Is the Psychopathic Brain an Artifact of Coding Bias? A Systematic Review

Is the Psychopathic Brain an Artifact of Coding Bias? A Systematic Review. Jarkko Jalava et al. Front. Psychol., April 12 2021. https://doi.org/10.3389/fpsyg.2021.654336

Abstract: Questionable research practices are a well-recognized problem in psychology. Coding bias, or the tendency of review studies to disproportionately cite positive findings from original research, has received comparatively little attention. Coding bias is more likely to occur when original research, such as neuroimaging, includes large numbers of effects, and is most concerning in applied contexts. We evaluated coding bias in reviews of structural magnetic resonance imaging (sMRI) studies of PCL-R psychopathy. We used PRISMA guidelines to locate all relevant original sMRI studies and reviews. The proportion of null-findings cited in reviews was significantly lower than those reported in original research, indicating coding bias. Coding bias was not affected by publication date or review design. Reviews recommending forensic applications—such as treatment amenability or reduced criminal responsibility—were no more accurate than purely theoretical reviews. Coding bias may have contributed to a perception that structural brain abnormalities in psychopaths are more consistent than they actually are, and by extension that sMRI findings are suitable for forensic application. We discuss possible sources for the pervasive coding bias we observed, and we provide recommendations to counteract this bias in review studies. Until coding bias is addressed, we argue that this literature should not inform conclusions about psychopaths' neurobiology, especially in forensic contexts.

Discussion

Neurobiological reviews of PCL-R and PCL:SV psychopathy significantly under-report null-findings in sMRI research, indicating widespread coding bias. The majority (64.18%) of original sMRI findings were nulls, whereas nulls made up a small minority (8.99%) of effects in review literature. Reviewers, in other words, preferentially reported data supporting neurobiological models of psychopathy. We found no evidence that the reporting imbalance was due to factors other than bias: systematic, narrative, and targeted reviews all reported disproportionately few nulls (though meta-analyses reported too few effects to evaluate), the pattern was stable across time, and not driven by exploratory research or outliers. Notably, reviews calling for forensic application of the data, such as treatment, criminal responsibility, punishment, and crime prediction, were no more accurate than purely theoretical reviews. Applied reviews were, however, more likely than theoretical reviews to conclude that the data supported neurobiological bases of psychopathy. These findings are surprising, as applied reviews in other fields—such as those examining drug safety and efficacy—typically face the highest burden of proof and are thus most likely to emphasize limitations in the data [see e.g., Köhler et al. (2015)].

Our study is the first to systematically examine coding bias in cognitive neuroscience. Although our findings are limited to structural imaging in psychopathy, they suggest that coding bias should be considered alongside more widely recognized Questionable Research Practices (QRPs) such as p-hacking, reporting bias, publication bias, citation bias, and the file drawer problem. QRPs in original research filter out null-findings at early stages of the research and publication process, while coding and citation bias further distort the state of scientific knowledge by eliminating null findings from reviews. In addition to coding bias, we found evidence of reporting bias during our review of sMRI studies. Null-findings in the original literature were rarely reported in the study abstracts and were frequently not reported fully in results sections. Nulls often appeared only in data or supplemental tables, and in some cases they had to be inferred by examining ROIs mentioned in the introduction but not in the results section. This illustrates how QRPs are not mutually exclusive, and the presence of one QRP may also signal the presence of another [see e.g., Agnoli et al. (2017)].

The coding bias we observed may have a number of explanations. First, reviewers may have been subject to confirmation bias. Confirmation bias refers to the tendency to weigh evidence that confirms a belief more heavily than evidence that does not (Nickerson, 1998). Reviewers in our study may have assumed neurobiological abnormalities in psychopaths—perhaps from previous reviews—and looked more carefully for data to confirm that assumption. Confirmation bias has been cited as a possible explanation for under-reporting of null-findings in original research (Forstmeier et al., 2017). Our findings suggest that it may play a role in review literature, where null-findings would be especially difficult to square with theories presuming group differences [see e.g., Sterling et al. (1995) and Ferguson and Heene (2012)], and reporting bias would make it very hard to locate disconfirming (null) findings. Second, reviewers may have been following convention. The earliest review studies did not generally include null-findings, and later reviews may have interpreted this as a precedent to follow. Third, explicit and tacit publication preferences may increase coding bias. Research tracking original studies from grant proposal to publication show that most null-findings are not even written up for publication, and that journals—particularly top-tier journals—show a marked preference for strong positive findings (Franco et al., 2014; Ioannidis et al., 2014). Similarly, review authors may have declined to submit reviews with inconclusive findings. Given the extent of publication bias, it is also possible that journal editors may have been more likely to reject inconclusive reviews in favor of those summarizing consistent, positive findings.

