The Wall Street Journal reports that Adrian Ward, a cognitive psychologist and marketing professor at the University of Texas at Austin, has been studying the way smartphones and the internet affect our thoughts and judgments for a decade. In his own work, as well as that of others, he has seen mounting evidence that using a smartphone, or even hearing one ring or vibrate, produces a welter of distractions that makes it harder to concentrate on a difficult problem or job. The division of attention impedes reasoning and performance.

A 2015 study, involving 166 subjects, found that when people's phones beep or buzz while they're in the middle of a challenging task, their focus wavers, and their work gets sloppier—whether they check the phone or not. Another 2015 study, showed that when people hear their phone ring but are unable to answer it, their blood pressure spikes, their pulse quickens, and their problem-solving skills decline.