For the past five, I’ve had a special focus: What has happened to face-to-face conversation in a world where so many people say they would rather text than talk? I’ve looked at families, friendships and romance. I’ve studied schools, universities and workplaces. When college students explain to me how dividing their attention plays out in the dining hall, some refer to a “rule of three.” In a conversation among five or six people at dinner, you have to check that three people are paying attention — heads up — before you give yourself permission to look down at your phone. So conversation proceeds, but with different people having their heads up at different times. The effect is what you would expect: Conversation is kept relatively light, on topics where people feel they can drop in and out.