Coding bias observed in our study has a number of potential effects. Aside from distorting the true state of knowledge about structural brain abnormalities in psychopaths, it may also have led at least some researchers and courts to believe that the abnormalities are consistent enough for forensic application. This may have encouraged practitioners to de-emphasize or overlook more reliable, behavioral indicators of criminal responsibility, future dangerousness and treatment amenability in favor of less reliable predictors, such as brain structure. Neuroprediction of crime has a number of empirical shortcomings, such as unknown measurement error and inadequate outcome variables (Poldrack et al., 2018). Using MRI data to predict crime can thus introduce substantial error into an already imperfect process (e.g., Douglas et al., 2017). Neurobiologically-informed assessments and treatments are even less likely to be effective if the population's neurobiology is fundamentally misunderstood. Given the extent of coding bias in the psychopathy literature, such interventions may in fact be harmful.

More broadly, coding bias may have contributed to reverse inference [see Scarpazza et al. (2018)] whereby reports of brain abnormalities are taken as proof that psychopathy is a legitimate diagnostic category [for an argument such as this, see e.g., Kiehl and Hoffman (2011)].5 Similarly, some researchers have suggested that psychopathy diagnoses could be enhanced by neuroimaging evidence (e.g., Hulbert and Adeli, 2015). Arguments of this sort can detract from problems in other aspects of the PCL-R, particularly in its psychometric properties. Recently, these critiques have intensified, with authors raising concerns about the reliability of the PCL-R, its utility in forensic contexts (DeMatteo et al., 2020), its factor structure, and its predictive validity (Boduszek and Debowska, 2016). Using neurobiology to validate psychopathy as a diagnostic category is doubly problematic: not only are presumed brain abnormalities in psychopathy broad and non-specific [for problems in reverse inference, see Poldrack (2011) and Scarpazza et al. (2018)], but as we have shown here, their consistency appears to be largely misunderstood as well.

In light of our findings, we recommend the following: First, published review literature on sMRI studies of PCL-R and PCL:SV psychopathy should be approached with caution, especially when the literature is used to influence forensic decisions. Second, we recommend that guidelines for conducting review literature be revised to include explicit guidance for avoiding coding bias. Although the problem of un- and under-reported null-findings is recognized [e.g., Pocock et al., 1987; Hutton and Williamson, 2000; guidelines for accurate reporting in review literature also exist; see Petticrew and Roberts (2008), American Psychological Association (2008), and Moher et al. (2015)], the role of coding bias, by and large, is not. Third, we recommend that review literature pay careful attention to the a priori likelihood of null-findings in their data. In our example, both the PCL-R (DeMatteo et al., 2020) and neuroimaging methods (Nugent et al., 2013) have relatively low reliability. The likelihood that sMRI research on psychopathy should yield more than 91% positive findings is therefore not realistic [for more extended discussions relating to fMRI, see Vul et al. (2009) and Vul and Pashler (2017)]. Fourth, we recommend that the production of new data should be complemented by closer examination of data already published. Among the 45 reviews we evaluated, we found a single study (Plodowski et al., 2009) that comprehensively reported all nulls in the original literature. Unfortunately, it was also among the least cited reviews, suggesting that accuracy and scientific impact do not necessarily go together. Finally, we recommend that reviewers pay close attention to potential biases—such as publication and reporting bias, p-hacking, and the file drawer problem—in the original literature, and take measures to compensate for them. Currently, it appears that reviews largely magnify them instead.

Limitations

Our study has a number of important limitations. First, in order to focus on forensically relevant studies, we limited our analysis to PCL-R and PCL:SV psychopathy. We also excluded studies that reported on PCL-R Factor scores only (e.g., Bertsch et al., 2013), that did not use case-control or correlational method (Sato et al., 2011; Kolla et al., 2014), and that included youth samples. It is possible that the excluded studies were reported more accurately in review literature than those we included. Second, we excluded original and review studies not published in English. This may have introduced a selection bias of our own, as it is possible that non-English publications use different standards of reporting and reviewing than those published in English. Third, our findings may have underestimated the extent of the bias. For example, one whole-brain analysis reviewed here (Contreras-Rodríguez et al., 2015) only reported positive findings, which means that the remaining brain regions were unreported nulls. Had these unreported null-findings been included in our analysis, the true percentage of nulls in the original studies would have been greater than 64.18%. Further, we did not account for possible publication bias. Since null-findings are presumed to be less likely than null-rejections to be published, the percentage of true nulls in the field is essentially unknown, though it may be significantly higher than we estimated (review literature examined here did not report any unpublished null-findings). Finally, we excluded fMRI and other imaging methods entirely. Future research could evaluate whether coding bias is present in reviews of this literature as well.

