Handedness in twins: meta-analyses

Handedness in twins: meta-analyses. Lena Sophie Pfeifer, Judith Schmitz, Marietta Papadatou-Pastou, Jutta Peterburs, Silvia Paracchini & Sebastian Ocklenburg. BMC Psychology volume 10, Article number: 11. Jan 15 2022. https://bmcpsychology.biomedcentral.com/articles/10.1186/s40359-021-00695-3

Abstract

Background: In the general population, 10.6% of people favor their left hand over the right for motor tasks. Previous research suggests higher prevalence of atypical (left-, mixed-, or non-right-) handedness in (i) twins compared to singletons, and in (ii) monozygotic compared to dizygotic twins. Moreover, (iii) studies have shown a higher rate of handedness concordance in monozygotic compared to dizygotic twins, in line with genetic factors playing a role for handedness.

Methods: By means of a systematic review, we identified 59 studies from previous literature and performed three sets of random effects meta-analyses on (i) twin-to-singleton Odds Ratios (21 studies, n = 189,422 individuals) and (ii) monozygotic-to-dizygotic twin Odds Ratios (48 studies, n = 63,295 individuals), both times for prevalence of left-, mixed-, and non-right-handedness. For monozygotic and dizygotic twin pairs we compared (iii) handedness concordance Odds Ratios (44 studies, n = 36,217 twin pairs). We also tested for potential effects of moderating variables, such as sex, age, the method used to assess handedness, and the twins’ zygosity.

Results: We found (i) evidence for higher prevalence of left- (Odds Ratio = 1.40, 95% Confidence Interval = [1.26, 1.57]) and non-right- (Odds Ratio = 1.36, 95% Confidence Interval = [1.22, 1.52]), but not mixed-handedness (Odds Ratio = 1.08, 95% Confidence Interval = [0.52, 2.27]) among twins compared to singletons. We further showed a decrease in Odds Ratios in more recent studies (post-1975: Odds Ratio = 1.30, 95% Confidence Interval = [1.17, 1.45]) compared to earlier studies (pre-1975: Odds Ratio = 1.90, 95% Confidence Interval = [1.59–2.27]). While there was (ii) no difference between monozygotic and dizygotic twins regarding prevalence of left- (Odds Ratio = 0.98, 95% Confidence Interval = [0.89, 1.07]), mixed- (Odds Ratio = 0.96, 95% Confidence Interval = [0.46, 1.99]), or non-right-handedness (Odds Ratio = 1.01, 95% Confidence Interval = [0.91, 1.12]), we found that (iii) handedness concordance was elevated among monozygotic compared to dizygotic twin pairs (Odds Ratio = 1.11, 95% Confidence Interval = [1.06, 1.18]). By means of moderator analyses, we did not find evidence for effects of potentially confounding variables.

Conclusion: We provide the largest and most comprehensive meta-analysis on handedness in twins. Although a raw, unadjusted analysis found a higher prevalence of left- and non-right-, but not mixed-handedness among twins compared to singletons, left-handedness was substantially more prevalent in earlier than in more recent studies. The single large, recent study which included birth weight, Apgar score and gestational age as covariates found no twin-singleton difference in handedness rate, but these covariates could not be included in the present meta-analysis. Together, the secular shift and the influence of covariates probably make it unsafe to conclude that twinning has a genuine relationship to handedness.

Discussion

In three sets of meta-analyses, we examined the influence of twin status and twin zygosity on handedness prevalence and handedness concordance. Our first set of meta-analyses confirmed that in line with Sicotte et al. [10], left-handedness (OR = 1.40, Fig. 3) and non-right-handedness (OR = 1.36, Fig. 5) occur more often among twins than among singletons. Moderator analyses found elevated levels of non-right-handedness among twins to be independent of all variables tested with respect to a potential moderating effect. However, we found that more recent studies reported smaller differences in prevalence of left-handedness between twins and singletons (Fig. 6). To test whether there is a higher left-handedness prevalence in twins compared to singletons in more recent studies at all, we estimated twin-to-singleton ORs for left-handedness for studies published pre and post 1975 separately. With a pre-1975 OR of 1.90 (95% CI = [1.59, 2.27]) and a post-1975 OR of 1.30 (95% CI = [1.17, 1.45]), ORs for more recent studies were smaller, but still indicated a significant twin effect on left-handedness.

Overall, the decrease in twin-to-singleton ORs might either be explained by a decrease in left-handedness in twins or an increase of left-handedness in singletons, or both. As already mentioned, complications occur more often in the course of multiple births [11,12,13], which might contribute to the development of atypical handedness [10]. However, most individual studies included in our meta-analysis did not provide information on pre- or perinatal conditions, so we could not test for a moderating effect of these conditions on the twin-to-singleton OR. Along these lines, future research might have a closer look on the relation between birth complications and handedness.

Assuming that higher proportions of left-handedness among twins might be the by-product of birth complications, a decrease in atypical handedness in twins must be assigned to a decrease in the occurrence of these complications. In fact, it is well conceivable that medical progress over the last decades, that is clearly detectable, e.g. in the United States [92, 93], may have helped to equalize the risks associated with multiple and single births. Such assumptions are supported by a study by Heikkilä et al. [77] who showed differences in left-handedness in twins and singletons to disappear when controlling for birth weight, Apgar score, and gestational age. We therefore tested whether there is evidence for a decrease in left-handedness prevalence in twins (Fig. 6b) by running meta-analyses on left-handedness prevalence in twins and singletons separately while including publication year as a moderator variable. However, while there was no evidence for an effect of publication year on left-handedness prevalence in twins, there seemed to be a trend towards an increase of left-handedness prevalence in singletons (Fig. 6c).

The overall prevalence of atypical handedness in our study was lower than expected. We found 9.13% of twins and 6.97% of singletons to be left-handed (Table 1), while Papadatou-Pastou et al. [3] reported a figure of 10.6% (95% CI 9.71%, 11.50%) for the general population. The low values in our study might be the result of a general effect of publication year in singletons, given that the prevalence of left-handedness has been shown to be higher in younger than in older cohorts [25, 94, 95]. The social stigma associated with left-handedness in the last century [96] may have driven left-handers to conceal their preference in self-reports [97] and to retrain to use their right hand [25, 98]. Most of the studies included in our meta-analysis were published in the previous century and their participants could have been subjected to environmental pressures against left-handedness, leading to underestimation of the true population prevalence of left-handedness. Similarly, we found low overall prevalence of mixed-handedness (3.39% in twins and 2.67% in singletons, Table 1), whereas Papadatou-Pastou et al. [3] gave a point estimate of 9.3% for the general population. This might also be due to an effect of publication year. Moreover, three of five studies that provided data for mixed-handedness classified handedness as writing hand so that data extracted from these studies most likely reflect not mixed-handedness, but ambidexterity, which is much rarer [99].

