The effect of masks on cognitive performance.

The use of face masks has been a key response to the COVID-19 pandemic in almost every country. However, despite widespread use of masks in classrooms and offices around the world, almost nothing is known about their effects on cognitive performance. Using a natural experiment, I show that mandatory mask wearing has a negative causal effect on the cognitive performance of competitive chess players. I analyzed the quality of almost 3 million chess moves played by 8,531 individuals (ages 5-98 y) in 18 countries before and during the pandemic. Wearing a mask decreased the quality of players' decisions-a measure of their cognitive performance-by approximately one-third of an SD. However, the disruptive effect of masks is relatively short-lived, gradually weakening such that there is no measurable disadvantage from wearing a mask after roughly 4 h of play. The mask effect is driven by a large, negative effect for experts, with minimal change in performance at lower levels, and is stronger in high-incentive competitions. I provide support for a distraction mechanism whereby masks interfere with performance when working memory load is high.