Those with low levels of conscientiousness, life satisfaction, & self-esteem, as well as high levels of neuroticism, used more drugs on average; in contrast, found little evidence for personality change following substance use

How Does Substance Use Affect Personality Development? Disentangling Between- and Within-Person Effects. Lara Kroencke et al. Social Psychological and Personality Science, July 7, 2020. https://doi.org/10.1177/1948550620921702

Abstract: Little is known about the effects of substance use on changes in broad personality traits. This 10-year longitudinal study sought to fill this void using a large, representative sample of the Dutch population (N = 10,872), which provided annual assessments of drug use (tobacco, alcohol, sedatives, soft drugs, ecstasy, hallucinogens, and hard drugs), Big Five personality traits, life satisfaction, and self-esteem. Using multilevel models, we examined the longitudinal associations between drug use and personality both between and within persons. Results indicated that individuals with low levels of conscientiousness, life satisfaction, and self-esteem, as well as high levels of neuroticism, used more drugs on average (between-person effects). In contrast, we found little evidence for personality change following substance use (within-person effects). We discuss these findings in the context of previous empirical and theoretical work and highlight opportunities for future research.

Keywords: substance use, drug use, personality development, life satisfaction, self-esteem

Discussion

This research examined the 10-year longitudinal associations between broad personality traits, life satisfaction, and self-esteem and use of different legal and illegal substances in a representative sample of the Dutch population. The purpose was to disentangle stable between-person effects from within-person associations to advance our understanding of the sources that may drive personality change. In what follows, we discuss our findings with respect to the previous literature and highlight their implications.

Consistent with our preregistration and past research, we found evidence for moderate between-person associations between drug use and personality traits. Specifically, individuals who were high in neuroticism and low in conscientiousness were more likely to consume drugs. These findings were mirrored by associations with life satisfaction and self-esteem (participants lower in life satisfaction and self-esteem were more likely to report substance use). As expected from our power analysis, even small to moderate effects (B > .30) were typically significant, except for infrequently consumed substances.

The fact that conscientiousness was related to use of nearly all substances is consistent with its association with a wide range of health behaviors (Bogg & Roberts, 2004). The relationships between substance use and neuroticism may indicate attempts of self-medication among neurotic individuals in an effort to decrease negative affective states (e.g., Khantzian, 1997). Interestingly, these between-person effects were more pronounced for less frequently consumed substances.

Regarding personality change, our study is among the first to fully disentangle between- from within-person effects and hence represents a more conservative test for the hypotheses at hand. Contrary to previous studies, we found few within-person effects of drug use on subsequent personality change. Even when significant, these effects were considerably smaller than the between-person effects, and none of the effects were predicted based on the existing literature. The within-person effects for the more malleable variables life satisfaction and self-esteem were also small and rarely significant, highlighting the robustness of the results. Below, we will discuss several possible reasons for the lack of predicted within-person effects.

First, our study was limited by selective attrition and somewhat lower power for rarely consumed drugs. Importantly, our power for relatively frequently consumed drugs was adequate even for small within-person effects. As such, the null findings for those effects are unlikely to represent Type II errors.

Second, we investigated whether a drug was consumed during the last month, but we did not measure substance use over longer periods of time, neither did our measures account for intensity and context of usage. We tried to control for these limitations (e.g., by investigating the effects of repeated use), but future studies should replicate our results using alternative measures of drug use.

Third, the intervals between personality and drug use assessments were relatively long, preventing us from examining transitory effects (less than 200 days). Our analyses were also restricted by the limited number of assessments per person. Future studies should include more measurement points and examine both the bivariate trajectories of substance use and personality and the effects of certain substance use life events (e.g., first onset of use) on personality trajectories.

Our findings have important theoretical implications. First, drug use has been proposed as a candidate mechanism for changes in personality that may be mediated via biological pathways (Costa et al., 2019) as well as behavioral or social mechanisms. Although theoretically plausible, we found little evidence for such effects. Second, we observed large variability in the associations between substance use and personality (i.e., random effects), indicating that, despite the lack of strong main effects, there are significant individual differences in within-person associations between substance use and personality. In other words, substance use might have negative effects for some people but no effects or even positive effects for others. Future studies should examine which moderator variables explain these different trajectories.

