Chimpanzees: Maternal lactational investment is higher for sons than for daughters

Maternal lactational investment is higher for sons in chimpanzees. Iulia Bădescu, David P. Watts, M. Anne Katzenberg & Daniel W. Sellen. Behavioral Ecology and Sociobiology volume 76, Article number: 44 (2022). Mar 10 2022. https://link.springer.com/article/10.1007/s00265-022-03153-1

Abstract: Maternal lactational investment can affect female reproductive rates and offspring survival in mammals and can be biased towards infants of one sex. We compared estimates of lactation effort among mothers, assessed as their potential milk contribution to age-specific infant diets (mother-infant differences in fecal stable nitrogen isotopes, δ15N), to the timing of weaning (infant age at last nursing bout) and to maternal inter-birth interval lengths for male and female infant chimpanzees (Pan troglodytes) at Ngogo, Uganda. Infant males had greater proportions of milk in their age-specific diets, indicated by higher mother-infant differences in δ15N (Generalized Estimating Equation, GEE: p < 0.01). This may mean that mothers of sons showed greater lactation effort than mothers of daughters. Infant males stopped nursing at older ages than infant females (Kaplan–Meier product limit estimate, Breslow estimator: p < 0.05). Mothers of sons showed longer interbirth intervals than mothers of daughters (GEE: p < 0.01). All three measures indicated maternal lactational investment was higher for sons. Male infants may cost mothers more to ensure infant survival than female infants because males are more vulnerable and/or because maternal genetic returns on investment are greater for sons than daughters, as male philopatry means that chimpanzee mothers can have more influence on the reproductive success of sons. Chimpanzee females may trade off growth-related benefits of high lactational investment in male offspring against reduced reproductive rates.

Significance statement: Maternal investment via lactation affects the reproductive success of female mammals and their offspring and can be biased towards infants of one sex. We investigated lactational variation among wild chimpanzees in relation to infant sex using three proxies for maternal lactational investment: fecal stable nitrogen isotopes, a physiological biomarker that may provide an estimate of lactation effort; observations of nursing, which we used to establish weaning ages; and the lengths of intervals between births of surviving infants. Chimpanzee mothers biased lactational investment toward sons on all three indicators and showed reduced fecundity due to longer inter-birth intervals for mothers of sons than for mothers of daughters. These results would be expected if greater maternal investment toward sons leads to better condition and higher reproductive success for sons later in life, thus to greater inclusive fitness for mothers.

Discussion

Our results collectively indicate that chimpanzee females invest more heavily via lactation in sons than in daughters, which supports the hypothesis. Physiological biomarker data revealed that sons had greater proportions of milk in their diets than daughters, which indicated that mothers could have made greater lactation effort for sons, and that sons were weaned at later ages than daughters. Variation in age at weaning had reproductive implications for adult females. Data on inter-birth intervals showed that mothers of sons experienced more delayed fecundity than mothers of daughters. That results of statistical analyses of demographic, behavioral, physiological data were in the same direction lends support to the argument that this is a true pattern. Our results are in line with previous studies that found evidence for higher maternal investment in sons for chimpanzees at Taï (Boesch 1997; Fahy et al. 2014) and Gombe (Lonsdorf et al. 2020); in other nonhuman primates (spider monkeys, A. paniscus: McFarland Symington 1987; mountain gorillas, G. beringei: Robbins et al. 2007; Eckardt et al. 2016; Robbins and Robbins 2021); and in other mammals (African elephants, L. africana: Lee and Moss 1986; seals, M. angustirostris: Reiter et al. 1978, Arctocephalus spp.: Trillmich 1986; Lunn and Arnould 1997; Iberian deer, C. e. hispanicus: Landete-Castillejos et al. 2005).

As assessed by isotopic data, the divergence in dependence on maternal milk between male and female infants was clearest early in infancy (≤ 1 year old, > 1.5 to 2 years old) and late in infancy (> 3.5 years old), when males continued relying on milk while many females were weaned (Figs. 1 and 3; when infants > 5 years old were removed from the analyses, results did not change: Supplementary Information). At some ages, however, infant females relied on milk more than males, and overlap between the mother-infant stable nitrogen isotope differences of male and female infants was considerable for all age categories. Thus, while analyses indicated that infant males relied on milk more than females overall, these results should be interpreted with caution as indications of potentially real effects that warrant further investigation to validate and replicate. Similarly, and consistent with an evolutionary conceptual framework in which infant sex is not expected to be the sole driver of maternal investment, the range of observed weaning ages and female interbirth intervals overlapped, which indicated that some sons were weaned earlier than most daughters and that some mothers of sons had shorter inter-birth intervals than most mothers of daughters. This suggests that other variables, including maternal, ecological, or social factors not measured here, also influenced developmental trajectories. For example, infant carrying is presumably the second most energetically expensive form of maternal investment in most primates (Altmann and Samuels 1992); we do not have data on age-independent variation in the time mothers carried infants, and thus cannot assess its possible contribution to variation in inter-birth intervals. Relatively long inter-birth intervals could result from poor maternal condition, as seems to be the case for olive baboons, Papio anubis (Patterson et al. 2021). However, no obvious reason exists why mothers with daughters would consistently be in poorer condition than mothers with sons. Also, Ngogo provides relatively favorable energetic conditions for chimpanzees, as indicated by data on feeding ecology (Potts et al. 2011; Watts et al. 2012a, b) and C-peptide data (Emery Thompson et al. 2009). Higher mortality of first-born than later-born infants at Ngogo (Wood et al. 2017) is likely to be an effect of maternal condition that results from trade-offs that primiparas face between investing in their own growth versus maternal investment, but we found no effect of parity on weaning ages.

