In 2004, Gloria Mark, a professor of informatics at the University of California, Irvine, watched knowledge workers go about a typical day at the office. Using a stopwatch, she noted every time they switched tasks on their computer, moving from a spreadsheet to an email to a web page to a different web page and back to the spreadsheet. She found that people averaged just two and a half minutes on a given task before switching.

When Dr. Mark repeated the experiment in 2012, the average time office workers spent on a task had dropped to 75 seconds. And it has continued to drop from there.

“Our attention spans while on our computers and smartphones have become short — crazily short — as we now spend about 47 seconds on any screen on average,” Dr. Mark wrote in her new book, “Attention Span: A Groundbreaking Way to Restore Balance, Happiness and Productivity.”

Read the full story on the New York Times.