To our knowledge, this is the first large-scale study examining the impact of a wide range of drugs on the Big Five personality traits, life satisfaction, and self-esteem. We analyzed data from more than 10,000 individuals that were collected over a period of more than 10 years with an average of three assessments for each participant, using highly reliable personality measures. In addition, we used statistical models that effectively distinguished between- and within-person effects. Overall, our study provides strong evidence for between-person relationships between substance use and personality differences but little evidence for within-person changes in personality following substance use.

Do Newborns Have the Ability to Imitate? We can now rule out some long-standing explanations for why the effect might be difficult to detect, only some research groups observe it, the published literature is biased

Do Newborns Have the Ability to Imitate? Virginia Slaughter. Trends in Cognitive Sciences, Vol 25, Issue 5, pp 377-387, March 13, 2021. https://doi.org/10.1016/j.tics.2021.02.006

Highlights

Although many assume that newborn infants imitate others, new data and analyses suggest it is not a reliable effect.

Meta-analysis of human neonatal imitation studies revealed an overall positive effect which was not moderated by major methodological variations, but did vary by research group.

Future studies of newborn imitation should adopt modern procedures to eliminate potential biases.

Researchers should also test models of how imitation could be learned. Associative Sequence Learning proposes that coincident experience of producing and perceiving body gestures over the first year of life, creates mirror systems to support imitation.

Neonatal imitation is widely accepted as fact and cited as evidence of an inborn mirror neuron system that underpins human social behaviour, even though its existence has been debated for decades. The possibility that newborns do not imitate was reinvigorated recently by powerful longitudinal data and novel analyses. Although the evidence is still mixed, recent research progresses the debate by ruling out some long-standing explanations for why the effect might be difficult to detect, by showing that only some research groups observe it, and by revealing indications that the published literature is biased. Further advances will be made with updated testing procedures and reporting standards, and investigation of new research questions such as how infants could learn to imitate.

Concluding Remarks

When considering all the evidence, it is hard to maintain the conviction that newborns imitate. However, there is still no definitive answer to the question. To find an answer, several things need to happen. Researchers should replace the 40-year-old methodology that has nurtured this controversy with modern approaches to data collection, analysis and reporting. It is also time to ask new questions: are newborns physically capable of imitating (Box 2)? To what extent do adults imitate babies in everyday interactions? Can imitation be trained in the first months of life? It also would be helpful if authors writing about newborns, imitation or mirror neurons, acknowledged the ongoing controversy rather than treating neonatal imitation as a fact.

Box 2

Do Newborns Have Voluntary Control of Oral–Facial Movements?

Putting aside the controversial evidence for and against newborn imitation, Keven and Akins [

57.

] considered whether newborn infants’ sensory–motor and brain development enables imitation. Their detailed analysis drawing on modern accounts of early neuromotor development suggested that imitation of mouth gestures, and tongue protrusion in particular, is beyond the capacity of neonates whose nervous systems are still adapting to postpartum life. It takes months for the newborn brain to coordinate breathing with sucking and swallowing liquids. As these functions mature, newborns engage in repetitive oral activity, including a lot of mouth opening and closing, and tongue protrusion and retraction. These patterned behaviours are involuntary, driven by subcortical brain mechanisms, and increase when newborns are aroused.

Keven and Akins’ analysis suggests that voluntary production of oral–facial movements in response to a matching model is physically impossible in newborns, because these gestures are generated by the brain’s subcortex in the first months of life. This would mean that so-called imitation in the newborn period is simply coincidental, since neonates’ involuntary mouth movements increase in response to the arousing sight of an experimenter’s animated face. This conclusion has been offered previously, based on observations that newborns increase their tongue protrusions in response to various arousing stimuli including light displays and orchestral music [

6.

]. Keven and Akins’ analysis also addresses the claim that newborn imitation fades out around 2–3 months of age: at that stage, the ‘wiring up’ of sucking, swallowing, and respiration functions are complete, so infants no longer involuntarily produce oral–facial movements in response to arousing stimuli.

Keven and Akins’ analysis demonstrates the value of asking different questions in relation to newborn imitation, rather than just focusing on ‘do they, or don’t they?’ However, their analysis was itself controversial, as evident in the open peer commentaries accompanying their article. For instance, some commentators dismissed the analysis as irrelevant to newborn imitation, relying on claims that a range of facial and manual gestures, in addition to tongue protrusion and mouth opening, are imitated by neonates [

58.

,

59.

]. Others accepted that newborns’ oral–facial movements promote maturation of sucking and swallowing but argued that they simultaneously function as communicative signals in face-to-face interactions with caregivers [

60.

,

61.

].