Male infants might have relied more on milk than non-milk foods than same-aged females because they ingested less solid food. If so, this could explain the higher mother-infant δ15N differences for males, because even if absolute milk intake was similar between the sexes, milk would still have contributed a greater proportion of the male infant diet relative to non-milk food. Infant solid food intake data at Ngogo are needed to resolve this issue. At Gombe, there were no differences in the amount of time that male and female infant chimpanzees spent feeding on solid foods up to 5 years of age (Lonsdorf et al. 2014). It may thus be that the higher mother-infant δ15N differences we found for infant males at Ngogo were due to chimpanzee mothers of sons synthesizing more milk, on average, than mothers of daughters. Also, the δ15N differences we obtained probably did not occur because mothers and infants ate different solid foods. Dependent chimpanzee offspring usually foraged at the same time and on the same foods as their mothers, and mothers always shared foods that were difficult to access or extract (Badescu et al. 2017, 2020).

Stable nitrogen isotope ratios primarily reflect the protein component of milk. We therefore cannot exclude the possibility that total energetic lactational investment was similar for mothers of sons and daughters, but mothers of daughters made milk lower in protein and richer in fats and/or sugars compared to mothers of sons. Differences in maternal milk compositions for sons and daughters have been documented in some species (Landete-Castillejos et al. 2005; Hinde 2007, 2009). Nevertheless, our findings that infant males are weaned later than infant females and that mothers of sons have longer IBIs are strong indications of higher total lactational costs of raising males.

In comparing physiological and behavioral assessments of weaning for the four infants for whom we could determine weaning ages isotopically, we found that behavioral and physiological weaning ages matched exactly for one male, but the second was not observed nursing during the two months before he was physiologically weaned. This disparity could have occurred because he was only night-time nursing for the last few months before he stopped drinking milk. If so, he was the only infant in our dataset who exhibited night-time nutritive nursing despite being identified as behaviorally weaned. We could only assess whether physiological and behavioral weaning ages matched for one of two females. This infant nursed during the month that she was physiologically weaned, which indicated that she was comfort nursing without milk transfer, a pattern described among several of our study infants (Bădescu et al. 2017). Because the sample of infants for whom we could establish weaning ages isotopically was so small, we could not conclusively say whether males were physiologically weaned later than females. However, this seems to be a strong possibility given that physiological weaning occurred an average of 23.5 months later for the two males than the two females for whom we had firm data.

Mothers may be under direct selective pressures to invest more in sons because infant males require greater maternal investment to survive. Infant males could also be more demanding of maternal investment and may solicit greater lactation effort from their mothers than infant females. In some highly sexually dimorphic species, infant growth is faster in males than females, and males therefore require more lactation effort (e.g., mountain gorillas, G. beringei: Eckardt et al. 2016; western gorillas, G. gorilla: Meder 1990; Leigh and Shea 1996; California sea lion, Zalophus californianus: Oftedal et al. 1987; Galápagos sea lion, Zalophus wollebaeki: Piedrahita et al. 2014). However, chimpanzee body mass dimorphism is moderate, and while growth data are not available for wild chimpanzee infants younger than 3 years old, the absence of sex differences in body mass at age 3 at Kasekela (Pusey et al. 2005) and the similarity of male and female growth trajectories there and at Kanyawara (Emery Thompson et al. 2016) imply that no consistent sex difference in infant growth exists. Second, male offspring may be biologically less resilient and more sensitive and may therefore be less buffered in the face of hardship than female offspring (“fragile male hypothesis”: Clutton-Brock et al. 1985; Stinson 1985; Lindstrom 1999; Wells 2000; Battles 2016). Higher infant mortality rates for males than females have been demonstrated in several mammals including Galápagos sea lions, Z. wollebaeki (Kraus et al. 2013), red deer, Cervus elaphus (Clutton-Brock et al. 1985), and humans, Homo sapiens (Kraemer 2000), as expected under this hypothesis. Infant mortality at Ngogo is substantial and resembles that at other chimpanzee research sites, but whether a sex difference exists is unclear because mortality is highest for very young infants, for whom determining sex is difficult (Wood et al. 2017). At Gombe, immature male chimpanzees between 10 and 15 years of age (but not at younger ages) showed higher mortality than females after maternal loss (Stanton et al. 2020); this suggests that early life mortality in chimpanzees is higher for males. Male offspring could suffer injuries more often, given that (as in other nonhuman primates), they spend more time in social play and engage in rough and tumble play more than females (Owens 1975; Forster and Cords 2005; Lonsdorf et al. 2014). Chimpanzee mothers may therefore face selective pressure to provide high maternal investment in sons, via higher lactation effort and longer lactation length, to increase the probability that sons survive, especially during times of food scarcity or infectious disease epidemics (Clutton-Brock et al. 1985; Stinson 1985; Lindstrom 1999; Wells 2000; Battles 2016). However, food scarcity probably did not affect the differential maternal investment of infants in our study, as noted above. Also, none of our study infants suffered major injuries during data collection. A respiratory virus outbreak at Ngogo in 2016–2017 led to a spike in infant mortality (Negrey et al. 2019), but we cannot assess whether a sex bias in mortality occurred because some young infants died before observers had been able to ascertain their sex.

Female chimpanzees may stand to gain greater inclusive fitness by investing more in sons than in daughters. Female mammals generally produce a limited number of offspring in their lifetimes, whereas males can theoretically produce few or no offspring, or many, depending on their condition and access to fertile females (Trivers 1972). Especially when conditions are good, such as when food availability is high, maximum potential reproductive output is much higher for males than for females (Trivers and Willard 1973; Bercovitch 2002). Similarly, mothers in good condition are predicted to bias investment towards offspring of the sex that is most likely to benefit from the increased maternal contribution (Trivers and Willard 1973; Bercovitch 2002). In male philopatric species, sons are more likely to benefit from the added maternal investment under good conditions than are daughters. At Taï, females identified as high-ranking, who were presumably in better condition than lower-ranking females because of better access to high quality resources, had longer inter-birth intervals following births of sons than births of daughters. Boesch (1997) argued that this showed they invested more via lactation in sons. In contrast, low-ranking females, who were presumably in worse condition, had longer inter-birth intervals after producing daughters and apparently made more lactational investment in daughters than sons (Boesch 1997). Compared to other chimpanzee research sites, food abundance at Ngogo is high and feeding competition is low (Potts et al. 2009, 2011, 2020), and female energetic condition there is probably generally good (Potts et al. 2011; Potts 2013), which helps explain why females do not form dominance hierarchies there (Wakefield 2008). All mothers in this favorable ecological context could benefit from investing more heavily in sons because the potential for high reproductive success, and hence greater inclusive fitness for the mothers, is higher for males than for females (Trivers and Willard 1973; Bercovitch 2002). However, how well the Trivers and Willard (1973) hypothesis applies to chimpanzees is still unclear. Moreover, the relatively high gregariousness of Ngogo females and relatively low variation in fruit abundance there argue against competition effects on female fecundity like those proposed for Gombe (Pusey et al. 1997) and Kanyawara (Kahlenberg et al. 2008). As Riedel et al. (2011) argue, chimpanzee socioecological circumstances are not universally the same, and care should be taken before generalizing findings from any one community to the species level.

