Wednesday, March 17, 2021

Hippocampal volume has been associated with impaired & expert navigation, but large pre-registered studies found no such correlation in healthy adults; network models offer greater explanatory power for flexibility & individual differences

Hippocampal volume and navigational ability: The map(ping) is not to scale. Steven M. Weisberg, Arne D. Ekstrom. Neuroscience & Biobehavioral Reviews, March 17 2021.

Rolf Degen's take: The way things are, we will probably never learn whether taxi drivers really have a larger hippocampus, as shaky science findings once seemed to show


• Hippocampal volume has been associated with impaired and expert navigation.

• Large pre-registered studies found no such correlation in healthy adults.

• Theoretical mechanisms supporting structure-behavior associations are tenuous.

• Navigation is a complex cognitive function, involving multiple brain networks.

• Network models offer greater explanatory power for flexibility and individual differences.

Abstract: A critical question regards the neural basis of complex cognitive skill acquisition. One extensively studied skill is navigation, with evidence suggesting that humans vary widely in navigation abilities. Yet, data supporting the neural underpinning of these individual differences are mixed. Some evidence suggests robust structure-behavior relations between hippocampal volume and navigation ability, whereas other experiments show no such correlation. We focus on several possibilities for these discrepancies: 1) volumetric hippocampal changes are relevant only at the extreme ranges of navigational abilities; 2) hippocampal volume correlates across individuals but only for specific measures of navigation skill; 3) hippocampal volume itself does not correlate with navigation skill acquisition; connectivity patterns are more relevant. To explore this third possibility, we present a model emphasizing functional connectivity changes, particularly to extra-hippocampal structures. This class of models arises from the premise that navigation is dynamic and that good navigators flexibly solve spatial challenges. These models pave the way for research on other skills and provide more precise predictions for the neural basis of skill acquisition.

Keywords: Hippocampusspatial navigationMRIfunctional connectivitybrain volume

Potential ‘super-spreaders’ –people with many social interactions, extraverts–, the people most likely to widely spread COVID-19, are the most willing to take a free test, despite the increased probability of being quarantined

Testing for COVID-19: willful ignorance or selfless behavior? Linda Thunstroem et al. Behavioural Public Policy , Volume 5, Issue 2, April 2021, pp 135-152.

Rolf Degen's take: Potential "super-spreaders," who would suffer the most from being quarantined, are nevertheless those who would most willingly submit to free COVID-19 testing

Abstract: Widespread testing is key to controlling the spread of COVID-19. But should we worry about self-selection bias in the testing? The recent literature on willful ignorance says we should – people often avoid health information. In the context of COVID-19, such willful ignorance can bias testing data. Furthermore, willful ignorance often arises when selfish wants conflict with social benefits, which might be particularly likely for potential ‘super-spreaders’ – people with many social interactions – given people who test positive are urged to self-isolate for two weeks. We design a survey in which participants (n = 897) choose whether to take a costless COVID-19 test. We find that 70% would take a test. Surprisingly, the people most likely to widely spread COVID-19 – the extraverts, others who meet more people in their daily lives and younger people – are the most willing to take a test. People's ability to financially or emotionally sustain self-isolation does not matter to their decision. We conclude that people are selfless in their decision to test for COVID-19. Our results are encouraging – they imply that COVID-19 testing may succeed in targeting those who generate the largest social benefits from self-isolation if infected, which strengthens the case for widespread testing.


Widespread testing is one of the most important actions that US governments at any level can undertake to help slow down the spread of COVID-19. Given budget and testing supply constraints, it is likely that random, but voluntary, testing will be the most effective policy. We design a survey to examine the risks from self-selection into taking a COVID-19 test.

Overall, we observe that around 70% of people would agree to a costless COVID-19 test. We find that people who are more worried about their own health due to COVID-19 are more likely to test, as are young healthy people, relative to older healthy people. Ability to afford self-isolation for 14 days does not seem to affect the decision to test. Furthermore, people who worry more about their health, and people with health insurance or health coverage through Medicare or Medicaid, are more likely to take the test, as are people identifying as Democrats compared to Republicans.

Contrary to our expectation, we also find that potential ‘super-spreaders’ are more likely than other individuals to agree to a costless COVID-19. It could be that extroverts are more willing than expected to take a COVID-19 test because their private cost of doing so is unusually low due to the broadly implemented social distancing at the time of data collection for this study. If extroverts are already relatively isolated (i.e., due to a stay-at-home order and mandated closures by the state governor of public spaces, such as gyms, restaurants and bars), the personal cost of testing might be low. Furthermore, extroverts might be more likely to get infected if they socialize more, which could be a ‘selfish’ motivation to get tested. However, we control for the current level of compliance with social distancing, which should address both of these private motivations for increased probability of testing, and we find that people who comply more are less motivated to take the test. We also control for their worry about own health due to COVID-19. Even so, the positive effect on willingness to test from being an extrovert persists. We therefore conclude that the positive effect of being an extrovert on willingness to test for COVID-19 is likely due to social health benefits weighing more heavily in their decision than their private costs from potential self-isolation for 14 days, should the test come back positive. The importance of the prosocial motive in determining COVID-19 testing is consistent with the results of the study by Jordan et al. (2020), who find that prosocial messages are more effective than self-interested messages in promoting behavior that prevent the spread of COVID-19 (e.g., hand washing, hand shaking, hugging).