There is no doubt that imitation is a central element of human development. Indeed, there is a vast literature documenting what children imitate, from whom, and under what circumstances [

55.

]. However, we still do not know when or how this ubiquitous behaviour emerges, which means that we do not truly understand it (see Outstanding Questions). If imitation turns out to be learned rather than inborn, this would not diminish the theoretical significance of imitation for infant–parent bonding, social learning or later-developing interpersonal skills. Rather, it would highlight the brain’s proclivity to create connections between ourselves and others, from the first months of life.

Outstanding Questions

Is there evidence of imitation when newborns are tested with objective measures such as EMG?

Does video modelling of gestures genuinely increase newborns’ imitative response as suggested by the meta-analysis? If so, why?

What accounts for the meta-analytic finding that neonatal imitation varies by research group?

How frequently do infants experience observation–action correspondences during a typical day and is this variable related to production of imitation?

Are different types of observation–action correspondence (e.g., self-observation, mirror exposure, and caregiver mimicry) related to different forms of imitation in infancy?

Can imitation be promoted in infants with observation-action training as predicted by ASL?

Delinquency: Substantial genetic origin for those of persistently bad or aggresive behaviour (heritability = 67%), whereas genetic influences were negligible for lower-risk subgroups

Developmental Trajectories of Delinquent and Aggressive Behavior: Evidence for Differential Heritability. Joshua Isen, Catherine Tuvblad, Diana Younan, Marissa Ericson, Adrian Raine & Laura A. Baker. Child Psychiatry & Human Development, Jan 15 2021. https://link.springer.com/article/10.1007/s10578-020-01119-w

Abstract: The developmental course of antisocial behavior is often described in terms of qualitatively distinct trajectories. However, the genetic etiology of various trajectories is not well understood. We examined heterogeneity in the development of delinquent and aggressive behavior in 1532 twin youth using four waves of data collection, spanning ages 9–10 to 16–18. A latent class growth analysis was used to uncover relevant subgroups. For delinquent behavior, three latent classes emerged: Non-Delinquent, Low-Level Delinquent, and Persistent Delinquent. Liability for persistent delinquency had a substantial genetic origin (heritability = 67%), whereas genetic influences were negligible for lower-risk subgroups. Three classes of aggressive behavior were identified: Non-Aggressive, Moderate, and High. Moderate heritability spanned the entire continuum of risk for aggressive behavior. Thus, there are differences between aggressive behavior and non-aggressive delinquency with respect to heterogeneity of etiology. We conclude that persistent delinquency represents an etiologically distinct class of rule-breaking with strong genetic roots.

Reaping a benefit at the expense of multiple others: We make more selfish choices, and judge others’ selfish choices more lightly, when the social losses are dispersed more thinly across a group

Reaping a benefit at the expense of multiple others: How are the losses of others counted? Meir Barneron, Shoham Choshen-Hillel, Ilan Yaniv. Organizational Behavior and Human Decision Processes, Volume 164, May 2021, Pages 136-146. https://doi.org/10.1016/j.obhdp.2021.02.004

Highlights

• We studied selfish choices that create social loss, harming the welfare of others.

• We theorized that empathy underlies perceptions of the harm caused to others.

• Participants should be sensitive to the individual harm, not to the aggregate harm.

• Our studies supported these predictions and revealed a dispersion effect.

• Rated feelings of empathy mediated the participants’ judgments of selfish decisions.

Abstract: We investigate individual decisions that produce gains for oneself, while imposing losses on a group of others. We theorize, based on the notion of empathy, that decision-makers consider the magnitude of the pain or loss they inflict on an individual in the group, but are largely insensitive to the number of individuals in the group who suffer losses. Studies involving personal choices or judgments of others’ choices largely confirmed these predictions. They also revealed a dispersion effect, whereby participants made more selfish choices, and judged others’ selfish choices more lightly, when the social losses were dispersed more thinly across a group. It appears that decision-makers’ empathy for others who suffer losses is not readily adjusted to the number of people affected or to the aggregated losses. It also appears that empathy mediates judgments of selfish behavior. The findings are related to theories of empathy, and decisions under conflicts of interest.

