When I compare working at home now to the last time I did it (1990-1992), I can see the difference in three letters: DSL.

When email meant dial-up and Compuserve charging me by the minute, I monitored my online time carefully.

Now concentration comes harder. Sometimes I work in the guest cabin, because it has no telephone — not even a cell-phone signal — and of course no Web access.

Furthermore, says Winifred Gallagher, author of Rapt: Attention and the Focused Life, “multitasking is a myth.”

“You cannot do two things at once. The mechanism of attention is selection: it’s either this or it’s that.” She points to calculations that the typical person’s brain can process 173 billion bits of information over the course of a lifetime.

“People don’t understand that attention is a finite resource, like money,” she said. “Do you want to invest your cognitive cash on endless Twittering or Net surfing or couch potatoing? You’re constantly making choices, and your choices determine your experience, just as William James said.”