Our second set of meta-analyses found no difference in the prevalence of atypical handedness between MZ and DZ twins (left-handedness OR = 0.98, mixed-handedness OR = 0.96, non-right-handedness OR = 1.01, Table 3). This result is consistent with the meta-analysis by Sicotte et al. [10] who interpreted this null-effect as indication against mirror imaging theories designed to explain heightened frequencies of left-handers and frequent handedness discordance among MZ twins [100,101,102]. Indeed, it weakens the hypothesis suggesting that the monozygotic twinning process is responsible for atypical handedness [10]. Moreover, it indicates that the overall heightened frequencies of left- and non-right-handers among twins are independent of the twins’ zygosity. A moderator analysis showed that this effect was not influenced by the method used to determine the twins’ zygosity, thus refuting the idea that the result was affected by the accuracy with which twins were classified as monozygotic or dizygotic. All in all, revealing comparable prevalence of atypical handedness for MZ and DZ twins cannot enrichen knowledge about genetic contribution to handedness per se. As already recognized by Sicotte et al. [10], to do so, it is crucial to look at pairwise handedness concordance or discordance of MZ and DZ twin pairs.

Our third set of meta-analyses found a small yet significant effect (OR = 1.11, Fig. 7) for higher handedness concordance among MZ (80.49%) as compared to DZ (79.27%) twins, consistent with the meta-analysis by Sicotte et al. [10]. Even though other publications have demonstrated the occurrence of handedness discordance among MZ twin pairs [100, 101, 103, 104], it was estimated to concern a minority of 20–25% of cases [2]. Stronger phenotypic variation among DZ compared to MZ pairs indicates a certain genetic foundation of that phenotype [2, 26]. Therefore, our results confirm handedness to rely on genetic factors to some extent [10] and are consistent with heritability estimates of 0.24–0.26 [31,32,33]. A moderator analysis suggested that the frequencies of handedness concordance did not differ between studies included in the meta-analysis by Sicotte et al. [10], studies explicitly excluded from Sicotte et al. [10], and more recent studies.

To allow future meta-analyses to perform comparisons on handedness prevalence in twins more specifically (e.g., handedness in male vs. female twins, or handedness in same sex pairs vs. opposite sex pairs), it is desirable that researchers report results broken down for parameters like zygosity, sex, and consider data on birth complications. As this might be beyond the scope of individual papers, we encourage authors to provide open raw data in publicly accessible repositories such as the osf.io.

The present study is not without limitations. We did not investigate relative hand skill but were restricted to hand preference. Measuring hand preference is far more established as compared to assessing relative hand skill, as it is easier and more convenient [105]. Most of the studies included in our meta-analysis only provided information on hand preference, not allowing for an additional analysis for hand skill. Moreover, hand preference and hand skill correlate to some extent [106,107,108], and the distribution of handedness categories overlaps for preference- and skill-related criterions in 90% of the cases [109].

Similarly, our study only dealt with handedness direction in terms of categorial handedness classification which does not take into account the fact that individual handedness can further be defined regarding its strength or its degree. Along these lines, other approaches consider handedness as a continuum, extending the question to how strong or how consistently one hand is preferred, used, or skilled over the other. Indeed, several findings obtained within laterality research on associations between handedness and structural brain lateralization [110] or cognitive performance [111, 112] as well as concerning the genetic foundation of handedness [113, 114] are linked to strength but not direction of handedness. However, since most studies included in the present meta-analyses did not assess handedness in a continuous manner, we were unable to account for handedness strength. Therefore, it falls to future studies to extend their assessment repertoire by measures of handedness strength.

From a methodological point of view, it is further crucial to mention that overall, our moderator analyses are low in power due to the investigated study sample sizes. Of note, in some cases, moderator levels included only three data points calling for an interpretation of these findings with caution.

Meta-analysis: People do not drink alcohol to drown their sorrows, but to indulge in their joys

Dora, Jonas, Marilyn Piccirillo, Katherine T. Foster, Kelly Arbeau, Stephen Armeli, Marc Auriacombe, Bruce D. Bartholow, et al. 2022. “The Daily Association Between Affect and Alcohol Use: A Meta-analysis of Individual Participant Data.” PsyArXiv. February 1. psyarxiv.com/xevct

Abstract: Influential psychological theories hypothesize that people consume alcohol in response to the experience of both negative and positive emotions. Despite two decades of daily diary and ecological momentary assessment research, it remains unclear whether people consume more alcohol on days they experience higher negative and positive affect in everyday life. In this preregistered meta-analysis, we synthesized the evidence for these daily associations between affect and alcohol use. We included individual participant data from 69 studies (N = 12,394), which used daily and momentary surveys to assess affect and the number of alcoholic drinks consumed. Results indicate that people do not drink more often on days they experience high negative affect, but are more likely to drink and drink heavily on days high in positive affect. People self-reporting a motivational tendency to drink-to-cope and drink-to-enhance were estimated to consume more alcohol, but not to consume more alcohol on days they experience higher negative and positive affect. Results were robust across different operationalizations of affect, study designs, study populations, and individual characteristics. Based on our findings, we collectively propose an agenda for future research to explore open questions surrounding affect and alcohol use.

Age, gender, geographical region, belonging to the host country, religious fractionalization, & stereotypic gender roles (proxied by labor force participation rate of women in the athlete’s country) are prominent predictors of crying in the Olympics

Golden tears: A cross-country study of crying in the Olympics. Alex Krumer, Andrew Musau. January 2022. https://www.researchgate.net/publication/358233754_Golden_tears_A_cross-country_study_of_crying_in_the_Olympics

Description: Previous psychological studies on emotional crying have overwhelmingly relied on self-reported data from individuals’ recollections of their own experiences. Apart from the bias that arises from faulty recollection, there is no incentive for an individual to truthfully reveal his or her own experiences in such surveys. In this paper, we address the methodological limitations associated with self-reporting and non-sufficient emotional elicitors, by exploring data on gold medalists of all 450 individual events at the 2012 and 2016 Summer Olympic Games at the end of the medalists’ respective competitions and during the medal ceremonies. We find that age, gender, geographical region, belonging to the host country, religious fractionalization, and stereotypic gender roles (proxied by labor force participation rate of women in the athlete’s home country) are likely to be prominent predictors of crying. Thus, our results suggest that emotional crying is not only a biological feature, but also a cultural phenomenon.

Social acceptance & social anxiety, embarrassment, jealousy, hurt feelings, guilt, & lowered self-esteem: We may do distance ourselves from other people, aggress rejecters, or engage in symbolic efforts to increase subjective acceptance

The relentless pursuit of acceptance and belonging. Mark R. Keary, Shira Gabriel. Advances in Motivation Science, January 31 2022. https://doi.org/10.1016/bs.adms.2021.12.001

Abstract: A great deal of human behavior is motivated by the desire for acceptance and belonging, and a high proportion of people's emotional reactions stems from concerns with actual or potential social rejection. The pervasive quest for acceptance can be seen in the attention and effort people devote to their physical appearance, their efforts to be liked, achievement-related behaviors, conformity, accumulating resources that others need, and generally being the sort of person with whom others want to have social connections. Depending on the context, concerns with social acceptance are typically accompanied by emotions such as social anxiety, embarrassment, jealousy, hurt feelings, and guilt, as well as lowered self-esteem. In addition, people who feel inadequately valued and accepted may behave in ways to increase acceptance, aggress against those who rejected them, distance themselves from other people, and/or engage in symbolic efforts to increase their subjective sense of being accepted. Concerns with acceptance and belonging exert a pervasive, ongoing effect on human thought, behavior, and emotion.

