Peter M. Todd’s research while affiliated with Indiana University Bloomington and other places

Did the COVID-19 pandemic bring people together or push them apart? While infectious diseases tend to push people apart, crises can also bring people together through positive interdependence. We studied this question by asking an international sample (N = 1,006) about their inclinations to cooperate, perceptions of interdependence (i.e., shared fate), and perceived risk as well as local prevalence of COVID-19 infection across 14 time points from March to August, 2020. While perceived interdependence with others tended to increase during this time period, inclinations to cooperate decreased over time. At the within-person level, higher local prevalence of COVID-19 attenuated increases in perceived interdependence with others, and was associated with lower inclinations to cooperate. At the between-person level, people with high perceived interdependence with others reported more stable, or increasing, inclinations to cooperate over time than people with low perceived interdependence. Establishing a high sense of perceived interdependence with others may thus allow people to maintain cooperation during crises, even in the face of challenging circumstances such as those posed by a highly transmissible virus.

We test the hypothesis that wealth is associated with lower empathic concern because wealthier people experience fewer challenges and give help less often to people in need. As predicted, Study 1 (N = 513; cross-sectional) showed wealth was negatively associated with trait empathic concern through experiencing fewer challenges and providing less help. Study 2 (N = 915; longitudinal) replicated this while also revealing unexpected curvilinear associations. At low levels of helping (measured monthly across one year), wealth led to lower empathy through experiencing fewer challenges and less helping. However, more helping led to decreasing empathy at higher levels of helping. Moreover, person-centered analyses showed that people experienced higher state-level empathic concern in months in which they provided moderate amounts of help relative to when they helped less than their usual amount of helping. Results suggest people can cultivate empathy through helping, but only for those who help a moderate amount.

Humans may retrieve words from memory by exploring and exploiting in “semantic space” similar to how nonhuman animals forage for resources in physical space. This has been studied using the verbal fluency test (VFT), in which participants generate words belonging to a semantic or phonetic category in a limited time. People produce bursts of related items during VFT, referred to as “clustering” and “switching.” The strategic foraging model posits that cognitive search behavior is guided by a monitoring process which detects relevant declines in performance and then triggers the searcher to seek a new patch or cluster in memory after the current patch has been depleted. An alternative body of research proposes that this behavior can be explained by an undirected rather than strategic search process, such as random walks with or without random jumps to new parts of semantic space. This study contributes to this theoretical debate by testing for neural evidence of strategically timed switches during memory search. Thirty participants performed category and letter VFT during functional MRI. Responses were classified as cluster or switch events based on computational metrics of similarity and participant evaluations. Results showed greater hippocampal and posterior cerebellar activation during switching than clustering, even while controlling for interresponse times and linguistic distance. Furthermore, these regions exhibited ramping activity which increased during within-patch search leading up to switches. Findings support the strategic foraging model, clarifying how neural switch processes may guide memory search in a manner akin to foraging in patchy spatial environments.

Food sharing is central to the human experience, serving biological and sociocultural functions. Historically, food sharing has allowed people to manage food shortages, creating positive interdependence among those who pool calories and other sources of risk. However, sharing food may lead to negative outcomes when food is scarce, or when there is a threat of disease. We found that sharing food (compared with sharing pencils) led to reduced cooperation with an experiment partner (Study 1) and that perceived scarcity partially mediated a negative association between zero-sum orientation and perceived interdependence with people involved in a recently shared meal (Studies 2-3). Disgust was also associated with lower perceived interdependence toward people involved in a shared meal (Study 3; Ntotal = 1126). Our results suggest that scarcity and disgust can interfere with the positive feelings people might otherwise experience when eating together, warning against lay beliefs that 'breaking bread’ necessarily brings people together.

Human sociality is governed by two types of social norms: injunctive norms, which prescribe what people ought to do, and descriptive norms, which reflect what people actually do. The process by which these norms emerge and their causal influences on cooperative behavior over time are not well understood. Here, we study these questions through social norms influencing mask wearing during the COVID-19 pandemic. Leveraging 2 years of data from the United States (18 time points; n = 915), we tracked mask wearing and perceived injunctive and descriptive mask wearing norms as the pandemic unfolded. Longitudinal trends suggested that norms and behavior were tightly coupled, changing quickly in response to public health recommendations. In addition, longitudinal modeling revealed that descriptive norms caused future increases in mask wearing across multiple waves of data collection. These cross-lagged causal effects of descriptive norms were large, even after controlling for non-social beliefs and demographic variables. Injunctive norms, by contrast, had less frequent and generally weaker causal effects on future mask wearing. During uncertain times, cooperative behavior is more strongly driven by what others are actually doing, rather than what others think ought to be done.

