I am going to do my best to hold your attention until the very last word of this column. Actually, I know it's futile. Along the way, your mind will wander off, then return, then drift away again. But I can console myself with some recent research on the subject of mind wandering. Mind wandering is not necessarily the sign of a boring column. It's just one of the things that make us human.

Everybody knows what it is like for our minds to wander, and yet, for a long time psychologists shied away from examining the experience. It seemed too elusive and subjective to study scientifically. Only in the past decade have they even measured just how common mind wandering is. The answer is very.

Some of the most striking evidence comes from Jonathan Schooler, a psychologist at the University of California at Santa Barbara who is one of the leading researchers on mind wandering. In 2005 he and his colleagues told a group of undergraduates to read the opening chapters of War and Peace on a computer monitor and then to tap a key whenever they realized they were not thinking about what they were reading. On average, the students reported that their minds wandered 5.4 times in a 45-minute session. Other researchers have gotten similar results with simpler tasks, such as pronouncing words or pressing a button in response to seeing particular letters and numbers. Depending on the experiment, people spend up to half their time not thinking about the task at hand—even when they've been told explicitly to pay attention.