Compared to other long-term research sites, reproductive skew among males at Ngogo is low and mean male reproductive success is high (Langergraber et al. 2017). Prior to the permanent community fission, all Ngogo males gained long-term reproductive benefits from participating in cooperative territory defense (Langergraber et al. 2017). Thus, females at Ngogo, in favorable ecological circumstances that allow a large community with many males who can do well in intergroup competition, could benefit from investing more heavily in sons because success in intergroup competition increases mean male reproductive success (Potts et al. 2009, 2011, 2020; Langergraber et al. 2017).

In contrast, daughters might benefit from relatively early nutritional independence. This could facilitate social independence, which is important because most chimpanzee females must establish social relationships with strangers in their new communities. In ursine red howler monkeys (Alouatta arctoidea), females who emigrated from natal groups were weaned faster than those who stayed in their natal groups (Crockett and Rudran 1987), which suggests that early weaning provides benefits associated with dispersal. However, the benefits of faster development for female chimpanzees, if any, are unclear, especially because juvenile and young adolescent females at Gombe associated more closely, not less, with their mothers than males did (Pusey 1983, 1990). Thus, it seems unlikely that chimpanzee females acquire social competence faster than males.

Whether early maternal investment in sons influences the sons’ reproductive success in chimpanzees is unclear, partly because we do not have data on infant and juvenile growth. Bonobos (Pan paniscus) are also male philopatric, and female bonobos can influence the mating opportunities, rank, and reproductive success of their sons after weaning. Such influence seems mostly due to the effect of mother-adult son alliances on male-male competition (Surbeck et al. 2011, 2019). Female chimpanzees rarely intervene in contests between adult males and do not directly influence their adult sons’ dominance ranks (Surbeck et al. 2019). Whether early maternal investment influences adult male chimpanzee competitive ability is unknown. At Taï, the presence of mothers was positively associated with post-weaning growth, although this applied to both offspring sexes (Samuni et al. 2020). Likewise, association between mothers and sons before maturity, but after weaning, was positively associated with male reproductive success (Crockford et al. 2020), but causality, if any, was unclear. Any causal influence is likely to act via early growth and nutrition provided by maternal milk, as happens in bighorn sheep (Festa-Bianchet et al. 2000). Adult body size presumably influences male dominance ranks in chimpanzees, and male rank and reproductive success are positively correlated (Wroblewski et al. 2009; Langergraber et al. 2013). If adult body size is also positively associated with early growth and size at weaning, high lactational investment for male offspring could indeed bring fitness payoffs (Clutton-Brock et al. 1984; Clutton-Brock 1991; Lee et al. 1991). Differential maternal investment in sons by chimpanzee females in our study may translate into better condition for male offspring later in life, which could lead to higher male reproductive success and greater inclusive fitness for mothers. Cross-sectional data showing longer inter-birth intervals following births of sons than births of daughters imply that females trade off any growth-related benefits of high lactational investment in males against reduced reproductive rates, as Emery Thompson et al. (2016) argued for chimpanzees at Kanyawara. Continued documentation of within-female variation in inter-birth intervals as a function of offspring sex will help address this issue.

Leftists explicitly describe themselves as completely separate from Liberals, who they claim cooperate with existing institutions and seek insufficient social change

Alto, Alix, Grace Flores-Robles, Kyle Anderson, Jordan Wylie, Levi Satter, and Ana P. Gantman. 2022. ““I Put Liberal but LOL”: Investigating Psychological Differences Between Political Leftists and Liberals” PsyArXiv. March 10. doi:10.31234/osf.io/3qgep

Abstract: Political ideology in the United States is typically described as a spectrum. This metaphor implies that the people who place themselves along the spectrum differ in degree from each other; an individual who places themselves all the way on the left of the spectrum, is an extreme version of another closer to the middle. Political polarization and elite extremism are on the rise in the United States (e.g., Finkel et al., 2020), and attention to political polarization has fueled efforts to understand the extreme right (e.g, Forscher & Kteily, 2020), and driven attempts to identify whether the extreme left may or may not share authoritarian tendencies with those on the extreme right (Conway et al., 2018; Costello et al., 2021; Badaan et al., 2020; Nilsson & Jost, 2020). The central focus of psychology on the extreme Left has been on Left-wing authoritarianism¬—whether it exists, is appropriately named, or logically possible (Conway et al., 2018; Costello et al., 2021; Badaan & Jost, 2020; Nilsson & Jost, 2020). However, this approach sidesteps a longstanding distinction that exists among politically left-leaning individuals–that between Leftists and Liberals (see Menand, 2021). While Leftists explicitly describe themselves as completely separate from Liberals¬, who they claim cooperate with existing institutions and seek insufficient social change (Ture, 1966), Liberals may more easily see themselves as part of a larger left-leaning political group, such that they express surprise and even anger when Leftists do not support their political agenda (Capeheart, 2020). It is the aim of this paper to investigate the psychological differences between Leftists and Liberals (i.e., in terms of ideology, morality, political preferences, and judgments of group boundaries) to further our understanding of how these two historical groups may differ and interact, and help us understand political ideology, identity, and radicalism, more broadly.