Aim Perceived uncontrollable mortality risk (PUMR) refers to people's beliefs regarding their risk of death due to factors outside of their control. Previous theoretical models and empirical studies provide evidence that those with greater PUMR are less motivated to invest in preventative health behaviors, but little is known about how accurately people estimate PUMR compared to objective measures of risk exposure, an important consideration for interventions designed to address the link between PUMR and health behavior. Here, we explore how objective risk indices and personal characteristics relate to PUMR. Subject and methods We performed a series of pre-registered analyses on a US-representative longitudinal study (N = 915), connecting these results to external data from the Global Burden of Diseases, Injuries, and Risk Factors Study. Results We show that (Study 1) PUMR is associated with objective measures of risk exposure, and that (Study 2) perceptions of risk due to disease drive PUMR, and more educated individuals report less perceived risk. Additionally, we find that (Study 3) estimates of PUMR are relatively stable over a 4-month period (R = 0.7), indicating that behaviors influenced by PUMR are likely to persist over time. Finally, we show that (Study 4) those who believe they are at greater risk of dying due to factors outside of their control (i.e., greater PUMR) are less likely to engage in general health behaviors. Conclusion By assessing the determinants of PUMR, we can create data-driven policy solutions that lead individuals to more accurate mortality risk assessments and improved health behavior.

Given the importance of friendships during challenging times and the mixed associations between personality traits and disease-related behaviors, we investigated the correlations between personality traits and perceptions of friendships during the COVID-19 pandemic. Data were collected as part of a longitudinal investigation of the correlations between the pandemic and various cooperative relationships. In this investigation, we found that agreeableness and neuroticism predicted participants being more concerned about COVID-19 and bothered by friends' risky behavior, and extraversion predicted enjoying helping friends during the pandemic. Our results suggest that personality differences are associated with how individuals cope with friends' risky behaviors during the COVID-19 pandemic.

Sometimes people help one another expecting to be repaid, while at other times people help without an expectation of repayment. What might underlie this difference in expectations of repayment? We investigate this question in a nationally representative sample of US adults (N = 915), and find that people are more likely to expect repayment when needs are perceived to be more predictable. We then replicate these findings in a new sample of US adults (N = 417), and show that people have higher expectations of repayment when needs are perceived to be more predictable because people assign greater responsibility to others for experiencing such predictable needs (e.g., needing money for utilities). This is consistent with previous work based on smaller-scale societies, which shows that the predictability of needs influences expectations of repayment. Our results also add to this previous work by (1) showing that the positive relationship between predictability of needs and expectations of repayment previously found in smaller-scale communities is generalizable to the US population, and (2) showing that attributions of responsibility partially mediate this relationship. This work shows that the predictability of needs and attributions of responsibility for that need are important factors underlying the psychology of helping in times of need.

The COVID-19 pandemic drastically changed the ways in which social interactions happened. This is particularly true for valued social relationships such as friendships. Friendships provide many physical and mental health benefits, including buffering against loneliness during the pandemic, so contact and interactions with friends may have become more important during the pandemic. Additionally, an additional benefit of friendships is that they may have provided individuals with the ability to reduce their uncertainty and lower their risks during the pandemic. But, if individuals or their friends are not being careful about their risky behavior during this time, this could lead to conflict within these valued relationships. In this study, we investigated how COVID-19, demographics, and preferences for risk management influenced participants’ perceptions of their friendship during the pandemic. We found that participants who were more concerned about contracting COVID-19 and more likely to use risk retention reported having more conflict with their friends during the pandemic. These results suggest that there may be individual differences in risk tolerance of contracting COVID-19 and these differences fundamentally influence social relationships, loneliness, or social connectedness during the pandemic.

Human sociality is governed by two types of social norms: injunctive social norms, which prescribe what people ought to do, and descriptive social norms, which reflect what people actually do. These norms enable people to cooperate in the face of group-wide challenges. While previous experimental work has shown that people’s behavior is influenced by social norms, several open questions remain about the natural emergence of injunctive and descriptive social norms within populations and their causal influences on cooperative behavior over time. To understand how cooperative behavior emerges and is shaped by changing social norms in a non-experimental setting, we studied mask wearing during the COVID-19 pandemic. Mask wearing has individual benefits, but it is also a cooperative behavior that provides collective benefits of reduced disease transmission in the community. Leveraging two years of longitudinal data from a representative sample of adults in the United States (18 time points; n = 915), we tracked people’s reported mask wearing and their perceived injunctive and descriptive mask wearing norms as the pandemic unfolded. Longitudinal trends of norm perceptions and self-reported mask wearing suggested that norms and behavior were tightly coupled and both changed quickly in response to recommendations from public health authorities. In addition, a random-intercept cross-lagged panel model revealed that perceived descriptive norms, but not perceived injunctive norms, caused future within-person increases in individuals' mask wearing. These findings show that, during uncertain times, cooperative behavior is driven by what others are actually doing, rather than what others think ought to be done.