were similar; however, in part of the superior frontal gyrus the distinction between threat to own and unknown infant faded. Fathers showing more protective behavior in daily life recruited part of the frontal pole more when confronted with threat to their own vs an unknown infant. This exploratory study is the first to describe neural mechanisms involved in paternal protection and provides a basis for future work on fathers’ protective parenting.

Phase of the menstrual cycle affects engagement of attention with emotional images

Changes that occur during the menstrual cycle affect various aspects of behavior, cognition, and emotion. Here, we focused on potential differences between early follicular and midluteal phases in the way women process images of behaviorally relevant content categories: children, threat, disgust, erotic scenes, low- and high-calorie food. Using eye-tracking, we examined women's engagement of attention in the key region of each image in a free-viewing condition. Specifically, we tested how quickly attention was attracted to these regions and for how long it was held there. Participants took part in two experimental sessions, one in the early follicular and one in the midluteal phase. The results showed that in the midluteal phase attention was attracted to the key region earlier than in the early follicular phase: the first fixation more often fell within the key region and there were fewer fixations preceding it. While the effect of the phase in terms of the capture of attention did not depend on the image category, the effect regarding the hold of attention was category-specific, concerning the disgust category only. Specifically, in the midluteal phase the duration of the exploration of the key region between reaching it for the first time and first exiting it was shorter, which might be due to heightened sensitivity to disgusting stimuli in this period. Overall, our results indicate the occurrence of changes in attentional processing of emotional scenes related to the menstrual cycle, which seem to differ depending on the aspect of attention deployment: in the midluteal phase the effect of enhancing orienting was general and concerned any important visual information, whereas the effect of the shortened hold of attention appeared to be limited to specific content.

Vasopressin Differentially Affects Handgrip Force of Expectant Fathers in Reaction to Own and Unknown Infant Faces

The underlying mechanisms of paternal responses to infant signals are poorly understood. Vasopressin has previously been proposed to affect these responses. Using a double-blind, placebo-controlled, within-subject design (N = 25 expectant fathers), we examined the effect of vasopressin administration on the use of excessive handgrip force during exposure to infant crying versus matched control sounds, while participants saw morphed images representing their own infant versus an unknown infant. We found that, compared to placebo, AVP administration elicited more excessive force while viewing an unknown infant image compared to viewing the image representing one’s own infant, while the reverse was true under placebo. The results are discussed in light of vasopressin’s role in parenting and parental protection among human fathers.

Functional significance of men's testosterone reactivity to social stimuli

Rapid testosterone fluctuations in response to social stimuli are observed across a wide range of species, and the highly conserved nature of these fluctuations suggests an adaptive function. This paper reviews the current literature on testosterone reactivity, primarily in human males, and illustrates how life-history theory provides an adequate theoretical framework to interpret findings. The review is structured around supporting evidence suggesting that situations implicated in mating effort either directly (e.g., interactions with a mate) or indirectly (e.g., intrasexual competition) are generally associated with a brief elevation of testosterone, while situations implicated in parenting effort (e.g., nurturant interactions with offspring) are generally associated with a decline in testosterone. Further, we discuss how these fluctuations in testosterone have been linked to future behaviors, and how situational, motivational, and physiological variables moderate the interplay between social stimuli, testosterone reactivity, and behavior. Supporting the notion that testosterone can play a causal role in modulating behavior in response to social stimuli, we also summarize recent single administration studies examining the effects of testosterone on physiology, neurobiology, and behavior. A conceptual model provides links between supported findings, and hypothesized pathways requiring future testing.

Testosterone, oxytocin, and the development of human parental care

The steroid testosterone (T) and neuropeptide oxytocin (OT) have each been implicated in the development of parental care in humans and animals, yet very little research addressed the interaction between these hormones at the transition to parenthood in mothers and fathers. One hundred and sixty mothers and fathers (80 couples) were visited 1 and 6months after the birth of their first child, plasma OT and T were assayed at each time-point, and interactions between each parent and the infant were observed and micro-coded for two key parental behaviors; affectionate touch and parent-infant synchrony. T showed gender-specific effects. While paternal T was individually stable across the first six months of parenting and predicted lower father-infant synchrony, maternal T was neither stable nor predictive of maternal behavior. An interaction of OT and T showed that T has complex modulatory effects on the relations of OT and parenting. Slope analysis revealed that among fathers, only when T was high (+1SD), negative associations emerged between OT and father affectionate touch. In contrast, among mothers, the context of high T was related to a positive association between OT and maternal touch. Our findings, the first to test the interaction of OT and T in relation to observed maternal behavior, underscore the need for much further research on the complex bidirectional effects of steroid and neuropeptide systems on human mothering and fathering.