Women were more aware of both their pleasant and unpleasant body odors than men

Croijmans, Ilja, Garmt Dijksterhuis, Natalia Majorov, and Monique A. M. Smeets. 2022. “A Psychological Scale for Body Odour Awareness.” PsyArXiv. March 10. doi:10.31234/osf.io/nf6sd

Abstract: People differ in their awareness for odours surrounding them. Body odours are a special category because they are a medium for social communication. Body odours evoke approach and avoidance behaviours such as withdrawing from social interaction, and personal hygiene behaviours like washing or using fragranced products. So far it has remained unclear what the role of conscious awareness of body odours is in guiding social behaviour. Here, we present a new psychological scale on odour awareness, focusing specifically on body odours: the Body Odour Awareness Scale (BOAS). The scale was validated measuring body odour awareness in two dimensions (valence and source) over four domains: awareness for one’s own body odours, both favourable and unfavourable, and awareness for other persons’ body odours, both favourable and unfavourable. An explorative follow-up study suggested regional differences exist in body odour awareness, but these are not the same for every dimension of body odour awareness. Taken together, these results suggest the new BOAS is a useful tool to assess differences in awareness for body odours, and uncover the application potential for this new and validated scale.

From 2019... The neuroscience of Romeo and Juliet: an fMRI study of acting

From 2019... The neuroscience of Romeo and Juliet: an fMRI study of acting. Steven Brown, Peter Cockett and Ye Yuan. Royal Society Open Science, March 13 2019. https://doi.org/10.1098/rsos.181908

Abstract: The current study represents a first attempt at examining the neural basis of dramatic acting. While all people play multiple roles in daily life—for example, ‘spouse' or ‘employee'—these roles are all facets of the ‘self' and thus of the first-person (1P) perspective. Compared to such everyday role playing, actors are required to portray other people and to adopt their gestures, emotions and behaviours. Consequently, actors must think and behave not as themselves but as the characters they are pretending to be. In other words, they have to assume a ‘fictional first-person' (Fic1P) perspective. In this functional MRI study, we sought to identify brain regions preferentially activated when actors adopt a Fic1P perspective during dramatic role playing. In the scanner, university-trained actors responded to a series of hypothetical questions from either their own 1P perspective or from that of Romeo (male participants) or Juliet (female participants) from Shakespeare's drama. Compared to responding as oneself, responding in character produced global reductions in brain activity and, particularly, deactivations in the cortical midline network of the frontal lobe, including the dorsomedial and ventromedial prefrontal cortices. Thus, portraying a character through acting seems to be a deactivation-driven process, perhaps representing a ‘loss of self'.

4. Discussion

Despite the central importance of role playing in both everyday social interactions and the theatrical arts, it has been little studied in either the psychology or neuroscience literatures. We sought to address this neglect by carrying out the first neuroimaging study of dramatic role playing, employing trained actors as participants. Because of the wide diversity of actor-training methods, we opted to work with a uniform population of actors, all of whom had a similar training in the dominant form of acting in North America and who possessed a similar amount of training and performance experience. In addition, because MRI experiments are so restrictive of body movement and facial gesturing, we chose to examine a group of actors specialized in the mentalistic approach to character portrayal most commonly taught in theatre schools.

The imaging results showed that acting led to deactivations in brain areas involved in self processing, with a focus on the dmPFC/SFG and vmPFC. This might suggest that acting, as neurocognitive phenomenon, is a suppression of self processing. The major increase in activation associated with role change was seen in the posterior part of the precuneus. Perhaps the most surprising finding of the study was that the British accent condition—during which the participants were instructed to maintain their self-identity—showed a similar deactivation pattern vis-à-vis the self that acting did, suggesting that gestural mimicry of even a completely unspecified other has an impact on brain areas involved in self processing. This supports the contention of acting theorists that gestural and psychological approaches might be related paths towards achieving the same goal, namely the embodied portrayal of a character [8,51,60]. It also lends support to theories of embodied cognition, which argue that a change in gestural expression can influence the way that people think and the emotions that they feel [61,62].

We are aware of only a single prior study that attempted anything like our Fic1P condition, that of Ames et al. [47], although their task was not intended as an acting condition per se. While our vmPFC deactivations were quite a bit dorsal to theirs, we found a similar increase in deactivation for Fic1P compared to 1P, as well as for 3P compared to 1P. The British accent showed a comparable deactivation in the vmPFC to the 3P condition (when both were compared with 1P), but less than that for acting. However, the most acting-specific deactivation we observed was not in the vmPFC but in the dmPFC/SFG. In addition, we observed an area of activation increase in the precuneus that was specific to acting compared to the other three conditions, although it emerged through the loss of deactivation compared to 1P. We would like to consider these findings in terms of the two processes of perspective change and role change.

4.1. Perspective change

One of the major objectives of the study was to compare the pattern of brain activation for acting with that for the well-studied process of 3P perspective taking, referred to as ToM processing. In several respects, our study was biased towards seeing an overlap between acting and mentalizing. First, the participant population consisted of actors with a mentalistic orientation towards getting into character that emphasizes inferring the thoughts, emotions and motivations of a character in a given situation. Second, our scanner task required participants to engage in the psychological process of formulating responses to hypothetical questions. It is perhaps not surprising that answering questions as Romeo or Juliet would tap not only into role playing but mentalizing as well in order for the participant to determine an appropriate answer from the perspective of the character. In other words, an actor would have to consult some degree of third-person knowledge about Romeo or Juliet—just as with any person other than the self—in order to formulate answers from their perspective. So, neural similarities between Fic1P and 3P may be more of a reflection of our question-answering task than of the nature of acting, since acting theorists believe that mentalizing about a character is far more important during the preparatory phase of studying a role than during the process of character portrayal in performance [7].

