Attention is the coin of the Internet.

In the economy of attention, Value is measured by Time X Intensity.

How long have you paid attention to me? And how intently have you stared at me? That is my net worth.

Of course, the Internet is built on the old economy of capital, labor, goods, services, and money.

But parallel to the traditional market there has always been another exchange, in which we trade attention with each other. And the Internet has dramatically increased the volume of trading on that floor.

Even though attention is not gold, it is valuable. When business people talk dreamily of eyeballs, click-through streams, stickiness, and ideas spreading virally, they are hoping, of course, that winning someone's attention may pay off in purchases, or at least good will.

But millions of other people simply post because they want us to notice what they care about, to share their focus, to get our attention. When a visitor writes to praise our text, we blossom; and when we respond thoughtfully to their e-mail or discussion post, their next message often shines with pleasure. We like the attention.

But what exactly is attention? It is an intangible energy, a subjective, and intensely personal experience. You cannot put your thumb on it.

Researchers can find no particular lobe of the brain in which attention resides.

Scientists can track eye movements, and guess what you are attending to on a Web page, but they cannot share your experience of attention as it is pulled here, sidetracked, or diffused.