Neural correlates of babyish adult face processing in men

The morphological characteristics of an infant's face are collectively referred to as baby schema or babyishness. It has been well established that infant traits are implicitly projected, or overgeneralized, to adults with babyish facial features. However, few studies to date have investigated the neural underpinnings of such overgeneralization. In the present study, we addressed this issue by comparing neural activations elicited by baby-faced and mature-faced adult faces in men using fMRI. We found increased activations in clusters surrounding the bilateral insula, bilateral anterior cingulate cortex, and right inferior frontal gyrus, which have been previously linked to the processing of facial attractiveness and infant-related information. We also discovered increased activation in the left medial prefrontal cortex, which might be related to emotional or empathic responses directed towards baby-faced adults. The activated region also included the left premotor cortex, which presumably reflects an embodied response or approach motivation directed toward infant-related information. Furthermore, the activation level of the left caudate correlated with the salivary concentration of oxytocin. Taken together, these findings indicate that passive viewing of babyish adult faces induces increased responses in neural regions linked to facial attractiveness and infant-related information processing, and that these responses are partially influenced by oxytocinergic factors.

Endogenous Testosterone and Exogenous Oxytocin Modulate Attentional Processing of Infant Faces

Evidence indicates that hormones modulate the intensity of maternal care. Oxytocin is known for its positive influence on maternal behavior and its important role for childbirth. In contrast, testosterone promotes egocentric choices and reduces empathy. Further, testosterone decreases during parenthood which could be an adaptation to increased parental investment. The present study investigated the interaction between testosterone and oxytocin in attentional control and their influence on attention to baby schema in women. Higher endogenous testosterone was expected to decrease selective attention to child portraits in a face-in-the-crowd-paradigm, while oxytocin was expected to counteract this effect. As predicted, women with higher salivary testosterone were slower in orienting attention to infant targets in the context of adult distractors. Interestingly, reaction times to infant and adult stimuli decreased after oxytocin administration, but only in women with high endogenous testosterone. These results suggest that oxytocin may counteract the adverse effects of testosterone on a central aspect of social behavior and maternal caretaking.

The endocrinology of human caregiving and its intergenerational transmission

Variation in the quality of parental care has a tremendous impact on a child's social–emotional development. Research investigating the predictors of this variability in human caregiving behavior has mostly focused on learning mechanisms. Evidence is currently accumulating for the complementary underlying role of steroid hormones and neuropeptides. An overview is provided of the hormones and neuropeptides relevant for human caregiving behavior. Then the developmental factors are described that stimulate variability in sensitivity to these hormones and neuropeptides, which may result in variability in the behavioral repertoire of caregiving. The role of genetic variation in neuropeptide and steroid receptors, the role of testosterone and oxytocin during fetal development and parturition, and the impact of experienced caregiving in childhood on functioning of the neuroendocrine stress and oxytocin system are discussed. Besides providing a heuristic framework for further research on the ontogenetic development of human caregiving, a neuroendocrine model is also presented for the intergenerational transmission of caregiving practices. Insight into the underlying biological mechanisms that bring about maladaptive caregiving behavior, such as neglect and insensitive parenting, will hopefully result in more efficient approaches to reduce the high prevalence of such behavior and to minimize the impact on those affected.

Exogenous testosterone increases men's perceptions of their own physical dominance

Men's testosterone is associated with several constructs that are linked to dominance rank, such as risk-taking, mating success, and aggression. However, no study has directly tested the relationship between men's self-perceived dominance and testosterone using an experimental design. We employed a within-subjects, double-blind, placebo-controlled paradigm to assess whether testosterone influences men's self-perceived dominance. Exogenous testosterone or a placebo was administered to healthy adult men and self-perceptions of physical dominance were subsequently assessed by having participants select what they believed to be their true face from an array of images digitally manipulated in masculinity. Men picked a more masculine version of their own face after testosterone versus placebo--an effect that was particularly pronounced among men with relatively low baseline testosterone. These findings indicate that a single administration of testosterone can rapidly modulate men's perceptions of their own physical dominance, which may explain links between testosterone and dominance-related behaviors.