Keywords: Judgment and decision makingSelfish vs prosocial behaviorEmpathySocial preferenceConflict of interestDecision ethics

People ascribe differing degrees of genetic influence to the same phenotype depending on whether it is expressed in socially favored or disfavored ways

Genetic attributions and perceptions of naturalness are shaped by evaluative valence. Matthew S. Lebowitz, Kathryn Tabb & Paul S. Appelbaum. The Journal of Social Psychology, Apr 9 2021. https://doi.org/10.1080/00224545.2021.1909522

Abstract: Genetic influences on human behavior are increasingly well understood, but laypeople may endorse genetic attributions selectively; e.g., they appear to make stronger genetic attributions for prosocial than for antisocial behavior. We explored whether this could be accounted for by the relationship of genetic attributions to perceptions of naturalness. Participants read about positively or negatively valenced traits or behaviors and rated naturalness and genetic causation. Positively valenced phenotypes were rated significantly more natural and significantly more genetically influenced than negatively valenced phenotypes, and the former asymmetry significantly mediated the latter (Experiments 1 and 2). Participants’ interpretation of what “natural” meant was not synonymous with valence or genetic attributions (Experiment 3). People ascribe differing degrees of genetic influence to the same phenotype depending on whether it is expressed in socially favored or disfavored ways, potentially representing a significant threat to public understanding of genetics.

KEYWORDS: Geneticssocial cognitioncausal attributionmotivated reasoning

Check also Antisocial behaviour was consistently rated as less genetically influenced than prosocial behaviour; asymmetry may stem from people’s motivating desire to hold wrongdoers responsible for their actions:

Asymmetrical genetic attributions for prosocial versus antisocial behaviour. Matthew S. Lebowitz, Kathryn Tabb & Paul S. Appelbaum. Nature Human Behaviour, volume 3, pages 940–949 (2019), July 29 2019. https://www.bipartisanalliance.com/2019/09/antisocial-behaviour-was-consistently.html

In all, results suggest that the relationships between physical activity, mental health, and well-being are tenuous, at best

Klussman, K., Langer, J., & Nichols, A. L. (2021). The relationship between physical activity, health, and well-being: Type of exercise and self-connection as moderators. European Journal of Health Psychology, Apr 2021. https://doi.org/10.1027/2512-8442/a000070

Rolf Degen's take: https://twitter.com/DegenRolf/status/1380794815277850624

Abstract

Background: Most people are comfortable asserting the beneficial effects of physical exercise on mental health and well-being. However, little research has examined how different types of physical activity affect these outcomes.

Aims: The current study sought to provide a comprehensive understanding of the differential relationships between different types of physical activity and various aspects of health and well-being. In addition, we sought to understand the role of self-connection in these relationships. Method: One hundred forty-three participants completed a questionnaire designed to measure their current weekly activity as well as their current health and well-being. Specifically, we examined three intensities of activity (walking, moderate, and vigorous) and three types of activity (team-based, community-based, and not team nor community-based) on self-reported health, anxiety, depression, affect, flourishing, job satisfaction, life satisfaction, and meaning in life. In addition, we examined self-connection as a possible moderator of these relationships.

Results: Results suggested that physical activity was inconsistently related to health and well-being, and activity intensity and type were important to understanding these relationships. In contrast, self-connection reliably related to health and well-being and moderated the relationship between activity type and the presence of meaning.

Limitations: The cross-sectional, self-report nature of the study limits its contribution. In addition, we only examined a subset of all physical activities that people engage in.

Conclusion: In all, results suggest that the relationships between physical activity, mental health, and well-being are tenuous, at best. Future research needs to examine these relationships further and continue to examine self-connection to determine how to best increase health and well-being through physical activity. 

Chest beats as an honest signal of body size in male mountain gorillas: Positive correlations among male body size, dominance rank and reproductive success

Chest beats as an honest signal of body size in male mountain gorillas (Gorilla beringei beringei). Edward Wright, Sven Grawunder, Eric Ndayishimiye, Jordi Galbany, Shannon C. McFarlin, Tara S. Stoinski & Martha M. Robbins. Scientific Reports volume 11, Article number: 6879. Apr 8 2021. https://www.nature.com/articles/s41598-021-86261-8

Abstract: Acoustic signals that reliably indicate body size, which usually determines competitive ability, are of particular interest for understanding how animals assess rivals and choose mates. Whereas body size tends to be negatively associated with formant dispersion in animal vocalizations, non-vocal signals have received little attention. Among the most emblematic sounds in the animal kingdom is the chest beat of gorillas, a non-vocal signal that is thought to be important in intra and inter-sexual competition, yet it is unclear whether it reliably indicates body size. We examined the relationship among body size (back breadth), peak frequency, and three temporal characteristics of the chest beat: duration, number of beats and beat rate from sound recordings of wild adult male mountain gorillas. Using linear mixed models, we found that larger males had significantly lower peak frequencies than smaller ones, but we found no consistent relationship between body size and the temporal characteristics measured. Taken together with earlier findings of positive correlations among male body size, dominance rank and reproductive success, we conclude that the gorilla chest beat is an honest signal of competitive ability. These results emphasize the potential of non-vocal signals to convey important information in mammal communication.

