Letters

A daily, city-level happiness metric constructed from the sentiment expressed in 210 million tweets on Sina Weibo from 144 cities shows that high levels of air pollution significantly reduce Chinese urbanites’ expressed happiness on social media.

Using data from 765 million online music plays chosen by 1 million individuals in 51 countries, Park et al. reveal diurnal and seasonal affective rhythms in musical intensity that are consistent across diverse cultures and demographic groups. They also report differences in baseline preferences for musical intensity across cultures and ages.

An individual’s social ties contain up to 95% of the potential predictive accuracy achievable about that individual. In principle, a social platform may therefore profile an individual from their ties only, without access to their data.

Askelund et al. show that remembering more specific positive life experiences is associated with fewer negative self-related thoughts and lower levels of stress hormones in a study of 427 adolescents at risk for depression.

Why do we continue processing external events during sleep, yet remain unresponsive? Legendre et al. use electroencephalography to show that sleepers enter a ‘standby mode’, continuing to track relevant signals but doing so transiently.

In the United States, France and Germany, as peoples’ opposition to genetically modified (GM) foods becomes more extreme, their self-rated understanding of genetic modification increases, but objectively, their knowledge of the science behind genetic modification tends to be poorer.

Nearby small objects appear larger than distal large objects, reflecting a dissociation between perceived and actual object size. Collegio et al. show that inferences of true object size scale spatial attention to objects.

Pryor et al. show that people conform to social norms, even when they understand that the norms have been determined arbitrarily and do not reflect people’s actual preferences. Prominent, rationality-based explanations of norm effects cannot explain these results.

Michelmann and colleagues investigated how humans search for information in episodic memory. Using MEG, the authors show fast, forward-directed memory replay, with speed changing flexibly depending on the task.

A new study by Keynan and colleagues provides evidence that training in amygdala self-regulation via EEG neurofeedback (‘electrical fingerprint’) results in neurobehavioural markers of stress resilience in a cohort of individuals undergoing military training.

Randomly informing people that they had a high or low genetic risk of obesity changed their gene-related physiology and subjective experience in a manner consistent with the perceived risk, regardless of their actual genetic risk of obesity.

Analysing the results from four major sports leagues and a multiplayer online game reveals that prior shared success as a team significantly improves the odds of winning beyond what is explained by the skill of individual players.

A century after being predicted by theory, the authors detect and quantify the genomic signature of assortative mating in ~400,000 contemporary human genomes, and report new genetic evidence for assortative mating on height and educational attainment.

When searching for rewards in complex, unfamiliar environments, it is often impossible to explore all options. Wu et al. show how a combination of generalization and optimistic sampling guides efficient human exploration in complex environments.

Bentz et al. estimate the phylogenetic signals of environmental factors and population size on more than 6,000 phylogenetic trees of 46 language families and find that environment influences the evolution of language families beyond neutral drift.

Kahn et al. show that learners capitalize on higher-order topological properties when they learn a probabilistic motor sequence based on a network traversal.

Analyses of transactions in a new monetary system (Sardex community currency) reveal that transaction cycles increase in prevalence over time and that economic activity within these cycles is higher compared to linear transactions through the network.

Reputational concerns reinforce the instinct to cooperate in social situations. McAuliffe et al. find that cooperative habits can be overturned in one-shot anonymous interactions, when people learn that defection will not damage their self-interest.

Having too many choices can lead to choice overload. Reutskaja et al. find that brain activity in striatum and anterior cingulate reflects subjects’ engagement in decision making as a function of choice set size and can serve as an indicator of choice overload.

A five-arm trial with 228,000 participants found that a single mailed letter increased absolute influenza vaccination rates in individuals ≥66 years of age by about 1%. The framing of the letter made no significant difference to the outcome.