A longitudinal analysis of women's salivary testosterone and intrasexual competitiveness

Research on within-subject changes in women's intrasexual competitiveness has generally focused on possible relationships between women's intrasexual competitiveness and estimates of their fertility. While this approach is useful for testing hypotheses about the adaptive function of changes in women's intrasexual competitiveness, it offers little insight into the proximate mechanisms through which such changes might occur. To investigate this issue, we carried out a longitudinal study of the hormonal correlates of changes in intrasexual competitiveness in a large sample of heterosexual women (N=136). Each woman provided saliva samples and completed an intrasexual competitiveness questionnaire in five weekly test sessions. Multilevel modeling of these data revealed a significant, positive within-subject effect of testosterone on intrasexual competitiveness, indicating that women reported greater intrasexual competitiveness when testosterone was high. By contrast, there were no significant effects of estradiol, progesterone, estradiol-to-progesterone ratio, or cortisol and no significant effects of any hormones on reported relationship jealousy. This is the first study to demonstrate correlated changes in measured testosterone levels and women's reported intrasexual competitiveness, implicating testosterone in the regulation of women's intrasexual competitiveness.

Neural systems and hormones mediating attraction to infant and child faces

We find infant faces highly attractive as a result of specific features which Konrad Lorenz termed “Kindchenschema” or “baby schema,” and this is considered to be an important adaptive trait for promoting protective and caregiving behaviors in adults, thereby increasing the chances of infant survival. This review first examines the behavioral support for this effect and physical and behavioral factors which can influence it. It then provides details of the increasing number of neuroimaging and electrophysiological studies investigating the neural circuitry underlying this baby schema effect in parents and non-parents of both sexes. Next it considers potential hormonal contributions to the baby schema effect in both sexes and the neural effects associated with reduced responses to infant cues in post-partum depression, anxiety and drug taking. Overall the findings reviewed reveal a very extensive neural circuitry involved in our perception of cuteness in infant faces, with enhanced activation compared to adult faces being found in brain regions involved in face perception, attention, emotion, empathy, memory, reward and attachment, theory of mind and also control of motor responses. Both mothers and fathers also show evidence for enhanced responses in these same neural systems when viewing their own as opposed to another child. Furthermore, responses to infant cues in many of these neural systems are reduced in mothers with post-partum depression or anxiety or have taken addictive drugs throughout pregnancy. In general reproductively active women tend to rate infant faces as cuter than men, which may reflect both heightened attention to relevant cues and a stronger activation in their brain reward circuitry. Perception of infant cuteness may also be influenced by reproductive hormones with the hypothalamic neuropeptide oxytocin being most strongly associated to date with increased attention and attraction to infant cues in both sexes.

Early and late event-related potentials are modulated by infant and adult faces of high and low attractiveness

The processing of infant faces may be somewhat distinct from that of adult faces. Indeed, recent neuroimaging studies have provided evidence of an early, "baby-specific" neural response whereby infant faces are perceived more rapidly than adult faces. Using event-related potentials, the present study aimed to determine whether the preferential response to infant faces is present at both early and late stages of face processing, and to investigate the effects of esthetic appearance on the processing of adult and infant faces by directly manipulating the perceived attractiveness or cuteness within a given face identity. Here, we find evidence for enhanced processing of infant faces, relative to adult faces, at both early (N170, P2) and late (LPC) stages of face processing. We also find that the esthetic appearance of both infant and adult faces modulates early neural responses, with enhanced responses to less attractive/cute faces as compared to more attractive/cute faces. Overall, our results provide additional evidence for a preferential response to infant faces at early stages of processing, and provide new evidence that this preferential response occurs at later stages of face processing as well, independent of the esthetic quality of the face or observer sex.

Facial coloration tracks changes in women's estradiol

Red facial coloration is an important social cue in many primate species, including humans. In such species, the vasodilatory effects of estradiol may cause red facial coloration to change systematically during females' ovarian cycle. Although increased red facial coloration during estrus has been observed in female mandrills (Mandrillus sphinx) and rhesus macaques (Macaca mulatta), evidence linking primate facial color changes directly to changes in measured estradiol is lacking. Addressing this issue, we used a longitudinal design to demonstrate that red facial coloration tracks within-subject changes in women's estradiol, but not within-subject changes in women's progesterone or estradiol-to-progesterone ratio. Moreover, the relationship between estradiol and facial redness was observed in two independent samples of women (N = 50 and N = 65). Our results suggest that changes in facial coloration may provide cues of women's fertility and present the first evidence for a direct link between estradiol and female facial redness in a primate species.