Discussion

Our results indicate that mountain gorilla chest beats reliably convey information about the body size of the sender. Larger males consistently emitted chest beats with lower median peak frequencies than smaller males. This finding is an important contribution to the growing literature on honest signaling of body size in acoustic communication, which has predominantly focused on vocalizations5,10,11,12,13,14,15,16,17,18. This is one of a few studies in mammals demonstrating that body size is reliably encoded in a non-vocal acoustic signal. In eland bulls, body size (skeletal measures and muscle mass) was shown to be negatively correlated with the peak frequency of knee clicks21. In adult male gorillas, body size (a composite measure combining crest height and back breadth) is thought to reflect competitive ability because it correlates with dominance rank in multi-male groups and reproductive success31. Additionally, silverbacks chest beat more frequently on days when females are in estrous, presumably as a courtship display28. Taken together, this strongly suggests that the chest beat is an extremely important signal in intrasexual competition and intersexual mate choice in gorillas. Moreover, given that different forms of drumming behaviour, incorporating substrates other than the chest or body, are surprisingly common in a wide range of animals19,20, it is likely that this understudied non-vocal acoustic mode of communication functions to reliably indicate competitive ability in many other species as well.

Our measure of body size, back breadth, likely correlates with a range of morphological traits, including chest volume, pulmonary capacity and hand size. Therefore it is unclear which specific trait or traits are responsible for driving the inverse relationship between back breadth and peak frequency. Moreover, gorillas like other non-human primates possess laryngeal air sacs which are thought to act as resonators, enhancing acoustic signals4,11,24. Indeed, gorillas appear to use laryngeal air sacs during growling vocalizations which often accompany chest beating24. The volume of laryngeal air sacs is likely to be directly correlated with body size, at least within-species (which in orangutans (Pongo) can reach a massive 6 L38). Thus larger males are expected to have larger laryngeal air sacs than smaller males, further lowering the resonating non-vocal frequencies produced whilst chest beating. However, our knowledge of the size and function of laryngeal air sacs in primates and other taxa remains poor39.

Both dominant and subordinate male gorillas emitted chest beats. In general, gorilla males likely chest beat to attract estrous females and intimidate rivals22,28,31. However, younger subordinate males may also chest beat as a means to fine tune this signal and acquire social feedback from conspecifics. The importance of practice is evident as infants as young as one year of age commonly start emitting chest beats during social play22,40. Interestingly, the chest beat rate (number of chest beats per unit time) in the current study (2014–2016) was over three times higher than what was previously reported (1968–1969)23. We are unsure why this is the case, but it could be due to a number of different factors, including a higher number of estrous females per group, younger males, or more intergroup encounters over time41.

Even though we have demonstrated that chest beats reliably convey the body size of the emitter, future studies need to show that receivers actually attend to this information. Gorilla chest beats are thought to play a key role in male–male competition allowing individuals to assess the fighting ability of competitors and thus influence whether they should initiate, escalate or retreat in intra- and intergroup contests22,31,42. Similarly, male gelada baboons (Theropithecus gelada) assess the competitive ability of rivals through vocalizations and compare it to their own, governing how they respond in contests43. Intense contact aggression between males is infrequent in gorillas, which is presumed to reflect the high costs of aggression and their ability to resolve conflicts without resorting to this high risk behaviour (within-group31,42; between-group44). We expect that chest beats to also play a critical role in mate choice22,28,45, providing females with information about the size of the males in their own group and in neighbouring groups, which may influence their decision to transfer to another group. Larger alpha males lead groups with more adult females than smaller males, strongly suggesting that females actively chose to transfer into groups with large alpha males29,30,31. Gorillas may be similar to red deer hinds in their ability to discriminate between the acoustic signals of their current harem-holder stag and those of neighbouring stags46. Lastly, because chest beats can be heard over long-distances, we predict that both male size and the number of different males emitting chest beats are two important factors influencing group movement. Recent work in Bwindi mountain gorillas speculated that one of the functions of chest beats is to mediate how groups use space, with smaller groups with fewer adult males likely avoiding larger ones with more males, which would help to explain their findings that larger groups having more exclusive home ranges and core areas than smaller groups47.