Keywords: BelongingAcceptanceRejectionExclusionOstracismRelational value

COVID-19 state anxiety is linked to everyday cognition and slower processing speed in women, but not men

COVID-19-Related Anxiety and Cognition in Middle-Aged and Older Adults: Examining Sex as a Moderator. Ashley F. Curtis et al. Psychological Reports, January 31, 2022. https://doi.org/10.1177/00332941211064820

Abstract: Aging populations experience disproportionate risk for cognitive decline, which may be exacerbated by coronavirus (COVID-19) illness, particularly among women. This study tested sex as a moderator of associations between COVID-19 state anxiety and cognition in middle-aged/older adults. Adults aged 50+ (N = 275; 151 men/124 women) completed the Coronavirus Anxiety Scale and Cognitive Failures Questionnaire online from remote locations in July/August 2020. A subset of participants (n = 62) completed an objective cognitive task (Stroop). Multiple regressions determined whether sex moderated associations between COVID-19 anxiety and cognitive outcomes. Sex was a significant moderator, such that for women (not men), greater COVID-19 anxiety was associated with more memory failures and blunders (subjective measures) and worse processing speed (objective measure). COVID-19 state anxiety is linked to everyday cognition and processing speed in women, but not men. Consistency across subjective and objective measures promotes the need for sex-specific understanding of the pandemic’s behavioral and cognitive effects in mid-to-late life.

Keywords: Cognition, coronavirus, anxiety, sex differences, middle-aged adults, older adults

37% of the participants contacted other persons because they dreamed about them; dream recall frequency, attitude towards dreaming, younger age, and female gender was associated with contacting the person(s) dreamed of

The Frequency of Contacting Persons you Dreamed About: A Social Aspect of Dreaming. Michael Schredl, Anja S. Göritz. Imagination, Cognition and Personality, January 31, 2022. https://doi.org/10.1177/02762366221077631

Abstract: Although dreams are very private, dreaming has also social components, i.e., dreams are shared quite often. We studied the frequency of how often the dreamer deliberately contacted another person because s/he dreamed about this person, as this might intensify the waking-life bonds with this person. Overall, 2929 participants completed the dream survey, and a subsample also completed a Big Five Personality inventory. The findings indicate that 37% of the participants contacted other persons because they dreamed about them. Dream recall frequency, attitude towards dreaming, younger age, and female gender was associated with contacting the person(s) dreamed of. Moreover, extraversion was also related to the frequency of contacting the person(s) dreamed of – similar to the relationship found for dream sharing frequency and extraversion. However, the association with low conscientiousness is a new finding. It would be very interesting to test whether this social behavior (contacting another person) motivated by dreams strengthens the social bonds between the dreamer and the contacted person(s) and thereby provide support for the Social Simulation Theory.

Keywords: social aspects of dreaming, dream recall frequency, attitude towards dreaming, extraversion, conscientiousness

A Free-Market Environmentalist Transition toward Renewable Energy: The Cases of Germany, Denmark, and the United Kingdom

A Free-Market Environmentalist Transition toward Renewable Energy: The Cases of Germany, Denmark, and the United Kingdom. William Hongsong Wang, Vicente Moreno-Casas, Jesús Huerta de Soto. Energies 2021, 14(15), 4659; July 31 2021. https://doi.org/10.3390/en14154659

Abstract: Renewable energy (RE) is one of the most popular public policy orientations worldwide. Compared to some other countries and continents, Europe has gained an early awareness of energy and environmental problems in general. At the theoretical level, free-market environmentalism indicates that based on the principle of private property rights, with fewer state interventionist and regulation policies, entrepreneurs, as the driving force of the market economy, can provide better services to meet the necessity of offering RE to protect the environment more effectively. Previous studies have revealed that Germany, Denmark, and the United Kingdom have made some progress in using the market to develop RE. However, this research did not analyze the three countries’ RE conditions from the perspective of free-market environmentalism. Based on our review of the principles of free-market environmentalism, this paper originally provides an empirical study of how Germany, Denmark, and the United Kingdom have partly conducted free-market-oriented policies to successfully achieve their policy goal of RE since the 1990s on a practical level. In particular, compared with Germany and Denmark, the UK has maintained a relatively low energy tax rate and opted for more pro-market measures since the Hayekian-Thatcherism free-market reform of 1979. The paper also discovers that Fredrich A. Hayek’s theories have strongly impacted its energy liberalization reform agenda since then. Low taxes on the energy industry and electricity have alleviated the burden on the electricity enterprises and consumers in the UK. Moreover, the empirical results above show that the energy enterprises play essential roles in providing better and more affordable RE for household and industrial users in the three sampled countries. Based on the above results, the paper also warns that state intervention policies such as taxation, state subsidies, and industrial access restrictions can impede these three countries’ RE targets. Additionally, our research provides reform agendas and policy suggestions to policymakers on the importance of implementing free-market environmentalism to provide more efficient RE in the post-COVID-19 era.

Keywords: free-market environmentalism; renewable energy; entrepreneurship; public policy; Germany; Denmark; United Kingdom; European Union; EU Green Deal; energy transition; energy production; electricity prices; taxation; state subsidies; industrial access restriction; decision-making; political economy

5. Conclusions

Based on the review of the theoretical principles of free-market environmentalism, this paper has originally provided an empirical study of how Germany, Denmark, and the UK partly conduct free-market-oriented policies to successfully achieve their policy goal of broader use of RE since the 1990s.

The paper’s empirical results show that in 28 years, from 1990 to 2018, all three countries have shown positive features in their respective RE transitions. This tendency is especially evident for the increasing trend in the share of RE in gross electricity production and gross available energy and the decreasing trend in GHG emissions. However, as the supply of RE increased, the prices of electricity in the three countries did not show the same downward trend. This result alters the traditional view on these countries’ energy transitions, with the UK being more successful in a critical aspect of any energy transition: affordability.

Simultaneously, by measuring the specific data on taxation, state subsidies, and industrial access restrictions in the three sampled countries, we pointed out how these interventionist and regulation policies have caused damage to the three countries’ RE transition goals. Given free-market environmentalism, the cases of Germany and Denmark serve to illustrate how vital the entrepreneurship-based bottom-up forces (led by organizations and entrepreneurs in the form of RE cooperatives) are for the relative success of an energy transition. The German experience emphasizes political decentralization for decision-making and a certain freedom in the RE market. Inside this framework, a wide range of decentralized initiatives still thrive. This policy is the reason for the country’s energy transition success. However, there are distorting effects of government intervention, such as high electricity prices. They are caused by taxes, subsidies, and industry access restrictions. In general, Germany’s energy prices are not entirely market-oriented but are taxed and subsidized by the German government. As we have pointed out above, Germany’s energy prices are artificially high due to the FIT system. Therefore, Germany cannot be considered an ideal sample of free-market environmentalism. As previous research indicated, we also suggest Germany reduce the degrees of the above three interventionist policies as best as possible to enhance RE production and reduce electricity and RE prices.