With respect to our ToM contrast, the most significant difference between 3P and 1P was a deactivation in the vmPFC and the ventral part of the dmPFC, which became the major marker of perspective change in this study. This same deactivation was seen more intensely in the contrast of acting to 1P. In both cases, the effect resulted from a decrease in the level of activation compared to the self condition. Hence, the presence of the vmPFC deactivation for acting might indicate that actors engage in 3P perspective-taking with their character while undergoing the process of acting, or that acting is a more intense form of perspective taking, since there was a greater reduction in vmPFC and dmPFC-v activities for Fic1P than for 3P. This interpretation is only reasonable if this process occurs in an implicit manner. This would also account for the same, but weaker, deactivation effect seen in the British accent condition. While participants in the 3P condition were told to explicitly assume the perspective of their close other, this was not the case during either the acting or accent conditions. If anything, during the accent condition, participants were clearly instructed not to stray from the self perspective. Hence, if an increasing deactivation in the vmPFC and dmPFC-v is a marker of deviation from the self perspective, then this would have to work during both explicit tasks (like 3P and other types of ToM tasks) and implicit tasks where people psychologically stray from the self perspective, but in which they are not told to assume another person's perspective. Van Overwalle & Vandekerckhove [63] reviewed both electroencephalography and fMRI evidence suggesting that implicit mentalizing employs the same mentalizing network as explicit mentalizing. If anything, the medial PFC has been shown to be more strongly linked with implicit than explicit mentalizing [64]. Similar results were obtained when comparing implicit and explicit forms of trait judgement [65].

4.2. Role change

Acting produced additional effects beyond the ones in the vmPFC and ventral dmPFC that were observed in the 3P condition, suggesting that acting is something more than just mentalizing about a character. One of these effects was a deactivation in the dmPFC/SFG for acting versus self that was also observed in British accent versus self, while the other was an activation increase in the precuneus that was found when acting was contrasted with either self (1P) or other (3P).

dmPFC and SFG. A large dorsoventral extent of the dmPFC was shown to be deactivated during acting when compared to the 1P condition, compatible with the loss of a self-related process during acting and gestural pretence. Denny et al.'s [26] meta-analysis of self/other processing argued for a dorsoventral distinction in the medial PFC such that the vmPFC showed an overlap between self and other processing (when each one was compared against a low-level baseline), while the dmPFC showed a preference for other compared to self processing. Our results seem incompatible with those findings, since we observed the highest level of dmPFC activity in the self condition, and less in each of the other conditions. Therefore, we would like to consider another dimension of self processing that may be tracked in our results.

D'Argembeau et al. [48] carried out a study of trait judgements about the self, but did so across the mental time frames of ‘present self' and ‘past self', as well as ‘present other' and ‘past other'. A peak in the dmPFC at MNI coordinate −2, 56, 26 (compared to Talairach coordinate −6, 50, 28 in Fic1P versus 1P) showed greater activity for the present self than the other three conditions. In addition, another dmPFC peak at MNI coordinate 4, 46, 44 (compared to Talairach coordinate −3, 38, 37 in Fic1P versus 1P) showed an interaction effect such that it was more active for the present self than the other three conditions. D'Argembeau et al. [66] followed up on these findings and showed that the dmPFC's preference for the present self extends beyond the past self to include the future self as well. Van der Cruyssen et al. [67] showed that both of the regions just mentioned were more active when people processed information about social categories of people (e.g. ambulance driver, kindergarten teacher) than simply adjectival trait descriptions (e.g. attentive, picky). Consistent with these studies on trait judgements about the self and others, the activation likelihood estimation (ALE) meta-analysis of Schurz et al. [28] showed that a dmPFC peak at Talairach coordinate 6, 26, 55 (compared to Talairach coordinate −12, 29, 55 in Fic1P versus 1P) is more active when people perform trait judgements than when they do false-belief mentalizing tasks. Likewise, Benoit et al. [68] found that the more ventral parts of the dmPFC have a preference for self over other trait-judgements, and Ma et al. [65] showed that the more dorsal part of the dmPFC is more active during spontaneous compared to intentional trait judgements. Garrison et al. [69] carried out a study in which participants were asked to make judgements about adjectives in terms of the self (Does the word describe you? Yes or no). The results of this task showed strong activations throughout the dorsoventral extent of the dmPFC. By contrast, several parts of the dmPFC were deactivated (when contrasted with rest) during a mindfulness meditation condition in the same participants, perhaps suggesting a reduction in the embodied self through meditation. Therefore, the dmPFC might encode more-enduring and stable features of the self, rather than a person's current mental states, the latter of which are examined in ToM tasks. If so, then the deactivations seen in the dmPFC for acting would represent a loss of self processing related to a trait-based conception of the self.

One possible interpretation of our results is that parts of the dmPFC encode information about not just an awareness of the self (with regard to both traits and states) but perhaps a sense of embodiment of the self. The embodied self can be considered as a zero-sum entity due to resource limitations. A person has only one voice, one face and one body as personal traits. The more that someone portrays another person, the fewer the resources there are to devote to him/herself. One cannot speak with a British accent and Canadian accent at the same time. Therefore, acting might be akin to a deliberate process of possession, i.e. a substitution of the actor's self by the character due to their embodiment of the character. The results of the British accent condition in our experiment suggest that even when a character is not being explicitly portrayed, gestural changes through personal mimicry can be a first step towards the embodiment of a character and the retraction of the self's resources. Certain entertainers, such as ventriloquists, rapidly switch between the self and a character within the time frame of a dialogue. It would be interesting to explore what is occurring in their brains as they make these rapid but seamless transitions between self and character.

Precuneus. The precuneus emerged as the major area of activation increase during role change in this study (along with a weak effect seen in the pSTS/TPJ). Activation was seen here for acting when it was compared against each of the three other conditions, although the activation itself resulted from a loss of deactivation compared to those conditions. The medial parietal cortex has been well established as a component of both the mentalizing network and the default mode network (DMN) [58], and emerges as a consensus region of activation in virtually all of the meta-analyses of the ToM literature that have been published [25–31]. However, before we interpret our acting effect as a mentalizing process, it is important to note that our precuneus activation is 20–30 mm posterior to the standard peaks found for ToM tasks. A typical y coordinate for ToM analyses is in the −50 to −60 range, whereas our peaks were in the −70 to −80 region. Hence, this establishes a distinction between the PCC (anteriorly) and precuneus (posteriorly), where mentalizing activations tend to be overwhelmingly in the PCC. Likewise, in keeping with the role of the PCC in the DMN, the PCC was strongly deactivated in all four of the conditions in this study when contrasted with fixation (see figure 1 for the 1P results). This preferential activation of the PCC during the resting state is the typical pattern for components of the DMN [56]. However, this region did not appear in any of the high-level contrasts, suggesting that the level of deactivation of the PCC was comparable across all of the task conditions and was therefore unaffected by either perspective change or role change. Only the precuneus, but not the PCC, showed a difference when acting was compared against the other three conditions.

