The Brain Drain Study

In a 2017 study at the University of Texas at Austin, about 500 people took working-memory and reasoning tests. Some kept their phones on the desk, silenced. Others left them in another room. The other-room group scored higher in that study, and lead researcher Adrian Ward called the pattern "brain drain."

Later evidence is more mixed: reviews find the effect is clearest for working memory and weaker or absent for other domains, and some preregistered replications find no effect. The practical lesson still holds: a nearby phone is an invitation to switch, so distance is useful when the work needs full attention.