Like the German case, the Danish energy policy has not wholly followed the principles of free-market environmentalism due to taxes, subsidies, and industry access restrictions. Denmark’s high electricity prices are due to high production costs and high taxes. As a result, Denmark faces a tough challenge to achieve an efficient and affordable RE transition concerning electricity prices. As previous research indicated, we also suggest Denmark should conduct tax reduction for its RE industry and eliminate state subsidies and industry access restrictions. However, despite the above policy deficiencies, Denmark is managing a RE transition due to the essential roles of decentralized local organizations and entrepreneurial activities. Moreover, more market-based RE innovation has created more jobs and reduced more GHG emissions since 1990. Even the literature that was not in favor of free-market environmentalism also acknowledged the Danish success in RE transition and its community and entrepreneurship-based characters [23].

On the other hand, compared with Germany and Denmark, the UK has maintained a relatively low energy tax rate and opted for more pro-market measures since the Hayekian-Thatcherism free-market reform of 1979. Fredrich A. Hayek’s theories have strongly impacted its energy liberalization reform agenda since then. Low taxes on the energy industry and electricity have alleviated the burden on electricity enterprises and consumers. Electricity prices have remained relatively low since 1990. However, interventionist policies such as state-regulated auctions and industry access restrictions have obstructed its energy transition. Moreover, RE policies are not as decentralized as Germany and Denmark, although RE innovation has increased in the three countries. Despite not having a purely free-market environmentalist energy policy, the UK has come closer to free-market environmentalism than the other two countries. Contrary to what some literature posits, the UK is achieving energy transition at a good pace, even beating Germany and Denmark by containing the rise in electricity prices. Therefore, with less intervention in the future, a better conducted RE market process could provide better conditions for British RE development.

Thus, during the post-COVID-19 era, to attain economic recovery and achieve a more advanced level of RE and protect the environment, it is essential to respect the principles of private property rights and free-market price coordination to acquire more and better RE. Hence, EU policymakers should adopt its RE policy from the perspective of free-market environmentalism to conduct better entrepreneurship for RE. Government RE’s intervention-regulation policies such as taxation, subsidies, and industry restrictions infringe on private property rights and cause economic discoordination and zero-sum games. Moreover, although the UK has not been an EU member since Brexit, its precious and successful experience of energy liberalization since the 1979 Hayekian-Thatcherism free-market energy reform could help other European countries to achieve better RE production and affordable energy prices. The UK experience and the free-market environmentalist policies that Germany and Denmark conduct could help other countries globally. Additionally, the empirical results in this paper show that the result of free-market environmentalism should be implemented over a long period. Policymakers should perceive that the free-market environmentalist policy approach and the entrepreneurial production of RE take time. Any interventionist eager for quick success may reverse the policy results. Hence, respecting entrepreneurship and reducing state intervention or regulation as much as possible is what global policymakers should execute during the post-COVID-19 era for a better energy transition.

Girls learn faster than boys when school is out (in both reading and math), but this advantage is completely eliminated when school is in session; schools act as a relatively standardizing institution, producing more similar patterns in learning

Schools as a Relatively Standardizing Institution: The Case of Gender Gaps in Cognitive Skills. Douglas B. Downey, Megan Kuhfeld, Margriet van Hek. Sociology of Education, January 27, 2022. https://doi.org/10.1177/00380407211070319

Abstract: Growing evidence suggests that contrary to popular belief, schools mostly do not generate achievement gaps in cognitive skills but, rather, reflect the inequalities that already exist. In the case of socioeconomic status, exposure to school often reduces gaps. Surprisingly little is known, however, about whether this pattern extends to gender gaps in cognitive skills. We compare how gender gaps in math and reading change when children are in school versus out (in the summer) among over 900,000 U.S. children. We find that girls learn faster than boys when school is out (in both reading and math), but this advantage is completely eliminated when school is in session. Compared to the family environment, schools act as a relatively standardizing institution, producing more similar gendered patterns in learning.

Keywords: quantitative research on education, summer setback, gender, school effects, standardized testing

Both facemasks and makeup tend to result in over-estimation of the young women's age compared to neutral faces, but the combination of both is not additive: 4 years on average

Your ID, please? The effect of Facemasks and Makeup on Perceptions of Age of Young Adult Female Faces. H. Davis, J. Attard-Johnson. Applied Cognitive Psychology, January 28 2022. https://doi.org/10.1002/acp.3923

Abstract: During the COVID-19 pandemic, wearing facemasks was mandatory in the United Kingdom except for individuals with medical exemptions. Facemasks cover the full lower half of the face, however the effect of facemasks on age perception is not yet known. The present study examined whether age estimation accuracy of unfamiliar young adult women is impaired when the target is wearing a facemask. This study also examined whether makeup, which has previously been shown to increase error bias, further impairs age estimation accuracy when paired with a facemask. The findings indicate that both facemasks and makeup tend to result in over-estimation of the young women's age compared to neutral faces, but the combination of both is not additive. Individual level analysis also revealed large individual differences in age estimation accuracy ranging from estimates within 1 year of the target's actual age, and age estimates which deviated by up to 20 years.

Does the Mafia Hire Good Accountants?

Bianchi, Pietro A. and Bianchi, Pietro A. and Francis, Jere R. and Marra, Antonio and Pecchiari, Nicola, Does the Mafia Hire Good Accountants? (November 5, 2021). SSRN: http://dx.doi.org/10.2139/ssrn.3957650

Abstract: We investigate if organized crime groups (OCG) are able to hire good accountants. We use data about criminal records to identify Italian accountants with connections to OCG. While the work accountants do for the OCG ecosystem is not observable, we can determine if OCG hire “good” accountants by assessing the overall quality of their work as external monitors of legal businesses. We find that firms serviced by accountants with OCG connections have higher quality audited financial statements compared to a control group of firms serviced by accountants with no OCG connections. The findings provide evidence OCG are able to hire good accountants, despite the downside risk of OCG associations. Results are robust to controls for self-selection, for other determinants of auditor expertise, direct connections of directors and shareholders to OCG, and corporate governance mechanisms that might influence auditor choice and audit quality.