Regardless of whether the relative increase in activation for the precuneus for acting was due to an increase in activation or a decrease in deactivation (as was in fact the case), the question we have to address is what processes activate the precuneus. We would like to consider two literatures where the precuneus is implicated. One is attention. The precuneus is a component of the dorsal attentional network of the brain, a network that is involved in functions such as attentional orienting, episodic retrieval and mental imagery [70–72]. It is telling to point out that acting theorists for over a century have talked about the ‘split consciousness' involved in the process of acting [4,8,10]. The actor has to be himself and someone else at the same time, and this could lead to a splitting of attentional resources devoted to the focalization of attention and consciousness. This is not simply the ‘divided attention' of multi-tasking procedures, but a fundamental split of resources devoted to a maintenance of one's identity as a conscious self. According to this interpretation, activation of the precuneus would represent a dispersion of self-related attentional resources, whereas deactivation would represent a focalization or internalization of such resources. If so, then deactivation should occur during situations like mindfulness meditation, where self-related attentional resources are focalized. Garrison et al. [69] conducted a study in which a combined group of experienced meditators and non-meditators performed three types of mindfulness meditation in the MRI scanner (i.e. concentration, loving kindness and choiceless answers). The baseline condition was rest. The results showed that the precuneus (in addition to the PCC) was strongly deactivated during meditation, in the same region as our Fic1P versus 1P contrast. In fact, deactivations in the posterior precuneus have been reported in a number of studies of meditation [73–75]. The question for our purposes is why the precuneus effect was mainly seen for acting and not for the 3P and accent conditions. All we can say is that neither gestural modification in the form of a foreign accent nor other-orientation in the form of 3P mentalizing had an influence on this neural mechanism, whereas the explicit psychological process of role change through character portrayal did, perhaps resulting in the double consciousness that acting theorists talk about. Again, acting was the only condition in which self-identity was explicitly split during the task. Further research will be required to explore these findings.

4.3. Impersonation

In an interesting study of vocal impressions, McGettigan et al. [76] had participants perform the opening lines of familiar nursery rhymes either (i) in their normal voice, (ii) while impersonating other individuals (such as celebrities or family members) or (iii) while putting on a foreign accent. While the study was more oriented towards sensorimotor aspects of vocal performance than towards role playing or acting, the study is one of the few to address the issue of impersonation. Their impersonation versus accent contrast is in some respects quite similar to our acting versus accent contrast, although their use of familiar texts creates a difference from our improvisational question-answering task. In other words, their task is closer to an act of pure mimicry than an attempt to portray a complex character the way our actors did. The contrast of impersonation versus accent revealed activations in the pSTS, anterior STS, superior temporal gyrus and PCC. The only point of commonality with our results is their activation in the left pSTS at MNI coordinate −45, −60, 15, compared to our activation in the right TPJ for Fic1P versus Accent at Talairach coordinate 42, −61, 22 (table 2). The authors argued that activations in the pSTS and temporoparietal region might reflect the fact that ‘the emulation of specific voice identities…requires accessing the semantic knowledge of individuals' [76, p. 1882]. Beyond semantics, the pSTS has a strong connection with the perception and production of emotional expression, including not only vocal prosody but also facial expression and body gesturing [77–80]. Hence, the pSTS activation for impersonation in McGettigan et al. [76] and for acting in our study might reflect something about resources related to expressiveness in prosodic production.

5. Limitations

The present study is the first of its kind, and so it will be important for other studies to replicate the findings reported here, not least given the complex patterns of activation and deactivation that were observed. While we attempted to use a uniform group of trained actors, there are many approaches to getting into character, and so other types of actors—most especially gesture-based actors—should be analysed in future studies. In addition, we used experienced amateurs rather than professionals as our participants. It would be interesting to carry out a follow-up study with professional actors, although this would undoubtedly lead to variability in the training and performance experience of the participants, compared to the more uniform population analysed in the present study. The results with our British accent condition suggest that even small gestural manipulations, such a change in the manner of speaking, can lead to neural differences similar to full-fledged character portrayal. Outside of the domain of professional acting, there has been an explosion of interest in role-playing video games [3,81–83], and neuroimaging studies have begun to look at brain activations in gamers perceiving avatars of themselves and others while in the scanner [84]. Gamers could be yet another type of non-professional population to explore in examining neural processes of role change.

Because of our desire to compare acting with self processing and ToM, we used an improvisational question-answering task during the acting condition, rather than having the actors recite rehearsed monologues. Importantly, improvisational methods are central to the training of actors, not least the actors used in the present study. The hot-seating technique that is commonly used in rehearsal for character development follows a question-and-answer format comparable to ToM studies, with the exception that the actors are expected to answer the questions in the 1P as their characters. The participants were familiar with hot-seating technique, which was used to help them develop an attachment to their characters during the workshop phase of this study (see Methods). They were therefore familiar and comfortable with responding to hypothetical questions while in character as Romeo or Juliet. However, we cannot rule out the possibility that some of the results may be due to the fact that the actors were more personally familiar with their answers in the 1P and 3P conditions, whereas they had to ‘make up' answers in the Fic1P condition. A future study could look at the production of rehearsed dramatic monologues compared with the production of pre-learned passages generated about self-experiences (i.e. rehearsed self-monologues). Overall, future studies need to explore (i) various types of participant populations (professional actors of different training backgrounds, gamers, ventriloquists, etc.) and (ii) different types of acting tasks (rehearsed versus improvised).

