David E. Levari

What are the consequences of encountering blatant falsehoods and “fake news”? Here we show that exposure to a high prevalence of very implausible claims can increase belief in other, more ambiguous false claims, as they seem more believable in comparison. Participants in five preregistered experiments (N=5,476) were exposed to lower or higher rates of news headlines that seemed blatantly false, as well as some more plausible true and false headlines. Being exposed to a higher prevalence of extremely implausible headlines increased belief in unrelated headlines which were more ambiguous (or even plausible), regardless of whether they were true or false. The effect persisted for headlines describing hypothetical events, as well as actual true and false news headlines. It occurred whether people actively evaluated the headlines or read them passively, among liberals and conservatives, and among those high or low in cognitive reflection. We observed this effect in environments where the plausibility of a claim was a reliable and useful cue to whether it was true or false, and in environments where plausibility and truth were unrelated. We argue that a high prevalence of blatantly implausible claims lowers the threshold of plausibility for other claims to seem believable. Such relative comparisons are a hallmark of the brain’s tendency towards efficient computations in perception and judgment. Even when consumers can reliably identify and disregard blatantly false news content, encountering such content may make subtler falsehoods more likely to be believed.

The concept of "trauma" was originally used by psychiatrists to describe horrific events such as rape and torture that characteristically provoke extreme emotional distress. Both colloquially and clinically, the concept of psychological trauma has broadened considerably. Although many clinical scientists have expressed concern about the broadening of the concept of trauma, it remains unclear how this concept expansion occurs. We present two experiments in which American adults (N = 276 and N = 267) sequentially classified descriptions of events (e.g., "broke a leg in a bicycle accident") as either "trauma" or "not trauma." In the first experiment, we manipulated the frequency of severe events (i.e., severe events became less and less common). In the second experiment, we manipulated the range of events (i.e., participants viewed only severe or only nonsevere events). Together, the findings suggest that an individual's frame of reference for the severity of events plays a role in narrowing or broadening the concept of trauma. Public Significance Statement This study suggests that when making decisions about whether an event qualifies as a "trauma," individuals rely on recent context. Specifically, when the context includes severe events (e.g., "was injured in an IED explosion") participants were less likely to classify any given event as traumatic. Accordingly, context may influence how individuals interpret potentially traumatic events in their lives.

In a 2011 article in this journal entitled “Whites See Racism as a Zero-Sum Game That They Are Now Losing” ( Perspectives on Psychological Science, 6, 215–218), Norton and Sommers assessed Black and White Americans’ perceptions of anti-Black and anti-White bias across the previous 6 decades—from the 1950s to the 2000s. They presented two key findings: White (but not Black) respondents perceived decreases in anti-Black bias to be associated with increases in anti-White bias, signaling the perception that racism is a zero-sum game; White respondents rated anti-White bias as more pronounced than anti-Black bias in the 2000s, signaling the perception that they were losing the zero-sum game. We collected new data to examine whether the key findings would be evident nearly a decade later and whether political ideology would moderate perceptions. Liberal, moderate, and conservative White (but not Black) Americans alike believed that racism is a zero-sum game. Liberal White Americans saw racism as a zero-sum game they were winning by a lot, moderate White Americans saw it as a game they were winning by only a little, and conservative White Americans saw it as a game they were losing. This work has clear implications for public policy and behavioral science and lays the groundwork for future research that examines to what extent racial differences in perceptions of racism by political ideology are changing over time.

Social interactions are dynamic and unfold over time. To make sense of social interactions, people must aggregate sequential information into summary, global evaluations. But how do people do this? Here, to address this question, we conducted nine studies (N = 1,583) using a diverse set of stimuli. Our focus was a central aspect of social interaction—namely, the evaluation of others’ emotional responses. The results suggest that when aggregating sequences of images and videos expressing varying degrees of emotion, perceivers overestimate the sequence’s average emotional intensity. This tendency for overestimation is driven by stronger memory of more emotional expressions. A computational model supports this account and shows that amplification cannot be explained only by nonlinear perception of individual exemplars. Our results demonstrate an amplification effect in the perception of sequential emotional information, which may have implications for the many types of social interactions that involve repeated emotion estimation.