Keywords: accountant connections to organized crime, accountant criminal record, criminal investigations, financial reporting quality

JEL Classification: G31,G32,G38, K42, K49

Rodent-hunting cat ownership in childhood was associated with higher psychotic experience scores in male participants, but not in female participants

Conditional associations between childhood cat ownership and psychotic experiences in adulthood: A retrospective study. Vincent Paquin et al. Journal of Psychiatric Research, Jan 30 2022. https://doi.org/10.1016/j.jpsychires.2022.01.058

Abstract: Ownership of cats in childhood has been inconsistently associated with psychosis in adulthood. Parasitic exposure, the putative mechanism of this association, may be more common with rodent-hunting cats, and its association with psychosis may depend on other environmental exposures. We examined the conditional associations between childhood cat ownership and the frequency of psychotic experiences in adulthood. Adults (n = 2206) were recruited in downtown Montreal to complete a survey about childhood cat ownership (non-hunting or rodent-hunting), winter birth, residential moves in childhood, head trauma history, and tobacco smoking. The frequency of psychotic experiences (PE) was measured with the 15-item positive subscale of the Community Assessment of Psychic Experiences. Associations between exposures and PE were examined in linear regressions adjusted for age and sex. Interactions among variables were explored using a conditional inference tree. Rodent-hunting cat ownership was associated with higher PE scores in male participants (vs. non-hunting or no cat ownership: SMD = 0.57; 95% CI: 0.27, 0.86), but not in female participants (SMD = 0.10; 95% CI: −0.18, 0.38). In the conditional inference tree, the highest mean PE score was in the class comprised of non-smokers with >1 residential move, head trauma history, and rodent-hunting cat ownership (n = 22; mean standard score = 0.96). The interaction between rodent-hunting cat ownership and head trauma history was supported by a post-hoc linear regression model. Our findings suggest childhood cat ownership has conditional associations with psychotic experiences in adulthood.

Keywords: Psychotic disordersToxoplasmaMachine learningCraniocerebral trauma

Gender Diffs in Childhood Trauma, Schizotypy, Negative Emotions: Cognitive Disorganisation (poor attention, concentration, decision-making, social cognition) positively corrs w/physical neglect & sexual abuse as children in women, no links among men

Thomas, Elizabeth H.X., Susan L. Rossell, and Caroline Gurvich. 2022. "Gender Differences in the Correlations between Childhood Trauma, Schizotypy and Negative Emotions in Non-Clinical Individuals" Brain Sciences 12, no. 2: 186. Jan 29 2022. https://doi.org/10.3390/brainsci12020186

Abstract: Early life trauma has a negative impact on the developing brain, and this can lead to a wide range of mental illnesses later in life. Childhood trauma is associated with increased psychotic symptoms and negative emotions such as depressive, anxiety, and stress symptoms in adulthood. Childhood trauma has also been shown to influence sub-clinical ‘schizotypy’ characteristics of psychosis in the general population. As it has been reported that mental health outcomes after early life trauma exposure are influenced by gender, the current study aimed to investigate the gender differences in the relationship between childhood trauma, schizotypy and negative emotions. Sixty-one non-clinical participants (33 men and 28 women) aged between 18 and 45 completed self-report questionnaires to measure early life trauma, schizotypy and negative emotions. Despite similar levels of childhood trauma in men and women, early life trauma in women was associated with increased schizotypy personality characteristics (Cognitive Disorganisation) and increased depression, anxiety and stress later in life, but no correlations were observed in men. Our findings suggest that the sociocultural and biological processes affected by early life adversities may differ between the genders. Women may be more vulnerable to the influence of childhood trauma, which may be associated with increased psychopathology later in life.

Keywords: schizophrenia spectrum; early life adversity; depression; anxiety; stress

Risk Perception and Behaviour Change, COVID-19: Socializing rebounded after partial vaccination; after full vaccination, communal activities recovered; however, the propensity for protective behaviours declined

Jia, Jayson S., Yun Yuan, Jianmin Jia, and Nicholas Christakis. 2022. “Risk Perception and Behaviour Change After Personal Vaccination for COVID-19 in the USA.” PsyArXiv. January 30. psyarxiv.com/afyv8

Abstract: Although vaccines are crucial for giving pandemic-stricken societies the confidence to return to socioeconomic normalcy, vaccination may also induce laxity in personal protective behaviours (e.g., handwashing, facemask use). We use the quasi-experimental context of the COVID-19 vaccine rollout across the United States to quantify the impact of different stages of personal vaccination on people’s risk perceptions, daily activities, and risk mitigation behaviours, which we measure in a three-wave national panel study (N wave-1 = 7,358, N wave-2 = 3,000, N wave-3 = 2,345) from March to June, 2021, and validate using vaccination, infection, and human mobility data. Socializing rebounded after only partial vaccination. After full vaccination, communal activities recovered; however, the propensity for protective behaviours declined. The effects were heterogenous depending on vaccination level, demographics, and infection history. We further use a utility theory framework to model risk-value trade-offs and risk-construction for different behaviours.

Rolf Degen summarizing... The sport science and coaching community is very susceptible to pseudoscientific bullshit

Stoszkowski, John, Shane Littrell, and Dave Collins. 2022. “Cutting the Crap: The Perceived Prevalence of Pseudoscientific Bullshit in Sport Science and Coaching.”PsyArXiv. January 29 2022. https://psyarxiv.com/7t2my/

Abstract: Recent literature has identified and examined the construct of bullshit as a notable threat to the promulgation and use of accurate information. The parallel challenges posed by increasing availability of unfiltered online information have been identified as further exacerbating factors. Accordingly, the present paper adds to this perspective by examining susceptibility to and perceived frequency of bullshit in the sport science and coaching domain. Participants (N = 280) completed several validated instruments examining susceptibility, tendency to engage in and perceived experience of bullshit in their professional environments. Data suggest similar ratings to more general population samples, with educational level acting as a key moderating factor. Implications for practice and psychosocial approaches to bullshit are discussed, in tandem with recommendations for refinements to communication.

Why men are the main COVID-19 transmitters: Despite no observed differences in viral load in nasopharyngeal samples, adult males showed a significantly higher viral load in saliva samples than adult women; plus men have higher aerosol emissions

Men are the main COVID-19 transmitters: behavior or biology? Monize V. R. Silva, Mateus V. de Castro, Maria Rita Passos-Bueno, Paulo A. Otto, Michel S. Naslavsky & Mayana Zatz. Discover Mental Health volume 2, Article number: 1, 2022. Jan 24 2022. https://link.springer.com/article/10.1007/s44192-022-00004-3

Abstract

Background: COVID-19 has affected millions of people worldwide. Clinical manifestations range from severe cases with lethal outcome to mild or asymptomatic cases. Although the proportion of infected individuals does not differ between sexes, men are more susceptible to severe COVID-19, with a higher risk of death than women. Also, men are pointed out as more lax regarding protective measures, mask wearing and vaccination. Thus, we questioned whether sex-bias may be explained by biological pathways and/or behavioral aspects or both.

Methods: Between July 2020 and July 2021, we performed an epidemiological survey including 1744 unvaccinated adult Brazilian couples, with there was at least one infected symptomatic member, who were living together during the COVID-19 infection without protective measures. Presence or absence of infection was confirmed by RT-PCR and/or serology results. Couples were divided into two groups: (1) both partners were infected (concordant couples) and (2) one partner was infected and the spouse remained asymptomatic despite the close contact with the COVID-19 symptomatic partner (discordant couples). Statistical analysis of the collected data was performed aiming to verify a differential transmission potential between genders in couples keeping contact without protective measures.