Social class and self-protection in romantic relationships

Emery, L. F., & Finkel, E. J. (2022). Connect or protect? Social class and self-protection in romantic relationships. Journal of Personality and Social Psychology, 122(4), 683–699. Mar 2022. https://doi.org/10.1037/pspi0000368

Abstract: Lower SES (socioeconomic status) couples tend to face particular challenges in their relationships. Relative to higher SES couples, they are less likely to marry and more likely to divorce—but they do not value their romantic relationships any less. Drawing on risk regulation theory and theories of social class as culture, we suggest that lower SES individuals adapt to their more chronically precarious environments by prioritizing self-protection more than higher SES individuals do, but that the need to self-protect may undermine relationship satisfaction. We investigate these ideas across 3 studies, using cross-sectional, longitudinal, and daily-diary methods. Lower SES individuals were more self-protective, both in their thoughts about their relationship (Studies 2–3), and in the judgments they made about their partner’s commitment level over 2 years (Study 1) and 2 weeks (Study 3). Self-protection, in turn, was associated with lower relationship satisfaction (Studies 2–3). However, lower SES individuals were only self-protective when feeling vulnerable in their relationships (Study 3). Taken together, these studies identify psychological mechanisms to explain why the structural challenges that lower SES individuals experience can make it more difficult to achieve satisfying relationships.

Parental presence intended to soothe children at bedtime buffers adverse effect of mothers’ parenting stress; findings challenge recommendations of parenting in Western cultures children do not depend on parental presence to fall asleep

Jahng, K. E., & Kim, E. (2022). Effects of parental bedtime involvement during children’s bedtime. Journal of Family Psychology, Mar 2022. https://doi.org/10.1037/fam0000980

Abstract: Abundant research has shown that parents’ parenting stress adversely affects their children’s well-being. However, limited attention has been provided to parental bedtime involvement as a moderating mechanism linking parents’ parenting stress to children’s happiness. This study examined the moderating effect of parent bedtime soothing and parent–child bed-sharing on the relationship between parents’ parenting stress and children’s subjective happiness. Data were extracted from the Panel Study on Korean Children (PSKC). The study participants included 1,360 7-year-old first-graders from South Korea who experienced a transition from preschool to formal schooling. The results demonstrated (a) a negative effect of parents’ parenting stress on children’s happiness and (b) a moderating effect of parental bedtime soothing, which included maternal and paternal bedtime soothing, on the relationship between mothers’ parenting stress and children’s happiness. Conversely, parent–child bed-sharing did not moderate the relationship between mothers’ parenting stress and children’s happiness. In addition, neither parent bedtime soothing nor parent–child bed-sharing moderated the relationship between fathers’ parenting stress and children’s happiness. The findings of the study indicate that parental presence intended to soothe children at bedtime, as a family routine, buffers the adverse effect of mothers’ parenting stress on their children’s subjective happiness, regardless of the parents’ gender. Our findings challenge the recommendations of parenting in Western cultures that children do not depend on a parental presence to fall asleep.

People’s aesthetic tastes are not arbitrarily different from each other in different sensory modalities but vary primarily along only a single dimension across sights and sounds: how similar a person’s taste is to the average taste

“Taste typicality” is a foundational and multi-modal dimension of ordinary aesthetic experience. Yi-Chia Chen et al.  Current Biology, March 01, 2022. https://doi.org/10.1016/j.cub.2022.02.039

Highlights

• Are individual differences in aesthetic impressions systematic or arbitrary?

• We measured “taste typicality” by comparing individuals’ tastes to the average taste

• We found that visual and auditory taste typicality was systematically correlated

• Taste typicality was also the primary way people’s tastes differed from each other

Summary: Aesthetic experience seems both regular and idiosyncratic. On one hand, there are powerful regularities in what we tend to find attractive versus unattractive (e.g., beaches versus mud puddles).1,  2,  3,  4 On the other hand, our tastes also vary dramatically from person to person:5,  6,  7,  8 what one of us finds beautiful, another might find distasteful. What is the nature of such differences? They may in part be arbitrary—e.g., reflecting specific past judgments (such as liking red towels over blue ones because they were once cheaper). However, they may also in part be systematic—reflecting deeper differences in perception and/or cognition. We assessed the systematicity of aesthetic taste by exploring its typicality for the first time across seeing and hearing. Observers rated the aesthetic appeal of ordinary scenes and objects (e.g., beaches, buildings, and books) and environmental sounds (e.g., doorbells, dripping, and dialtones). We then measured “taste typicality” (separately for each modality) in terms of the similarity between each individual’s aesthetic preferences and the population’s average. The data revealed two primary patterns. First, taste typicality was not arbitrary but rather was correlated to a moderate degree across seeing and hearing: people who have typical taste for images also tend to have typical taste for sounds. Second, taste typicality captured most of the explainable variance in people’s impressions, showing that it is the primary dimension along which aesthetic tastes systematically vary.

Discussion

The stimuli used in many studies of aesthetic appreciation are beautiful—sometimes encompassing ravishing works of art

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,

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 or arresting musical passages.

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,

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 This is not so for the current study, which instead employed stimuli one might encounter during everyday life. (We suspect that few would find the bench from Figure 1 to be ravishing.) Nevertheless, observers often agreed with each other about how appealing these images and sounds were, and we suspect that this is a hallmark of “everyday aesthetics”—the sort of aesthetic experiences one has, not when listening to a concert, but when walking back to your car afterward. The use of such ordinary stimuli also rules out other potential concerns. When studying taste typicality, in particular, some people may just want to be—or seem—different and so intentionally respond in ways that set them apart from the crowd. Here, in contrast, not a single observer’s aesthetic preferences were anticorrelated with the population mean. This may be because of the nature of our stimuli: you can’t “fight the crowd” if you have no idea what the crowd would think in the first place, and we don’t generally have stereotypes about, for example, the degree to which the noise of two rubbing hands is appealing. In the present study, we used aesthetic judgments of such stimuli in order to address two particular questions.