Everyone knows that if you want to learn how to do something, you should get advice from people who do it well. But is everyone right? In a series of studies ( N = 8,693), adult participants played a game after receiving performance advice from previous participants. Although advice from the best-performing advisors was no more beneficial than advice from other advisors, participants believed that it had been—and they believed this despite the fact that they were told nothing about their advisors’ performance. Why? The best performers did not give better advice, but they did give more of it, and participants apparently mistook quantity for quality. These studies suggest that performing and advising may often be unrelated skills and that in at least some domains, people may overvalue advice from top performers.

Norton and Sommers (2011) assessed Black and White Americans’ perceptions of anti-Black and anti-White bias across the previous six decades—from the 1950s to the 2000s. They presented two key findings: White (but not Black) respondents perceived decreases in anti-Black bias to be associated with increases in anti-White bias, signaling the perception that racism is a zero-sum game; White respondents rated anti-White bias as more pronounced than anti-Black bias in the 2000s, signaling the perception that they were losing the zero-sum game. We collected new data to examine whether the key findings would be evident nearly a decade later, and whether political ideology would moderate perceptions. Liberal, moderate, and conservative White (but not Black) Americans alike believed that racism is a zero-sum game. Liberal White Americans saw racism as a zero-sum game they were winning by a lot, moderate White Americans saw it as a game they were winning by only a little, and conservative White Americans saw it as a game they were losing. This work has clear implications for public policy and behavioral science, and lays the groundwork for future research that examines to what extent racial differences in perceptions of racism by political ideology are changing over time.

Social interactions are dynamic, and unfold over time. To make sense of social interactions, people must aggregate sequential information into summary, global evaluations. But how do people do this? To address this question, we conducted 9 studies (N= 1,583), using a diverse set of stimuli. Our focus was a central aspect of social interaction, namely the evaluation of others’ emotional responses. Results suggest that when aggregating sequences of images and videos expressing varying degrees of emotions, perceivers overestimate the sequence’s average emotional intensity. This tendency for overestimation, which we term the sequential amplification effect, is driven by stronger memory of more emotional expressions. A computational model further supports this account, and shows that amplification cannot be driven merely by nonlinear perception. The current paper demonstrates amplification in social cognition of sequential information, which is especially important given the prevalence of such information in many social interactions.

Prevalence-induced concept change describes a cognitive mechanism by which someone’s definition of a concept shifts as the prevalence of instances of that concept changes. The phenomenon has real-world implications because this sensitivity to environmental characteristics may lead to substantial biases in judgements. While prevalence-induced concept change has been established in young adults, it is unclear how it changes as a function of human ageing. In this cross-sectional study, we explore how prevalence-induced concept change affects older adults’ lower-level, perceptual, and higher-order, ethical, judgements. We find that older adults are less sensitive to prevalence-induced concept change than younger adults across domains. Using a combination of computational and experimental approaches, we demonstrate that these changes in judgements are sensitive to the pace with which the stimuli occur in the environment and are affected by the effort that subjects invest in order to make accurate decisions. Based on findings from three experiments we argue that older adults’ concept spaces are more rigid than those of younger adults. However, what appear as an age-related cognitive “deficit” may turn out to be beneficial because it makes older adults less susceptible to biases in judgments.

Prevalence-induced concept change describes a cognitive mechanism by which someone’s definition of a concept shifts as the prevalence of instances of that concept changes. While this phenomenon has been established in young adults, it is unclear how it affects older adults. In this study, we explore how prevalence-induced concept change affects older adults’ lower-level, perceptual, and higher-order, ethical, judgement and decision-making. We find that older adults are less sensitive to prevalence-induced concept change than younger adults across both domains. Using computational modeling, we demonstrate that these age-related changes in judgements reflect more cautious and deliberate responding in older adults. Based on these findings, we argue that while overly cautious responding may be maladaptive in some cognitive domains, in the case of prevalence-induced concept change, it can be protective against biased decision-making.