Results: The combination of our collected data showed that the man is the first (or the only) affected member in most cases when compared to women and that this difference may be explained by biological and behavioral factors.

Conclusions: The present study confirmed the existence of gender differences not only for susceptibility to infection and resistance to COVID-19 but also in its transmission rate.

Discussion

All the results obtained in the present study strongly suggest that males are not only more susceptible to COVID-19 severity, as shown in worldwide epidemiological surveys, but they are also more likely to transmit the virus to their partners when compared to females in the household transmission context. The epidemiological findings in the present survey are consistent with the results of other published studies involving couples where one of the partners was infected by their spouses [40, 41]. Female individuals aged between 17 and 65 years were also frequently found to be secondary cases [41].

Aiming to analyze a more homogeneous cohort and since age is an important predictor of severity and risk of death by COVID-19, we focused our survey on couples of comparable ages and economic status and therefore similar access to health care. It is also important to note that the survey was performed before the vaccination was started.

One of the possible current biological hypotheses for such gender variable transmission rate is a differential viral load in saliva, which has been explored as an important clinical measure of disease severity due to its positive association with many COVID-19 inflammatory markers [42]. These factors, together with the higher adoption of hygiene and protective measures among females, may justify the lower transmission rates in this group.

Interestingly, in a recent study of our group [43] it was observed that, although there were no observed gender differences in viral load in nasopharyngeal samples, adult males showed a significantly higher viral load in saliva samples (verified by RT-LAMP viral testing) than adult women.

These observations, together with the evidence of higher aerosol emission by men which makes them more likely to be “superspreaders” than women, support the hypothesis that male individuals are more efficient virus transmitters than females, which is related to biological and behavioral aspects.

This study has some limitations regarding the relatively modest number of couples included in the present cohort when compared with other epidemiological surveys of in-house transmission [40, 41]. Additionally, the couples who responded the questionnaire are on average younger than the mean age of the population since, in Brazil, younger people have more access and familiarity with internet than older adults [44]. Nevertheless, our study brings new knowledge to the field of public health regarding SARS-CoV-2 transmission dynamics.

In short, the present study confirmed the existence of gender differences not only for susceptibility to infection and resistance to COVID-19 but also in the transmission rate.

Unattractive faces are more attractive when the bottom-half is masked, an effect that reverses when the top-half is concealed

Unattractive faces are more attractive when the bottom-half is masked, an effect that reverses when the top-half is concealed. Farid Pazhoohi & Alan Kingstone. Cognitive Research: Principles and Implications volume 7. Jan 24 2022. https://link.springer.com/article/10.1186/s41235-022-00359-9

Abstract: Facial attractiveness in humans signals an individual’s genetic condition, underlying physiology and health status, serving as a cue to one’s mate value. The practice of wearing face masks for prevention of transmission of airborne infections may disrupt one’s ability to evaluate facial attractiveness, and with it, cues to an individual's health and genetic condition. The current research investigated the effect of face masks on the perception of face attractiveness. Across four studies, we tested if below- and above-average attractive full faces are equally affected by wearing facial masks. The results reveal that for young faces (Study 1) and old faces (Study 2) a facial mask increases the perceived attractiveness of relatively unattractive faces, but there is no effect of wearing a face mask for highly attractive faces. Study 3 shows that the same pattern of ratings emerged when the bottom-half of the faces are cropped rather than masked, indicating that the effect is not mask-specific. Our final Study 4, in which information from only the lower half of the faces was made available, showed that contrary to our previous findings, highly attractive half-faces are perceived to be less attractive than their full-face counterpart; but there is no such effect for the less attractive faces. This demonstrates the importance of the eye-region in the perception of attractiveness, especially for highly attractive faces. Collectively these findings suggest that a positivity-bias enhances the perception of unattractive faces when only the upper face is visible, a finding that may not extend to attractive faces because of the perceptual weight placed on their eye-region.

General discussion

In the current research we investigated the effect of facial masks on the perception of facial attraction. Specifically, we tested whether below- and above-average full faces are equally affected by wearing facial masks. Our first study revealed that for younger faces a facial mask will increase the perceived attractiveness if the unmasked face is relatively unattractive, but wearing a mask will not help or hinder highly attractive faces. Study 2 revealed that this pattern of results generalises to old faces. And our Study 3 showed that the same effect occurs even when the bottom half of young faces are cropped rather than masked, i.e., the effect is not mask-specific.

Collectively, our first two studies, which show that face masks will help and never hinder one's perceived attractiveness conflicts with the findings of Miyazaki and Kawahara (2016) who showed that facial mask decrease the perceived attractiveness in a pre-COVID-19 pandemic era. Interestingly, the same lab has tested the same question recently during the pandemic and reported a similar result to our first two studies—attractiveness of below-average faces increased (Kamatani et al., 2021). A similar pattern of improvement in attractiveness ratings of unattractive faces is confirmed in another post-pandemic study (Patel et al., 2020), signifying the change in attitudes in response to social norms associated with mask wearing (Carbon, 2021). However, the results of Kamatani et al. (2021) for masked faces of above-average attractiveness showed a reduction in perception of attractiveness compared to unmasked faces—a result not found in the studies here and those of Patel et al. (2020). Such discrepancy might be a result of cultural differences (Japanese vs. Western) or due to differences in the stimuli used, in terms of their range of attractiveness.

Our final Study 4 examined if our previous findings are specific to the removal of information from the lower half of the face, or does it reflect a more general positivity bias where any incomplete face information is inferred to be attractive (Orghian & Hidalgo, 2020). The results did not support this possibility. When observers were asked to judge the attractiveness of faces that had the upper half of the face removed (including the eyes), the effect was to reduce the perceived attractiveness of highly attractive faces, and to have no positive effect on less attractive faces. This latter study demonstrates that in North America the effect of perceiving an incomplete face can be detrimental; and it supports previous work indicating that the eye-region has a special status in perceptions of facial attractiveness (Kwart et al., 2012; Nguyen et al., 2009). Indeed, the fact that in Studies 1–3 the eye region of the face was preserved helps to explain why masking or cropping the lower half of the face had no effect on the perceived attractiveness of highly attractive faces. Collectively, across four experiments, our study reveals that facial masks increase the perceived attractiveness of less attractive faces, while they do not affect those that are highly attractive. This finding applies to young and old faces, and it extends to other methods of isolating the region of the upper face; but it does not apply to the situation when the lower half of the face is isolated. These findings suggest that a positivity-bias enhances the perception of unattractive faces when only the upper face is visible, a finding that may not extend to attractive faces because of the perceptual weight placed on their eye-region.