Our results suggest that the risks of adverse selection (in terms of failing to target the people most likely to spread the virus) in testing for COVID-19 might be fairly low. This underscores the value of widespread testing, even if it cannot be truly random, and the importance of making such testing available nationwide in the USA as soon as possible.

An important shortcoming of our analysis is that it builds on hypothetical survey data. It is well documented that survey answers may be affected by a ‘hypothetical bias’, meaning that people answer one way in a survey and behave in a different way when faced with real, incentivized decisions. This risk pertains to our study as well, and the hypothetical bias might be particularly pronounced if the choice to test for COVID-19 is regarded as prosocial. Several studies suggest that a hypothetical bias is particularly likely when measuring prosocial behavior – people often exaggerate the extent to which they engage in such behavior (e.g., Murphy et al.2005; Vossler et al.2012; Jacquemet et al.2013). Furthermore, it is possible that personal costs to the testing decision are less salient in a hypothetical context. Once testing is more widespread in the USA, it will be important to examine who actually chooses to get tested, and the extent to which they deviate from the general population. That said, hypothetical and incentivized behavior generally correlate, such that an analysis like ours can provide important insights into the potential pitfalls of voluntary testing, prior to the actual testing. This is useful information to have on hand when designing an efficient and cost-effective testing strategy.

Facet-level personality development in the transition to adolescence: Girls increase their conscientiousness, boys' stay relatively constant; agreeableness and introversion increase for both boys & girls

Brandes, C. M., Kushner, S. C., Herzhoff, K., & Tackett, J. L. (2020). Facet-level personality development in the transition to adolescence: Maturity, disruption, and gender differences. Journal of Personality and Social Psychology, Mar 2021.

Abstract: The transition to adolescence is marked by enormous change in social, biological, and personality development. Although accumulating evidence has offered insight into the nature of higher-order personality trait development during this period, much less is known about the development of lower-order personality traits, or “facets.” The current study used a cohort-sequential longitudinal design to examine domain- and facet-level trajectories for mother-reported personality traits during the early adolescent transition. Personality trait domains and facets were assessed with the Inventory of Child Individual Differences–Short Form (Deal, Halverson, Martin, Victor, & Baker, 2007). Participants were 440 children followed at 4 annual timepoints from middle childhood (Mage = 9.97, SD = 0.81) to early adolescence (Mage = 13.11, SD = 0.84). Results of latent growth curve models showed substantial facet-level personality stability in this period, as well as small to moderate linear change in 13 of 15 facets. Gender differences in change were evident for 9 facets. Overall patterns suggested consistent increases in agreeableness facets with null to small gender differences. Neuroticism and openness to experience facet change was heterogeneous within each domain, but patterns were similar for boys and girls. Extraversion primarily decreased, though the magnitude and direction of change differed between facets and genders. Conscientiousness increased across all facets, but only among girls. These findings overall demonstrate a high degree of developmental consistency in facets within each domain as well as some notable differences. Further, this study contributes to a small and somewhat mixed evidence base for current theories of adolescent personality development.

Self-rated Attractiveness Predicts Preferences for Sexually Dimorphic Facial Characteristics: Evidence from a Culturally Diverse Sample

Marcinkowska, Urszula M., Benedict C. Jones, and Anthony J. Lee. 2021. “Self-rated Attractiveness Predicts Preferences for Sexually Dimorphic Facial Characteristics: Evidence from a Culturally Diverse Sample.” PsyArXiv. March 10. doi:10.31234/

Abstract: Individuals who are more attractive are thought to show a greater preference for facial sexual dimorphism, potentially because individuals who perceive themselves as more physically attractive believe they will be better able to attract and/or retain sexually dimorphic partners. Evidence for this link is mixed, however, and recent research suggests the association between self-rated attractiveness and preferences for facial sexual dimorphism may not generalise to non-Western cultures. Here, we assess whether self-rated attractiveness and health predict facial sexual dimorphism preferences in a large and culturally diverse sample of 6907 women and 2851 men from 41 countries. We also investigated whether ecological factors, such as country health/development and inequality, might moderate this association. Our analyses found that men and women who rated themselves as more physically attractive reported stronger preferences for exaggerated sex-typical characteristics in other sex faces. This finding suggests that associations between self-rated attractiveness and preferences for sexually dimorphic facial characteristics generalise to a culturally diverse sample and exist independently of country-level factors. We also found that country health/development moderated the effect of men’s self-rated attractiveness on femininity preferences, such that men from countries with high health/development showed a positive association between self-rated attractiveness and femininity preference, while men from countries with low health/development, showed exactly opposite trend.