We found no support for body size to influence the duration of chest beats, the number of beats, or the beat rate. Acoustic signals are thought to be energetically expensive to produce34,35,36,37 and we expected chest beats to be as well, with anecdotal accounts of gorillas that emit a high frequency of chest beats showing signs of exhaustion (personal observation). This is in contrast to studies of savannah baboons (Papio ursinus), showing that males with higher competitive ability produce longer vocalizations than weaker ones48,49. It is possible that the duration of chest beats (and the beat rate) decreases over time during periods of high chest beating frequency, and this decrease may be stronger in smaller males. In general the relationship between body size and the duration of vocalizations and other acoustic sounds has been understudied in mammals4,50.

In addition to conveying information on body size (and other phenotypic traits), we would expect it to be important for chest beats to be individual-specific, thereby allowing receivers to discriminate the identity of the emitter. Further study is needed to determine if there are individual signatures to the chest beats. Interestingly, we found smaller within-individual than between-individual coefficients of variation, particularly for chest beat duration and number of beats (39.0 vs. 85% and 31.6 vs. 67.9%, respectively). Notably, several temporal aspects of non-vocal drumming displays by chimpanzees (Pan troglodytes), ruffed grouse (Bonasa umbellus) and great spotted woodpeckers (Dendrocopos major) show significant individual variation, similar to many vocalizations in a wide range of species19,51,52. For example, the buttress drumming of individual chimpanzees significantly differ in the mean duration and the mean number of beats52,53.

The gorilla chest beat has both an acoustic and visual component, making it a multimodal signal. Individuals in visual proximity can benefit from seeing and hearing the gorilla emitting the chest beat, whereas individuals further away rely on the acoustic component. Researchers have been interested in determining whether the different components of multimodal signals convey the same (redundant signal or backup hypothesis) or different information (multiple messages hypotheses)54. Gorillas live in tropical forests with dense vegetation, meaning that it is often difficult to see conspecifics even if they are close by. Therefore, we argue that the evolution of the chest beat as a multimodal signal is at least in part to enhance signal transmission in an environment with limited visibility. We would expect the same messages to be transmitted in both visual and acoustic modalities, which would provide support for the redundant signal hypothesis. However, these two hypotheses are not mutually exclusive, as the chest beat signal may transmit additional information, other than body size, which is then repeated in the visual and acoustic modalities, providing support for both hypotheses.

Women endorsed self-estimates of storge (friendship and intimacy), pragma (practical ventures) and agape (altruistic love) more than men did; males assessed their female partners higher in mania (obsession and possessiveness)

Gender Differences in Estimates of Love Styles for Self and Others. Félix Neto. Sexuality & Culture, Apr 6 2021. https://link.springer.com/article/10.1007/s12119-021-09855-4

Abstract: This study investigated gender differences in how people estimate the intensity and style of love in themselves and in others. The six orientations toward love analyzed were: Eros (sex and passion), Ludus (game-playing), Storge (friendship and intimacy), Pragma (practical ventures), Mania (obsession and possessiveness), and Agape (altruistic love). The sample included 265 students (170 females and 95 males). Respondents evaluated their parents’, romantic partners’, and own overall love and the six love styles. Women endorsed self-estimates of storge, pragma and agape more than men did. Males assessed their female partners higher in mania. Gender differences in estimates of parental love styles were not found. Concerning self-partner differences, participants estimated their partners as being higher in ludic and manic love. Regarding generational differences, children well-tended to assess themselves higher in love than their fathers and mothers. Multiple regressions indicated that erotic, storgic and agapic love styles were significant predictors of overall love for self, romantic partners, and parents. Results are discussed with reference to previous research and some suggestions for further research are also noted.

How Social Relationships Shape Moral Judgment

Earp, Brian D., Killian L. McLoughlin, Joshua Monrad, Margaret S. Clark, and Molly Crockett. 2020. “How Social Relationships Shape Moral Judgment.” PsyArXiv. September 18. osf.io/e7cgq

Abstract: Our judgments of whether an action is morally wrong depend on who is involved and their relationship to one another. But how, when, and why do social relationships shape such judgments? Here we provide new theory and evidence to address this question. In a pre- registered study of U.S. participants (n = 423, nationally representative for age, race and gender), we show that particular social relationships (like those between romantic partners, housemates, or siblings) are normatively expected to serve distinct cooperative functions – including care, reciprocity, hierarchy, and mating – to different degrees. In a second pre- registered study (n = 1,320) we show that these relationship-specific norms, in turn, influence the severity of moral judgments concerning the wrongness of actions that violate cooperative expectations. These data provide evidence for a unifying theory of relational morality that makes highly precise out-of-sample predictions about specific patterns of moral judgments across relationships. Our findings show how the perceived morality of actions depends not only on the actions themselves, but also on the relational context in which those actions occur.