Claim: Like other creative workds, computer programs have aesthetic value, computer programming is a form of art

Kershaw, T. C., Clifford, R. D., Khatib, F., & El-Nasan, A. (2022). An initial examination of computer programs as creative works. Psychology of Aesthetics, Creativity, and the Arts. Jan 2022. https://doi.org/10.1037/aca0000457

Abstract: Products from many domains (art, music, engineering design, literature, etc.) are considered to be creative works, but there is a misconception that computer programs are limited by set expressions and thus have no room for creativity. To determine whether computer programs are creative works, we collected programs from 23 advanced graduate students that were written to solve simple and complex bioinformatics problems. These programs were assessed for their variability of expression using a new measurement that we designed. They were also evaluated on several elements of their creativity using a version of Cropley and Kaufman’s (2012) Creative Solution Diagnosis Scale that was modified to refer to programming. We found a high degree of variation in the programs that were produced, with 11 unique solutions for the simple problem and 20 unique solutions for the complex problem. We also found higher ratings of propulsion-genesis and problematization for the complex problem than for the simple problem. This combination of variation in expression and differences in level of creativity based on program complexity suggests that computer programs, like many other products, count as creative works. Implications for the creativity literature, computer science education, and intellectual property law, particularly copyright, are discussed.

From 2014... For both males and females, mathematical precocity early in life predicts later creative contributions and leadership in critical occupational roles

Life Paths and Accomplishments of Mathematically Precocious Males and Females Four Decades Later David Lubinski, Camilla P. Benbow, and Harrison J. Ke. Psychological Science, 2014, Vol. 25(12) 2217–2232.  https://www.gwern.net/docs/iq/smpy/2014-lubinski.pdf

Abstract: Two cohorts of intellectually talented 13-year-olds were identified in the 1970s (1972–1974 and 1976–1978) as being in the top 1% of mathematical reasoning ability (1,037 males, 613 females). About four decades later, data on their careers, accomplishments, psychological well-being, families, and life preferences and priorities were collected. Their accomplishments far exceeded base-rate expectations: Across the two cohorts, 4.1% had earned tenure at a major research university, 2.3% were top executives at “name brand” or Fortune 500 companies, and 2.4% were attorneys at major firms or organizations; participants had published 85 books and 7,572 refereed articles, secured 681 patents, and amassed $358 million in grants. For both males and females, mathematical precocity early in life predicts later creative contributions and leadership in critical occupational roles. On average, males had incomes much greater than their spouses’, whereas females had incomes slightly lower than their spouses’. Salient sex differences that paralleled the differential career outcomes of the male and female participants were found in lifestyle preferences and priorities and in time allocation.

Men say "I love you" before women do... and it happens across the globe

Men say "I love you" before women do: Robust across several countries. Christopher Watkins et al. Journal of Social and Personal Relationships, January 27, 2022. https://doi.org/10.1177/02654075221075264

Abstract: Feeling and expressing love is at the core of romantic relationships, but individuals differ in their proclivity to worry about their relationships and/or avoid intimacy. Saying ‘I love you’ signals a commitment to a future with our romantic partner. Contrary to gender stereotypes, research in the US demonstrates that men are more likely to confess love first. We aimed to replicate this sex difference in an online cross-national sample (seven countries, three continents), while testing for variation according to attachment style and environment (the national sex ratio). Men were more likely to confess love first in a relationship, with preliminary evidence that this was more likely when men had more choice (more female-biased sex ratio). Independent of biological sex, highly avoidant respondents were less happy to hear ‘I love you’ than less avoidant respondents, and highly anxious respondents were happier to hear ‘I love you’ than less anxious respondents. Our findings suggest that prior observations generalize beyond an ethnically homogenous sample, and incorporate attachment theory into the study of love confessions. Our research suggests a dissociation between initial declarations of love (moderated by biological sex) and emotional responses to love confessions, moderated by attachment style but not by biological sex.

Keywords: Affectionate communication, Attachment, Close relationships, Error Management Theory, Sex differences, Sex ratio, Speech acts

Chimps have more interests toward strange body parts, compared to typical parts, suggesting that they might have a body representation that is sufficiently sensitive to detect these aspects of strangeness

Chimpanzees (Pan troglodytes) detect strange body parts: an eye-tracking study. Jie Gao, Ikuma Adachi & Masaki Tomonaga. Animal Cognition, Jan 28 2022. https://link.springer.com/article/10.1007/s10071-021-01593-2

Abstract: This study investigated chimpanzee body representation by testing whether chimpanzees detect strangeness in body parts. We tested six chimpanzees with edited chimpanzee body pictures in eye-tracking tasks. The target body parts were arms or legs. For either target, there were four conditions: “normal” condition as control, where all bodies were normal; “misplaced” condition, where one arm or one leg was misplaced to an incorrect body location in each picture; “replaced by a chimpanzee part” condition, where one arm or one leg was replaced by a chimpanzee leg or arm, respectively, in its original place in each picture; and “replaced by a human part” condition, where one arm or one leg was replaced by a human arm or leg in each picture. Compared to the looking times toward the normal parts, chimpanzees had significantly longer looking times toward the human arms or legs. The looking times toward the misplaced parts were also longer than the normal parts, but the difference just failed to meet significance. These results indicate more interests toward strange body parts, compared to typical parts, suggesting that chimpanzees might have a body representation that is sufficiently sensitive to detect these aspects of strangeness.

Discussion

In this study, we tested six chimpanzees in eye-tracking tasks to examine whether they specifically attended to strange arms or legs of chimpanzee pictures, compared to normal arms or legs, to determine whether they possessed visual body representation. Compared with looking durations toward the normal body parts, the chimpanzees had significantly longer looking times toward the human arms and legs in place of the original chimpanzee arms and legs. This suggests that the chimpanzees noticed that the human parts were strange. They also showed longer looking times towards the misplaced parts than towards the normal parts, but the difference just failed to meet significance.

The “misplaced” condition and “replaced by a human part” condition showed different contrasts against the control condition: the former did not reach significance, although close, while the latter showed significance. The longest attention to the human parts is probably due to the inconsistency of the shapes, or their interests on human parts. Chimpanzees are able to detect an odd stimulus out of uniform distractors (Tomonaga 1998). Human arms and legs are hairless, and look differently from chimpanzee arms and legs, although the overall shapes are similar. In the other two experimental conditions, the manipulation was done with the body parts of the same chimpanzee body. Therefore, the special look of human body parts may have grabbed more attention. The chimpanzees we tested were very familiar with humans. They see and interact with multiple humans every day, and they could see humans in the institute and on the street. Therefore, they had been exposed to human body parts. That said, it is unlikely that they have seen the whole naked arms and legs of humans as were shown in the task; but the experience of exposure to partial human arms and legs may have triggered them to pay more attention to the human parts appearing on chimpanzee bodies and replacing chimpanzee body parts. Therefore, for the results in the “replaced by a human part” condition alone, the longer looking time could be attributed to their body representation, visual inconsistency, or interests to human bodies. To rule out the possibility that they showed longer looking time in this condition solely because of visual inconsistency or interests to humans, more control conditions could be added, or chimpanzees who have less exposure of partially naked humans could be tested. Nevertheless, when we combine all the results, we still tend to think chimpanzees may be able to detect strangeness in terms of body representation, because of the strong tendency of longer looking times towards the misplaced body parts than the normal parts and the tendency of shorter time to first fixation in the “misplaced” leg condition than the “normal” leg condition.