We first asked whether one’s taste typicality for seeing was fully independent of one’s taste typicality for hearing. The answer was clearly no: these two dimensions were robustly correlated with each other to a moderate degree—such that it is possible to predict taste typicality in one modality from taste typicality in another modality. We next asked how central taste typicality is to individual differences in aesthetic taste: even when robust, it might nevertheless be a peripheral factor in aesthetic taste, which is eclipsed by other factors that are able to explain more variance in aesthetic tastes. Here, the data provided a clear and powerful answer: taste typicality appears to be the primary determinant of individual differences in aesthetic preferences—in both seeing and hearing—with no other factor able to explain even one fourth as much variance.

These results might initially seem to be at odds with past research, which has identified many specific factors that appear to drive aesthetic impressions. For example, past work has shown that people prefer stimuli that are blue,

2

 curvy,

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 symmetrical,

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 inward-facing,

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,

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 moderately complex,

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 balanced,

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 typical

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 (but see Vogel, Ingendahl, and Winkielman

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), and presented in a canonical size.

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,  

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,  

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 One possibility is that such properties are orthogonal to taste typicality, and they instead contribute to other principal components of the variance in aesthetic impressions—although, this would mean that they could collectively explain no more than 7.5% of such variance (Figure 4). A second possibility, however, is that these other factors are central after all, insofar as they all contribute to the dimension of typicality. In this case, however, our data add to previous work by demonstrating indirectly that the individual tastes for these seemingly independent properties (e.g., curviness and complexity) must in fact be related—since for them to collectively constitute taste t<ypicality, they would have to be strongly correlated with each other (since otherwise, they would be split into multiple principal components).

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 This same lesson also applies to other less perceptual factors. Others have attempted to explain individual differences in aesthetic appreciation by appealing to factors such as personality

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 (but see McManus, Cook, and Hunt

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), expertise,

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,

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 life history,

2

,

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 and neuroanatomy.

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,

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 For example, more art education leads to less typical preferences for harmony and symmetry

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,

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,

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 (potentially through social learning

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). However, at least for the “ordinary” stimuli explored in here, these other seemingly disparate factors could only play a substantive role if they were also correlated with each other—such that they too contribute to the first principal component of the variability in aesthetic impressions.

Of course, it will come as a surprise to nobody that people vary in how typical their aesthetic tastes are. Most of us know others whose tastes in music or film are either “mainstream” or “alternative.” The present work demonstrates that this form of typicality is fundamental to our aesthetic impressions in two ways: it is a broad factor that operates to some degree across sensory modalities, and it explains more variability in aesthetic impressions than any other single factor does.

These discoveries open the door for a new way to explore aesthetic experiences. For example, in addition to asking what factors give rise to typical aesthetic experiences, we may ask how people come to share many aesthetic responses and how an individual comes to deviate from that. While the former can arise from interactions between the stimulus properties and the evolutionary goals

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 or common experiences

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 of humans, our findings demand a different kind of answer to the latter question. Given the idiosyncratic ways in which people’s tastes differ from what is typical—and the similar degree of such deviations across different modalities within each individual—the responsible mechanisms must operate in a broad and coherent way over multiple domains rather than being reducible to any processes that lead to specific instances of preferences, such as familiarity with specific stimuli. We hope that this work will spur future research on just what constitutes these mechanisms and how they give rise to systematic individual aesthetic tastes.

Selfless individuals were happier and that more selfless moments of an individual were also happier moments

Selflessness Meets Higher and More Stable Happiness: An Experience Sampling Study of the Joint Dynamics of Selflessness and Happiness. Nicolas Pellerin, Michael Dambrun & Eric Raufaste. Journal of Happiness Studies, Mar 8 2022. https://link.springer.com/article/10.1007/s10902-022-00503-8

Abstract: Previous studies have demonstrated the existence of a positive relationship between selflessness and happiness. However, none of these studies yet differentiated the between—and within—person levels of analysis. Moreover, the Selflessness/Selfcenteredness Happiness Model (SSHM) suggests that selflessness might stabilize happiness. In this experience sampling study, we explored the relationships between selflessness and happiness—baseline and stability—at both the within and betweenperson levels. During five consecutive days, participants responded seven times a day to short questions about happiness and selflessness. Our results showed that more selfless individuals were happier and that more selfless moments of an individual were also happier moments. Moreover, more selfless individuals were more stable from one day to the other. Finally, people becoming more selfless experienced more happiness stability at the following assessment moment and the next day. This study brings new evidence of the importance of selflessness for happiness.

Roughly one-third of men disliked their nude appearance, compared to approximately half of women

Demographic and sociocultural predictors of sexuality-related body image and sexual frequency: The U.S. Body Project I. David A. Frederick et al. Body Image, Volume 41, June 2022, Pages 109-127. https://doi.org/10.1016/j.bodyim.2022.01.010

Highlights

• We examined sexuality-related body image in a national sample of men and women.

• Women reported higher sexuality-related body image on three of four measures.

• Sexual orientation was tied to sexuality-related body image among men.

• Body mass and ethnicity were linked to sexuality-related body image.

• Appearance surveillance was associated with sexuality-related body image.

Abstract: Body image is a critical component of an individual’s sexual experiences. This makes it critical to identify demographic and sociocultural correlates of sexuality-related body image: the subjective feelings, cognitions, and evaluations related to one’s body in the context of sexual experience. We examined how sexuality-related body image differed by gender, sexual orientation, race, age, and BMI. Four items assessing sexuality-related body image were completed by 11,620 U.S. adults: self-perceived sex appeal of their body, nude appearance satisfaction, and the extent to which they believed that body image positively or negatively affected their sexual enjoyment and feelings of sexual acceptability as a partner. Men reported slightly less nude appearance dissatisfaction and fewer negative effects of body image on sexual enjoyment and sexual acceptability than women, but did not differ in reported sex appeal. Poorer sexuality-related body image was reported by people with higher BMIs, not in relationships, who had sex less frequently, among White compared to Black women and men, and among gay compared to heterosexual men. Data also revealed a subgroup of respondents who reported that their body image had a positive impact on their sex lives. The findings highlight a need for interventions addressing sexuality-related body image.

Keywords: Body ImagePositive Body ImageSexual SatisfactionGenderSexual AttitudesSexual Orientation