In the analyses of time-to-first-fixation data, we found that there was a significant interaction between condition and body part. The pairwise comparison showed significant differences in three pairs in leg data: the “misplaced” condition had shorter time to first fixation on AOIs than those in all three other conditions. It is possible that the misplaced legs make the whole body configuration look much stranger than a normal body as well as a body with its leg replaced by another part in the original typical position, leading to a much quicker detection. This was not the case for arm manipulation, and this is where the difference of the effect of condition lies for arm and leg manipulations.

The difference of results between arm and leg manipulations was not found in fixation duration, but time to first fixation, as mentioned above. In this specific case, the quicker detection to misplaced legs than legs in other conditions, but not in arms, may come from the fact that legs do not move in the same amplitude as arms. When chimpanzees move in a quadrupedal posture on the ground or in a bipedal posture when climbing, their arms and legs move in similar ranges. However, when manipulating objects on the ground, they reach for objects in places that are a bit far from them using arms not legs, and it could be seen as if the arms were “misplaced” from a distance (e.g., Hayashi and Matsuzawa 2003; Hayashi et al. 2005); chimpanzees also often raise their arms for social communications (Hobaiter and Byrne 2011), but they seldom “raise” their legs. The different function and use of arms and legs could cause chimpanzees detect misplaced legs more quickly.

In this study, we did not manipulate other body parts, such as head and torso. It will be interesting to further examine how their representation differ across various body parts. In a broader comparison counting all body parts, the difference between arms and legs may not be as large as that between head and limbs, or other contrasts. Studies asking children to recognize, name, and point at body parts do not demonstrate large differences between arms and legs, but the performances for eyes was much earlier in the development (MacWhinney et al. 1987; Waugh and Brownell 2015; Witt et al. 1990). Atypical body parts may suggest injury and care, so it is meaningful to examine whether and how knowledge for body parts differ, and which factors are related to this, such as function of the parts. Also, it will be interesting to examine the body representation of other species, too, e.g., preys. Do chimpanzees (and humans) have certain body representation and anatomy knowledge about their preys’ bodies, and do the knowledge help with efficient foraging and feeding?

All the manipulations in this study created strange images that will not occur in real life, yet the chimpanzees did not show significant differences in all manipulated conditions compared to control. One of the reasons could be due to the limited sample size. The significance of the random effect participant ID in both analyses of time-to-first-fixation data and fixation-duration data also indicates individual difference (Figs. 4, 5, 6, 7). If more individuals were tested, the results might have been more consistent. Because of the limited sample size, the conclusions should be generalized with caution, and data from more chimpanzee individuals or populations will be helpful to understand chimpanzees’ perception for atypical body parts.

The participants in this study were captive chimpanzees with a lot of exposure of humans. As discussed above, these individuals might be more sensitive to human body parts on chimpanzee bodies, compared to captive chimpanzees with limited human exposure or wild chimpanzees. However, the experience with humans may not affect chimpanzees’ body representation too much, according to our previous findings (Gao et al. 2020; Gao and Tomonaga 2020b). We tested the same chimpanzees, who were very familiar with humans, to see if they show the inversion effect for human bodies. We used humans in bipedal postures doing Tai chi, but the chimpanzees did not show any inversion effect. We then used bipedal humans showing daily postures (waving hands, walking, etc.), and the chimpanzees showed the inversion effect to these bodies, suggesting that visual experience is important to them. We also used images of crawling humans and horses in quadrupedal postures, which the chimpanzees had never seen previously, but they showed the inversion effect. Their limited inversion effects to humans, a familiar species, and the inversion effects to the quadrupedal animals that they had no visual experience about, suggest a strong tendency to refer to embodied cues, i.e., cues from their own bodies, in their body perception. Therefore, experience with humans may not affect chimpanzees’ body representation for conspecific bodies too much.

The random effect, picture ID, was significant in fixation-duration analysis (Fig. 8). This suggests that the results vary across the pictures. There are several outlier points, but not many. It is possible that the significance is related to the limited data we have: not every picture in each condition received a lot of fixations. As will be discussed below, it is inevitable to have many trials without any fixations in a chimpanzee experiment, and future studies could use more trials for more useful data points. Nevertheless, because the 20 pictures (with different kinds of manipulations) were used across conditions, this significant effect of picture ID does not interfere with the significance of condition, the main effect in the analysis.

There were several other limitations in this study. The number of trials in which the chimpanzees showed fixations to AOIs was less than half of the total trial numbers. Chimpanzees do not consistently look at the screen during a task. When they do, they typically view face and genital areas of a chimpanzee picture, while they allocate less attention to other body parts (Kano et al. 2015). More importantly, because the AOIs in this study were arms or legs (i.e., a small proportion of the whole picture), it is reasonable to have many trials without fixations on AOIs. Nevertheless, future studies in a similar setting could use a larger stimulus set to ensure more data points.

When we prepared the stimuli, the pictures were chosen randomly, and the body parts for manipulations were chosen based on picture editing convenience; we hoped to minimize editing to avoid any effects of unnatural picture manipulations. Overall, we edited 10 left arms, 10 right arms, 5 left legs, and 15 right legs. This should not fundamentally affect the experiment, because chimpanzees were in various positions (e.g., sitting, walking to the left, walking to the right, and bipedal standing), and left/right discrimination was less prominent than in a situation involving only bipedal animals. Nonetheless, future studies should carefully consider left/right bias to ensure a more balanced experimental design.

In summary, our results showed a significant longer looking time towards human body parts on chimpanzee bodies, and two non-significant tendencies: (1) shorter latencies for fixating misplaced legs, and (2) longer looking times towards misplaced parts, compared to normal body parts. These detections of strange body parts indicate that chimpanzees might have a body representation of the typical chimpanzee body. Conspecific body representation has ecological value. For example, it helps animals discriminate among conspecific individuals and individuals of other species (and then they can decide whether to fight them, socially interact with them, prey and feed on them, or ignore them). Strangeness on body parts of living individuals can indicate injury, and body representation can help trigger emotional and behavioral changes to facilitate care for these individuals (Hirata et al. 2017; Matsumoto et al. 2016; Sato et al. 2019). From an evolutionary perspective, evidence of body representation among chimpanzees indicates that the common ancestor of chimpanzees and humans might also have this type of visual representation. Of course, this conclusion needs to be supported by more data from more participants and from studies with further examinations besides arm and leg manipulations. Nevertheless, if this is true, it will lead to many interesting questions. Because both chimpanzees and humans are highly social species, and both encounter many other individuals, it is important to investigate whether body representation originates from the accumulated visual experience of conspecifics’ bodies. Investigation of this point requires examination of more solitary species, such as orangutans, as well as examination of body representation development. If the representation is present in solitary species or develops before intensive social interactions with other individuals, body representation may have more fundamental functions in animals’ life as follows: apart from aiding interactions with other individuals, body representation may be involved in many self-centered activities (Shapiro 2019). Further investigations of body representation and its interactions with other psychological processes are important for understanding how animals coordinate themselves with the outside world.